Crystal chemistry, modulated structure, and electrical conductivity in the oxygen excess scheelite-based compounds [formula omitted] and [formula omitted

Abstract

For La 1−x Th x NbO 4+ x 2 , three phases with broad homogeneity regions occur, for 0.075 ≤ x ≤ 0.37, 0.41 < x < 0.61, and 0.65 ≤ x ≤ 0.74. All are related to the scheelite structure type, with at least the first exhibiting an incommensurate structural modulation. An analogous structurally modulated phase was found for LaNb 1−x W x O 4+ x 2 for 0.11 ≤ x ≤ 0.22. Additional phases occur at La 0.2Th 0.8NbO 4.4 and LaNb 0.4W 0.6O 4.3. The electrical conductivity and the direction and wavelength of the structural modulation have been characterized for the La 1−x Th x NbO 4+ x 2 phase with 0.075 ≤ x ≤ 0.37.