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	Author	Michel, K.H.; Verberck, B.
	Title	Theory of phonon dispersions and piezoelectricity in multilayers of hexagonal boron-nitride			Type	A1 Journal article
	Year	2011	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	248	Issue	11	Pages	2720-2723
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Taking into account covalent, Coulomb and van der Waals interactions, we construct the dynamical matrix and calculate the phonon dispersion relations for multilayer crystals of hexagonal boron-nitride. Coulomb interactions account for a strong overbending of optical phonons. Applying and extending Born's long-wave theory to the case of multilayer crystals, we calculate the piezoelectric stress constant equation image as a function of the number of layers equation image. In agreement with group theory, we find that equation image for equation image even; for an uneven number equation image of layers we obtain equation image, i.e. the piezoelectric constant decreases as equation image.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000297517100069	Publication Date	2011-10-18
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	13	Open Access
	Notes	; Discussions with G. Heger, B. Partoens and F. M. Peeters are gratefully acknowledged. This work has been supported by the Flemish Science Foundation (FWO-Vl) and the Bijzonder Onderzoeksfonds, Universiteit Antwerpen (BOF-UA). ;			Approved	Most recent IF: 1.674; 2011 IF: 1.316
	Call Number	UA @ lucian @ c:irua:94034			Serial	3618
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	Author	Michel, K.H.; Verberck, B.
	Title	Theory of the elastic constants of graphite and graphene			Type	A1 Journal article
	Year	2008	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	245	Issue	10	Pages	2177-2180
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Born's long wave method is used to study the elastic properties of graphite and graphene. Starting from an empirical force constant model derived from full inplane phonon dispersions of graphite [Mohr et al., Phys. Rev. B 76, 035439 (2007)] we calculate the tension coefficients of graphene. Extending the model by interplanar interactions, we calculate the elastic constants of graphite. The agreement of our theoretical values with inelastic x-ray scattering results on elastic constants of graphite [Bosak et al., Phys. Rev. B 75, 153408 (2007)] is very satisfactory.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000260581800066	Publication Date	2008-08-25
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	47	Open Access
	Notes				Approved	Most recent IF: 1.674; 2008 IF: 1.166
	Call Number	UA @ lucian @ c:irua:75660			Serial	3621
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	Author	Michel, K.H.; Costamagna; Peeters, F.M.
	Title	Theory of thermal expansion in 2D crystals			Type	A1 Journal article
	Year	2015	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	252	Issue	252	Pages	2433-2437
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The thermal expansion alpha(T) in layered crystals is of fundamental and technological interest. As suggested by I. M. Lifshitz in 1952, in thin solid films (crystalline membranes) a negative contribution to alpha(T) is due to anharmonic couplings between in-plane stretching modes and out-of-plane bending (flexural modes). Genuine in-plane anharmonicities give a positive contribution to alpha(T). The competition between these two effects can lead to a change of sign (crossover) from a negative value of alpha(T) in a temperature (T) range T <= T-alpha to a positive value of alpha(T) for T > T-alpha in layered crystals. Here, we present an analytical lattice dynamical theory of these phenomena for a two-dimensional (2D) hexagonal crystal. We start from a Hamiltonian that comprises anharmonic terms of third and fourth order in the lattice displacements. The in-plane and out-of-plane contributions to the thermal expansion are studied as functions of T for crystals of different sizes. Besides, renormalization of the flexural mode frequencies plays a crucial role in determining the crossover temperature T-alpha. Numerical examples are given for graphene where the anharmonic couplings are determined from experiments. The theory is applicable to other layer crystals wherever the anharmonic couplings are known. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000364690400014	Publication Date	2015-08-06
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	21	Open Access
	Notes	; We thank B. Verberck, D. Lamoen, and A. Dobry for useful comments. We acknowledge funding from the FWO (Belgium)-MINCyT (Argentina) collaborative research project. This work is supported by the Euro GRAPHENE project CONGRAN. ;			Approved	Most recent IF: 1.674; 2015 IF: 1.489
	Call Number	UA @ lucian @ c:irua:130281			Serial	4264
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	Author	Michel, K.H.; Neek-Amal, M.; Peeters, F.M.
