Converting photon energy to chemical energy using inorganic materials requires successful capturing of photons, excitons dissociation and charge carriers diffusions. The present study reports thorough analysis of optoelectronic properties of visible--light--responsive SrTaO 2 N perovskites to quantify its absorption coefficient, the generated charge carriers' effective masses, dielectric constants, and electronic structures. The measurements on such intrinsic properties were attempted using both epitaxial and polycrystalline SrTaO 2 N films deposited by radio frequency (RF) magnetron sputtering under N 2 reactive plasma. Density functional theory calculations using the HSE06 functional provided reliable values of these optoelectronic properties. Such quantities obtained both by the measurements and the calculations gave excellent correspondences, but also provide possible variations that account for the small discrepancies observed. One of the significant factors determining the optical properties was found to be the anion ordering in the perovskite structure imposed by the cations. As a result, the different anion ordering has noticeable influence in the optical properties and the large sensitivity of hole effective mass. Determination of relative band positions to the water redox properties was also attempted by Mott--Schottky plots. All these results offer the opportunity to understand why SrTaO 2 N material possesses intrinsically all the ingredients to lead to a highly efficient water splitting device.

Ceramics of the La 2 O 3 -TiO 2 system have very good dielectric properties, which make La 2 Ti 2 O 7 a good candidate for microwave applications. Using radio-frequency magnetron sputtering, we have deposited LaTiO x N y oxynitride thin films on (0 0 1) strontium titanate and glass substrates, starting from a homemade oxide target. The microwave dielectric properties of La 2 Ti 2 O 7 ceramic have been investigated in the 100 Hz to 10 GHz range in order to have a reference for further studies. The evolution of ε and ε shows a space charge domain with a critical frequency F c = 1 GHz. Measurements in the temperature range from 20 to 880 • C have been carried out to study phase transitions and conduction mechanisms.

International audiencePerovskite lanthanum titanium thin films were deposited on Nb-doped (001) SrTiO3 substrates by reactive RF magnetron sputtering using a La2Ti2O7 target. Oxynitride LaTiO2N films were obtained using N2 rich plasma; they display a variation of their dielectric constant as a function of DC bias in the low frequency range but not in microwaves. The dielectric constant (epsilon) values are high with, for example, epsilon = 325 at 100 kHz. The oxide films, obtained in O2 rich plasma, are composed of an unusual La2Ti2O7 phase with an orthorhombic cell. The films are (101) epitaxied on Nb:SrTiO3 substrates. The dielectric constant value of films is around 77 with losses 0.076 at 100 kHz; no agility of epsilon in low and high frequencies is detected. Composite and bilayer films, with oxynitride and oxide phases, exhibit a variation of epsilon under DC bias in low frequencies with, for example, an agility of 15% at 100 kHz with a maximum applied field of 40 kV/cm for the LaTiO2N (200 nm)/La2Ti2O7 (250 nm) bilayer