Role of Oxygen Vacancies in the Electrical Properties of WO_3−<i>x</i> 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 19 O 55 (WO 2.89 ), and W 18 O 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:math>, 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 18 O 49 device was roughly 8 times, about 500 times, and even 1000 times larger than that of the W 19 O 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.