	Title	Static flexural modes and piezoelectricity in 2D and layered crystals			Type	A1 Journal article
	Year	2016	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	253	Issue	253	Pages	2311-2315
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Piezo- and flexoelectricity are manifestations of electromechanical coupling in solids with potential applications in nanoscale materials. Naumov etal. [Phys. Rev. Lett. 102, 217601 (2009)] have shown by first principles calculations that a monolayer BN sheet becomes macroscopically polarized in-plane when in a corrugated state. Here, we investigate the interplay of layer corrugation and in-plane polarization by atomistic lattice dynamics. We treat the coupling between static flexural modes and in-plane atomic ion displacements as an anharmonic effect, similar to the membrane effect that is at the origin of negative thermal expansion in layered crystals. We have derived analytical expressions for the corrugation-induced static in-plane strains and the optical displacements with the resulting polarization response functions. Beyond h-BN, the theory applies to transition metal dichalcogenides and dioxides. Numerical calculations show that the effects are considerably stronger for 2D h-BN than for 2H-MoS2.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000390339000002	Publication Date	2016-10-21
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	5	Open Access
	Notes	; The authors acknowledge useful discussions with L. Wirtz, A. Molina-Sanchez, and C. Sevik. This work was supported by the ESF-Eurographene project CONGRAN, and the Flemish Science Foundation (FWO-Vl). ;			Approved	Most recent IF: 1.674
	Call Number	UA @ lucian @ c:irua:140309			Serial	4462
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	Author	Michel, K.H.
	Title	Sequence of orientational phase transitions in solid C₆₀			Type	A1 Journal article
	Year	1992	Publication	Chemical physics letters	Abbreviated Journal	Chem Phys Lett
	Volume	193	Issue		Pages	478-480
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Amsterdam	Editor
	Language		Wos	A1992HZ32900006	Publication Date	2002-07-25
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0009-2614;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.897	Times cited	14	Open Access
	Notes				Approved	MATERIALS SCIENCE, MULTIDISCIPLINARY 96/271 Q2 #
	Call Number	UA @ lucian @ c:irua:2971			Serial	2985
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	Author	Bussmann-Holder, A.; Dalal, N.; Michel, K.H.
	Title	Polarizability induced cooperative proton ordering, coexistence of order/disorder and displacive dynamics and isotope effects in hydrogen-bonded systems			Type	A1 Journal article
	Year	2000	Publication	The journal of physics and chemistry of solids T2 – Williamsburg Workshop on Ferroelectrics 99, JAN 31-FEB 03, 1999, WILLIAMSBURG, VIRGINIA	Abbreviated Journal	J Phys Chem Solids
	Volume	61	Issue	2	Pages	271-274
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Despite the general belief that hydrogen-bonded ferro- and antiferroelectrics undergo a pure order/disorder transition at the structural instability, new NMR data and a new theoretical concept yield convincing evidence that a pronounced displacive component is present in these systems, which modifies substantially the temperature dependencies of the tunnel and lattice mode frequencies. The experiments and their interpretation are presented. (C) 1999 Elsevier Science Ltd. All rights reserved.
	Address
	Corporate Author				Thesis
	Publisher	Pergamon-elsevier science ltd	Place of Publication	Oxford	Editor
	Language		Wos	000084147000020	Publication Date	2002-07-25
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0022-3697;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.059	Times cited	8	Open Access
	Notes				Approved	Most recent IF: 2.059; 2000 IF: 1.003
	Call Number	UA @ lucian @ c:irua:103469			Serial	2660
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	Author	Michel, K.H.; Lamoen, D.; David, W.I.F.
	Title	Orientational order and disorder in solid C₆₀ : theory and diffraction experiments			Type	A1 Journal article
	Year	1995	Publication	Acta crystallographica: section A: foundations of crystallography	Abbreviated Journal	Acta Crystallogr A
	Volume	51	Issue	3	Pages	365-374
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Starting from a microscope model of the intermolecular potential, a unified description is presented of the Bragg scattering law in the orientationally disordered and in the ordered phase of solid C-60. The orientational structure factor is expanded in terms of symmetry-adapted surface harmonics. The expansion coefficients are calculated from theory and compared with experiment Their temperature evolution is studied in the disordered phase at the 260 K transitions and in the ordered phase. In the ordered phase, new results from high-resolution neutron powder diffraction are given. In the disordered phase, space group Fm $($) over bar$$ 3m, the reflections have A(1g) symmetry; in the ordered phase, space group Pa $$($) over bar 3, reflections of T-2g symmetry appear and in addition the A(1g) reflections are renormalized. The orientational density distribution is calculated. The effective crystal-field potential is constructed, its temperature evolution in the ordered phase is studied and related to the occurrence of an orientational glass.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Copenhagen	Editor
	Language		Wos	A1995RB59400018	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0108-7673;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.307	Times cited	14	Open Access
	Notes				Approved	CHEMISTRY, MULTIDISCIPLINARY 65/163 Q2 # CRYSTALLOGRAPHY 10/26 Q2 #
	Call Number	UA @ lucian @ c:irua:12189			Serial	2518
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	Author	Copley, J.R.D.; Michel, K.H.
