Mani Rohini, Selvamani P, Joy Joby E, Gopalakrishnan J, Mandal Tapas Kumar
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India.
Inorg Chem. 2007 Aug 6;46(16):6661-7. doi: 10.1021/ic7007655. Epub 2007 Jul 14.
We describe an investigation of Ba3MIIMIVWO9 oxides for MII = Ca, Zn, and other divalent metals and MIV = Ti, Zr. In general, a 1:2-ordered 6H (hexagonal, P63/mmc) perovskite structure is stabilized at high temperatures (1300 degrees C) for all of the Ba3MIITiWO9 oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba2(Zn2/3Ti1/3)(W2/3Ti1/3)O6, is obtained at 1200 degrees C for Ba3ZnTiWO9. Sr substitution for Ba in the latter stabilizes the cubic 3C structure instead of the 6H structure. A metastable Ba3CaZrWO9 that adopts the 3C (cubic, Fmm) structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the present investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d0-induced distortion of metal-oxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the Ba3MIIMIVWO9 series.
我们描述了对 Ba3MIIMIVWO9 氧化物（其中 MII = Ca、Zn 及其他二价金属，MIV = Ti、Zr）的一项研究。一般来说，对于所有所研究的 Ba3MIITiWO9 氧化物，一种 1:2 有序的 6H（六方，P63/mmc）钙钛矿结构在高温（1300 摄氏度）下得以稳定。对于 Ba3ZnTiWO9，在 1200 摄氏度时获得了一种具有部分有序的 1:1 双钙钛矿（3C）结构且阳离子分布为 Ba2(Zn2/3Ti1/3)(W2/3Ti1/3)O6 的中间相。在后者中用 Sr 取代 Ba 可稳定立方 3C 结构而非 6H 结构。一种采用 3C（立方，Fmm）结构的亚稳 Ba3CaZrWO9 也已通过低温复分解路线合成出来。除了得到几种可能用作介电陶瓷的新型钙钛矿氧化物外，本研究还为 Ba3MIIMIVWO9 系列中 6H 与 3C 钙钛矿结构稳定化过程中晶体化学（容忍因子）和化学键合（阴离子极化以及 d0 诱导的金属 - 氧八面体畸变）之间的复杂相互作用提供了新的见解。
