Enormous electrothermal conductivity disparity in multiphase structure Sr4-xYxCo4O12- (x=0-1.2) polycrystals

SrCoO3-delta system has garnered significant attention as the active material in solid-state thermal transistors. Herein, we have synthesized and characterized hexagonal, cubic, and ordered tetragonal Sr4-xYxCo4O12-delta (x = 0-1.2) polycrystals with enormous electrothermal conductivity disparity. The hexagonal phase (H, SrCoO3-delta) exhibits quite low electrothermal conductivity (sigma-708.1 S m-1, kappa-0.982 W m-1 K-1) and considerable thermopower (175.4 mu V K-1), resulting in lattice thermal conductivity dominates 98 % at 723 K. The onedimensional chain structure (H) restricts hole carrier transmission, while the CoO6 octahedral unit induces phonon scattering (phonon mean free path in 0.206-0.261 nm). The cubic phase (CP, Sr3 & sdot;6Y0 & sdot;4Co4O12-delta) exhibits good electrothermal conductivity (sigma-8 x 104 S m-1 in 400-650 K, kappa-2.718 W m- 1 K-1 at 723 K) and thermopower close to zero, thus the carrier thermal conductivity contributing up to 46 %. The highly symmetrical CP phase with three-dimensional electron-phonon transport channels displays higher mobility (-1505.7 cm2 V-1 s- 1) and carrier concentration (Co4+). The ordered tetragonal phase (OT, Sr3YCo4O12-delta) exhibits an electrothermal performance between the hexagonal and cubic phases, due to oxygen-deficient CoO4.25 tetrahedral layers restricting the electron-phonon transport. The multiphase structure Sr4-xYxCo4O12-delta exhibits a significant contrast in electrothermal transport and holds promise as an active material for electron and phonon logic circuits.