Effect of Ag doping on the structure, morphology and magnetocaloric properties of La_0.67Ca_0.205Sr_0.125MnO₃

In recent years, the escalating global energy consumption and environmental safety concerns have necessitated the development of greener and more sustainable refrigeration technologies. In this work, the magnetocaloric properties of La_0.67Ca_0.205Sr_0.125MnO₃ are correlated with the concentration of Ag⁺ dopants at the B-site, where Sr²⁺ partially substitutes Ca²⁺ at the A-site. Perovskite powder samples of La_0.67Ca_0.205Sr_0.125Mn_1−xAg_xO₃ (x = 0.025, 0.05, 0.075) were obtained through a conventional sol-gel technique. X-ray diffraction confirmed the formation of single-phase perovskite structures without secondary phases, with all samples crystallizing in the Pnma space group. Fourier-transform infrared spectroscopy analysis verified the presence of MnO₆ octahedra in the crystal lattice. X-ray photoelectron spectroscopy revealed mixed-valence states of Mn⁴⁺/Mn³⁺, with the Mn⁴⁺/Mn³⁺ ratio increasing systematically with Ag⁺ doping concentration. Magnetic measurements indicated that all samples undergo second-order magnetic phase transitions near their Curie temperatures, which remain within the near-room-temperature range. Among the series, the composition x = 0.05 showed a Curie temperature with the closest proximity to ambient conditions, under an applied magnetic field of 5T, the recorded values of 4.086 J/(kg·K) for maximum magnetic entropy change of and 276.113 J/kg for RCP represent the maximum performance achieved. These results demonstrate that Ag⁺ doping effectively enhances the magnetocaloric performance of La_0.67Ca_0.205Sr_0.125MnO₃, providing valuable insights for the design of advanced near-room-temperature magnetocaloric materials.