Pure, lithium- or magnesium-doped ferroelectric single crystals of Ca9Y(VO4)7: cation arrangements and phase transitions

Lazoryak, B.I.; Deyneko, D.V.; Aksenov, S.M.; Stefanovich, S.Y.; Fortalnova, E.A.; Petrova, D.A.; Baryshnikova, O.V.; Kosmyna, M.B.; Shekhovtsov, A.N.

Авторы: Lazoryak Bogdan I., Deyneko Dina V., Aksenov Sergey M., Stefanovich Sergey Yu, Fortalnova Elena A., Petrova D.A., Baryshnikova Oksana V., Kosmyna Miron B., Shekhovtsov Aleksey N.
Журнал: Zeitschrift für Kristallographie – Crystalline Materials
Том: 233
Номер: 7
Год издания: 2018
Издательство: Walter de Gruyter
Местоположение издательства: Berlin, Germany
Первая страница: 453
Последняя страница: 462
DOI: 10.1515/zkri-2017-2132
Аннотация: Single crystals of Ca9Y(VO4)7 (1), Ca9Y(VO4)7:Li⁺ (2) and Ca9Y(VO4)7:Mg²⁺ (3) were grown by the Czochralski method. Their chemical composition was analyzed by ICP spectroscopy and their crystal structure was examined by single crystal X-ray analysis. The crystals are characterized by trigonal symmetry, space group R3c. Hexagonal unit-cell parameters are as follows: a=10.8552(1) Å, c=38.0373(2) Å, V=3881.65(1) Å³ for 1; a=10.8570(1) Å, c=38.0161(3) Å, V=3880.77(4) Å³ for 2; a=10.8465(1) Å, c=38.0366(2) Å, V=3875.36(3) Å³ for 3. All crystals are characterized by β-Ca3(PO4)2-type structure with statistical distribution of Ca²⁺ and Y³⁺ over M1, M2 and M5 sites in different ratios and with completely empty M4-cationsite. The impurity of Mg²⁺cations in structure 2 has been detected in octahedral M5 site. Ferroelectric phase transitions are evidenced by DSC and SHG. At about 1220 and 1300 K, they demonstrate phase transitions. Upon heating the symmetry of the crystal structure changes according to the scheme R3c→R3̅c→R3̅m and is restored during consequent cooling. The first of them is of ferroelectric and the second of non-ferroelectric nature. Even a small amount of impurities in Ca9Y(VO4)7 structure is accompanied by a noticeable decrease in the temperature of the ferroelectric-paraelectric phase transition.
Добавил в систему: Дейнеко Дина Валерьевна

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Pure, lithium- or magnesium-doped ferroelectric single crystals of Ca9Y(VO4)7: cation arrangements and phase transitionsстатья

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