CuBi2O4 Prepared by the Polymerized Complex Method for Gas-Sensing Applications

Multicomponent oxides can be extensively explored as alternative gas-sensing materials to binary oxides with their structural and compositional versatilities. In this work, the gas-sensing properties of CuBi 2 O 4 have been investigated toward various reducing gases (C 2 H 5 OH, NH 3, H 2, CO, and H 2 S) and oxidizing gas (NO 2 ) for the first time. For this, the powder synthesis has been developed using the polymerized complex method (Pechini method) to obtain a single-phase polycrystalline CuBi 2 O 4 . The defect, optical, and electronic properties in the prepared CuBi 2 O 4 powder were modulated by varying the calcination temperature from 500 to 700 °C. Noticeably, a high concentration of Cu + –oxygen vacancy ( ) defect complexes and isolated Cu 2+ ion clusters was found in the 500 °C-calcined CuBi 2 O 4, where they were removed through air calcination at higher temperatures (up to 700 °C) while making the compound more stoichiometric. The change in the intrinsic defect concentration with the calcination temperature led to the variation of the electronic band gap energy and hole concentration in CuBi 2 O 4 with the polaronic hopping conduction (activation energy = 0.43 eV). The CuBi 2 O 4 sensor with 500 °C-calcined powder showed the highest gas responses (specifically, 10.4 toward 1000 ppm C 2 H 5 OH at the operating temperature of 400 °C) with the highest defect concentration. As a result, the gas-sensing characteristics of CuBi 2 O 4 are found to be dominantly affected by the intrinsic defect concentration, which is controlled by the calcination temperature. Toward reducing H 2 S and oxidizing NO 2 gases, the multiple reactions arising simultaneously on the surface of the CuBi 2 O 4 sensor govern its response behavior, depending on the gas concentration and the operating temperature. We believe that this work can be a cornerstone for understanding the effect of chemical defect on the gas-sensing characteristics in multicomponent oxides.