کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1331237 | 979000 | 2007 | 7 صفحه PDF | دانلود رایگان |
The structures of eight members of the series of double perovskites of the type Ba2LnB′O6 (Ln=La3+–Sm3+ and Y3+ and B′=Nb5+ and Ta5+) were examined both above and below room temperature using synchrotron X-ray powder diffraction. The La3+ and Pr3+ containing compounds had an intermediate rhombohedral phase whereas the other tantalates and niobates studied have a tetragonal intermediate. This difference in symmetry appears to be a consequence of the larger size of the La3+ and Pr3+ cations compared to the other lanthanides. The temperature range over which the intermediate symmetry is stable is reduced in those compounds near the point where the preferred intermediate symmetry changes from tetragonal to rhombohedral. In such compounds the transition to the cubic phase involves higher order terms in the Landau expression. This suggests that in this region the stability of the two intermediate phases is similar.
Variable temperature structural studies of Ba2LaTaO6 show the presence of a unexpected rhombohedral phase. Other Ba2LnB′O6 (B′=Nb, Ta) have a tetragonal intermediate phase.Figure optionsDownload as PowerPoint slide
Journal: Journal of Solid State Chemistry - Volume 180, Issue 11, November 2007, Pages 3001–3007