Thermoelectric properties of tungsten-titanium-phosphate glass-ceramics

The thermoelectric properties of tungsten-titanium phosphate glass-ceramics, which were described in previous articles, were measured as a function of composition, ceram temperature, and measurement temperature. The glass-ceramics comprise tungsten monophosphate crystals, (PO2)(4)(WO3)(2 m), in a matrix of TiP2O7. The glass-ceramics behave as n-type semiconductors with nearly metallic behavior. Conduction occurs along percolating networks of primarily m6 and m7 crystals. The highest electrical conductivities and (absolute) Seebeck coefficients were measured on a glass-ceramic containing large, interconnecting, prismatic, m7 crystals. At 777 degrees C, the electrical conductivity reached nearly 5500 S/m and the Seebeck coefficient was -60 mu V/K. Thermal conductivity was in the 2.5-3 W/m.K range, and the maximum ZT obtained was 0.007. This ZT is two orders of magnitude lower than those of the best bulk, polycrystalline, n-type, oxide thermoelectric materials. The exceptional property of the tungsten-titanium phosphate glass-ceramics is their high electrical conductivity when compared with oxide glasses.