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

Abstract

SrCoO3-δ 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-δ (x = 0∼1.2) polycrystals with enormous electrothermal conductivity disparity. The hexagonal phase (H, SrCoO3-δ) exhibits quite low electrothermal conductivity (σ∼708.1 S m−1, κ∼0.982 W m−1 K−1) and considerable thermopower (175.4 μV K−1), resulting in lattice thermal conductivity dominates 98 % at 723 K. The one-dimensional 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, Sr3·6Y0·4Co4O12-δ) exhibits good electrothermal conductivity (σ∼8 × 104 S m−1 in 400∼650 K, κ∼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-δ) 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-δ exhibits a significant contrast in electrothermal transport and holds promise as an active material for electron and phonon logic circuits.