Role of Oxygen Vacancies in the Electrical Properties of WO3−x Nano/Microrods with Identical Morphology

Abstract

Tungsten oxide (WO _{3− x} ) crystalline nano/microrods with identical morphology but different contents of oxygen vacancies were prepared by thermally evaporating fixed amount of WO ₃ powder in reductive atmosphere from different amounts of S power at 1150°C in a vacuum tube furnace, in which both sources were loaded in separate ceramic boat. With increasing amount of S powder, a series of tungsten oxides, WO ₃, WO _2.90, W ₁₉O ₅₅ (WO _2.89), and W ₁₈O ₄₉ (WO _2.72), could be obtained. And devices were fabricated by screen-printing the obtained WO _{3− x} crystals on ceramic substrates with Ag-Pd interdigital electrodes. With increasing content of oxygen vacancies, the devices fabricated with WO _{3− x} crystals present a negative to positive resistance response to relative humidity. Under dry atmosphere, for the devices with increasing $x$, the strong response to light changed from short to long wavelength; under light irradiation, the conducting ability of the devices was enhanced, due to the more efficient separation and transportation of the photogenerated carriers; and under simulated solar irradiation, the photocurrent intensity of the W ₁₈O ₄₉ device was roughly 8 times, about 500 times, and even 1000 times larger than that of the W ₁₉O ₅₅, WO _2.90, and WO ₃ one, respectively. With the versatile optoelectrochemical properties, the obtained WO _{3− x} crystals have the great potential to prepare various humidity sensors and optoelectrical devices.