How does substituting lead for barium change the Curie point of barium titanate?

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Figure 1: Ferroelectric properties of barium titanate (BaTiO3). (Left) Above 120° C the structure of the BaTiO3 crystal is cubic, and there is no net polarization of charge; (right) below 120° C the structure changes to tetragonal, shifting the relative positions of the ions and causing a concentration of positive and negative charges toward opposite ends of the crystal. — capacitor dielectric and piezoelectric ceramics Figure 1: Ferroelectric properties of barium titanate (BaTiO₃). (Left) Above 120° C the structure of the BaTiO₃ crystal is cubic, and there is no net polarization of charge; (right) below 120° C the structure changes to tetragonal, shifting the relative positions of the ions and causing a concentration of positive and negative charges toward opposite ends of the crystal.

In the context of barium titanate (BaTiO₃) ceramics, substituting lead (Pb²⁺) for barium (Ba²⁺) ions increases the Curie point of the material.1

This type of chemical substitution is often employed to modify the ferroelectric properties of the ceramic, as pure barium titanate exhibits a large peak in its dielectric constant near the Curie point, which can be undesirable for stable capacitor applications.1