	Title	Neutron and X-ray scattering cross sections of orientationally disordered solid C₆₀			Type	A1 Journal article
	Year	1993	Publication	Journal Of Physics-Condensed Matter	Abbreviated Journal	J Phys-Condens Mat
	Volume	5	Issue		Pages	4353-4370
	Keywords	A1 Journal article; Electron Microscopy for Materials Science (EMAT);
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	London	Editor
	Language		Wos	A1993LK74100008	Publication Date	0000-00-00
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0953-8984	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.346	Times cited	34	Open Access
	Notes				Approved	MATERIALS SCIENCE, MULTIDISCIPLINARY 96/271 Q2 #
	Call Number	UA @ lucian @ c:irua:5778			Serial	2297
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	Author	Copley, J.R.D.; Michel, K.H.
	Title	Neutron and X-ray-scattering cross sections of orientationally disordered solid C₆₀			Type	A1 Journal article
	Year	1993	Publication	Journal of physics : condensed matter	Abbreviated Journal	J Phys-Condens Mat
	Volume	5	Issue	26	Pages	4353-4370
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Differential cross sections for neutron and x-ray scattering have been derived for the orientationally disordered phase of solid C60. Interaction centres are placed at nuclei and at the centres of interatomic bonds. Bragg and diffuse scattering cross sections, for single crystals and for powders, are formulated using symmetry-adapted rotator functions. Thermal averages are calculated taking account of crystal field effects. Thermally averaged orientational distribution functions have also been calculated.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	London	Editor
	Language		Wos	A1993LK74100008	Publication Date	2002-08-25
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0953-8984;1361-648X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.346	Times cited	34	Open Access
	Notes				Approved	MATERIALS SCIENCE, MULTIDISCIPLINARY 96/271 Q2 #
	Call Number	UA @ lucian @ c:irua:102972			Serial	2298
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	Author	Verberck, B.; Michel, K.H.
	Title	Nanotube field of C₆₀ and C₇₀ molecules in carbon nanotubes			Type	A1 Journal article
	Year	2007	Publication	International journal of quantum chemistry	Abbreviated Journal	Int J Quantum Chem
	Volume	107	Issue	13	Pages	2294-2319
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000249459800002	Publication Date	2007-02-20
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0020-7608;1097-461X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.92	Times cited	6	Open Access
	Notes				Approved	Most recent IF: 2.92; 2007 IF: 1.368
	Call Number	UA @ lucian @ c:irua:65785			Serial	2282
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	Author	Lamoen, D.; Michel, K.H.
	Title	Crystal field, orientational order, and lattice contraction in solid C₆₀			Type	A1 Journal article
	Year	1994	Publication	The journal of chemical physics	Abbreviated Journal	J Chem Phys
	Volume	101	Issue		Pages	1435-1443
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	A model of the intermolecular potential in solid C-60, which is based on Born-Mayer repulsions, van der Waals attractions, and electrostatic multipoles, is presented. The potential is expanded in terms of multipolar rotator functions. The orientation-orientation interaction and the crystal field are calculated. The orientational phase transition to the Pa3 phase is studied with the methods of statistical mechanics. The discontinuity of the order parameter at the transition and the temperature evolution of the order parameter are calculated. The lattice contraction at the phase transition is evaluated. The influence of the lattice contraction on the crystal field and on the orientational order is studied.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	A1994NW97900058	Publication Date	2002-07-26
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0021-9606;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.952	Times cited	39	Open Access
	Notes				Approved	CHEMISTRY, PHYSICAL 54/144 Q2 # PHYSICS, ATOMIC, MOLECULAR & CHEMICAL 9/35 Q2 #
	Call Number	UA @ lucian @ c:irua:9361			Serial	554
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	Author	Michel, K.H.
