Order Parameter Expansion of Free Energy and Spin-Glasses. I: Random Bond Model

Recent work has provided independent information about the behavior of the hole concentration c in TlxTe1−x as a function of temperature T and composition x in the range 0.2 ≤ x ≤ 0.6. This makes possible a critical reexamination of a molecular bond model for the structure of the alloy, in which holes are generated by broken Te—Te bonds. The earlier theory is revised to formulate an unrestricted independent bond model (ibm), for which the equations are simple and have obvious physical interpretations. This provides a good description of c(T) but only a qualitatively correct c(x). Using a Thomas–Fermi model for the screening interaction between holes and the acceptor ions, it is shown that the equilibrium constant can be expected to increase rapidly with c at large enough values. A modification in which the free energy of a dangling bond is decreased by proximity to a Tl—Te bond is found to significantly improve the result for c(x). The thermochemical behavior is derived. The entropy of mixing is in fair agreement with experiment, but the enthalpy of mixing is grossly wrong. This reflects the neglect of intermolecular interactions in the theory, which, it seems, can easily account for the remaining discrepancies in the predicted behavior of c.

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The stationarity of the free energy in the Ising model of spin glasses

Physics Letters A ◽

10.1016/0375-9601(81)90966-x ◽

1981 ◽

Vol 85 (5) ◽

pp. 301-302

Author(s):

V.A. Moskalenko ◽

L.A. Dogotar ◽

M.I. Vladimir

Keyword(s):

Free Energy ◽

Ising Model ◽

Spin Glasses

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TEMPERATURE DEPENDENCE OF SURFACE TENSION OF LIQUID CRYSTALS AT THE PHASE TRANSITION

Modern Physics Letters B ◽

10.1142/s0217984995000231 ◽

1995 ◽

Vol 09 (03n04) ◽

pp. 237-242 ◽

Cited By ~ 7

Author(s):

R. MOLDOVAN ◽

M. TINTARU ◽

T. BEICA ◽

S. FRUNZA ◽

D. N. STOENESCU

Keyword(s):

Experimental Data ◽

Phase Transition ◽

Surface Tension ◽

Free Energy ◽

Surface Layer ◽

Order Parameter ◽

Unit Area ◽

Negative Slope ◽

First Order ◽

First Order Transition

The surface tension is calculated as the excess of the free energy per unit area, due to the presence of a surface layer, using Landau–de Gennes expansions, in the hypothesis of a first order transition in the bulk and taking into account the dependence of the surface free energy from the surface tilt angle. The surface order parameter is calculated and surface-ordered phase above the phase transition temperature has been found. A variety of calculated surface tension versus temperature curves with a jump at the phase transition, with positive or negative slope, well describing the experimental data from literature, have been attained.

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