Refined Sr ion ratio to improve room-temperature TCR of La_1-xSr_xMnO₃ (0.175 ≤ x ≤ 0.235) polycrystalline ceramics

Perovskite manganite oxides have attracted considerable attention due to their strong electronic correlation. However, their practical application is challenged by high manufacturing costs and inferior electrical properties. In this study, the sol–gel method was employed to precisely control the Sr content in La_1−xSr_xMnO₃ (LSMO, x = 0.175, 0.195, 0.215, and 0.235) polycrystalline ceramics, the relationship between doping levels and electrical transport properties was systematically investigated. The results show that substituting La³⁺ with Sr²⁺ can effectively tune the electrical transport properties of LSMO ceramics. X-ray diffraction analysis indicates that all samples exhibit a single-phase perovskite structure with no secondary phases detected. Scanning electron microscopy images reveal that the sample surfaces have good grain connectivity, with grain size increasing as the Sr doping level increases. The resistivity–temperature curves of the samples were measured using the standard four-probe method, and significant differences of electrical transport properties were observed within the range of Sr doping studied. Notably, when the Sr doping level is x = 0.195, the temperature coefficient of resistivity (TCR) value of LSMO ceramics increases significantly to 10.3% K⁻¹ at the peak TCR temperature (T_k) of 296.3 K. In summary, these results offer a theoretical basis and guidance for future development of highly sensitive uncooled infrared bolometers.