Tuning structure and magnetotransport in La0.67Ca0.25Sr0.08MnO3 manganite via sintering-induced lattice modulation

Abstract

The structural and magnetotransport properties of polycrystalline La_0.67Ca_0.25Sr_0.08MnO₃ (LCSMO) ceramics are systematically investigated as a function of final sintering temperature. Samples sintered at 1100–1400 °C (S1100, S1200, S1300, and S1400) all crystallize in the orthorhombic Pbnm perovskite structure, yet Rietveld refinement reveals a nonmonotonic evolution of the Mn–O framework. The S1200 sample exhibits the longest Mn–O bond and the smallest Mn–O–Mn bond angle, indicating the strongest octahedral distortion, while higher temperatures partially restore the Mn–O–Mn network. Resistivity measurements show a broad maximum, characteristic of a transport crossover rather than a sharp phase transition. The S1200 sample shows the highest resistivity, whereas S1400 exhibits the lowest, with zero-field room-temperature resistivity below 0.5 Ω·cm. Applied magnetic fields reduce the resistivity, shift the resistivity maximum toward higher temperatures, and yield a nearly symmetric negative magnetoresistance, consistent with the suppression of spin-disorder scattering. Quantitative fitting in the metallic-like region indicates that disorder-enhanced electron–electron interaction and spin-dependent scattering contribute to the transport, while the semiconducting-like region can be empirically described by small-polaron and variable-range hopping models. These results demonstrate that sintering temperature modulates the magnetotransport through coupled modifications of the Mn–O–Mn network and carrier localization, providing a route for tuning the functional response of LCSMO manganite ceramics.