TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Properties: Plane-to-plane spacing varies within the thermoelectric oxide material in range of 0.5-5 nm. The thermoelectric oxide material has plane-to-plane periodicity of 1-2 nm, thermoelectric figure of merit of more than 0.15 at 1050 K, lattice thermal conductivity of less than 3 W/mK at 450-1050 K, Seebeck coefficient of more negative than (-80) mu V/K, and electrical conductivity of more than 2000 S/m at 450-1050 K. The niobium oxide powder has average particle size of 20 nm to 100 mu m. Preferred Process: Plane-to-plane spacing coincides with mean free path of phonons in the oxide material. During preparation of sub-stoichiometric, composite thermoelectric oxide material, the niobium oxide powder and the phase powder are dispersed in liquid and mixed ultrasonically to form the mixture. The mixture is heated in reducing environment comprising exposure(s) of the mixture to solid state reducing agent chosen from elemental carbon, carbide, nitride, boride, metal or suboxide, or exposure of mixture to reducing gas mixture chosen from hydrogen/water, carbon monoxide/carbon dioxide and carbon/carbon monoxide. The sub-stoichiometric, composite material is densified via spark plasma sintering. Preferred Composition: The thermoelectric oxide material comprises two groups of intersecting periodic planar crystallographic defect planes each having plane-to-plane spacing of 0.5-5 nm. The sub-stoichiometric, composite thermoelectric oxide material containing 1-30 wt.% phase (M) chosen from carbon, niobium, tungsten, molybdenum, niobium oxide, titanium dioxide, titanium carbide, titanium nitride, niobium carbide, zinc oxide, copper and tungsten carbide, further contains dopant(s) chosen from tungsten, molybdenum, titanium, tantalum, zirconium, cerium, lanthanum and yttrium, and has group(s) of shear defect planes. The carbide is chosen from titanium carbide, niobium carbide and tungsten carbide. The nitride is chosen from titanium nitride and tungsten nitride.