1. Cation Distribution Studies in Double Orthophosphates with Whitlockite Structure
- Author
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R. G. Aziev, B. N. Wieting, V. N. Golubev, Bogdan I. Lazoryak, and L. N. Ivanov
- Subjects
Diffraction ,Rare-earth element ,Chemistry ,Coordination number ,Organic Chemistry ,Infrared spectroscopy ,Cation distribution ,engineering.material ,Biochemistry ,Inorganic Chemistry ,Crystallography ,Whitlockite ,engineering ,Isostructural ,Luminescence - Abstract
The structure of β-Ca3 (PO4)2 is known to be similar to that of whitlockite (R3c, Z =21). The cations are distributed in five different positions, the position Ca(4) being only half occupied. The whitlockite network is stable while the filling of the Ca(4) position changes from 0 to 1. The presence of vacancies allows to provide heterovalent substitutions 3Ca2+ = 2M3+ + and Ca2+ + 0 = 2Me+ with limits of compositions Ca9M (PO4)7 and CaloMe(PO4)7 respectively. The possible cation size can be changed from 0.55 A (Fe3+) to 1.51 A (K+). In order to check these suggestions we have synthesized Ca9M(PO4)7 (M = rare earth element, Y, Bi, Fe, Al, In, Sc) compounds, The double phosphates were studied by luminescence, infrared spectroscopy and X-ray diffraction. All these compounds are isostructural to β-Ca3(PO4)2. The cell parameters gradually decrease for M = La-Ho, Y and remain constant for M = Er-Lu. This divergence can be attributed to the change of the coordination number of the rare earth element. A ...
- Published
- 1990
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