Crystal chemistry of lead titanate in relation to its electrical properties

The origin of the discrepancy between the measured average parameter of the perovskite unit cell of PbTiO3 and the unit-cell parameter calculated for an ideal perovskite structure is analyzed with the use of extended x-ray ab sorption fine structure spectroscopy data, which demonstrate that PbTiO3 co ntains Pb4+ ions. The amount of Pb4+ depends on the preparation conditions and may attain similar or equal to6 at. %. Assumption is made, that the pre sence of crystallographic shear planes allows a fraction of the PP, ions to occupy octahedral sites near the shear planes. The maximum content of Pb2 on the B site is similar or equal to2.5 at. %. The formula proposed for th e cation composition of imperfect lead titanate differs from the ideal form ula Pb2+Ti4+O3 and indicates that lead titanate can be thought of as an int ernal solid solution. It is shown that the composition of lead titanate inf luences its electrical properties: epsilon/epsilon (o) increases with Pb4concentration and exceeds that in single crystals by an order of magnitude.