Evaluation of low-temperature specific heats and thermal conductivities of Er-Ag alloys as regenerator materials

The low-temperature specific heat for a series of Er_xAg_100-x (x = 40, 50, 60 and 70) alloys has been measured over the temperature range 1.6-30 K to evaluate their applicability as regenerator materials. In the temperature range 10-20 K, the volumetric specific heat for the x = 50-70 samples exceeds that for Er₃Ni, which is currently known as the most efficient regenerator material. The x = 40 sample is superior to Er₃Ni below 6 K. In addition, we found that the thermal conductivity for the present Er-Ag alloys is 5-10 times that for Er₃Ni below 25 K. We conclude that the present Er-Ag alloys are suitable as regenerator materials, particularly if a composition-gradient composite regenerator material, in which the Er concentration varies from 70 to 40 along the direction of the gas flow, is fabricated.