Gd-tb-ga And Gd-bi-sb Ternary Phase Diagram And Magnetic Refrigeration Performance

Magnetic refrigeration offers high efficiency, low noise, high reliability and non-pollution, which is considered as a high-tech environment-friendly cooling technology. The key for magnetic refrigeration technology is material with high magnetocaloric effect (MCE). Seeking for the novel materials with high MCE at different temperature, especially at room temperature or synthesis techniques is a hot topic nowdays. In order to provide a guide for the preparation and study the influence of alloying on MCE for the room temperature magnetic refrigerants in Gd-Bi-Sb and Gd-Tb-Ga ternary systems, we investigated the phase diagram, phase structure and magnetocaloric effect of these two ternary systems.The investigation of the Gd-Tb-Ga ternary system confirmed the existence of eight binary compounds: Gd₅Ga₃, Gd3Ga2, GdGa, GdGa2, Tb5Ga3, TbGa, TbGa2 and TbGa3 at 500 oC. No ternary compound was found in this system. The isothermal section of this system at 500 oC was constructed, which is composed of seven single-phase regions, eight two-phase regions and two three-phase regions. Four continuous solid solutions: (Gd, Tb), (Gd, Tb)5Ga3, (Gd, Tb)Ga, (Gd, Tb)Ga2 were formed in this isothermal section. The maximum solid solubilities of Ga in (Gd, Tb) at 500 oC is 5.0 at.%. The homogeneity range of GdGa2 is from 20 to 33.3 at.% Ga. The solid solubilities of Ga in the other phases can not be detected.The magnetocaloric effect for a serial alloys Gd60Tb40-xGax with x = 0, 1, 3 ,5 was studied. All these alloys formed a solution (Gd, Tb, Ga). It means Ga can substitute for Tb or Gd, and thus affects its magnetocaloric effect. The Curie temperatures (Tcs) of the Gd60Tb40-xGax alloys with x = 0, 1, 3, 5 are 272.5, 283.5, 297 and 72.5 K respectively, while the maximum magnetic entropy changes ?SM, max are 5.15, 4.43, 3.32 and 4.58J/(kg·K) respectively. The Tcs of the Gd60Tb40-xGax alloys increase from 270 K to 297 K as x increases from 0 to 0.03. Further increasing Ga doping leads to decrease its Tc.The investigation of Gd-Bi-Sb ternary system, confirmed the existence of the seven binary compounds: Gd5Sb3, Gd4Sb3, GdSb, Gd16Sb39, Gd5Bi3, Gd4Bi3 and GdBi at roomtemperature. No ternary compound was found in this system. The isothermal section of this system at room temperature was determined, which consists of six single-phase regions, six two-phase regions and one three-phase regions. Four ternary continuous solid solutions: (Sb, Bi, Gd), Gd(Sb, Bi), Gd4(Sb, Bi)3, Gd5(Sb, Bi)3 were formed in this isothermal section. The binary compounds GdBi2 does not exist in the Gd-Bi phase diagram. The maximum solid solubility of Gd in (Sb, Bi, Gd) at room temperature is 7.5 at.%, while the solid solubility of Gd in the other solid solubility are non-observable. Due to the small solid solubility of Gd in Gd4(Sb, Bi)3 and high volatility of Bi and Sb, a pure single-phase may not be easy to obtained Gd4(Sb, Bi)3 by arc melting, it can be obtained by high frequency melting.The influence of phosphorus on magnetocaloric effect of Gd4Sb3 and Gd4(Bi0.5Sb0.5)3 alloys was investigated in this work. Experimental results show that a small amounts of phosphorus in both serial alloys is favorable for the formation of the Mn5Si3-type phase but deleterious for the formation of the Th3P4-type structure phase. The Curie temperature Tc does not change obviously, while the maximum magnetic entropy change (︱?SM, max︱) reduce with P content increasing.A thermodynamic assessment for the binary Gd–Sb system was performed using the CALPHAD approach (calculation of phase diagram) based on Gd-Sb phase diagram and thermodynamic data reported in literatures. For the thermodynamic assessment, the Redlich–Kister polynomial was used to describe the excess Gibbs energies of solution phases, liquid (L), hcp (αGd) and bcc (βGd). The sublattice-compound energy model was employed to describe the intermediate phases (the stoichiometric compounds): Gd5Sb3, Gd4Sb3,htGdSb, rtGdSb and Gd16Sb39. A set of reliable, reasonable and self-consistent thermodynamic parameters of the Gd-Sb system has been obtained.