Syntheses and electrical properties of tetragonal tungsten bronze type solid solution Ba_6-xLa_xNb₁₀O_30+δ (x = 0, 1, 2, 3) and Sr₆Nb₁₀O₃₀

Tetragonal tungsten bronze (TBB) type niobium compounds Sr₆Nb₁₀O₃₀ and a solid solution series Ba_6-xLa_xNb₁₀0₃₀ (x = 0, 1, 2, 3) were synthesized and their resistivity was measured in the temperature range 10-300 K. The Sr compound is a semiconductor, the high temperature data (100 ≤ T ≤ 300 K) for which can be fitted to the T^-1/4 law. Ba₆Nb₁₀O₃₀ also is a semiconductor, but with a different temperature dependency. La-substitution in the Ba compound caused a conduction mechanism to change from semiconducting (x = 0) to metallic (x ≥ 1).