Nanoscale nickel containing powders for use in CO and NO₂ gas sensors

The study covers physicochemical characteristics and gas sensitivity mechanisms of nickel oxide (NiO) and nickel ferrite (NiFe 2 O 4 ) obtained by levitation-jet synthesis. The properties of synthesized materials were studied using various spectroscopic methods. XPS showed that the presence of Ni 3+ ions in samples decreased significantly with an increase in the specific surface area of the powders and decrease in the average diameter of their particles. In this regard, it can be concluded that the number of uncompensated Ni 2+  vacancies in such samples also decreases, and concentration of O 2– vacancies, on the contrary, increases significantly. The Raman spectra of nanoscale NiO lacked the magnon band, which is usually observed at ν = 1500 cm –1 , whereas the spectrum of nanoferrite sample had a pronounced 2M band, which indicates an increase in spin correlation. According to the analysis of UV spectra of the samples obtained, there is an increase in reflectivity values with an increase in wavelength for large nanoparticles compared to the corresponding values for small particles. In this regard, we assumed that Ni-based oxide nanoparticles are semiconductors with an indirect transition to band gap energy, and this is in sharp contrast to the data obtained earlier by other researchers. Gas sensitivity of nanoscale powders was investigated in relation to carbon monoxide and nitrogen dioxide at operating temperatures of 350–500 °C. Evaluation of the obtained results allowed us to conclude that the operating characteristics of sensors proposed by us are superior in a number of parameters to the similar characteristics of sensors made of commercial powders, as well as of powders obtained by other synthetic methods.