Temperature Ferroelastic Phase Transition in Hydroxyapatite. Hydroxyl Solubility, Configuration Heat-Capacity, Hysteresis Effect, Elasticity Modulus

The statistical theory of ferroelastic-paraelastic phase transition has been elaborated in this paper. The equation of thermodynamic equilibrium state has been examined and the temperature of transition between phases has been estimated. The calculation of temperature dependence of hydroxyl solubility in crystal has been carried out. The manifestation hysteresis effect has been considered. The temperature dependence of elastic compliance and elasticity modulus has been evaluated and the verity of the rule of "negative two" and Curie-Weiss law has been found. The dependence configuration heat capacity on temperature has been calculated, its extremality has been ascertained and the abrupt change of heat capacity has been defined in the point of phase transition. The established regularities are consistent qualitatively with literature experimental data.