Thermodynamic Self-consistency Research Articles

Elastic properties of Se and As2Se3 glasses under pressure and temperature

The sound velocities and their pressure and temperature variations of Se and As2Se3 glasses have been determined by means of a pulse superpositions method, and other elastic constants and their pressure and temperature derivatives were calculated from these data. The bulk modulus was found to be 94·6 kbar for Se glass and 143·7 kbar As2Se3 glass, both of which are higher than the values calculated from the previous compression data. No anomaly was observed in any of the pressure and temperature dependence of elastic behavior of these glassses. Furthermore, the comparison of the pressure and temperature derivatives of the bulk modulus indicates that the thermodynamic self-consistency is satisfied on these materials. The bulk moduli of these glasses and crystalline As and Se were used to obtain an empirical bulk modulus-volume relationship for compounds in the As−Se system. The acoustic Grüneisen parameter was calculated and compared with the thermal Grüneisen parameter.

Theory of domain walls in ordered structures—III: Effect of substitutional deviations from stoichiometry

The structure of an equilibrium {100} domain wall between two antiphase domains of a b.c.c. binary ordered alloy of non-stoichiometric composition is investigated by minimizing the appropriate free energy in the inhomogeneous system using the Bragg-Williams and the pair approximations. Thermodynamic self-consistency requirements, similar to the Gibbs adsorption equation for interfaces, are derived and proved to hold for either approximation. The surface free energy is zero at T = 0°K, goes through a maximum as T increases and comes back to zero again at the order-disorder transition temperature. The chemical potential and the surface excess values of free energy, energy, entropy and amount of each species are given as a function of temperature and composition.