Investigation of Ca substitution on the gas sensing potential of LaFeO₃ nanoparticles towards low concentration SO₂ gas

Abstract

The present work investigates the superior ability of LaFeO₃ (LaFeO) and La_0.8Ca_0.2FeO_2.95 (LaCaFeO) nanoparticles to detect 3 ppm SO₂ gas. The influence of calcium substitution on the sensing behaviour of LaFeO has been studied. High resolution TEM images show that the particle sizes of LaFeO and LaCaFeO are less than 100 nm and SEM images show the agglomeration of interconnected nanoparticles. Both LaFeO and LaCaFeO crystallize in the orthorhombic crystal system with the space group Pbnm. Rietveld analysis of neutron diffraction data showed that LaCaFeO has lattice oxygen vacancies. In addition, magnetic refinements on both the samples have been carried out. The presence of lattice oxygen vacancies in LaCaFeO is qualitatively supported by Raman and XPS measurements. Electrical characterization showed increased conductivity for the LaCaFeO sample, influencing their sensing performance significantly. The LaCaFeO nanoparticles exhibit higher sensitivity, faster response time, rapid recovery time and good recyclability for sensing 3 ppm SO₂ gas. This enhanced sensing behavior is attributed to the increased oxygen vacancies in the lattice as well as the surface. As a consequence, increased active sites are created in LaCaFeO, promoting redox reaction between the analyte and the sensing material. The results demonstrated that while LaFeO is a good gas sensor, p-type substitution by Ca²⁺ renders this material an improved resistivity based gas sensor to detect low concentration SO₂.