Cation distribution in the Bi4 − xRExTi3O12 (RE = La, Nd) solid solution and Curie temperature dependence

Bi4 − xRExTi3O12 (RE = La, Nd) ferroelectric powders were prepared by a co-precipitation route. Raman spectroscopy and X-ray diffraction were employed to determine the crystal site of La3+ and Nd3+ as well as the effect of their addition on the crystal structure. It was found that La atoms were not only placed preferentially in pseudo-perovskite A sites for concentrations x ≤ 1.2 but also substituted for Bi3+ in (Bi2O2)2 + layers for greater concentrations. A similar behavior was observed with the limit value x = 0.8 in case of Nd3+. In solid solution La or Nd3+ ions diminish the distortions in the octahedron formed by oxygen atoms, so there is a tendency to undergo a transition in crystal symmetry from orthorhombic to tetragonal. Finally differential scanning calorimetry (DSC) shows a linear dependence of the Curie temperature (Tc) when the amount of La3+ or Nd3+ was increased.