ABSTRACT CeO 2− δ (0 ≤ δ ≤ 0.5) has attracted attention as an active material for electrochemical thermal switches that control heat flow electrically because of its wide thermal conductivity ( κ ) switching width between CeO 2 with fluorite structure (12.5 W m −1 K −1 ) and Ce 2 O 3 with bixbyite structure (2.2 W m −1 K −1 ). Although understanding κ of structurally analogous oxides Ln O 2 and Ln 2 O 3 ( Ln = Pr and Tb) is useful for the selection of active materials for thermal switches, κ of Ln O 2 and Ln 2 O 3 has not been reported due to the lack of single‐phase crystals. In this study, we fabricated Ln O 2 and Ln 2 O 3 ( Ln = Ce, Pr, and Tb) epitaxial films by pulsed laser deposition followed by the electrochemical redox control and measured the κ by time‐domain thermoreflectance method. The oxidized PrO 2 exhibits markedly lower κ (5.2 W m −1 K −1 ) than CeO 2 or TbO 2 (10.0 W m −1 K −1 ). By comparison, the reduced Pr 2 O 3 and Tb 2 O 3 display comparable κ values, whereas reduced CeO x remains multiphase with a slightly lower κ . First‐principles calculation results support the observed κ well. Since the specific heat capacities and densities among these oxides are similar, the present results indicate that the thermal diffusivity of PrO 2 is intrinsically lower than CeO 2 or TbO 2 .
Yoshimura et al. (2026) studied this question.