Wide-range thermal conductivity modulation based on protonated nickelate perovskite oxides

The perovskite oxides ReNiO₃ (Re = rare-earth elements) are promising functional materials due to their strongly correlated electrons. Except for the well-known intrinsic metal-insulating transition in these materials, recent progresses have proved that protonation of ReNiO₃ can bring about interesting Mott transition in this series. To date, in these protonated species (H-ReNiO₃), huge resistance switching, fast ionic diffusion, and their applications as an iontronic transistor, memristor, and fuel cell are reported. In this work, the thermal conductivities of H-ReNiO₃ (Re = La, Nd, Sm, and Eu) epitaxial thin films are investigated. The protonation-induced Mott transition can effectively modulate the electronic thermal conductivity while the lattice thermal conductance is less affected. Hence, at room temperature, the metallic LaNiO₃ and NdNiO₃ exhibit reversible wide thermal conductivity modulation, in ranges of 2.6–12.0 and 1.6–8.0 W m⁻¹ K⁻¹, respectively. These values are much larger than other thermal regulation materials based on transition metal oxides. Thus, our work reveals the great potential of ReNiO₃ being applied as a thermal-regulating material. The fast ionic diffusion in H-ReNiO₃ also guarantees that a fast response and wide-range thermal transistor can be realized by H-LaNiO₃ and H-NdNiO₃ in the future.