THE GAS-SENSING PROPERTIES OF BISMUTH MOLYBDATE EVAPORATED-FILMS

A gas sensor that operates by the detection of changes in the bulk conductivity of a bismuth molybdate semiconductor catalyst is presented. The reduction of the catalyst by organic vapors produces highly mobile oxygen vacancies, which have a direct effect on the carrier density throughout the sample. This reaction is completely reversible in air. The sensor can be prepared as a mixture of the alpha and gamma phases of bismuth molybdate evaporated onto a quartz substrate. The prototype sensors studied show long-term stability of response and insensitivity to water vapor. A degree of selectivity to alcohols and ketones and some alkenes over other reducing agents such as alkanes, hydrogen and carbon monoxide is shown. At an operating temperature of 330 degree C, increases in conductivity of a factor of 30 after exposure to 200 ppm of ethanol were commonly observed, with sensitivities down to 5 ppm. This class of sensors may find use in breathalyser devices.