	Title	Molecular structure and orientational ordering in solid C₆₀			Type	A1 Journal article
	Year	1992	Publication	The journal of chemical physics	Abbreviated Journal	J Chem Phys
	Volume	97	Issue	7	Pages	5155-5162
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	A microscopic theory, which describes the orientational dynamics of C60 molecules in the face-centered cubic phase of C60-fullerite, is formulated or the case of a complex molecular structure. Interaction centers which comprise atoms, double bonds, and single bonds as molecular constituents contribute to the intermolecular potential. Orientation dependent physical properties are described in terms of symmetry-adapted rotator functions. It is found that a same set of rotator functions is sufficient even in the case of a complex molecular structure. Phase transition temperatures are discussed for various models of molecular structure.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	A1992JR33800062	Publication Date	2002-07-26
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0021-9606;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.952	Times cited	20	Open Access
	Notes				Approved	no
	Call Number	UA @ lucian @ c:irua:2973			Serial	2185
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	Author	Nikolaev, A.V.; Prassides, K.; Michel, K.H.
	Title	Charge transfer and polymer phases in AC₆₀ (A=K, Rb, Cs) fullerides			Type	A1 Journal article
	Year	1998	Publication	The journal of chemical physics	Abbreviated Journal	J Chem Phys
	Volume	108	Issue		Pages	4912-4923
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000072588400025	Publication Date	2002-07-26
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0021-9606;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.965	Times cited	14	Open Access
	Notes				Approved	Most recent IF: 2.965; 1998 IF: 3.147
	Call Number	UA @ lucian @ c:irua:23985			Serial	338
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	Author	Verberck, B.; Michel, K.H.; Nikolaev, A.V.
	Title	Crystal structures of polymerized fullerides AC₆₀, A=K, Rb, Cs, and alkali-mediated interactions			Type	A1 Journal article
	Year	2002	Publication	The journal of chemical physics	Abbreviated Journal	J Chem Phys
	Volume	116	Issue	23	Pages	10462-10474
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Starting from a model of rigid interacting C-60 polymer chains on an orthorhombic lattice, we study the mutual orientation of the chains and the stability of the crystalline structures Pmnn and I2/m. We take into account (i) van der Waals interactions and electric quadrupole interactions between C-60 monomers on different chains as well as (ii) interactions of the monomers with the surrounding alkali atoms. The direct interactions (i) always lead to an antiferrorotational structure Pmnn with alternate orientation of the C-60 chains in planes (001). The interactions (ii) with the alkalis consist of two parts: translation-rotation (TR) coupling where the orientations of the chains interact with displacements of the alkalis, and quadrupolar electronic polarizability (ep) coupling, where the electric quadrupoles on the C-60 monomers interact with induced quadrupoles due to excited electronic d-states of the alkalis. Both interactions (ii) lead to an effective orientation-orientation interaction between the C-60 chains and always favor the ferrorotational structure I2/m, where C-60 chains have a same orientation. The structures Pmnn for KC60 and I2/m for Rb- and CsC60 are the result of a competition between the direct interaction (i) and the alkali-mediated interactions (ii). In Rb- and CsC60 the latter are found to be dominant, the preponderant role being played by the quadrupolar electronic polarizability of the alkali ions. (C) 2002 American Institute of Physics.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000175905800044	Publication Date	2002-07-26
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0021-9606;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.965	Times cited	12	Open Access
	Notes				Approved	Most recent IF: 2.965; 2002 IF: 2.998
	Call Number	UA @ lucian @ c:irua:103350			Serial	578
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	Author	Nikolaev, A.V.; Michel, K.H.
