Pure, lithium- or magnesium-doped ferroelectric single crystals of Ca9Y(VO4)7: cation arrangements and phase transitions
| Autor: | Darya A. Petrova, A.N. Shekhovtsov, Sergey Yu. Stefanovich, E. A. Fortalnova, Bogdan I. Lazoryak, Sergey M. Aksenov, M. B. Kosmyna, O. V. Baryshnikova, Dina V. Deyneko |
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| Rok vydání: | 2018 |
| Předmět: |
Phase transition
Materials science Magnesium Doping chemistry.chemical_element 02 engineering and technology Crystal structure engineering.material 010402 general chemistry 021001 nanoscience & nanotechnology Condensed Matter Physics 01 natural sciences Ferroelectricity 0104 chemical sciences Inorganic Chemistry Crystallography chemistry Whitlockite engineering General Materials Science Lithium 0210 nano-technology |
| Zdroj: | Zeitschrift für Kristallographie - Crystalline Materials. 233:453-462 |
| ISSN: | 2196-7105 2194-4946 |
| DOI: | 10.1515/zkri-2017-2132 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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