Crystallographic Evolution of La0.7Ca0.3-xKxMnO3 (0 ≤ x ≤ 0.09) and Its Implications for Magnetocaloric Materials

Abstract

Magnetic refrigeration utilizing the magnetocaloric effect (MCE) is becoming a sustainable option compared to conventional gas-compression cooling technologies. In this study, the structural properties of potassium-doped La_0.7Ca_0.3-xK_xMnO₃ (x = 0.01, 0.03, 0.05, 0.07, and 0.09) polycrystalline materials were investigated to assess their potential for magnetocaloric applications. The samples were synthesized via wet mechanical milling followed by sintering at 1000 °C, using high-purity La₂O₃, CaCO₃, K₂CO₃, and MnCO₃. X-ray diffraction (XRD) served as a technique for structure analysis, and the Rietveld method played a role in the refinement process. The results showed that single-phase perovskite structures with orthorhombic symmetry (Pnma space group) were successfully formed for all compositions up to x = 0.07, whereas the x = 0.09 sample exhibited a secondary CaO phase. The increase in K⁺ levels caused the unit cell volume to grow, mainly due to the lengthening of the a-axis, while the b and c dimensions saw a reduction. Crystallinity also improved with increasing K content up to x = 0.07. These crystallographic modifications suggest potential implications for magnetocaloric behavior, although direct measurements were not performed.