Influence of annealing on structure and thermochromic property of spark plasma sintered La1−xSrxMnO3 compounds

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Sr-doped lanthanum manganite (La1−xSrxMnO3) compounds as potential thermal control materials have been prepared by spark plasma sintering followed by annealing at different temperatures. The structure, transport behavior and thermochromic property of the samples were then studied as a function of annealing. With the increasing of annealing temperature, the relative density was increased, and well-crystallized La1−xSrxMnO3 compounds with a dense texture (relative density > 98 %) were obtained after annealing at 1,273–1,373 K. The measurement of transport property showed an improvement in electrical conductivity due to the increasing of Mn4+/Mn3+ratio after annealing, which as a result enhanced the Mn3+–O–Mn4+ double exchange interaction. The conduction mechanisms above the metal–insulator transition temperature (TP) was further discussed, and we found that the small polaron hopping model could be applied in this regime. Moreover, the annealed samples tended to reduce the localization of the charge carriers and thereby a decreasing in hopping energy was observed. The infrared emissivity (e) of the La1−xSrxMnO3 compounds changed with temperature and an shape change near TP was observed, which was considered to be associated with the metal–insulator transition. The thermochromic properties were also affected by annealing process, where a larger variability in emissivity (Δe = 0.38) was obtained for the annealed samples.