The thermodynamic potential of the Pb_xSr_1-xTiO₃ solid solutions has been determined for the entire range of component concentrations. A phase diagram has been constructed, which contains: a critical point at which the line of second-order phase transitions passes into the line of first-order transitions between the cubic and tetragonal phases; a tricritical point at which the cubic, tetragonal, and rhombohedral phases converge; the multicritical point at which at low temperatures six phases converge along the lines of second-order transitions. The obtained T-x phase diagram of Pb_xSr_1-xTiO₃ shows the possibility of the existence of ferroelectric phases that were not previously observed in experiments.

Pb _x Sr _1-x TiO ₃固溶体的热力学势已在整个组分浓度范围内确定。已经构建了一个相图，其中包含： 二阶相变线进入立方相和四方相之间的一阶相变线的临界点；立方、四方和菱形相会聚的三临界点；在低温下六相沿二阶转变线会聚的多临界点。得到的Pb _x Sr _1-x TiO _{3 的}Tx相图 显示了以前在实验中未观察到的铁电相存在的可能性。