Nonstoichiometric Doping of La_0.9FeSn_1-O₃ Hollow Microspheres for an Ultrasensitive Formaldehyde Sensor

Oxygen vacancies play an essential role in gas-sensitive materials, but the intrinsic oxides are poorly controlled and contain low oxygen vacancy concentrations. In this work, we prepared La_0.9Fe_1-SnO₃ microspheres with high sensitivity and controllability by a simple hydrothermal method, and then, we demonstrated that it has many oxygen ion defects by X-ray photoelectron spectroscopy and electron paramagnetic resonance characterization. The gas sensor exhibited ultrahigh response, specific recognition of formaldehyde gas, and excellent moisture resistance. By comparing the composites with different doping ratios, it was found that the highest catalytic activity was reached when x = 0.75, and the response value of La_0.9Fe_0.75Sn_0.25O₃ hollow microspheres at 200 °C reached 73-10 ppm of formaldehyde, which is 188% higher than that of intrinsic LaFeO₃ hollow microspheres. On the one hand, due to the absence of A-site La³⁺ and the replacement of B-site Fe³⁺ by Sn⁴⁺, a large number of oxygen vacancies are induced on the surface and in the interior of the materials; on the other hand, it is also related to the large specific surface area and gas channels caused by the particular structure.