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.

The present study reveals the ferroelectric nature of the novel (Sr 2 Ta 2 O 7 ) 100-x (La 2 Ti 2 O 7 ) x layered perovskite materials and highlights a large variation of their permittivity under electric fields associated with very low dielectric loss in the radio-frequency range. More precisely, an ideal solid solution has been evidenced within the composition range 0 ≤ x ≤ 5 with lattice parameters and cell volume varying linearly with x. The relative permittivity also depends on the composition and reaches a maximum value (365 @10kHz, RT), associated with a high tunability (17.6 % @0.38 kV/mm) with very low dielectric loss lower than 2.10 -3 . Variation of the relative permittivity as a function of the temperature is also demonstrated, with the existence of a temperature maximum, increasing with the composition. Polarization-electric field (P-E) measurements feature hysteresis loops for compositions x ≥ 1.85, in conjunction with current peaks in the I-E curves originating from ferroelectric domains switching.Keywords : perovskiteferroelectrictunability -Sr 2 Ta 2 O 7 -La 2 Ti 2 O 7

and dielectric study as function of thickness of perovskite oxynitride SrTaO2N thin films elaborated by reactive sputtering. Surface and Coatings Technology, Elsevier, 2017, 324, pp.607-613. 10.1016/j.surfcoat.2016 A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT AbstractThe present study concerns the deposition of perovskite oxynitride SrTaO 2 N films and their dielectric characterization at low frequencies. Those radio frequency sputtered thin films have been obtained under a reactive plasma (92.3 vol.% Ar / 7.7 vol.% N 2 ) for substrate temperatures ranging from 600 to 900°C. As shown by X-rays diffraction and band-gap measurements, the deposition temperature (T S ) determines the film structure and leads to films with band-gap and cell volume approaching the ones of the SrTaO 2 N bulk material with increased T S . The dielectric study has been performed on polycrystalline, textured and