Gas sensing properties of Nd2O3 nanostructured microspheres

Nd2O3 microspheres were prepared by a solution-coprecipitation method. The dissolution of neodymium nitrate in formic acid produced, at room temperature, semispherical particles of neodymium formate (Nd(HCOO)3). The size of these particles was in the range 0.5 to 1.4 μm. The thermal decomposition at 600 °C transformed Nd(HCOO)3 to single-phase Nd2O3, with cubic crystal structure. A decrease of size of ~15% also took place. A detailed inspection of their surface revealed the formation of a sponge-like solid, possessing extensive nanoporosity. The gas sensing characterization was performed on thick films made with the as-prepared Nd2O3 microspheres. Based in the response to the test gases an n-type semiconductor behavior was observed. A reliable detection of CO was observed from 300 °C, using an applied frequency of 100 kHz; however, better results were obtained at 400 °C. For CO2, the best results were registered at 400 °C and 100 kHz; whereas in ethanol vapor these were obtained at lower temperature and frequency (300 °C and 100 Hz). Quantitative detection of CO and ethanol vapor was achieved; however, the results were not satisfactory for CO2.