The Nonempirical Calculation of the Cation Ordering and Lattice Dynamics in the Solid Solutions of PbSc1/2Nb1/2O3 and PbSc1/2Ta1/2O3

2006 ◽  
Vol 115 ◽  
pp. 305-310
Author(s):  
V.I. Zinenko ◽  
S.N. Sofronova
Keyword(s):  
Solid Solutions ◽  
Ionic Crystal ◽  
Mean Field ◽  
Nonempirical Calculation ◽  
Cation Ordering ◽  
Effective Hamiltonian ◽  
The Monte Carlo Method ◽  
Ordered Phases ◽  
Phase Transition Temperatures ◽  
Crystal Model

An effective Hamiltonian for the study of Sc–Nb(Ta) cation ordering in PbSc1/2Nb(Ta)1/2O3 solid solutions is worked out. To determine the parameters of the effective Hamiltonian, a nonempirical calculation is performed within an ionic-crystal model taking into account the deformation, dipole, and quadrupole polarizabilities of ions. The phase transition temperatures are calculated by the mean field, the cluster approximations, and the Monte-Carlo method. Within the same ionic-crystal model, we calculated the high-frequency permittivity, Born dynamic charges, and the phonon spectrum for completely disordered and ordered phases.

EFFECT OF THE SURFACES ON ORIENTATIONAL PROPERTIES AND PECULIARITIES OF PHASE TRANSITIONS IN THERMOTROPIC NEMATICS

2005 ◽  
Vol 19 (18) ◽  
pp. 2975-2987 ◽  
Author(s):  
ARIF NESRULLAJEV ◽  
FATMA Z. TEPEHAN
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Liquid Phase ◽  
Mean Field Theory ◽  
Mean Field ◽  
Eutectic Mixture ◽  
Transition Temperatures ◽  
Isotropic Liquid ◽  
Liquid Phase Transition ◽  
Phase Transition Temperatures

In this work, the effect of thin films on the orientational, thermotropic and optical properties and on the peculiarities of the nematic–isotropic liquid phase transition has been carried out. The planar textures of MBBA+EBBA eutectic mixture on the surfaces coated with Al 2 O 3 and ZrO 2 thin films have been obtained. The optical and thermodynamical parameters of the obtained, oriented textures have been determined. The effect of thin films on the temperature width of heterophase region and on the nematic–isotropic liquid phase transition temperatures has been investigated. The shift of the phase transition temperatures and the change of the temperature width of the heterophase region have been revealed. For the analysis of peculiarities of the nematic–isotropic liquid phase transition and the heterophase regions of this transition, the mean field theory has been used.

Mean field theory of the orientational properties of (J = 1) hydrogen molecules on the surface of Grafoil

1979 ◽  
Vol 57 (11) ◽  
pp. 1852-1869 ◽  
Author(s):  
A. B. Harris ◽  
A. J. Berlinsky
Keyword(s):  
Field Theory ◽  
Model Comparison ◽  
Nearest Neighbor ◽  
Mean Field Theory ◽  
Computer Calculation ◽  
Mean Field ◽  
Free Energy Calculations ◽  
Axially Symmetric ◽  
Hydrogen Molecules ◽  
Ordered Phases

A mean field theory is developed which is applicable to the orientational behavior of (J = 1) hydrogen molecules on the surface of Grafoil. The hydrogen molecules are assumed to form a triangular lattice in a weak, axially symmetric crystal field, Vc. perpendicular to the substrate and to interact via the electric quadrupole–quadrupole interaction with nearest-neighbor coupling constant Γ. Free energy calculations for the various possible ordered phases are presented, and a Landau expansion is used to investigate the phase boundary between the disordered and ordered phases. A computer calculation, based on the iterative method of James, is used to determine the lines of transition between ordered phases. For almost all values of Vc < 22.5Γ, the disordered to ordered state phase transition is continuous. Four distinct types of ordered phases are found — a four-sublattice phase, two two-sublattice phases, and a one-sublattice phase which resembles an X–Y model. Comparison is made to the recent nmr data of Kubik and Hardy for H2 and D2 on Grafoil.