	Title	Superexchange and electron correlations in alkali fullerides AC₆₀, A=K, Rb, Cs			Type	A1 Journal article
	Year	2005	Publication	The journal of chemical physics	Abbreviated Journal	J Chem Phys
	Volume	122	Issue	6	Pages	064310-64314
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Superexchange interactions in alkali fullerides AC(60) are derived for C-60 molecular ions separated by interstitial alkali-metal ions. We use a multiconfiguration approach which comprises the lowest molecular orbital states of the C-60 molecule and the excited s and d states of the alkali-metal atom A. Interactions are described by the valence bond (Heitler-London) method for a complex (C-60 – A – C-60) – with two valence electrons. The electronic charge transfer between the alkali-metal atom and a neighboring C-60 molecule is not complete. The occupation probability of excited d and s states of the alkali atom is not negligible. In correspondence with the relative positions of the C-60 molecules and A atoms in the polymer crystal, we consider 180degrees and 90degrees (angle) superexchange pathways. For the former case the ground state is found to be a spin singlet separated from a triplet at similar to20 K. For T < 20 K there appear strong spin correlations for the 180degrees superexchange pathway. The results are related to spin lattice relaxation experiments on CsC60 in the polymerized and in the quenched cubic phase. (C) 2005 American Institute of Physics.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000226918100018	Publication Date	2005-02-02
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0021-9606;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.965	Times cited	11	Open Access
	Notes				Approved	Most recent IF: 2.965; 2005 IF: 3.138
	Call Number	UA @ lucian @ c:irua:102740			Serial	3377
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	Author	Michel, K.H.; Verberck, B.; Hulman, M.; Kuzmany, H.; Krause, M.
	Title	Superposition of quantum and classical rotational motions in Sc₂C₂@C₈₄ fullerite			Type	A1 Journal article
	Year	2007	Publication	The journal of chemical physics	Abbreviated Journal	J Chem Phys
	Volume	126	Issue	6	Pages	064304,1-15
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000244250200008	Publication Date	2007-02-09
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0021-9606;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	2.965	Times cited	14	Open Access
	Notes				Approved	Most recent IF: 2.965; 2007 IF: 3.044
	Call Number	UA @ lucian @ c:irua:63628			Serial	3381
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	Author	Bostoen, C.; Michel, K.H.
	Title	Dynamics of a quadrupolar glass			Type	A1 Journal article
	Year	1991	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	43	Issue		Pages	4415-4422
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1991EX92100073	Publication Date	0000-00-00
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121; 0163-1829	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	33	Open Access
	Notes				Approved	no
	Call Number	UA @ lucian @ c:irua:939			Serial	773
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	Author	Zieliński, P.; Michel, K.H.
	Title	Microscopic model of surfaces in orientationally disordered ionic crystals : the (001) surface of KCN			Type	A1 Journal article
	Year	1992	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	46	Issue	8	Pages	4806-4815
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The crystallographic structure and the distribution of orientations of molecular ions are studied near the surface in an orientationally disordered crystal with the use of a Green-function formalism. The orientational degrees of freedom are treated by means of symmetry-adapted functions of angular coordinates. The structure of the (001) surface of KCN in its cubic fcc phase is then predicted using the existing data on the interaction of the ions K+ and CN-. A local antiferroelectric and antiferroelastic order i shown to exist in the surface region. The magnitude of the order and the spatial extent of the ordered re ion increase as the temperature approaches the point of the phase transition to the ordered phase. The,influence of the external electric field on the structure of the surface is predicted.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1992JK72500049	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	4	Open Access
	Notes				Approved	PHYSICS, CONDENSED MATTER 16/67 Q1 #
	Call Number	UA @ lucian @ c:irua:2974			Serial	2029
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	Author	Callebaut, A.K.; Michel, K.H.
	Title	Microscopic theory of orientational disorder and lattice instability in solid C₇₀			Type	A1 Journal article
	Year	1995	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	52	Issue	21	Pages	15279-15290
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	We have developed a microscopic theory which describes the orientational dynamics of C-70 molecules and its coupling to lattice displacements in the face-centered-cubic phase of C-70 fullerite. The single-molecule orientational density distribution in the disordered phase is calculated. The ferroelastic transition to the rhombohedral phase is investigated. The discontinuity of the orientational order parameter at the phase transition is calculated. It is found that the transition leads to a stretching of the primitive unit cell along a [111] cubic direction. A softening of the elastic constant c(44) at the transition is predicted.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1995TK97900042	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	20	Open Access
	Notes				Approved	PHYSICS, APPLIED 28/145 Q1 #
	Call Number	UA @ lucian @ c:irua:104421			Serial	2031
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	Author	Nikolaev, A.V.; Michel, K.H.
