10 - On the theory of phase transitions of the second order: I. Changes of the elementary cell of a crystal in phase transitions of the second order

Abstract

As it is known, there are two types of phase transitions—the usual phase transitions (transitions of the first order) and transitions of the second order (also known as the Curie points). The phase transitions of the first order are in principle possible between any two phases. The possibility of the existence of phase transitions of the second order is found to be essentially limited. In a phase transition of the second order, the state of the body, that is, the distribution of the atoms, changes continuously, which is also connected with the absence of the latent heat. The symmetry of the body changes suddenly at the Curie point; this change in the symmetry of the body leads to a discontinuity in the heat capacity and other first derivatives of the thermodynamic quantities of the body—the coefficient of thermal expansion, the coefficient of compression, etc.