WEAKLY FIRST-ORDER OR NEARLY 2ND-ORDER PHASE-TRANSITIONS

In this study we have developed a model which is mainly for a spin sys tem (Ising model) superimposed on a system of lattice vibrations (Eins tein and/or Debye model). Under this model we have derived the thermod ynamic functions and predicted their critical behaviour near T-c. Our predictions are that C-V and beta(-1) have a temperature dependence de scribed by a power law formula with critical exponent alpha, whereas C -p and alpha remain constant but show anomalous behaviour near T-c. Th is then implies that the gamma Gruneisen parameter remains constant th roughout the phase transitions. Regarding some previous model studies, our predictions seem to indicate that the model under consideration e xhibits a phase transition of weakly first-order or nearly second-orde r.