Dimensional modification of oxyfluoride lattice: Preparation and structure of A ' ANb(2)O(6)F (A '= Na, K, A = Ca, Sr)

作者：Yoo Chung Yul; Kim Seung Joo^*

来源：Journal of Physics and Chemistry of Solids, 2008, 69(5-6): 1475-1478.

DOI：10.1016/j.jpcs.2007.09.013

• inorganic compounds
• chemical synthesis
• X-ray diffraction
• crystal structure

A series of oxyfluorides, A'ANb(2)O(6)F (A' = Na, K, A = Ca, Sr) have been prepared employing solid-state reaction. X-ray diffraction patterns show that NaCaNb2O6F, NaSrNb2O6F and KCaNb2O6F exhibit the cubic pyrochlore structure, while KSrNb2O6F crystallizes in the Dion-Jacobson type layered perovskite. For the A'ANb(2),O6F compounds, the size of A' and A ion plays a crucial role in the modification of crystal structure. When A' and A ions are large, the layered perovskite structure is more favorable than the pyrochlore structure. The phase boundary of pyrochlore and layered perovskte is around 2.1 of R-A'A/R-Nb ratio for A'ANb(2)O(6)/F, where R-A'A is the average radius of A' and A cations and R-Nb is the radius of Nb5+ ion. The plot of cell volume vs. RA'A/RNb ratio indicates that the layered perovskite has an expanded cell as compared with the pyrochlores, which may be closely related to the excellent ion-exchange ability of the layered perovskite.

• 出版日期2008-6