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Materials Data on KTaWO6 by Materials Project

KTaWO6 crystallizes in the orthorhombic Ima2 space group. The structure is three-dimensional. K1+ is bonded in a hexagonal planar geometry to six O2- atoms. There are a spread of K–O bond distances ranging from 2.70–2.80 Å. Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent TaO6 octahedra and corners with four equivalent WO6 octahedra. The corner-sharing octahedra tilt angles range from 37–39°. There is four shorter (1.99 Å) and two longer (2.00 Å) Ta–O bond length. W6+ is bonded to six O2- atoms to form WO6 octahedra that share corners with two equivalent WO6 octahedra and corners with four equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 36–38°. There are a spread of W–O bond distances ranging from 1.94–1.97 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent K1+ and two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent W6+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Ta5+, and one W6+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one K1+, one Ta5+, and one W6+ atom.

36 MATERIALS SCIENCE↗

Materials Data on KTaWO7 by Materials Project

(KTaWO6)2O2 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional and consists of four water molecules and one KTaWO6 framework. In the KTaWO6 framework, K is bonded in a hexagonal planar geometry to six O atoms. There are two shorter (2.72 Å) and four longer (2.76 Å) K–O bond lengths. Ta is bonded to six O atoms to form TaO6 octahedra that share corners with two equivalent TaO6 octahedra and corners with four equivalent WO6 octahedra. The corner-sharing octahedra tilt angles range from 37–38°. There is two shorter (1.99 Å) and four longer (2.00 Å) Ta–O bond length. W is bonded to six O atoms to form WO6 octahedra that share corners with two equivalent WO6 octahedra and corners with four equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 36–37°. There is four shorter (1.94 Å) and two longer (1.96 Å) W–O bond length. There are three inequivalent O sites. In the first O site, O is bonded in a 4-coordinate geometry to two equivalent K and two equivalent Ta atoms. In the second O site, O is bonded in a bent 150 degrees geometry to two equivalent W atoms. In the third O site, O is bonded in a 3-coordinate geometry to one K, one Ta, and one W atom.

36 MATERIALS SCIENCE↗

Alkali oxide-tantalum, niobium and antimony oxide ionic conductors

The phase equilibrium relations of four systems were investigated in detail. These consisted of sodium and potassium antimonates with antimony oxide and tantalum and niobium oxide with rubidium oxide as far as the ratio 4Rb2O:llB2O5 (B=Nb, Ta). The ternary system NaSbO3-Sb2O4-NaF was investigated extensively to determine the actual composition of the body centered cubic sodium antimonate. Various other binary and ternary oxide systems involving alkali oxides were examined in lesser detail. The phases synthesized were screened by ion exchange methods to determine mobility of the mobility of the alkali ion within the niobium, tantalum or antimony oxide (fluoride) structural framework. Five structure types warranted further investigation; these structure types are (1) hexagonal tungsten bronze (HTB), (2) pyrochlore, (3) the hybrid HTB-pyrochlore hexagonal ordered phases, (4) body centered cubic antimonates and (5) 2K2O:3Nb2O5. Although all of these phases exhibit good ion exchange properties only the pyrochlore was prepared with Na(+) ions as an equilibrium phase and as a low porosity ceramic. Sb(+3) in the channel interferes with ionic conductivity in this case, although relatively good ionic conductivity was found for the metastable Na(+) ion exchanged analogs of RbTa2O5F and KTaWO6 pyrochlore phases.

Roth, R. S.↗