Effect of Crystal Defect on Gas Sensing Properties of Co₃O₄ Nanoparticles

Crystal growth-controlled Co₃O₄ nanoparticles were prepared to examine gas sensing properties. A cube-like, an irregular shaped, and three kinds of raspberry-type structures were observed by morphology analysis. The raspberry-type structures have an expanded lattice volume with a large oxygen deficiency area, and the cube-like structure has a contracted lattice volume as compared to the irregular shaped structure. The raspberry-type structures exhibited a higher sensor signal response than the others. A relationship between sensor properties and crystal defect was investigated, and it was revealed that the gas selectivity to a high dipole moment value of a reducing gas molecule increased with increasing oxygen deficiency area of the Co₃O₄ nanoparticle. It was considered that the oxygen deficiency area acted as an important reaction site, which can be attributed to the selective reaction of the Co₃O₄ nanoparticle with gas molecules.