HUMIDITY SENSORS BASED ON SnO2 -Co3 O4 -Nb2 O5 -Cr2 O3 SEMICONDUCTOR VARISTOR CERAMICS

Metal Oxide ZnO-Based Varistor Ceramics

Semiconductor Gas Sensors Based on Pd/SnO2 Nanomaterials for Methane Detection in Air

Semiconductor sensors based on nanosized Pd-containing tin dioxide have been obtained by a sol-gel technique. Semiconductor gas-sensitive materials were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. Influence of Pd additives on sensitivity of the sensors to methane has been studied. Temperature dependences of electrical resistance in air and sensor...

Homogenized Maxwell’s Equations; a Model for Varistor Ceramics

A model for a semiconducting ceramic material used in devices to protect electrical equipment against overvoltages is presented. The fine structure in the material induces highly oscillating coefficients in the Maxwell equation. Maxwell equations are homogenized to obtain a coupled system. The fine scales in the model yield a local problem coupled with the homogenized Maxwell’s equations. In th...

Crystal phase analysis of SnO2-based varistor ceramic using the Rietveld method

A second addition of lmol% of CoO to a pre calcined SnO2-based ceramic doped with 1.0mol% of CoO, 0.05mol% of Nb2O5 and 0.05mol% of Cr2O3 promotes the appearance of a secondary phase, Co2SnO4, besides the SnO2 cassiterite phase, when the ceramic was sintered at 1350°C/2h. This was observed using X-ray powder diffraction, scanning electron microscopy and energy dispersive X-ray techniques. Rietv...

A Comparative Study of Thermal Conductivity in ZnO- and SnO2-Based Varistor Systems

We performed a comparative study of electrical and thermal properties of ZnOand SnO2-based varistor. The electrical properties of commercial ZnO-based varistor are equivalent to that found in SnO2-based varistor system. In spite of this, the SnO2 showed a thermal conductivity higher than commercial samples of ZnO-based varistor, which allied with its simpler microstructure and lower dopant conc...