	Title	Microscopic theory of the rhombohedral phase and transition to the monoclinic phase of solid C₇₀			Type	A1 Journal article
	Year	1996	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	54	Issue	18	Pages	12733-12743
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Starting from a model of microscopic interactions between C-70 molecules, we have developed a theory which describes the orientational dynamics and its coupling to lattice displacements in the rhombohedral phase of C-70 fullerite. The Landau free energy is calculated. We obtain a first-order phase transition to a monoclinic structure with the space group P2(1)/m. The transition is driven by the condensation of orientational quadrupoles at the F point of the Brillouin zone of the rhombohedral lattice. We find no evidence that the monoclinic structure is connected with the freezing in of orientations around the fivefold molecular axis. We calculate the lattice strains that are associated with the transition to the monoclinic structure. The theory is compared with a range of experimental data on the phase transition.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1996VT68200028	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	5	Open Access
	Notes				Approved	no
	Call Number	UA @ lucian @ c:irua:16357			Serial	2034
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	Author	Lamoen, D.; Michel, K.H.
	Title	Microscopic theory of thermoelastic phenomena and pressure dependence in solid C₆₀			Type	A1 Journal article
	Year	1993	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	48	Issue	2	Pages	807-813
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	A microscopic theory for the coupling of molecular orientations with acoustic lattice displacements is proposed. The relevant interaction is quadratic in the orientational-order-parameter variables and linear in longitudinal strains. The coupling is evaluated for a complex molecular structure. The intermolecular potential is obtained from interaction centers placed at nuclei and at the centers of interatomic bonds. The free energy is derived and the experimental consequences of the theory are studied. The Clausius-Clapeyron equation for orientational melting is obtained. The theory explains the decrease of the lattice constant at the first-order phase transition and the increase of the transition temperature with applied pressure.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1993LM88500014	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	32	Open Access
	Notes				Approved	PHYSICS, CONDENSED MATTER 16/67 Q1 #
	Call Number	UA @ lucian @ c:irua:5779			Serial	2035
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	Author	Beheshtian, J.; Sadeghi, A.; Neek-Amal, M.; Michel, K.H.; Peeters, F.M.
	Title	Induced polarization and electronic properties of carbon-doped boron nitride nanoribbons			Type	A1 Journal article
	Year	2012	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	86	Issue	19	Pages	195433-195438
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The electronic properties of boron nitride nanoribbons (BNNRs) doped with a line of carbon atoms are investigated using density functional calculations. By replacing a line of alternating B and N atoms with carbons, three different configurations are possible depending on the type of the atoms which bond to the carbons. We found very different electronic properties for these configurations: (i) the NCB arrangement is strongly polarized with a large dipole moment having an unexpected direction, (ii) the BCB and NCN arrangements are nonpolar with zero dipole moment, (iii) the doping by a carbon line reduces the band gap regardless of the local arrangement of the borons and the nitrogens around the carbon line, and (iv) the polarization and energy gap of the carbon-doped BNNRs can be tuned by an electric field applied parallel to the carbon line. Similar effects were found when either an armchair or zigzag line of carbon was introduced.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000311694200006	Publication Date	2012-11-29
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	41	Open Access
	Notes	; We would like to thank J. M. Pereira and S. Goedecker for helpful discussions. This work was supported by the Flemish Science Foundation (FWO-Vl), the ESF-EuroGRAPHENE project CONGRAN. M. N.-A is supported by EU-Marie Curie IIF postdoc Fellowship/299522. ;			Approved	Most recent IF: 3.836; 2012 IF: 3.767
	Call Number	UA @ lucian @ c:irua:105136			Serial	1603
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	Author	Tsvyashchenko, A.V.; Nikolaev, A.V.; Velichkov, A.I.; Salamatin, A.V.; Fomicheva, L.N.; Ryasny, G.K.; Sorokin, A.A.; Kochetov, O.I.; Budzynski, M.; Michel, K.H.
