Calculation of the (GaAs)m(AlAs)n Superlattice Piezoelectric Constants

1994 ◽  
Vol 356 ◽  
Author(s):  
Vadim. Yu. Mirovitskii
Keyword(s):  
Phase Transitions ◽  
Order Parameter ◽  
Thermodynamic Potential ◽  
Mixed Crystal ◽  
Piezoelectric Properties ◽  
Phenomenological Theory ◽  
Initial Structure ◽  
Spatial Correlations ◽  
Specific Calculations ◽  
Piezoelectric Constants

AbstractA new method for calculation of superlattice (SL) piezoelectric properties is proposed. It is used for derivation of the piezoelectric constants of ultrathin [001] oriented (GaAs)m(AlAs)n SL. These SL are formally considered to result from complete ordering Ga (Al) atoms over a-positions of a hypothetical initial structure of a bulk mixed crystal of (GaxAl1-x)As with x=m/(m+n). This viewpoint allows us to develop a method which is close to the Landau phenomenological theory of second- order phase transitions and which is intended for calculation of the SL crystal-lophysical constants. It is shown that a nontrivial term has much significance in changing one of the piezoelectric constants, γz,xy, when the initial structure is transformed into a SL. This term is composed of coefficients at three translational invariants (Dzyaloshinskii invariants) in the expansion of the thermodynamic potential of the “ordering” system in a power series of the order parameter components. The values of these coefficients must be obtained from microscopic calculations which take account of spatial correlations in Ga(Al) atomic distribution. Specific calculations are carried out for a SL with m+n=3.

Method for Calculation of Dielectric Properties of Modulated Semiconducting Structures

1995 ◽  
Vol 417 ◽  
Author(s):  
V. Yu. Mirovitskii ◽  
O. Yu. Mashtakov
Keyword(s):  
Dielectric Properties ◽  
Thermodynamic Potential ◽  
Mixed Crystal ◽  
Landau Theory ◽  
Point Of View ◽  
Dielectric Constants ◽  
Initial Structure ◽  
Numerical Estimation ◽  
Spatial Correlations ◽  
Phenomenological Landau Theory

AbstractA new method for calculation the effects of composition modulation upon the dielectric properties of semiconductors is proposed. Specific consideration is carried out for ultrathin [001] oriented (AIIICV)m(BIIICV)n superlattices (SL). These SL are formally considered to result from complete A(B) atoms orderiig over a-sublattice in a hypothetical initial structure –bulk mixed crystal (AxB1−x)C with zincblende lattice and x = m/(m + n). From this point of view a variation in dielectric constants tensor (DCT) induced by the ordering can be calculated nearly in a spirit of the phenomenological Landau theory of second-order phase transitions. It is shown that the changes in spatial dispersion of the DCT are expressed through the coefficients at invariants in the expansion of SL thermodynamic potential in a power series of the order parameter components. The way is described for numerical estimation of the thermodynamic potential coefficients from microscopic model of the initial alloy which take account of spatial correlations in A(B) atoms distribution.

Elastic Modulus of the (GaA.s)m(A.l A.s)n Superlattices

1992 ◽  
Vol 291 ◽  
Author(s):  
Vadim Yu. Mirovitskii
Keyword(s):  
Elastic Modulus ◽  
Order Parameter ◽  
Thermodynamic Potential ◽  
Mixed Crystal ◽  
Landau Theory ◽  
Point Of View ◽  
The Other ◽  
Symmetry Properties ◽  
Phenomenological Landau Theory ◽  
Elastic Modulus Tensor

ABSTRACTThe ultrathin (GaAs)m (AlAs)n superlattices ( SL ) grown along [001] are formally considered as a result, of ordering-type phase transition from an initial hypothetical mixed crystal (Gax Al1-x)As with x = m/(m+n) . From this point of view changes of elastic modulus tensor (EMT) induced by ordering can he calculated nearly in a spirit of phenomenological Landau theory of second-order phase transitions. It .is shown that a change of EMT component. S66 is completely determined by symmetry properties of two translational (Dzyaloshinskji) invariants of m+n power .in the expansion of SL thermodynamic potential in a power series .in order parameter components. The changes of the other EMT components depend on the second power of order parameter .The expressions are found out to connect. EMT of a definite ordered phase (SL - family with m+n = 3) with that, of the initial one.

scholarly journals Unveiling Phase Transitions In 1D Systems With Short-Range Interactions

2021 ◽  
Author(s):  
Lucas Souza Ferreira ◽  
Lucas Nunes Jorge ◽  
Cláudio J DaSilva ◽  
Minos A Neto ◽  
Álvaro A Caparica
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Order Parameter ◽  
Short Range ◽  
Exchange Interactions ◽  
Spatial Correlations ◽  
One Dimensional ◽  
Entropic Sampling ◽  
Different Order ◽  
Inappropriate Choice

Abstract The statement that any phase transition is related to the appearance or disappearance of long-range spatial correlations precludes a finite transition temperature in one-dimensional (1D) systems. In this paper we demonstrate that the 1D Ising model with short-range exchange interactions exhibits a second-order phase transition at a finite temperature relying on the proper choice of the order parameter. To accomplish this, we combined analytical calculations and high-precision entropic sampling simulations and chose a slightly different order parameter, namely the module of the magnetization. Notably, we detected a phase transition with a corresponding critical temperature around 15 K, which is in excellent agreement with experimental results. Our study indicates that an inappropriate choice of the order parameter may mask phase transitions in one-dimensional systems.

Optical Properties and Phenomenological Theory of Ferri-Ferri Phase Transitions in Antiferroelectric Liquid Crystals

1997 ◽  
Vol 7 (12) ◽  
pp. 1817-1828 ◽  
Author(s):  
P. Gisse ◽  
M. Sidir ◽  
V. L. Lorman ◽  
R. Farhi ◽  
J. Pavel ◽  
...  
Keyword(s):  
Optical Properties ◽  
Phase Transitions ◽  
Liquid Crystals ◽  
Phenomenological Theory ◽  
Antiferroelectric Liquid Crystals
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