Currently, no known material retains its photoinduced metallic conductivity over a long time while also exhibiting repeatable metal-to-insulator recovery. Here, we demonstrate such a highly repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride (YO x H y ) epitaxial thin films. The temperature (T) dependence of the electrical resistivity (ρ) of the films transforms from the insulating to the metallic state (dρ/dT > 0) under ultraviolet laser illumination. The YO x H y film recovers its original insulating state when heated (125 °C) under an Ar atmosphere and regains metallic conductivity when subsequently subjected to ultraviolet laser illumination again, showing a repeatable photoinduced insulator-to-metal transition. First-principles calculations show that the itinerant carriers originate from the variations in the charge states of the hydrogen atoms that occupy octahedral interstitial sites. This study indicates that tuning the site occupancy (octahedral/tetrahedral) of the hydrogen atoms exerts a significant effect on the photoresponse of metal hydrides.

This paper reports the epitaxial growth of EuH 2 thin films with an ω-scan full width at half-maximum of 0.07°, the smallest value for metal hydride thin films reported so far. The thin films were deposited on yttria-stabilized ZrO 2 (111) substrates using reactive magnetron sputtering. The magnetization measurement showed that the saturation magnetization is ∼7 μ B /Eu atom, indicating that the EuH x films are nearly stoichiometric (x ≈ 2.0) and that the Curie temperature is ∼20 K. The optical measurements showed a bandgap of ∼1.81 eV. These values are similar to those previously reported for bulk EuH 2 . This study paves the way for the application of metal hydrides in the field of electronics through the fabrication of high-quality metal hydride epitaxial thin films.

We report the growth of YF 3 epitaxial thin films by magnetron sputtering using MgF 2 (100) substrates as a fluorine source instead of fluorination gases. We find that the substrate selection based on the relative film/substrate Gibbs free energies of formation can drive F-ion diffusion from the fluoride substrates into the Y thin films. Due to the high diffusivity of F ions in YF 3, this method can grow ∼40 nm thick epitaxial thin films with uniform F distribution. These results indicate that fluoride substrates can serve as the F-ion source, providing a novel synthetic route for growing metal-fluoride thin films.

This article presents a Bayesian sparse modeling method to analyze extended x-ray absorption fine structure (EXAFS) data with basis functions built on two-body signals. This method does not require any structural model and allows us to evaluate regression coefficients proportional to the radial distribution functions of the respective elements and their errors and is very effective for analysis of EXAFS with weak absorption intensity and severe signal-to-noise ratios. As an application example, we used it to analyze the EXAFS of an yttrium oxyhydride (YOxHy) epitaxial thin film. These EXAFS data show weak absorption intensity and a severe signal-to-noise ratio due to the small amount of x-ray absorption in the thin film sample. However, this approach revealed that the radial distance ratio of the second neighbor yttrium to the first neighbor oxygen coincides with that of a tetrahedral configuration. This result demonstrates that the interstitial oxygen position is tetrahedral in the YOxHy thin film.

Grain-oriented Nd-modified bismuth titanate (BNIT) ceramics with the a-b-plane perpendicular to the direction of magnetic field (MF) were successfully fabricated by applying MF-assisted forming at lower field strengths. A BNIT powder, in which 25% of the Bi 3+ -site were substituted with Nd , was synthesized by coprecipitation in an alkaline solution and successive calcination at 600°C. Green compacts of the BNIT powder were formed by applying various MF strengths (212 T) during slip casting and then sintered at 900 and 1000°C for different times. The cation substitution with Nd 3+ allowed very fine BNIT particles in a slurry to be magnetically aligned at lower field strengths. For BNIT ceramics sintered at 1000°C, the degree of grain orientation increased with increasing MF according to the parabolic relationship. Additionally, the grain orientation was enhanced by the preferential growth of anisotropic BNIT grains occurring at later stage of the sintering.