Thermal fluctuations in a realistic ionic-crystal model

2022 ◽  
Vol 586 ◽  
pp. 126463
Author(s):  
Fabrizio Gangemi ◽  
Roberto Gangemi ◽  
Andrea Carati ◽  
Luigi Galgani
Keyword(s):  
Ionic Crystal ◽  
Thermal Fluctuations ◽  
Crystal Model

Phase transitions of (1−x) PbZrO3 + x (Na1/2Bi1/2)TiO3 (0.01 ≤ x ≤ 0.15) solid solutions

1999 ◽  
Vol 14 (1) ◽  
pp. 83-89 ◽  
Author(s):  
Jung-Kun Lee ◽  
Hyuk-Joon Youn ◽  
Kug Sun Hong
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Solid Solutions ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Two Phase ◽  
Phase Transition Temperatures ◽  
Temperature Phase Transition ◽  
Increasing Temperature

Morphotropic phase boundaries and temperature dependent phase transitions of (1 – x) PbZrO3 + x (Na1/2Bi1/2)TiO3 (0.01 ≤ x ≤ 0.15) solid solutions were investigated by x-ray diffraction, differential scanning calorimetry (DSC), and dielectric property analysis. Two morphotropic phase transitions at room temperature were found at x = 0.1 and 0.13, which were from antiferroelectric orthorhombic (with 4 × 4 × 2 superlattice [orthorhombic (I)]) to antiferroelectric orthorhombic (with 2 × 2 × 2 superlattice [orthorhombic (II)]) and from orthorhombic (II) to ferroelectric rhombohedral, respectively. With increasing temperature, the samples with 0.01 ≤ x < 0.1 showed two phase transitions, i.e., from orthorhombic (I) to orthorhombic (II) and from orthorhombic (II) to cubic. The other samples had only one phase transition with increasing temperature. Phase transition temperatures of all the samples were measured using DSC, and a phase diagram for the solid solutions was constructed. A model illustrating the antiparallel shift of Pb ions in the orthorhombic (II) phase was also proposed.

POSSIBLE COEXISTENCE OF ANTIFERROMAGNETISM AND SUPERCONDUCTIVITY IN THE HUBBARD MODEL

1988 ◽  
Vol 01 (09n10) ◽  
pp. 341-347 ◽  
Author(s):  
SHEN JUE-LIAN ◽  
SU ZHAO-BIN ◽  
DONG JIN-MING ◽  
YU LU
Keyword(s):  
Hubbard Model ◽  
High Temperature Superconductivity ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Antiferromagnetic Order ◽  
Effective Hamiltonian ◽  
Hamiltonian Approach ◽  
Theoretical Approaches ◽  
The Mean

The Hubbard model in the nearly half-filled case was studied in the mean field approximation using the effective Hamiltonian approach. Both antiferromagnetic order parameter and condensation of singlet pairs were considered. In certain parameter range the coexistence of antiferromagnetism and superconductivity is energetically favorable. Relations to the high temperature superconductivity and other theoretical approaches are also discussed.

Comparative Study of Cation Ordering Effects in Single Crystals of 1:1 and 1:2 Complex Perovskites Solid Solutions

2004 ◽  
Vol 298 (1) ◽  
pp. 267-274 ◽  
Author(s):  
I. P. Raevski ◽  
S. A. Prosandeev ◽  
S. M. Emelyanov ◽  
V. G. Smotrakov ◽  
V. V. Eremkin ◽  
...  
Keyword(s):  
Comparative Study ◽  
Single Crystals ◽  
Solid Solutions ◽  
Cation Ordering ◽  
Ordering Effects ◽  
Complex Perovskites

Formation and Characterization of “1:1” Ordered Phases in Am4+O3 - A(B2+1/3Ta2/3)O3 (A= Ba, Sr; B2+ = Mg, Zn; M4+ = Ti, Sn, Zr, Ce) Perovskites

1996 ◽  
Vol 453 ◽  
Author(s):  
L. Chai ◽  
M. A. Akbas ◽  
P. K. Davies
Keyword(s):  
Dielectric Loss ◽  
Crystal Chemistry ◽  
Random Distribution ◽  
Cation Ordering ◽  
Layer Model ◽  
Ordered Phases ◽  
Perovskite Ceramics ◽  
Low Levels

AbstractPrevious research has demonstrated that the formation of nano-sized “1:1” cation ordered domains in Zr4+ substituted Ba(Zn1/3Ta2/3)O3 may be responsible for the anomalies in the dielectric loss properties of these perovskite ceramics. To explore the structure and crystal chemistry of these phases, the effect of a series of M4+ substitutions (Zr4+, Ce4+, Sn4+, and Ti4+) on the B-site cation ordering in Ba(Zn1/3Ta2/3)O3, Ba(Mg1/3Ta2/3)O3, and Sr(Mg1/3Ta2/3)O3 has been examined. In all cases the substitution of low levels (∼ 5 mole %) of “over-sized” tetravalent cations (e.g. Zr4+, Ce4+) promotes a transformation to a 1:1 ordered phase, while the introduction of “under-sized” cations (e.g. Ti4+) stabilizes a disordered perovskite. Using Rietveld methods the structures of the 1:1 ordered A(βI1/2βII1/2)O3 phases were found to conform to a “random layer” model in which the βII positions are occupied by Ta, and the βI sites by a random distribution of the Mg(Zn), M4+ and residual Ta cations.

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