	Title	Lowering of the spatial symmetry at the gamma ->alpha phase transition in cerium			Type	A1 Journal article
	Year	2010	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	82	Issue	9	Pages	1-4
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Using time-differential perturbed angular correlation spectroscopy we have measured the electric field gradient (EFG) at 111Cd probe nuclei in solid Ce in a pressure range up to 8 GPa. Covering various allotropic phases of Ce, we find that the value of the EFG in the cubic α phase is almost four times larger than in the cubic γ phase and close to values in the noncubic phases α′ and α″. These results together with the differences in time modulation of the spectra are interpreted as evidence for quadrupolar electronic charge-density ordering and symmetry lowering at the γ→α transition while the lattice remains face-centered cubic
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000282004400001	Publication Date	2010-09-16
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	11	Open Access
	Notes	; This work is supported by the Program of the Presidium of the Russian Academy of Sciences “Physics of Strongly Compressed Matter.” We are grateful to S. M. Stishov, B. Verberck, A. N. Grum-Grzhimailo, V. B. Brudanin and G. Heger for support of this work and discussion of the results. ;			Approved	Most recent IF: 3.836; 2010 IF: 3.774
	Call Number	UA @ lucian @ c:irua:85464			Serial	1854
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	Author	Nikolaev, A.V.; Michel, K.H.
	Title	Microscopic theory of quadrupolar oredring in TmTe			Type	A1 Journal article
	Year	2001	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	63	Issue		Pages	1-10
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	000167402100025	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	7	Open Access
	Notes				Approved	Most recent IF: 3.836; 2001 IF: NA
	Call Number	UA @ lucian @ c:irua:36882			Serial	2033
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	Author	Verberck, B.; Michel, K.H.
	Title	Nanotube field and orientational properties of C₇₀ molecules in carbon nanotubes			Type	A1 Journal article
	Year	2007	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	75	Issue	4	Pages	045419,1-14
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The orientation of a C(70) fullerene molecule encapsulated in a single-walled carbon nanotube (SWCNT) depends on the tube radius. First we confirm that chirality effects do not affect the orientation as well by comparing discrete atomistic calculations with the results of a continuous tube approximation for a variety of SWCNTs. The molecular and the tube symmetry are exploited by using symmetry-adapted rotator functions. We accurately determine the optimal molecular orientation as a function of the tube radius; for low (less than or similar to 7 A) and high (greater than or similar to 7.2 A) tube radii, lying and standing molecular orientations are recovered, respectively. In between, we observe a transition regime. In addition, we consider off-axis positions. We perform a one-dimensional liquid description of a chain of on-axis C(70) molecules inside a SWCNT. All results agree well with recent x-ray diffraction experiments.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	000243895600128	Publication Date	2007-01-17
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	23	Open Access
	Notes				Approved	Most recent IF: 3.836; 2007 IF: 3.172
	Call Number	UA @ lucian @ c:irua:63752			Serial	2280
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	Author	Verberck, B.; Michel, K.H.
	Title	Nanotube field of C₆₀ molecules in carbon nanotubes: atomistic versus continuous approach			Type	A1 Journal article
	Year	2006	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	74	Issue	4	Pages	045421,1-14
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	000239426800113	Publication Date	2006-07-22
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	31	Open Access
	Notes				Approved	Most recent IF: 3.836; 2006 IF: 3.107
	Call Number	UA @ lucian @ c:irua:60090			Serial	2281
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	Author	Verberck, B.; Nikolaev, A.V.; Michel, K.H.
	Title	Orientational charge density waves and the metal-insulator transition in polymerized KC₆₀			Type	A1 Journal article
	Year	2005	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	71	Issue	16	Pages	165117-11
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	A theoretical model is presented for the description of the metal-insulator transition which accompanies the structural phase transition at T approximate to 50 K in polymerized KC60. The model involves orientational charge density waves (along the C-60 polymer chains) which were introduced previously for a description of the structural phase transition. A satisfactory qualitative and quantitative understanding is obtained when the three-dimensionality of the crystal and the presence of the K+ counterions is properly taken into account.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000228763100035	Publication Date	2005-04-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	1	Open Access
	Notes				Approved	Most recent IF: 3.836; 2005 IF: 3.185
	Call Number	UA @ lucian @ c:irua:104076			Serial	2514
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	Author	Michel, K.H.; Verberck, B.
