Fabrication and characterization of a printable semiconductor based on the V2O5-P2O5 system for thermoelectric application

Abstract

A printable semiconductor based on the V2O5P2O5 system for thermoelectric (TE) applications was fabricated by treatment under reductive conditions. 65V2O5-15P2O5-15CuO-5Fe2O3 (Tg∼305°C) glass films with a thickness of ∼40μm were prepared on polycrystalline -Al2O3 substrates via a melt-quenching synthesis, subsequent milling and powder application, and then a viscous flow in air. The glass films heat-treated at 450650 °C in ultra-high vacuum (UHV; ∼1 × 10-6 Pa) and further reductive hydrogen atmosphere indicated advanced crystallization at the higher temperature, and the reduction demonstrated by the increase of V4+/V5+ and Cu1+,0/Cu2+ ratios. The surface morphology of the crystallized films demonstrated significant crystal growth up to ∼5μm with increased heating temperature in UHV as well as a change in their characteristic shapes. Nano and micropores were homogeneously dispersed throughout the film crystallized at 450°C in UHV, which reduced thermal conductivity. The hydrogen treatment resulted in a volume shrinkage of the precipitated crystals, which is assumed to be due to the reduction and desorption of volatile components. The temperature dependency of the resistivity and the Seebeck coefficient of the crystallized glass-ceramic films were measured. The glass-ceramic films revealed semiconductor behavior in resistivity, and the precipitation in UHV at 650°C decreased the resistivity to 7 × 10-2∼cm at 300°C. A lower resistivity of 2 × 10-2∼cm was obtained after reduction by hydrogen. The films crystallized in UHVat 550 and 650°C had Seebeck coefficients lower than-120μV/K and were almost flat in the temperature range 50300 °C. On the other hand, the hydrogen-treated films revealed a Seebeck coefficient of ∼+10μV/K. It is noteworthy that both n-and p-type TE semiconductors were fabricated from the same starting V2O5P2O5 glass system.