Phase transition in the PbTiO - A(B _{2 3}Nb _{1 3})O₃ (A = La, Bi; B = Zn, Mg) solid solutions

Phase transition in the (1-x)PbTiO₃-xA(B _{2 3}Nb _{1 3})O₃ (A=La, Bi; B=Zn,Mg) solid solution systems has been investigated by means of x-ray diffraction, dilatometric and dielectric measurements. Complete solid solutions with a perovskite structure are formed in the ranges of 0 < x < 0.7 and 0 < x < 0.3 for the PbTiO₃-La(B _{2 3}Nb _{1 3})O₃ and PbTiO₃-Bi(B _{2 3}Nb _{1 3})O₃ systems, respectively. The tetragonal distortion at room temperature decreases with increasing the La(B _{2 3}Nb _{1 3})O₃ or Bi(Mg _{2 3}Nb _{1 3})O₃ molar fraction, while it increases with the Bi(Zn _{2 3}Nb _{1 3})O₃ content. The ferroelectric Curie temperature determined by the dielectric and/or dilatometric measurements decreases rapidly with the increase of the La(B _{2 3}Nb _{1 3})O₃ content, but slightly decreases or increases with Bi compounds in the case of the Bi(Mg _{2 3}Nb _{1 3})O₃ or Bi(Zn _{2 3}Nb _{1 3})O₃ series, respectively.