Heat Capacity Study of Relaxors

The thermodynamic properties of various relaxors of PMN, PMT, PZN, PST, PMN–PT, PZN–PT, and BTZ have been reviewed and the excess thermodynamic properties are discussed. In lead-containing complex perovskite, excess heat capacity owing to the formation of PNR and glass-like low-temperature excitations are clearly observed. Studies of solid solutions indicate the difficulty of forming PNR with rhombohedral symmetry in the ferroelectric phase and the possible growth of a polar region with tetragonal symmetry in the compounds. Thus, the lead-free Ba-based relaxor BTZ35 can be considered as the frozen state of a displacive-type phase transition without disorder.