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[17a-D511-3] Active Layer for Solid-State Electrochemical Thermal Transistors I:
SrCoOx−SrFeOx solid solutions
Keywords:Thermal transistor
Very recently, we realized solid-state electrochemical thermal transistors with thermal conductivity (κ) ON/OFF ratio of ~4 by utilizing phase transition of SrCoOx by the redox treatment. In order to further improve the ON/OFF ratio, detailed κ modulation mechanism needs to be clarified. Here, we show that high electronic κ (κele) of perovskite (P) SrCoO3 and low κ of defect perovskite (DP) SrCoO2 are the origins of the rather high ON/OFF ratio. We fabricated several solid-state thermal transistors using SrCo1−xFexOy solid solutions as the active layer. Figure (a) shows changes in the κ of the reduced SrCo1−xFexO2 and the oxidized SrCo1−xFexO3 as a function of x. In the reduced state (y = 2, OFF), κ slightly increases when x exceeds 0.5. On the other hand, in the oxidized state (y = 3, ON), κ drops with x and becomes constant (κ ~2.9 W m−1 K−1). In the case of ON state (oxidized), all SrCo1−xFexOy films belong to P structure and show similar lattice parameter c (Fig. (b)). On the other hand, in the case of OFF state (reduced), DP disappeared when x ≥ 0.5, infinite layer (IL) structure appeared. Thus, DP-to-IL phase transformation occurred when x ≥ 0.5. As shown in Fig. (c), The κele that was calculated by assuming Wiedemann-Franz law gradually decreased with x and keep the similar tendency of κ. This confirmed that high κ of SrCoO3 with high electron contribution and low κ of DP SrCoO2 are the origin of the high ON/OFF.