New Titanium-Vanadium Phosphates of Nasicon and Langbeinite Structures, and Differences between the Two Structures toward Deintercalation of Alkali Metal
✍ Scribed by K.Kasthuri Rangan; J. Gopalakrishnan
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 232 KB
- Volume
- 109
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
Mixed metal phosphates of the general formula (A_{x} \mathrm{TiV}^{\mathrm{II}}\left(\mathrm{PO}{4}\right){3}), where (A=\mathrm{Na}), (\mathrm{K}), or (\mathrm{Ba}) and ((0<x \leq 3)), have been synthesized. While the sodium phosphate, (\mathrm{Na}{3} \mathrm{TiV}\left(\mathrm{PO}{4}\right){3}), adopts the NASICON structure, the potassium compound, (\mathrm{K}{2} \mathrm{TiV}\left(\mathrm{PO}{4}\right){3}), crystallizes with the langheinite structure. (\mathrm{BaTtiV}\left(\mathrm{PO}{4}\right){3}) is dimorphic, adopting the NASICON structure at lower temperatures and the langbeinite structure at ligher temperatures. (\mathrm{Ba}{1.5} \mathrm{~V}{2}\left(\mathrm{PO}{4}\right){3}) and (\mathrm{BaKV}{2}\left(\mathrm{PO}{4}\right){3}), on the other hand, crystallize only with the langbeinite structure. Oxidative deintercalation of sodium from (\mathrm{Na}{3} \mathrm{TiV}\left(\mathrm{PO}{4}\right){3}) readily occurs, yielding (\mathrm{Na}{x} \mathrm{TiV}\left(\mathrm{PO}{4}\right){3}(x \sim 1.0)) and retaining the NASICON framework, while a similar deintercalation of potassium does not occur from the langbeinite (\mathrm{K}{2} \mathrm{TiV}\left(\mathrm{PO}{4}\right){3}), revealing a difference in reactivity between the two structures: NASICON, being a skeleton structure with an interconnected interstitial space, facilitates mobility of alkali metal ions through the crystal, while langbeinite, being a true cage structure, does not permit a similar mobility. O 1994 Academic Press, Inc.