Relaxors with multiple substitutions in octahedral sites of the perovskite structure

We have analyzed and experimentally studied compounds with an ABO$_3$ perovskite structure with multiple substitutions in the B site by different ions in different valence states. It is shown that increasing the number of such ions n from 2 to 6 gives rise to the appearance of superstructural reflections in the X-ray diffraction spectra of the corresponding compounds. These reflections evidence a phase transition to an ordered state with cell doubling and the order-disorder phase transition temperature of not less than 1000$^\circ$C.