Effects of Cr3+ incorporation on structure, surface morphology, and the magnetocaloric effect in La0.8Sr0.2Mn1-xCrxO3 ceramics by means of first-principles calculations and wet chemical method

Abstract

The investigation focused on the impact of Cr³⁺ incorporation on structural features, surface morphology, and the magnetocaloric effect in La_0.8Sr_0.2Mn_1-xCr_xO₃ ceramics, with x values of 0.05, 0.10, and 0.15, employing both experimental methods and theoretical simulations. Synthesis of La_0.8Sr_0.2Mn_1-xCr_xO₃ ceramics was achieved using the sol-gel method. Analyses via transmission electron microscopy and X-ray diffraction confirmed that La_0.8Sr_0.2Mn_1-xCr_xO₃ ceramics possess a rhombohedral crystal structure, corresponding to space group No.167 (R-3c). Scanning electron microscopy revealed that La_0.8Sr_0.2Mn_1-xCr_xO₃ ceramics comprise irregular ellipsoidal particles. The average particle size ranged from 173 nm to 226 nm. XPS confirmed the presence of all elements in La_0.8Sr_0.2Mn_1-xCr_xO₃ ceramics. Mixed valence states of Mn (Mn³⁺/Mn⁴⁺) and Cr (Cr³⁺/Cr⁴⁺) were identified, with Sr at +2 and La at +3. The Tc of La_0.8Sr_0.2Mn_1-xCr_xO₃ ceramics (x = 0.05, 0.10, 0.15) were determined using a Magnetic Property Measurement System to be 301 K, 278 K, and 253 K, respectively. A decrease in Tc with increasing Cr³⁺ doping was observed. Analysis of isothermal magnetization and Arrott plots reveals that La_0.8Sr_0.2Mn_1-xCr_xO₃ ceramics undergoes a second-order transition from paramagnetism to ferromagnetism. It was found that the net magnetic moment (The vector sum of all magnetic moments) and magnetic entropy change of La_0.8Sr_0.2Mn_1-xCr_xO₃ ceramics decreased with increasing of Cr³⁺ doping. For samples with a chromium doping level of x = 0.05, the Tc is recorded at 301 K. At this doping concentration, the peak magnetic entropy change is observed to be 3.50 J/(kg K) (H = 5 T).