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Materials Data on NaTaWO6 by Materials Project

NaTaWO6 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. Na1+ is bonded in a hexagonal planar geometry to six O2- atoms. There are two shorter (2.65 Å) and four longer (2.67 Å) Na–O bond lengths. 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 39–43°. There is two shorter (1.98 Å) and four longer (1.99 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 36–39°. There is four shorter (1.93 Å) and two longer (1.95 Å) W–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+, one Ta5+, and one W6+ atom. 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 4-coordinate geometry to two equivalent Na1+ and two equivalent Ta5+ atoms.

36 MATERIALS SCIENCE↗

Search for solid conductors of Na(+) and K(+) ions: Five new conductors

Five conductors of three structure types were discovered which, as solids, can transport Na(+) or K(+) ions with conductivities of approximately .00001/(omega cm) at 300 K. These compounds are: (1) the pyrochlores NaTaWO6 and NaTa2O5F, both with an activation energy for conduction delta E of 21 kJ/mole; (2) the bodycentered cubic form of NaSbO3, with delta E = 42 kJ/mole; and (3) the niobates 2Na2O with 3Nb2O5 and 2K2O with 3Nb2O5, with the alkali ions probably in open layers of the incompletely determined structure; delta E = 17 kJ/mole. On the basis of approximately 40 structure types, some generalizations were made regarding the relation between structure and ionic transport.

Singer, J.↗

Search for solid conductors of Na/+/ and K/+/ ions - Five new conductors

Five new conductors of positive Na and K ions, for use as separators in high energy secondary batteries, have been discovered. They include: (1) the pyrochlores NaTaWO6 and NaTa2O5F; (2) the bcc form of NaSbO3; and (3) the niobates 2Na2O-3Nb2O5 and 2K2O-3Nb2O5, with the alkali ions probably in open layers of the completely determined structure. On the basis of approximately 40 structure types, generalizations have been made regarding the relation between structure and ionic transport.

Singer, J.↗

New solid conductors of Na/+/ and K/+/ ions

About 40 structure types for solid conductors of Na(+) and K(+) ions are surveyed. Five compounds in three structure types are discovered to be good solid conductors of alkali metal ions, capable of ion transport with conductivities in the vicinity of 0.00001/ohm-cm at 25 C. These compounds are a bcc form of NaSbO3, an orthorhombic layer structure of the composition 2M2O.3Nb2O5 with M equal to Na or K, and the Na pyrochlores NaTa2O5F and NaTaWO6. Ion exchange is required to produce each of these Na compounds. Only the 2K2O.3Nb2O5 can so far be synthesized directly from the oxides and thus is the only one which can be sintered readily. The niobate is about as good a conductor of K(+) ion as is K-beta alumina. The NaSbO3 compares well with Na beta at 280 C. A number of phase diagrams are developed.

Singer, J.↗