Classification of transition temperature behavior in ferroelectric PbTiO ₃-Bi (Me′ Me″)O ₃ solid solutions

The ferroelectric transition temperature (Tc) behavior of perovskite solid solutions based on PbTi O3 -Bi (Me′ Me″) O3 (Me′ = Fe3+, Zn2+, Sc3+, In3+, Mg2+, Ni2+, etc., and Me″ = Ti4+, Nb5+, W6+) was considered. Trends in the Tc compositional dependence near the PbTi O3 end member could be described with a geometrical polynomial expression. Three main cases were observed: Case 1, a continued increase in transition temperature above the end member PbTi O3 (495 °C); case 2, an increase and then decrease of the transition temperature; and case 3, a continuous decrease in the transition temperature with Bi (Me′ Me″) O3 additions. It was noted that for all case 2 examples the enhancement of Δ Tc = Tc (max) - Tc (PT) increased as the distribution of B -site ionic radii increased. A correlation was therefore proposed between the maximum enhancement in transition temperature and the spread of tolerance factor (Δt) andor variance in B -site ionic radius (σ2). Finally, it was proposed that these observations are consistent with random-field effects created by local strain-field fluctuations within the perovskite lattice.