Characteristics of a thin-film LaF3 solid electrolyte for oxygen sensing

Abstract

A solid electrolyte oxygen sensor has been prepared by the implementation of r.f. magnetron sputtering and electron-beam evaporation methods. Thin films of LaF3 are applied as F- ion-conducting solid electrolytes and a sensing electrode made of platinum black or an electron-beam evaporated Pt film is coated on the surface of the solid electrolytes. Co-sputtered Sn-SnF2 films or electron-beam evaporated Sn/SnF2 multilayered films are used as a reference electrode. The potential of the sensing electrode relative to that of the reference electrode changes logarithmically with the dissolved oxygen concentration in distilled water, but small e.m.f. changes are observed in a gas environment. The structure of LaF3 is found to be microcrystalline when formed by electron-beam evaporation and the r.f. magnetron sputtering method. The capacitance of a thin-film type sensor has been examined with the aid of an impedance technique. When the sensor is exposed to oxygen, the capacitance value decreases because of the increase of F- ion migration flux due to the adsorption of oxygen atoms on the sensing electrode surface. ？ 1991.