Thermal transistors that electrically control heat flow have attracted growing attention as thermal management devices and phonon logic circuits. Although several thermal transistors are demonstrated, the use of liquid electrolytes may limit the application from the viewpoint of reliability or liquid leakage. Herein, a solid‐state thermal transistor that can electrochemically control the heat flow with an on‐to‐off ratio of the thermal conductivity (κ) of ≈4 without using any liquid is demonstrated. The thermal transistor is a multilayer film composed of an upper electrode, strontium cobaltite (SrCoOx), solid electrolyte, and bottom electrode. An electrochemical redox treatment at 280 °C in air repeatedly modulates the crystal structure and κ of the SrCoOx layer. The fully oxidized perovskite‐structured SrCoO3 layer shows a high κ ≈3 .8 W m−1 K−1, whereas the fully reduced defect perovskite‐structured SrCoO2 layer shows a low κ ≈ 0.95 W m−1 K−1. The present solid‐state electrochemical thermal transistor may become next‐generation devices toward future thermal management technology.

Charge transfer is of particular importance in manipulating the interface physics in transition-metal oxide heterostructures. In this work, we have fabricated epitaxial bilayers composed of polar 3d LaMnO3 and nonpolar 5d SrIrO3. Systematic magnetic measurements reveal an unexpectedly large exchange bias effect in the bilayer, together with a dramatic enhancement of the coercivity of LaMnO3. Based on first-principles calculations and x-ray absorption spectroscopy measurements, such a strong interfacial magnetic coupling is found closely associated with the polar nature of LaMnO3 and the strong spin-orbit interaction in SrIrO3, which collectively drives an asymmetric interfacial charge transfer and leads to the emergence of an interfacial spin glass state. Our study provides new insight into the charge transfer in transition-metal oxide heterostructures and offer a novel means to tune the interfacial exchange coupling for a variety of device applications. .cn (X.Q.S) † These authors contributed equally to this work IntroductionThe synthesis of dissimilar complex oxide heterostructures is currently one of the hottest areas in the design of novel functional materials. Due to the strong interplay among charge, spin, orbital, and lattice degrees of freedom, the interface between different transition-metal oxides (TMOs) in artificially layered heterostructures exhibits many exotic physical properties that are absent in the constituent bulk materials. 1-5 Among many factors, the interfacial charge transfer has been identified as an effective knob to tune the interface physics, such as mediating the interfacial magnetic coupling in YBa2Cu3O7/La0.66Ca0.33MnO3 8,9 and La0.75Sr0.25MnO3/LaNiO3 10 heterostructures. Generally, the charge transfer can be driven by the work function differences between the contact TMOs 11 or even by their polarity discontinuity 1,[12][13][14] .The most prominent model of polarity discontinuity is the emergence of two-dimension electron gas at the interface of two band insulators: polar LaAlO3 and nonpolar SrTiO3 1,12,13 . Novel phenomena, such as the insulator-to-metal transition and magnetism emerged at the interface of such heterostructures have been reported.Therefore, by manipulating the polarity discontinuity at the interface, one can effectively modulate the interfacial physical properties of TMO heterostructures 15 . Recently, the 5d iridium oxides, in which the large spin-orbit coupling (SOC) and on-site Coulomb interaction exhibit a comparable energy scale, have attracted considerable attention due to theoretical predictions of unconventional phases like superconductivity, topological Mott insulator, and Weyl semi-metals 16-19 . But so far, only a few exotic phenomena arising from the strong interfacial coupling in perovskite SrIrO3-based heterostructures have been reported 20-24 . One typical example is the observation of ferromagnetic ground state and strong anomalous Hall effect at the interface between antiferromagnetic (AFM) SrMnO3 and paramagnetic (PM) SrIrO3 2 . Despite the nonpo...

Thermal transistors have potential as thermal management devices because they can electrically control the thermal conductivity (κ) of the active layer. Recently, we realized solid-state electrochemical thermal transistors by utilizing the electrochemical redox reaction of SrCoO y (2 ≤ y ≤ 3). However, the guiding principle to improve the on/off κ ratio has yet to be clarified because the κ modulation mechanism is unclear. This study systematically modulates κ of SrCo1–x Fe x O y (0 ≤ x ≤ 1, 2 ≤ y ≤ 3) solid solutions used as the active layers in solid-state electrochemical thermal transistors. When y = 3, the lattice κ of SrCo1–x Fe x O y is ∼2.8 W m–1 K–1 and insensitive to x. When x = 0 and y = 3, κ increases to ∼3.8 W m–1 K–1 due to the contribution of the electron κ. When y = 2, κ slightly depends on the ordered atomic arrangement. Materials that are high electrical conductors with highly ordered lattices when the transistor is on but are electrical insulators with disordered lattices when the transistor is off should be well-suited for the active layers of solid-state electrochemical thermal transistors.

Hydrogenation, an effective way to tune the properties of transition metal oxide (TMO) thin films, has been long awaited to be performed safely and without an external energy input. Recently, metal-acid-TMO has been reported to be an effective approach for hydrogenation, but the requirement of acid limits its application. In this work, the reversible and rapid hydrogen doping of WO3 in NaOH­(aq) | Al(s) | WO3(s) is revealed by structural and electrical measurements. Accompanied by the structural phase transition identified by in situ X-ray diffraction, the electric resistance of the WO3 film is found to be able to change by 5 orders of magnitude. A significant electrical response of touching, 8-fold in amplitude and 3 s in a cycle, can be achieved in the low-resistance state. These reactions are reversible at room temperature. This study unambiguously proves that the hydrogenation-driven dynamic phase transition of WO3 in metal-solution-WO3 systems could occur not only in acid solutions but also in some non-acid environments. Unlike the monotonic increase of resistance revealed during HδWO3 to WO3 transition, an intriguing non-monotonic evolution was found for crystal lattice parameter c, indicating that the mechanism of WO3 hydrogenation involves a series of metastable states, more comprehensive and reasonable. This work sheds light on the potential applications of metal-solution-TMO hydrogenation in touching sensors, circuits survey, and information storage.