Enthalpies of formation of lead zirconate titanate (PZT) solid solutions

The formation energetics and heats of mixing of lead zirconate titanate (PZT) PbZrxTi1-xO3 solid solutions have been investigated using high-temperature oxide melt solution calorimetry. While the heat content (H-973-H-298) is almost constant (80-82 kJ/mol) for x = 0.15-1.0, its value for PbTiO3 (x = 0.0) is larger (86.15 +/- 0.55 kJ/mol). Linear variation in the enthalpy of drop solution, DeltaH(ds), and the enthalpy of formation from the oxides, DeltaH(f,ox) (298 K), is observed in the tetragonal region (0 < x < 0.5) and continues smoothly into part of the rhombohedral region (0.5 < x < 0.65). Fitting the data in the tetragonal phase region (0 < x < 0.5) to a straight line enables an extrapolation to give the heat of the virtual transformation PbTiO3 (tetragonal --> orthorhombic) as 24.0 +/- 3.9 kJ/mol. An extrapolation from the rhombohedral region gives 33.3 +/- 3.6 kJ/mol for DeltaH of the virtual transition PbZrO3 (orthorhombic or rhombohedral --> tetragonal). The transition enthalpy between orthorhombic and rhombohedral PbZrO3 is zero within experimental error. The enthalpy of formation from the oxides, DeltaH(f,ox)(298 K), varies from -36.7 +/- 2.7 kJ/mol for PbTiO3 to 0.7 +/- 4.3 kJ/mol for PbZrO3. The DeltaH(f,ox)(973 K) values agree with previously reported DeltaH(f,ox) values measured in alkali borate solvent at 1073 K. Fitting DeltaH(mix) (973 K) to a regular solution model yields an interaction parameter, W, of 39.8 +/- 4.6 kJ/mol. However, structural complexity makes the regular solution model only a crude physical description. (C) 2001 Academic Press.