Phase transformation (cubic to rhombohedral): the effect on the NO2 sensing performance of Zn-doped flower-like In2O3 structures

Abstract

Cubic In₂O₃ (bcc-In₂O₃) was transformed into a mixture of bcc-In₂O₃ and rhombohedral In₂O₃ (rh-In₂O₃) by Zn doping. The Zn-doped flower-like In₂O₃ structures consisted of many thin sheets with a length of 0.4–1 μm, and cubes with a length of 200 nm, while the size of the microflowers was 1–3.5 μm. The Zn doping concentration significantly affected the phase transformation and the overall morphology of In₂O₃. Furthermore, the analysis of N₂ adsorption–desorption measurements showed that the Zn-doped flower-like In₂O₃ structures (sample S5) adsorbed the largest amount of N₂ and had the biggest surface area (46.41 m² g⁻¹), which contributed to an improvement in gas sensing performance. Finally, sensors based on the mixture of bcc- and rh-In₂O₃ structures exhibited a much higher response to NO₂ than the pure bcc-In₂O₃ (sample S1), and the Zn-doped flower-like In₂O₃ structures (sample S5) exhibited the highest response of 27.4 ± 2.5 for 5 ppm NO₂. Thus, the gas sensing performance of In₂O₃ was enhanced significantly by the phase transformation.