Electronically conducting doped chromium oxides

Samples of polycrystalline chromium oxide doped with Li/sub 2/O, MgO, NiO, and Ta/sub 2/O/sub 5/ were prepared by hot-pressing to test for suitability as current collector materials of the sulfur electrode in the sodium-sulfur cell. Density, grain size, dopant uniformity, and resistivity (to 350/sup 0/C) were measured. X-ray photoelectron spectroscopy (XPS) tends to support the established model of Ni/sup 2 +/ on Cr/sup 3 +/ sites to explain the compositional dependence of electrical resistivity after air anneal. A higher level of Cr/sub 2/O/sub 3/ powder purity was required to obtain the low resistivities with the Li/sub 2/O dopant than with the MgO or NiO dopant. An observed increase in the bulk resistivity during several months of electrochemical cycling in sodium polysulfide/sulfur melts is attributed to loss of electronic carriers caused by equilibration of those carriers with the low oxygen partial pressure of the melt. Li/sub 2/O- and (to a lesser extent) MgO-doped Cr/sub 2/O/sub 3/ appear to be suitable as container coating materials.