The particle-size dependence on the ferroelectric phase transition in nanocrystalline PbSc1/2Ta1/2O3 ceramics has been investigated for particles in the 0.01–0.16 μm size range. The phase transition was monitored through measurement of the dielectric constant as a function of temperature, variable temperature x-ray diffraction, and differential scanning calorimetry. The c/a tetragonality ratio decreased monotonically with particle size, reducing to unity at 0 °C for particles ⩽0.053 μm in size. The ferroelectric transition temperature Tc decreased gradually and the phase transition became more diffuse in nature as the particle size decreased. Below a mean particle size of 0.02 μm there was no peak in either the dielectric constant or the differential scanning calorimetry curve as a function of temperature, even though variable temperature x-ray diffraction could detect tetragonality indicative of ferroelectric distortions at sufficiently low temperatures down to the smallest crystallite size of 0.01 μm.

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The effect of internal stress on the physical properties (the temperature dependence of the dielectric constant and the lattice constant, and the diffuseness (␥)) of solid solutions of 0.97BaTiO 3 -0.03Gd 2 O 3 :1.5TiO 2 and 0.97BaTiO 3 -0.03CeO 2 :1.5TiO 2 was investigated using various particle sizes of the starting BaTiO 3 , pressure-dielectric spectroscopy, and high-pressure X-ray analysis. The grain size was almost proportional to the particle size of the starting BaTiO 3 and was inversely proportional to the internal stress. A sudden change in internal stress occurred at grain sizes of ∼2 µm for cerium-doped BaTiO 3 and ∼3 µm for gadolinium-doped BaTiO 3 . With an increase in external pressure and a decrease in grain size, the lattice anomalies of the cubic-to-tetragonal transformation and two other factors (the tetragonal-to-orthorhombic and orthorhombic-torhombohedral transformations) shifted to lower and higher temperatures, respectively. The temperature dependencies of the dielectric constant and the lattice constant were less sensitive to external pressure in cerium-doped core-shellgrained BaTiO 3 than in gadolinium-doped homogeneousgrained BaTiO 3 ; this difference was attributable to internal stress. In cerium-doped BaTiO 3 , ␥ was related to internal stress.