Thermal Conductivity of Monazite‐Type REPO 4 (RE=La, Ce, Nd, Sm, Eu, Gd)

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Abstract
Low‐thermal conductivity ceramics in monazite‐type REPO 4 (RE=La, Ce, Nd, Sm, Eu, Gd) ceramics are expected to have potential in structural (refractories, thermal insulator) and nuclear applications. To this end, the present study determines their thermal conductivities and examines how differences of the rare earth ions change their thermal conductivity at different temperatures. The results show that their conductivities are remarkably low from 25° to 1000°C. In addition, different conductivity variation mechanisms exist that change gradually upon altering from LaPO 4 to GdPO 4 at low and high temperatures. At relatively lower temperatures (≤400°C), the thermal conductivities of all the REPO 4 ceramics decrease nearly at first, reach a minimum value, and then rise with gradual altering from LaPO 4 to GdPO 4 . It may be due to the combined effects of the increase of both the anharmonicities in lattice vibrations and the bond strength. As the temperature increases, the conductivity trends become obscure, and the conductivities of the monazite‐type REPO 4 approach their minimum thermal conductivities when the temperature is above 800°C.

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