Effect of Boron addition on the microstructure, phase transitions and magnetocaloric properties in Gd-Si-Ge alloy

The Gd5Si2Ge2Bx (0 < x ≤ 0.125) alloys were investigated to study the influence of Boron addition on the structure, microstructure, magnetic and magnetocaloric properties. Except x = 0.05 alloy, all the other Boron containing alloys under study displayed the presence of major monoclinic Gd5Si2Ge2-type phase along with low volume fraction of hexagonal GdSi-type (5:5 H) secondary phase at room temperature (RT). In the case of alloy with x = 0.05, monoclinic Gd5Si2Ge2-type and orthorhombic Gd5(Si,Ge)4 type mixed phases along with low volume fraction of Gd5Si3-type (5:3 H) secondary phase were observed at RT. The structural transition (Ts) (orthorhombic to monoclinic) and the Curie transition (TC) of the monoclinic phase in the x = 0.05 alloy occurred at 293 K and 305 K respectively. These transitions occurred at relatively higher temperatures than those reported in parent Gd5Si2Ge2 alloy. At higher concentrations of Boron (x > 0.05), both the transitions, Ts and TC shifted to lower temperatures. A maximum magnetic entropy change of 13.6 J/(kg-K) (at 293 K) and refrigerant capacity (RC) of 378 J/kg were obtained in Gd5Si2Ge2B0.05 alloy which conveys that this alloy has an edge over the parent alloy in terms of operating temperature and refrigeration capacity.