Temperature Dependence Of The Frequency Shifts Related To The Thermodynamic Quantities Close To Phase Transitions In Nano2

Abstract

This study examines a linear relationship between the frequency shifts, (1/W)(partial derivative w/partial derivative T)p, and the variation of the dielectric constant, (1/epsilon)(partial derivative epsilon/partial derivative T)p, close to phase transitions in ferroelectric crystalline systems, in particular, ferroelectric NaNO2 as studied here. Both quantities (frequency and dielectric constant) are described by the power-law formulae below the Curie temperature T-c (ferroelectric phase), T-c < T < T-i (incommensurate phase) and T > T-i (paraelectric phase). The divergence behaviour of the mode Gruneisen parameter (gamma(p)) is obtained, whose temperature dependence can also be described by a power-law formula in NaNO2. It is also shown that the heat capacity C-p can be evaluated from the thermal expansion (alpha(p)) by means of the same critical exponent since they exhibit similar critical behaviour near T-c and T-i in this crystal.