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	Author	Lamoen, D.; Michel, K.H.
	Title	Molecular structure, crystal field and orientational order in solid C₆₀			Type	H1 Book chapter
	Year	1994	Publication		Abbreviated Journal
	Volume		Issue		Pages	183-202
	Keywords	H1 Book chapter; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	s.l.	Editor
	Language		Wos	A1994BE86T00011	Publication Date	0000-00-00
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN		ISBN	0-7923-3109-5	Additional Links	UA library record; WoS full record;
	Impact Factor		Times cited		Open Access
	Notes				Approved
	Call Number	UA @ lucian @ c:irua:9355			Serial	2186
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	Author	Lynden-Bell, R.M.; Michel, K.H.
	Title	Translation-rotation coupling, phase transitions and elastic phenomena in orientationally disordered crystals			Type	A1 Journal article
	Year	1994	Publication	Reviews of modern physics	Abbreviated Journal	Rev Mod Phys
	Volume	66	Issue		Pages	721-762
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York	Editor
	Language		Wos	A1994PG73600003	Publication Date	2002-09-05
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0034-6861;1539-0756;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	29.604	Times cited	128	Open Access
	Notes				Approved	no
	Call Number	UA @ lucian @ c:irua:9359			Serial	3702
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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	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	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.; Nikolaev, A.V.
	Title	Anisotropic packing and one-dimensional fluctuations of C₆₀ molecules in carbon nanotubes			Type	A1 Journal article
	Year	2005	Publication	Physical review letters	Abbreviated Journal	Phys Rev Lett
	Volume	95	Issue	18	Pages	185506-185506,4
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The confinement of a C-60 molecule encapsulated in a cylindrical nanotube depends on the tube radius. In small tubes with radius R-T less than or similar to 7 A, a fivefold axis of the molecule coincides with the tube axis. The interaction between C-60 molecules in the nanotube is then described by a O-2-rotor model on a 1D liquid chain with coupling between orientational and displacive correlations. This coupling leads to chain contraction. The structure factor of the 1D liquid is derived. In tubes with a larger radius the molecular centers of mass are displaced off the tube axis. The distinction of two groups of peapods with on- and off-axis molecules suggests an explanation of the apparent splitting of A(g) modes of C-60 in nanotubes measured by resonant Raman scattering.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000232887400041	Publication Date	2005-10-28
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0031-9007;1079-7114;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	8.462	Times cited	40	Open Access
	Notes				Approved	Most recent IF: 8.462; 2005 IF: 7.489
	Call Number	UA @ lucian @ c:irua:94717			Serial	127
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	Author	Michel, K.H.; Verberck, B.; Nikolaev, A.
	Title	Mercator maps of orientations of a C₆₀ molecule in single-walled nanotubes with distinct radii			Type	A1 Journal article
	Year	2005	Publication	AIP conference proceedings	Abbreviated Journal
	Volume	786	Issue		Pages	69-72
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	We study the confinement of a C-60 molecule encapsulated in a cylindrical nanotube as a function of the tube radius. Drawing the Mercator maps of the potential, we find two distinct molecular orientations; for tubes with small radii, R-T less than or similar to 7 angstrom, a fivefold axis of the molecule coincides with the tube long axis, for larger radii, R-T less than or similar to 8 angstrom, a threefold axis of the molecule coincides with the tube long axis. These different orientations are caused by the relative importance of the repulsive and the attractive parts of the van der Waals potentials of the molecule with the tube wall for small and large tubes respectively. Experimental evidence is provided by the apparent splitting of A(g) modes of the C-60 molecule in resonant Raman scattering.
	Address
	Corporate Author				Thesis
	Publisher	Amer inst physics	Place of Publication	Melville	Editor
	Language		Wos		Publication Date	0000-00-00
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0094-243x	ISBN		Additional Links	UA library record; WoS full record;
	Impact Factor		Times cited		Open Access
	Notes				Approved	Most recent IF: NA
	Call Number	UA @ lucian @ c:irua:94738			Serial	1993
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	Author	Mattauch, S.; Heger, G.; Michel, K.H.
