Estimation of La<sub>1-<i>x</i></sub>Sr<sub><i>x</i></sub>MnO<sub>3</sub> (<i>x</i>=0.15~0.5) Emittance by Thermal Irradiation Theory

Abstract

La1-xSrxMnO3 (LSMO) has recently shown promising features as a metal-insulator material over a limited range of Sr doping (x=0.175 to 0.25). Its thermal property has been commonly measured through the very expensive calorimetric method. In this paper, a considerably more convenient thermal investigation approach to this issue through the thermal irradiation theory is proposed. LSMO compounds were synthesized with a wide range of x (0.15 to 0.5) using the precisely controlled Pechini sol-gel method. XRD phase structure analysis and XPS composition and chemical state study were adopted for quality assurance of the compounds. Resistance and infrared reflectance of the samples were measured respectively with the help of the four probe technique in temperature range of 150K to 380K and an infrared spectrometer over a temperature range of 153 K to 544 K. Investigations showed a good correlation between these two measures approving the metal-insulator characteristic of all the samples. Calculation of the total normal emittance (εN(T)) of the compounds was innovatively simplified using the measured reflectivity data through the thermal irradiation theory for graybody. Moreover, the results showed that every x ratio fabricated through the precisely controlled Pechini method presented a unique εN(T) characteristic with a different metal-insulator transition temperature.