Nonlinearity of the concentration dependence of the Curie temperature in ferroelectric perovskite solid solutions

The dependence of the Curie temperature of many ferroelectric perovskite solid solutions on the component concentration is nonlinear. Causes of the nonlinearity (limited solubility of components, ion ordering, influence of the morphotropic phase boundary, diffusion of the ferroelectric phase transition, frustration of the crystal lattice) are discussed practically for the first time. In some cases, it is impossible to explain the nonlinearity without solution of some common problems.