Excellent mechanical properties and specific heat capacity of Er3+xNi binary alloys

Lead is often used as regenerator material in cryocoolers because of its larger specific heat capacity in 20-30 K However, Lead is potentially damaging to the environment and is prohibited in any device by RoHs Therefore, it is necessary to find alternative regenerator materials^[1]. Bismuth is a promising alternative material, but its specific heat is less than lead^[2]. In the other hand, Er₃Ni compound has much larger specific heat capacity relative to lead below 20K^[3]. However, it is too brittle to be a proper durable regenerator material used in cryocoolers Meanwhile, Er metal is ductile, and its the specific heat is larger than that of lead from 20 to 80K but decline rapidly below this temperature^[4] Thus we add Er into the Er₃Ni compound as the second phase to obtain an regenerator material with excellent mechanical properties and large specific heat capacity.