March 9 | Reinis Ignatāns

Reinis Ignatāns (ISSP UL Laboratory of Functional Materials Physics and Applications)

ABO3-type perovskites are interesting both academically and in terms of applications. Perovskites are characterized by phonon oscillation mode instabilities resulting from rich phase diagrams. On the other hand, the polar crystalline phases of the ABO₃ perovskite are attractive in applications - they are the basis for the operation of various actuators, sensors and piezoelectric sound transducers.

Although SrTiO₃, BaTiO₃, PbTiO₃ and their tetragonal and cubic phases are given as examples of typical ferroelectric perovskites in the textbooks, in fact most perovskites have other crystalline phases characterized by oxygen octahedron rotations. Oxygen octahedron rotations have long been thought to prevent the ferroelectric state, however, in most cases this is not a sufficient reason - anti-parallel cation shifts are also required.

The Na_1/2Bi_1/2TiO₃-CdTiO₃ solid solution system exhibits a polar – ferroelectric – crystalline phase that also has oxygen octahedron rotations. In addition, the complex octahedron rotation system a + b + c + found for the first time in this system (this type of notation will be explained in the workshop).