High temperature calcination for analyzing influence of 3d transition metals on gas sensing performance of mixed potential sensor Pt/YSZ/LaMO3 (M = Mn, Fe, Co, Ni)

High-Quality Perovskite Thin Films for NO2 Detection: Optimizing Pulsed Laser Deposition of Pure and Sr-Doped LaMO3 (M = Co, Fe)

This study investigates the structural and catalytic properties of pure and Sr-doped LaCoO3 and LaFeO3 thin films for potential use as resistive gas sensors. Thin films were deposited via pulsed laser deposition (PLD) and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation, and scratch tests. XRD analysis confirmed the formation of the desired perovskite phases without secondary phases. XPS revealed the presence of La3+, Co3+/Co4+, Fe3+/Fe4+, and Sr2+ oxidation states. SEM and AFM imaging showed compact, nanostructured surfaces with varying morphologies (shape and size of surface irregularities) depending on the composition. Sr doping led to surface refinement and increased nanohardness and adhesion. Transmission electron microscopy (TEM) analysis confirmed the columnar growth of nanocrystalline films. Sr-doped LaCoO3 demonstrated enhanced sensitivity and stability in the presence of NO2 gas compared to pure LaCoO3, as evidenced by electrical resistivity measurements within 230 ÷ 440 °C. At the same time, it was found that Sr doping stabilizes the catalytic activity of LaFeO3 (in the range of 300 ÷ 350 °C), although its behavior in the presence of NO2 differs from that of LaCo(Sr)O3-especially in terms of response and recovery times. These findings highlight the potential of Sr-doped LaCoO3 and LaFeO3 thin films for NO2 sensing applications.

Existence of La-site antisite defects in [Formula: see text] ([Formula: see text], Fe, and Co) predicted with many-body diffusion quantum Monte Carlo

The properties of [Formula: see text] (M: 3d transition metal) perovskite crystals are significantly dependent on point defects, whether introduced accidentally or intentionally. The most studied defects in La-based perovskites are the oxygen vacancies and doping impurities on the La and M sites. Here, we identify that intrinsic antisite defects, the replacement of La by the transition metal, M, can be formed under M-rich and O-poor growth conditions, based on results of an accurate many-body ab initio approach. Our fixed-node diffusion Monte Carlo (FNDMC) calculations of [Formula: see text] ([Formula: see text], Fe, and Co) find that such antisite defects can have low formation energies and are magnetized. Complementary density functional theory (DFT)-based calculations show that Mn antisite defects in [Formula: see text] may cause the p-type electronic conductivity. These features could affect spintronics, redox catalysis, and other broad applications. Our bulk validation studies establish that FNDMC reproduces the antiferromagnetic state of [Formula: see text], whereas DFT with PBE (Perdew-Burke-Ernzerhof), SCAN (strongly constrained and appropriately normed), and the LDA+U (local density approximation with Coulomb U) functionals all favor ferromagnetic states, at variance with experiment.

High Performance Mixed Potential Type NO2 Gas Sensor Based on Porous YSZ Layer Formed with Graphite Doping

High performance mixed potential type NO₂ sensors using porous yttria-stabilized zirconia (YSZ) layers doped with different concentration graphite as solid electrolyte and LaFeO₃ as sensing electrode were fabricated and characterized. LaFeO₃ was prepared by a typical citrate sol-gel method and characterized using XRD. The surface morphology and porosity of porous YSZ layers were characterized by field emission scanning electron microscope (FESEM). The sensor doped with 3 wt% graphite shows the highest response (-76.4 mV to 80 ppm NO₂) and the response is linearly dependent on the logarithm of NO₂ concentration in the range of 10-200 ppm. The sensor measurement results also present good repeatability and cross-sensitivity.