Structure and Thermal Stability of La0.10WO3+y; A Hexagonal Tungsten Bronze Related Phase Formed at High Pressure
✍ Scribed by V.P. Filonenko; C. Grenthe; M. Nygren; M. Sundberg; I.P. Zibrov
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 447 KB
- Volume
- 163
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The structure and thermal stability of a hexagonal tungsten bronze (HTB) related compound, La x WO 3؉y with x+0.10 and y+0.15, has been studied by X-ray di4raction, thermal analysis, and electron microscopy. The structure was re5ned by the Rietveld method from X-ray powder di4ractometer data of a La 0.10 WO 3 sample prepared at T ؍ 12503C and P ؍ 25 kbar, which consisted of two tungsten bronze related phases in 1 : 1 proportion. The unit cell dimensions are as follows: La 0.108 WO 3؉y (y+0.16), a ؍ 7.40890(5), and c ؍ 3.79239(4) A > (HTB-related structure); La 0.091 WO 3 , a ؍ 3.82458(6) A > (cubic perovskite tungsten bronze (PTB) structure). The lanthanum atoms in La 0.108 WO 3؉y are located on the hexagonal axis and statistically distributed on two sites close to the tungsten atom plane. Thermal stability studies of the La 0.10 WO 3 sample in an argon atmosphere under ambient pressure conditions revealed that the HTB-related compound is metastable, decomposing to the stable PTB-type structure and WO 3 . It was also found from the TG experiments in argon and oxygen that additional oxygen atoms (y) are present in the structure, thus forming a lanthanum tungsten oxide of the above composition. The electron di4raction and microanalysis studies con5rmed that crystals of the HTBand PTB-type structures were formed, with a lanthanum content of x+0.1.