Relationships between the Texture and Structure of BaTiO 3and Its Tetragonal → Cubic Transition Enthalpy

A nanometric BaTiO ₃powder sample with a medium crystallite size D= 157 Å has been prepared from the thermal decomposition of BaTiO(C ₂O ₄) · 4.5H ₂O by constant rate thermal analysis (CRTA). Rietveld analysis of the XRD pattern shows that this BaTiO ₃sample presents a crystalline cubic structure. The evolution of the texture, the structure, and the ferroelectric → paraelectric enthalphy transition as a function of the annealing temperature of BaTiO ₃has been followed from XRD and DSC experiments. A relationship has been found between the reaction enthalphy of the tetragonal → cubic polymorphic transition and the tetragonality of the sample, as measured from the c/ aratio. Therefore, the calorimetric data can be used for predicting the structure of this material. The Curie temperature seems to independent of the crystallite size D, provided that it is higher than about 400 Å.