Studies of the heat capacity and thermal expansion of the Na0.95K0.05NbO3 solid solution

The heat capacity and thermal expansion of ceramic samples of the Na_0.95K_0.05NbO₃ solid solution have been investigated over a wide temperature range of 100–750 K. The observed anomalies in the heat capacity and thermal expansion at T ₄ = 297 K, T ₃ = 535 K, T ₂ = 665 K, and T ₁ ≈ 710 K correspond to the sequences of phase transitions N → Q → G → S → T1. It has been shown that, as a result of the phase transitions, the unit cell volume at T ₄ and T ₂ decreases, and at T ₃ and T ₁, increases with increasing temperature. The directions of the shift of the phase transition temperatures induced by hydrostatic pressure have been determined. It has been established that all structural transformations are accompanied by relatively small variations in the entropy. Different mechanisms of the structural distortions have been discussed.