Perovskite LaVO3 is a typical Mott insulator that exhibits insulator to metal transition by hole doping via substitution of an alkali earth element for La (La1–xSrxVO3 or La1−xCaxVO3). In this study, we investigated the electrical transport properties of its anion-substituted counterpart, LaVO3−xNx (0 ≤ x ≤ 0.71). LaVO3−xNx epitaxial thin films with high crystallinities and smooth surfaces were grown by plasma-assisted pulsed laser deposition. The electrical resistivity (ρ) of the thin films was remarkably lower than previously reported values for bulk polycrystals of LaVO3−xNx, indicating a suppressed contribution of the resistive grain boundaries to ρ in the present films. Plots of ρ against temperature for the LaVO3−xNx thin films showed that they were insulating (dρ/dT < 0) even at the highest doping level (x = 0.71), which is much larger than the threshold values for insulator to metal transition in La1−xSrxVO3 (x = 0.18) and La1−xCaxVO3 (x = 0.3). The curves of ρ against temperature were well described using the Efros–Shklovskii-like variable range hopping model, suggesting that random potential introduced by N substitution in the VX6 conduction path induces strong carrier localization in LaVO3−xNx.

We report on a new route for synthesizing metastable anatase tantalum oxynitride (TaON) in thin film form on lattice-matched (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT) single crystals by using nitrogen plasma assisted pulsed laser deposition. Epitaxial stress from the substrate stabilized the anatase structure without the need for doping an impurity, such as Sc or Mg, which is required in conventional bulk synthesis by ammonolysis. X-ray diffraction measurements and cross-sectional transmission electron microscope (TEM) observations demonstrated the growth of phase-pure anatase TaON thin films with the epitaxial relationships (001)TaON ∥ (001)LSAT and [100]TaON ∥ [100]LSAT. A high growth temperature (≥750 °C) and a balanced supply of oxygen and nitrogen are crucial for obtaining high-quality anatase TaON thin films. The films grown at 800 °C exhibited good n-type conduction with a resistivity of ∼1 × 10–2 Ω cm. The source of the carrier electrons was likely anion vacancies. The Hall mobility of anatase TaON (∼17 cm2 V–1 s–1 at 300 K) is comparably high to that of anatase TiO2, which is a well-known oxide semiconductor with the same crystal structure and d0 electronic configuration. The bandgap and refractive index of anatase TaON thin films were 2.37 eV and approximately 3.0, respectively, in the visible region.Keywords: anatase; high mobility; semiconductor; tantalum oxynitride; thin film;

We demonstrated heteroepitaxial growth of perovskite CaTaO2N on SrTiO3 (100) substrates by using nitrogen plasma assisted pulsed laser deposition (NPA-PLD). The CaTaO2N films grew coherently on SrTiO3 substrates, showing a layer-by-layer growth mode in the initial stages. The obtained films possessed high crystallinity, a sharp film/substrate interface, and flat surfaces. Impedance measurements revealed that CaTaO2N has a much smaller dielectric constant than those of SrTaO2N or BaTaO2N. These results indicate that heteroepitaxial growth by NPA-PLD is a promising approach for preparing high-quality perovskite oxynitride single crystals, which are desirable for investigation of electrical properties of perovskite oxynitrides.

•InOxFy epitaxial thin films with high fluorine concentration were grown on Y:ZrO2.•Anion composition and structural, optical and transport properties were studied.•Fluorine is topotactically inserted into the oxygen vacancy sites in bixbyite cell.•Bixbyite-like ordering of the anion site occupancy was conserved in y / (x + y) ≤ ~ 0.3.InOxFy thin films were epitaxially grown on Y-stabilized ZrO2 (111) substrates by reactive pulsed laser deposition. By changing the substrate temperature (TS), we were able to control the fluorine content of the film. Phase-pure epitaxial thin films with bixbyite-like ordering in the anion-site occupancy were obtained at high TS (≥ 240 °C), where fluorine was inserted into the vacancy sites in the bixbyite lattice up to y / (x + y) ~ 0.3. By decreasing TS, y / (x + y) increased and the bixbyite-like ordering disappeared; simultaneously, fluorine-rich and fluorine-poor subphases emerged. The films grown at TS ≤ 150 °C were amorphous and exhibited higher optical absorbance and electrical resistivity than the epitaxial films.

We developed a technique to fabricate oxide thin films with uniaxially controlled crystallographic orientation and lateral size of more than micrometers on amorphous substrates. This technique is lateral solid-phase epitaxy, where epitaxial crystallization of amorphous precursor is seeded with ultrathin oxide nanosheets sparsely (≈10% coverage) deposited on the substrate. Transparent conducting Nb-doped anatase TiO2 thin films were fabricated on glass substrates by this technique. Perfect (001) orientation and large grains with lateral sizes up to 10 μm were confirmed by X-ray diffraction, atomic force microscopy, and electron beam backscattering diffraction measurements. As a consequence of these features, the obtained film exhibited excellent electrical transport properties comparable to those of epitaxial thin films on single-crystalline substrates. This technique is a versatile method for fabricating high-quality oxide thin films other than anatase TiO2 and would increase the possible applications of oxide-based thin film devices.Keywords: lateral solid-phase epitaxy; oxide nanosheets; perovskite; thin film; TiO2; transparent conducting electrode

Perovskite LaVO3 is a typical Mott insulator that exhibits insulator to metal transition by hole doping via substitution of an alkali earth element for La (La1–xSrxVO3 or La1−xCaxVO3). In this study, we investigated the electrical transport properties of its anion-substituted counterpart, LaVO3−xNx (0 ≤ x ≤ 0.71). LaVO3−xNx epitaxial thin films with high crystallinities and smooth surfaces were grown by plasma-assisted pulsed laser deposition. The electrical resistivity (ρ) of the thin films was remarkably lower than previously reported values for bulk polycrystals of LaVO3−xNx, indicating a suppressed contribution of the resistive grain boundaries to ρ in the present films. Plots of ρ against temperature for the LaVO3−xNx thin films showed that they were insulating (dρ/dT < 0) even at the highest doping level (x = 0.71), which is much larger than the threshold values for insulator to metal transition in La1−xSrxVO3 (x = 0.18) and La1−xCaxVO3 (x = 0.3). The curves of ρ against temperature were well described using the Efros–Shklovskii-like variable range hopping model, suggesting that random potential introduced by N substitution in the VX6 conduction path induces strong carrier localization in LaVO3−xNx.