	Title	High resolution neutron and X-ray diffraction studies as a function of temperature and electric field of the ferroelectric phase transition of RDP			Type	A1 Journal article
	Year	2004	Publication	Crystal research and technology	Abbreviated Journal	Cryst Res Technol
	Volume	39	Issue	12	Pages	1027-1054
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Neutron and high resolution X-ray diffraction investigations on perfect single crystals of RbH2PO4 (RDP), a hydrogen bonded ferroelectric of KDP type are reported. The results of crystal structure analysis from diffraction data, below and above the paraelectric – ferroelectric phase transition, support a disorder – order character Of [PO4H2](-)-groups. The tetragonal symmetry of the paraelectric phase with the double well potential of the hydrogen atoms obtained by diffraction, results simply from a time-space average of orthorhombic symmetry. According to the group – subgroup relation between the tetragonal space group 142d and the orthorhombic Fdd2 a short range order of ferroelectric clusters in the tetragonal phase is observed. With decreasing temperature the ferroelectric clusters increase and the long range interaction between their local polarisation vectors leads to the formation of lamellar ferroelectric domains with alternating polarisation directions at T-C = 147 K. From the high resolution X-ray data it is concluded that below T-C the ferroelastic strain in the (a,b)-plane leads to micro-angle grain boundaries at the domain walls. The tilt angle is enhanced by an applied electric field parallel to the ferroelectric axis. The resulting dislocations at the domain walls persist in the paraelectric phase leading to a memory effect for the arrangement of twin lamellae. With increased electric field the phase transition temperature T-C is decreased.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000225681100001	Publication Date	2004-11-12
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0232-1300;1521-4079;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1	Times cited	12	Open Access
	Notes				Approved	Most recent IF: 1; 2004 IF: 0.770
	Call Number	UA @ lucian @ c:irua:94785			Serial	1459
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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	2004	Publication	AIP conference proceedings	Abbreviated Journal
	Volume	723	Issue		Pages	339-342
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Polymerized KC60 undergoes a structural phase transition accompanied by a metal-insulator transition around 50 K. To explain the structural aspect, a mechanism involving small orientational deviations of the valence electron density on every C-60 monomer orientational charge density waves (OCDWs) – has already been proposed earlier. In the present work, we address the metal-insulator transition using the OCDW concept. We are inspired by the analogy between a polymer chain exhibiting an OCDW and a linear atomic chain undergoing a static lattice deformation doubling the unit cell: such a deformation implies a band gap at the zone boundary, yielding an insulating state (Peierls instability). Within our view, a similar mechanism occurs in polymerized KC60; the OCDW plays the role of the lattice deformation. We present tight-binding band structure calculations and conclude that the metal-insulator transition can indeed be explained using OCDWs, but that the threedimensionality of the crystal plays an unexpected key role.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York	Editor
	Language		Wos		Publication Date	0000-00-00
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0094-243x	ISBN		Additional Links	UA library record; WoS full record;
	Impact Factor		Times cited		Open Access
	Notes				Approved	Most recent IF: NA
	Call Number	UA @ lucian @ c:irua:94831			Serial	2513
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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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	Author	Michel, K.H.; Copley, J.R.D.; Neumann, D.A.
	Title	Microscopic theory of orientational disorder and the orientational phase transition in solid C₆₀			Type	A1 Journal article
	Year	1992	Publication	Physical review letters	Abbreviated Journal	Phys Rev Lett
	Volume	68	Issue	19	Pages	2929-2932
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	We have developed a microscopic theory which describes the orientational dynamics of C60 molecules in the face-centered-cubic phase of C60 fullerite. The molecular interaction potential and the crystal-field potential are formulated in terms of symmetry-adapted rotator functions. The phase transition to the Pa3BAR structure is driven by an active multipolar mode of T2g symmetry belonging to the l = 10 manifold. The Birman criterion is satisfied. The transition is found to be of first order.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	A1992HT64800019	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0031-9007;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	7.512	Times cited	94	Open Access
	Notes				Approved
	Call Number	UA @ lucian @ c:irua:95492			Serial	2032
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	Author	Michel, K.H.; Verberck, B.
	Title	Theory of rigid-plane phonon modes in layered crystals			Type	A1 Journal article
	Year	2012	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	85	Issue	9	Pages	094303-094303,11
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The lattice dynamics of low-frequency rigid-plane modes in metallic (graphene multilayers, GML) and in insulating (hexagonal boron-nitride multilayers, BNML) layered crystals is investigated. The frequencies of shearing and compression (stretching) modes depend on the layer number N and are presented in the form of fan diagrams. The results for GML and BNML are very similar. In both cases, only the interactions (van der Waals and Coulomb) between nearest-neighbor planes are effective, while the interactions between more distant planes are screened. A comparison with recent Raman scattering results on low-frequency shear modes in GML [Tan et al., Nat. Mater., in press, doi: 10.1038/nmat3245, (2012)] is made. Relations with the low-lying rigid-plane phonon dispersions in the bulk materials are established. Master curves, which connect the fan diagram frequencies for any given N, are derived. Static and dynamic thermal correlation functions for rigid-layer shear and compression modes are calculated. The results might be of use for the interpretation of friction force experiments on multilayer crystals.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000301646000006	Publication Date	2012-03-19
	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	38	Open Access
	Notes	; The authors are indebted to J. Maultzsch for bringing Ref. 20 to their attention. They thank D. Lamoen, F.M. Peeters, B. Trauzettel, and C. Van Haesendonck for useful discussions. This work has been financially supported by the Research Foundation Flanders (FWO). ;			Approved	Most recent IF: 3.836; 2012 IF: 3.767
	Call Number	UA @ lucian @ c:irua:97787			Serial	3619
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