High temperature CO2 sensing properties and mechanism of nanocrystalline LaCrO3 with rhombohedral structure: experiments and ab initio calculations

Abstract

LaCrO₃ nanocrystalline powders with perovskite structure were prepared by sol–gel method with annealing at 700 °C, 900 °C for 4 h, respectively. At room temperature, LaCrO₃ nanocrystalline powders crystallizes as the orthorhombic structure. At high temperatures above the transition temperature from orthorhombic to rhombohedral, when exposed to CO₂ the optimum operating temperature for sensing is 360 °C and the resistance of the rhombohedral LaCrO₃ sensor decreases, which is different from other p-type semiconductors. First principles calculations (GGA + U) were performed to investigate the possible CO₂ sensing mechanism for rhombohedral LaCrO₃ sensor. The calculation results show that when exposed to CO₂, the C atom of CO₂ molecule chemically binds with the surface O atom of rhombohedral LaCrO₃ (012) surface, meanwhile the two O atoms of CO₂ molecule chemically bind with the adjacent surface Cr atoms on LaCrO₃ (012) surface. For this case, the CO₂ molecule captures electrons from the LaCrO₃ (012) surface, which is consistent with the experimental observation.