Gas response enhancement of nanocrystalline LaFeO₃ perovskite prepared using the microwave-assisted solution method

Perovskite oxides are a type of interesting advanced materials for the development of gas sensors with enhanced properties. In this work, LaFeO3 nanocrystalline powders were synthesized through the simple and economical microwave-assisted solution method. Thermal decomposition of precursors allowed the formation of orthorhombic LaFeO3 at relatively low temperatures compared with the conventional solid-state synthesis. The influence of the chelating agent (ethylenediamine) content on the perovskite's crystallite size was investigated. Our results indicated that increasing the ethylenediamine/metallic ions (E:M) molar ratio reduced the LaFeO3 crystallite size. Crystallite sizes varied from 50.4, 37.3, and 22.8 nm for E:M ratios 1:1, 2:1, and 4:1, respectively. Synthesized LaFeO3 powders were pressed to form pellets to evaluate the sensing response toward carbon monoxide at different concentrations (0, 5, 50, 100, 200, and 300 ppm) and different temperatures (25, 100, 200, and 300 degrees C). The pellets exhibited high sensitivity to CO, which increased with gas concentration and temperature. To corroborate LaFeO3's ability for gas detection, dynamic tests were carried out in C3H8 atmospheres at different concentrations and operating temperatures. In this case, the measurements were done on thick films, showing good sensitivity, final stability, and reproducibility. In addition, it was observed that by reducing the crystallite size, the material's sensitivity (or response) increased, having a more significant effect on changes in electrical resistance. Crystal size reduction is crucial in the sensor's ability to detect low gas concentrations.