High dielectric constant ceramics in the PbSc_0.5Ta_0.5O₃-PbZrO₃ and PbSc_0.5Ta_0.5O₃-PbTiO₃ systems

The properties of (1-x) PbSc_0.5Ta_0.5O₃-(x) PbZrO₃ ceramics (0.075 <x < 0.2), have been investigated using three different mixed oxide preparation routes. These were (i) a single-stage calcination (at 900°C) between lead, scandium, tantalum and zirconium oxides, (ii) the reaction between single phase PbSc_0.5Ta_0.5O₃ and PbZrO₃ powders (also at 900°C), and (iii) the formation of zirconium-modified scandium tantalate (via a high-temperature prereaction stage) prior to calcination with lead oxide. It was found that this third preparation route results in transparent, 100% dense, single-phase perovskite ceramics which exhibit particularly sharp first-order ferroelectric to paraelectric phase transitions. Material with a maximum relative permittivity of 36 × 103 at 64°C, and a dielectric loss of 7.5 × 10^-4, was obtained for an x value of 0.125. Results are compared with those for ceramics in a similar range of compositions in the (1-x) PbSc_0.5Ta_0.5O₃-(x)PbTiO₃ system; these were prepared using only one of the above routes, and involved calcining PbSc_0.5Ta_0.5O₃ with PbTiO₃ powder.