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 mechanism s. The reaction sequences in the formation of Sr-cloped PbHfO3, Sr-doped Pb TiO3 and Sr-doped PbHf1-xTixO3 were investigated using X-ray powder diffrac tion 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 PbHf 1-xTixO3 oxide is obtained from a solid-state reaction between Sr-doped PbH fO3 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 electromechani cal properties. By means of X-ray powder diffraction, the boundaries of the morphotropic region, in the (Pb0.94Sr0.06)Hf1-xTixO3 system have been dete rmined for x ranging between 0.42 and 0.58. Finally, electrical and piezoel ectric characterizations have been performed on Sr-cloped PHT ceramics crys tallizing in the morphotropic region. The compositional dependence of the e lectromechanical coupling factor (kp), piezoelectric coefficients (d(33) an d g(33)) and relative permittivity (epsilon (r)) has been studied. An optim um composition has been determined as x equal to 0.51. (C) 2001 Kluwer Acad emic Publishers.