	Title	Phonon dispersions and piezoelectricity in bulk and multilayers of hexagonal boron nitride			Type	A1 Journal article
	Year	2011	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	83	Issue	11	Pages	115328-115328,14
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	A unified theory of phonon dispersions and piezoelectricity in bulk and multilayers of hexagonal boron nitride (h-BN) is derived. The dynamical matrix is calculated on the basis of an empirical force constant model of intralayer valence and interlayer van der Waals interactions. Coulomb interactions are calculated by Ewalds method, adapted for the three-dimensional (3D) and the multilayer case. The deformation of the ionic charge distribution with long-wave lattice displacements is taken into account. Special attention is devoted to the nonanalytic long-range Coulomb contribution to the dynamical matrix which is different for the 3D crystal and the multilayer case. Consequently there is a splitting of the transverse optical (TO) and longitudinal optical (LO) phonon branches of E1u symmetry and a discontinuity of the A2u branch at the Γ point in 3D h-BN. No such splitting and discontinuity at Γ are present in multilayer crystals with a finite number N of layers. There a diverging bundle of N overbending optical phonon branches emerges from Γ. Borns long-wave theory is applied and extended for the study of piezoelectricity in layered crystals. While 3D h-BN and h-BN multilayers with an even number of layers (symmetry D6h) are not piezoelectric, multilayers with an uneven number of Nu layers (symmetry D3h) are piezoelectric; the piezoelectric coefficient e1,11 is inversely proportional to Nu.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000288783700005	Publication Date	2011-03-24
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	82	Open Access
	Notes	; Discussions with G. Heger, B. Partoens, and F. M. Peeters are gratefully acknowledged. This work has been supported by the Flemish Science Foundation (FWO-V1) and the Bijzonder Onderzoeksfonds, Universiteit Antwerpen (BOF-UA). ;			Approved	Most recent IF: 3.836; 2011 IF: 3.691
	Call Number	UA @ lucian @ c:irua:89602			Serial	2603
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	Author	Nikolaev, A.V.; Michel, K.H.
	Title	Symmetry lowering at the structural phase transitions in NpO₂ and UO₂			Type	A1 Journal article
	Year	2003	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	68	Issue	5	Pages	054112-054112,7
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The structural phase transitions with electric-quadrupole long-range order in NpO2 (Fm (3) over barm-->Pn (3) over barm) and UO2 (Fm (3) over barm-->Pa (3) over bar) are analyzed from a group theoretical point of view. In both cases, the symmetry lowering involves three quadrupolar components belonging to the irreducible representation T-2g (Gamma(5)) of O-h and condensing in a triple-q structure at the X point of the Brillouin zone. The Pa (3) over bar structure is close to Pn (3) over barm, but allows for oxygen displacements. The Pa (3) over bar ordering leads to an effective electrostatic attraction between electronic quadrupoles while the Pn (3) over barm ordering results in a repulsion between them. It is concluded that the Pn (3) over barm structure can be stabilized only through some additional process such as strengthening of the chemical bonding between Np and O. We also derive the relevant structure-factor amplitudes for Pn (3) over barm and Pa (3) over bar, and the effect of domains on resonant x-ray scattering experiments.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000185240100038	Publication Date	2003-08-29
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	15	Open Access
	Notes				Approved	Most recent IF: 3.836; 2003 IF: NA
	Call Number	UA @ lucian @ c:irua:94847			Serial	3405
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	Author	Verberck, B.; Nikolaev, A.V.; Michel, K.H.
	Title	Theoretical model for the structural phase transition at the metal-insulator transition in polymerized KC₆₀			Type	A1 Journal article
	Year	2002	Publication	Physical Review B	Abbreviated Journal	Phys Rev B
	Volume	66	Issue	16	Pages	165425-165425,14
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The recently discovered structural transition in polymerized KC60 at about 50 K results in a doubling of the unit cell volume and accompanies the metal-insulator transition. Here we show that the ((a) over right arrow+(c) over right arrow,(b) over right arrow,(a) over right arrow-(c) over right arrow) superstructure results from small orientational charge density waves along the polymer chains and concomitant displacements of the surrounding K+ ions. The effect is specific for the space group Pmnn of KC60 and is absent in RbC60 and CsC60 (space group I2/m). The mechanism is relevant for the metal-insulator transition.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000179286400135	Publication Date	2002-10-30
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	10	Open Access
	Notes				Approved	Most recent IF: 3.836; 2002 IF: NA
	Call Number	UA @ lucian @ c:irua:94907			Serial	3608
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