La-doped SrSnO 3 (LSSO) is known as one of deep-ultraviolet (DUV)-transparent conducting oxides with an energy bandgap of ~4.6 eV. Since LSSO can be grown heteroepitaxially on more wide bandgap substrates such as MgO (E g ~7.8 eV), LSSO is considered to be a good candidate as a DUV-transparent electrode. However, the electrical conductivity of LSSO films are below 1000 S cm −1 , most likely due to the low solubility of La ion in the LSSO lattice. Here we report that high electrically conducting (>3000 S cm −1 ) LSSO thin films with an energy bandgap of ~4.6 eV can be fabricated by pulsed laser deposition on MgO substrate followed by a simple annealing in vacuum.From the X-ray diffraction and the scanning transmission electron microscopy analyses, we found that lateral grain growth occurred during the annealing, which improved the

Among many thermoelectric materials, oxide-based materials draw significant interest due to their environmental compatibility. In particular, layered cobaltite, Na0.75CoO2, shows a large thermoelectric power factor parallel to the layers. However,...

shows rather high carrier mobility at room temperature (≈320 cm 2 V −1 s −1 ). [3,4] The crystal structure of BaSnO 3 is cubic perovskite type, ABO 3 with space group of Pm-3m (a = 0.4116 nm), and the A-site can be fully substituted with Sr (SrSnO 3 ), though the crystal structure is orthorhombic perovskite with space group of Pbnm (a = 0.57082 nm, b = 0.57035 nm, c = 0.80659 nm). [5] The bandgap of SrSnO 3 is ≈4.1 eV [2] and the La-doped SrSnO 3 films also show high carrier mobility (40-55 cm 2 V −1 s −1 [6,7] ) at room temperature. Thus, BaSnO 3 -SrSnO 3 solid-solutions (E g = 3.1-4.1 eV) [8] are good candidates to realize large bandgap (≈4 eV) TOS-based TFTs. Very recently, a metal-semiconductor TFT operating as depletion-mode has been reported by Chaganti et al. [9] They used the La-doped SrSnO 3 film as the channel layer. However, the TFT performance of undoped BaSnO 3 -SrSnO 3 solid-solutions, which would be better to fabricate an accumulation-mode TFT, has not been reported thus far probably due to the lack of fundamental knowledge especially the effective thickness (t eff ) and the carrier effective mass (m*), which are essential information to design the TFTs.Although several researchers have reported on the m* of SrSnO 3 , the reported m* values are scattered ranging from 0.14 to 4 m 0 . In 2007, Hadjarab et al. [10] measured the magnetic susceptibility of Sr 0.98 La 0.02 SnO 3−δ ceramic and extracted m* of 4 m 0 . Moreira et al. [11,12] and Liu et al. [13] performed the band structure calculation of SrSnO 3 and BaSnO 3 , and reported much lighter m* values; SrSnO 3 : m* = 0.14-0.23 m 0 , BaSnO 3 : 0.03-0.20 m 0 . Recently, Ong et al. [14] reported that the m* of SrSnO 3 is ≈0.4 m 0 , whereas the calculated effective mass of BaSnO 3 is m* = 0.26 m 0 with the same method. Generally, the m* of n-type TOS, in which the conduction band is composed of ns orbitals, strongly depends on the overlap integral of the neighboring ns orbitals. [15] Further, the overlap integral of ns orbitals would be insensitive to the bond angle. [16] If this assumption is correct, since the interatomic distances of neighboring Sn ions in SrSnO 3 and BaSnO 3 crystals are 0.4035 and 0.4116 nm, respectively, the m* of SrSnO 3 should be lighter than that of BaSnO 3 , which is in opposite relationship with the band calculation results. [11][12][13]

Wide bandgap (Eg ∼ 3.1 eV) La-doped BaSnO3 (LBSO) has attracted increasing attention as one of the transparent oxide semiconductors since its bulk single crystal shows a high carrier mobility (∼320 cm2 V−1 s−1) with a high carrier concentration (∼1020 cm−3). For this reason, many researchers have fabricated LBSO epitaxial films thus far, but the obtainable carrier mobility is substantially low compared to that of single crystals due to the formation of the lattice/structural defects. Here we report that the mobility suppression in LBSO films can be lifted by a simple vacuum annealing process. The oxygen vacancies generated from vacuum annealing reduced the thermal stability of LBSO films on MgO substrates, which increased their carrier concentrations and lateral grain sizes at elevated temperatures. As a result, the carrier mobilities were greatly improved, which does not occur after heat treatment in air. We report a factorial design experiment for the vacuum annealing of LBSO films on MgO substrates and discuss the implications of the results. Our findings expand our current knowledge on the point defect formation in epitaxial LBSO films and show that vacuum annealing is a powerful tool for enhancing the mobility values of LBSO films.

Among many transition-metal oxides (TMOs), strontium cobalt oxide (SrCoO x ) is a promising active material for advanced memory devices due to the versatile valence state of cobalt ions. Several SrCoO x -based electrochemical devices have been proposed, but solid-state protonation from SrCoO 2.5 to H x SrCoO 2.5 (x = 1, 1.5, and 2) at room temperature has not been demonstrated thus far due to the absence of an appropriate solid electrolyte. Here, we demonstrate a solid-state electrochemical protonation of SrCoO 2.5 using mesoporous amorphous 12CaO• 7Al 2 O 3 (CAN) film as the solid electrolyte. The crystalline phase discretely changed from SrCoO 2.5 to HSrCoO 2.5 (phase A), H 1.5 SrCoO 2.5 (phase B), and H 2 SrCoO 2.5 (phase C) through formation of an intermediate phase of H 1.25 SrCoO 2.5 . H 1.5 SrCoO 2.5 (phase B) was colorless transparent and showed weak ferromagnetism. The present results indicate that the CAN film can be used as the solid electrolyte for the protonation treatment of TMOs.

Paper published as part of the special topic on Advanced Thermoelectrics Note: This paper is part of the special topic on Advanced Thermoelectrics. ARTICLES YOU MAY BE INTERESTED IN Influence of pressure assisted sintering and reaction sintering on microstructure and thermoelectric properties of bi-doped and undoped calcium cobaltite

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.

Transparent amorphous oxide semiconductors (TAOSs) based transparent thin-film transistors (TTFTs) with high field effect mobility (μFE) are essential for developing advanced flat panel displays. Among TAOSs, amorphous (a-) SnO2 has several advantages against current a-InGaZnO4 such as higher μFE and being indium free. Although a-SnO2 TTFT has been demonstrated several times, the operation mechanism has not been clarified thus far due to the strong gas sensing characteristics of SnO2. Here we clarify the operation mechanism of a-SnO2 TTFT by electric field thermopower modulation analyses. We prepared a bottom-gate top-contact type TTFT using 4.2-nm-thick a-SnO2 as the channel without any surface passivation. The effective thickness of the conducting channel was ~1.7 ±0.4 nm in air and in vacuum, but a large threshold gate voltage shift occurred in different atmospheres; this is attributed to carrier depletion near at the top surface (~2.5 nm) of the a-SnO2 due to its interaction with the gas molecules and the resulting shift in the Fermi energy. The present results would provide a fundamental design concept to develop a-SnO2 TTFT.