Solidification behaviour and microstructural correlations in magnetocaloric Gd–Si–Ge–Nb alloys

Abstract

Abstract Polycrystalline Gd 5 Si 2− x Ge 2− x Nb 2 x alloys (0 ≤ 2 x ≤ 0.2) were investigated for microstructure and magnetocaloric effect. The 2 x = 0.05 and 0.1 alloys were mainly composed of monoclinic Gd 5 Si 2 Ge 2 -type and orthorhombic Gd 5 Si 4 -type phases whereas other alloys exhibit monoclinic Gd 5 Si 2 Ge 2 -type phase at room temperature. The microstructural studies reveal that Nb addition results in the formation of Nb 5 (Si,Ge) 3 and α-Nb phases. The former promotes the nucleation of Gd 5 Si 3 -type phase while the latter suppresses it. At low Nb addition (2 x ≤ 0.1) the microstructural modification results in low volume fraction of detrimental Gd 5 Si 3 -type phase leading to enhanced magnetocaloric effect (Δ S ) M value compared to that of the parent compound. A maximum (Δ S ) M value of −9.6 J/kg K with refrigerant capacity of 98 J/kg was obtained for the 2 x = 0.1 alloy for a field change of 2 T near room temperature. The magneto-structural transitions shifted to higher temperatures with increase in Nb content up to 2 x = 0.1.