Étude de la Solution Solide Entre Tungstate et Tellurate de Magnésium: Pb2MgWxTe(1−x)O6
✍ Scribed by N Rivezzi; Ph Sciau
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 379 KB
- Volume
- 139
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The solid solutions Pb 2 MgW x Te (1؊x) O 6 was prepared and investigated by dielectric measurements, DSC, X-ray, and neutron powder diffraction. A phase diagram is proposed. Above 312 K the structure is cubic (space group Fm3 m) for all x values (04 x41). Around 190 K and for x40.4, the incommensurate phase transition of Pb 2 MgTeO 6 is observed. It is little affected in this range by the W rate.The compositions x50.8 undergo the orthorhombic/commensurate phase transition of Pb 2 MgWO 6 . This transition is very sensitive to the amount of Te present. The transition temperature and the orthorhombic distortion decrease quickly with increasing Te content. For 0.6 < x < 0.8 the transition is partial. In the range 0.4 < x < 0.6 the situation is more complex, both commensurate and incommensurate phases being observed at low temperature. The structure corresponding to x ؍ 0.4 has been determined by neutron powder diffraction at 12 K. It is isostructural to the incommensurate phase of Pb 2 Mg TeO 6 . The orthorhombic/commensurate structures (space group Pmcn) of x ؍ 0.5, 0.7, and 0.9 were determined by X-ray powder diffraction at 80 K. The atomic displacements from the cubic positions decrease with increasing Te content.