Temperature dependence of transport behavior and thermochromic property of spark plasma-sintered (La,Sr)MnO₃ bulk ceramics

Dense (La,Sr)MnO₃ bulk ceramics were prepared by spark plasma sintering to study the temperature dependence of transport behavior and thermochromic property in these materials as a function of Sr concentration. The measurement of transport property showed an improvement in electron mobility and electrical conductivity as increasing Sr doping content. The doping of Sr²⁺ led to the increasing in Mn⁴⁺ amount, which enhanced the Mn³⁺–O–Mn⁴⁺ double exchange and reduced the Jahn–Teller effect, and as a result improved the electrical properties of the samples. Concentrating on the variation of temperature-dependent resistivity, it is noted that all the samples exhibited metal–insulator transition temperature (denoted by T _p), showing metallic behavior for T < T _p and semiconducting character for T > T _p. We then fitted the resistivity data in the semiconducting region by the small polaron hopping (SPH) model and found that the transport behavior in this regime could be described by the SPH mechanism. The infrared emissivity (ε) of the (La,Sr)MnO₃ ceramics changed with testing temperature, and a shape increase in the emittance value was observed near T _p, which was considered to be associated with the metal–insulator transition. The La_1−x Sr _x MnO₃ (x = 0.1−0.2) bulk ceramics exhibited a significant transition in emissivity around T _p, indicating good variable-emittance by appropriate Sr doping.