X-ray diffraction analysis of lanthanum and titanium substituted lead zirconate

The change in the orthorhombic structure of PbZrO₃ was studied as a function of the La substitution for Pb and Ti substitution for Zr. Two types of changes can occur: (1) a change in the atom coordinates toward the positions for a perfect cubic perovskite lattice; and (2) a change of orthorhombic unit cell parameters so that a_o, b_o, and c_o exactly fit with the cubic cell parameter a_c. Therefore, a_o = a_c√2, b_o = a_c 2√2, and c_o = a _c2, where a_o, b_o, and c_o are the orthorhombic cell parameters, and a_c is the cubic cell parameter. Substitution of Pb by La in the orthorhombic PLZT leads to both a change in atom coordinates and a change in unit cell parameters toward the perfect cubic structure, especially for La≥4. Substitution of Zr by Ti in the orthorhombic PLZT leads to similar atom coordinate changes, but the unit cell parameters do not change. The composition 0/92.5/7.5 contains a major tetragonal phase and a minor orthorhombic phase. There are only small differences in the orthorhombic structure between the A and the B composition of PLZT. The A composition has a structure closer to the cubic structure than the B composition.