[17a-D511-1~9] 22.1 Joint Session M "Phonon Engineering"

▼ [17a-D511-3] Active Layer for Solid-State Electrochemical Thermal Transistors I:
SrCoO_x−SrFeO_x solid solutions

〇(D)Zhiping Bian¹, Qian Yang², Mitsuki Yoshimura³, Joonhyuk Lee⁴, Hyoungjeen Jeen⁴, Jinghuang Lin⁵, Bin Feng⁵, Yuichi Ikuhara⁵, Hai Jun Cho⁶, Hiromichi Ohta⁶ (1.IST-Hokudai, 2.Jiangsu U., 3.Eng.-Hokudai, 4.Pusan Nat'l U., 5.U. Tokyo, 6.RIES-Hokudai)

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 SrCoO_x 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 (κ_ele) 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 SrCo_1−xFe_xO_y solid solutions as the active layer. Figure (a) shows changes in the κ of the reduced SrCo_1−xFe_xO₂ and the oxidized SrCo_1−xFe_xO₃ 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 SrCo_1−xFe_xO_y 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 κ_ele 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.