The effect of high-temperature annealing on LaFe_(11.5)Si_(1.5) and the magneto-caloric properties of La_(1-x)Ce_xFe_(11.5)Si_(1.5) compounds

The powder X-ray diffraction patterns of LaFe_11.5Si_1.5 compounds annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h) show that a large amount of 1:13 phase begins to form in LaFe_11.5Si_1.5 compound annealed at 1423 K (5 h). In the temperature range from 1423 to 1523 K, α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed, and the most amount of 1:13 phase is obtained in the compound annealed at 1523 K (5 h). With the annealing temperature increasing to 1573 and 1623 K, LaFeSi is detected again in the LaFe_11.5Si_1.5 compound. According to the results of annealing at different high-temperatures, the La_1−x Ce _x Fe_11.5Si_1.5 compounds are annealed at high temperatures of 1373 K (2 h) + 1523 K (5 h). The main phase is NaZn₁₃-type phase, and the impurity is a small amount of α-Fe in La_1−x Ce _x Fe_11.5Si_1.5 compounds with 0 ≤ x ≤ 0.35, and there is a large amount of Ce₂Fe₁₇ phase in La_0.5Ce_0.5Fe_11.5Si_1.5. It indicates that the substitution of cerium atoms for La in LaFe_11.5Si_1.5 compounds has limit. At the same time, the substitution of Ce for La has large effect on magnetocaloric properties. With increasing Ce content from x = 0 to x = 0.35, the Curie temperature decreases linearly from 196 to 168 K, the magnetic entropy change increases from 16.5 to 57.3 J·kg⁻¹·K⁻¹ in a low magnetic field change of 0–2 T, and the thermal hysteresis also increases from 3 K to 8 K.