SHORT ANNOTATION AND MAIN RESULT

SCIENTIFIC TASKS AND RESULTS

In the results of searching for new perspective solid state materials for the quantum electronics, non-linear optics and other fields of physics more than 200 various oxide compounds were synthesized and peculiarities of their atomic structure and physical properties are studied. Single crystals of 80 such the compounds are grown and thoroughly investigated.

Four new large family of ferroelectrics are found and the existence of crystalline materials of a new specific type: ferroelectrics - superionics in which phenomena of electrical ordering are combine with anomalous high ionic conductivity is established.

In particular the structure and properties of rare-earth tungstates and molybdates Ln₂W(Mo)O₆ are investigated and their polymorphism as well as polytypism of the La₂WO₆ crystals are discovered. Perfect single crystals of Bi₂WO₆ and other related bismuth-bearing ferroelectric compounds with the ordinary and mixed layered perovskite like structures are obtained and the symmetry of such the crystals with various layer thickness and sequence was analyzed. Phase transitions of the above compounds were investigated.

Ferroelectric properties were observed also for a number of new compounds AB_nW_3-nO₉ with the structure of hexagonal tungsten bronze and AB_nW_2-nO₆ of the "defect" pyrochlore type.

Special attention was paid to the crystals of KTiOPO₄ family and their solid solutions which are now widely used in non-linear optics and attract much attention. As it was shown for the first time these crystals undergo second order ferroelectric phase transition, show high piezoelectric activity and superionic conductivity. They are the most typical examples of the ferroelectrics - superionics.

In course of studies on the high-temperature superconductors, single crystals of several families of the such compounds are grown and studied. In particular the highly perfect, domain-free single crystals of the YBa₂Cu₃O_7-x - family were obtained. Large review on the atomic structures and physical properties of the HTSC of various types was published.

Superionic properties in ferroelectric-ferroelastic K⁺ ion conductor K₃Nb₃B₂O₁₂ have been discovered. Complex polymorphism of the compound and its solid solutions was investigated and a sequence of six phase transitions have been revealed in temperature region -120 - 900^oC.

Single crystals of oxygen ion conductors on the base of La₂Mo₂O₉ have been grown for the first time and their complex polymorphism have been investigated.

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