High-Pressure Tungsten Bronzes, RExWO3 with RE=La and Nd, Studied by X-Ray Diffraction and Electron Microscopy

✍ Scribed by C. Grenthe; M. Sundberg; V.P. Filonenko; I.P. Zibrov

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 858 KB
• Volume: 154
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2000.8866

✦ Synopsis

Rare earth tungsten bronzes, La 0.1 WO 3 and Nd x WO 3 with x ‫؍‬ 0.1 and 0.2, have been prepared by solid state reaction at P ‫؍‬ 30 kbar and T ‫؍‬ 1320+1620 K and structurally characterized by X-ray di4raction and electron microscopy. The hexagonal tungsten bronze (HTB) structure was found in all samples, whereas intergrowth tungsten bronzes of (n)-ITB and (1, n)-ITB structure types have only been observed in samples prepared at T >1500 K. The ITB structures can be considered as an intergrowth of slabs of WO 3 -type, n octahedra wide, and slices of HTB-type. In the (n)-ITB family the slices of HTB-type are one hexagonal tunnel row wide, whereas they are two hexagonal tunnel rows wide in the (1, n)-ITB phases. Members of the (n)-ITB family were frequently observed in the high-temperature samples. The La x WO 3 bronzes, (2)-ITB, (3)-ITB, (1, 2)-ITB, and HTB, are new. In the Nd x WO 3 system a perovskite tungsten bronze (PTB) of composition Nd +0.1 WO 3 and a (3)-ITB bronze were found in addition to the previously reported high-pressure phases (2)-ITB and HTB. The bronze structures were wellordered, but a few exceptions were observed. A couple of defects are described along with proposed defect models. Microanalyses show that the hexagonal tunnel sites in the ITB and HTB structures are less than half-5lled with RE atoms. The relationships between the RE x WO 3 bronzes and the alkali tungsten bronzes, A x WO 3 , are discussed. 2000 Academic Press EXPERIMENTAL Samples of starting compositions La WO and Nd V WO with x"0.1 and 0.2 were prepared by mixing appropriate amounts of RE O (RE"La and Nd), WO , and W-metal powder in an agate mortar, both as dry powders and under acetone. The resulting mixtures were dried and pressed into pellets, which were wrapped up in 466