Structure, Conductivity, and Sensor Properties of Nanosized ZnO-In 2 O 3 Composites: Influence of Synthesis Method.

The influence of the method used for synthesizing ZnO-In 2 O 3 composites (nanopowder mixing, impregnation, and hydrothermal method) on the structure, conductivity, and sensor properties is investigated. With the nanopowder mixing, the size of the parent nanoparticles in the composite remains practically unchanged in the range of 50-100 nm. The impregnation composites consist of 70 nm In 2 O 3 nanoparticles with ZnO nanoclusters < 30 nm in size located on its surface. The nanoparticles in the hydrothermal composites have a narrow size distribution in the range of 10-20 nm. The specific surface of hydrothermal samples is five times higher than that of impregnated samples. The sensor response of the impregnated composite to 1100 ppm H 2 is 1.3-1.5 times higher than the response of the mixed composite. Additives of 15-20 and 85 wt.% ZnO to mixed and impregnated composites lead to an increase in the response compared with pure In 2 O 3 . In the case of hydrothermal composite, up to 20 wt.% ZnO addition leads to a decrease in response, but 65 wt.% ZnO addition increases response by almost two times compared with pure In 2 O 3 . The sensor activity of a hydrothermal composite depends on the phase composition of In 2 O 3 . The maximum efficiency is reached for the composite containing cubic In 2 O 3 and the minimum for rhombohedral In 2 O 3 . An explanation is provided for the observed effects.