Investigation of the morphotropic region in the Sr-doped lead hafnate-titanate solid solution Pb0.94Sr0.06Hf1-xTixO3

Sr-doped lead hafnate titanate (PHT) oxides were synthesized by solid-state reaction and carefully studied in order to identify the reaction mechanisms. The reaction sequences in the formation of Sr-cloped PbHfO3, Sr-doped PbTiO3 and Sr-doped PbHf1-xTixO3 were investigated using X-ray powder diffraction and differential thermal analysis. The Sr-doped PbHfO3 oxide is mainly elaborated from the reaction between PbO and HfO2, while Sr-cloped PbTiO3 oxide is formed from the reaction between Pb3O4 and TiO2. The Sr-doped PbHf1-xTixO3 oxide is obtained from a solid-state reaction between Sr-doped PbHfO3 and Sr-doped PbTiO3 solid solutions. For x close to 0.5, tetragonal and rhombohedral ferroelectric phases coexist in a region commonly called the 'morphotropic region' which presents the best dielectric and electromechanical properties. By means of X-ray powder diffraction, the boundaries of the morphotropic region, in the (Pb0.94Sr0.06)Hf1-xTixO3 system have been determined for x ranging between 0.42 and 0.58. Finally, electrical and piezoelectric characterizations have been performed on Sr-cloped PHT ceramics crystallizing in the morphotropic region. The compositional dependence of the electromechanical coupling factor (kp), piezoelectric coefficients (d(33) and g(33)) and relative permittivity (epsilon (r)) has been studied. An optimum composition has been determined as x equal to 0.51. (C) 2001 Kluwer Academic Publishers.