Structure and properties of Ba6 − xLnxNb10O30, Ln = La, Ce and Nd compounds

Ba6 − xLnxNb10O30 compounds, Ln = La, Ce and Nd, with a tetragonal tungsten bronze-type structure have been synthesized and were characterized by X-ray powder diffraction and EDS analysis. The homogeneity regions of the obtained compounds were found to be 0 ≤ x ≤ 2 for La, and 0 ≤ x ≤ 1.5 for Ce and Nd. The crystal structures of Ba5LaNb10O30 and Ba4La2Nb10O30 were refined using X-ray powder diffraction data. Refinement indicated the presence of vacancies in the BaLa positions. This observation was supported by oxidation studies of the La-substituted compounds. The temperature dependence of the normalized resistivity of the compounds showed a nonmetallic behavior. The increase in the RR273 ratio with decreasing temperature is less distinct for the phases with the higher concentration of rare-earth cation.