We report a large photovoltaic (PV) effect in multiferroic Bi2FeCrO6 (BFCO) films under monochromatic illumination at 635 nm with an intensity of 1.5 mW cm−2. These multiferroic films exhibit a large photocurrent at zero bias voltage and an open-circuit voltage of about 0.6 V. A high PV power conversion efficiency of about 6% for red light is achieved and attributed to a high degree of B-site cationic ordering between Fe and Cr sublattices, the tuning of which is likely to play a key role in further improvements of the PV properties in BFCO.

Chemically -driven isothermal close space vapour transport was used to prepare pure MoO2 films which were eventually converted to MoO3 by annealing in air. According to temperaturedependent Raman measurements, the MoO2/MoO3 phase transformation was found to occur in the 225 -350 o C range; no other phases were detected during the transition. A clear change in composition and Raman spectra, as well as noticeable modifications of the band gap and the absorption coefficient confirmed the conversion from MoO2 to MoO3. An extensive characterization of films of both pure phases was carried out. In particular, a procedure was developed to determine the dispersion relation of the refractive index of MoO2 from the shift of the interference fringes the used SiO2/Si substrate. The obtained refractive index was corrected taking into account the porosity calculated from elastic backscattering spectrometry. The Debye temperature and the residual resistivity were extracted from the electrical resistivity temperature dependence using the Bloch -Grüneisen equation. MoO3 converted samples presented very high resistivity and a typical semiconducting behaviour. They also showed intense and broad luminescence spectra, which were deconvoluted considering several contributions; and its behaviour with temperature was examined. Furthermore, surface photovoltage spectra were taken and the relation of these spectra with the photoluminescence is discussed.

We report a power conversion efficiency of ~0.01% in multistacking of BiFeO3/BiCrO3 bilayer thin films used as active layers in a photovoltaic (PV) device. The films were epitaxially deposited by pulse laser deposition onto (100) oriented CaRuO3‐coated LaAlO3 substrates and were subsequently illuminated with 1 sun (AM 1.5). The fill factor is determined to be 0.31%, a remarkable value for ferroelectric‐ and multiferroic‐based PV devices. Our results demonstrate that photocurrent density and photovoltage can be tuned by varying the thickness and number of respective bilayers in the improvement of PV properties of multiferroic heterostructures. The maximum photocurrent is generated at an optimal multilayer thickness of 60 nm, with its origin being mainly ascribed to the contribution of ferroelectric polarization.

Bi 2 FeCrO 6 thin films were epitaxially grown by pulsed laser deposition on (100)-oriented LaAlO 3 , (LaAlO 3 ) 0.3 (Sr 2 LaTaO 6 ) 0.7 and SrTiO 3 single crystalline substrates with and without epitaxial CaRuO 3 buffered layer. The in-plane compressive strain induces monoclinic distortion of the Bi 2 FeCrO 6 lattice cell. The strain originates from lattice mismatch between CaRuO 3 and single crystal substrates. The similar crystal structure of the substrate and the layer lead to coherent epitaxial growth of the heterostructures and avoid strain relaxation in particular for BFCO films deposited on LaAlO 3 substrates. The ferroelectric character is demonstrated for all grown BFCO films. The residual in-plane strain weakly affects the effective piezoelectric coefficient of BFCO layers.Keywords: Pulsed laser deposition (PLD); perovskite thin films; complex oxides; epitaxy; piezoresponse (PFM); crystal structure; cation ordering; double perovskite.An important area of research in recent years has been to understand exactly why the properties of epitaxial films differ from related bulk materials, and to learn how to use these differences to engineer desirable properties. Effects due to strain in the films are often thought of as analogous to those of high pressure experiments in bulk. The main differences are (i) the stress in the films is typically biaxial rather than hydrostatic or uniaxial, (ii) films can have much larger strains than is usually achievable in pressure cells, and (iii) films are easier to work with for many experiments and applications. Ferroelectricity in strained perovskite films has been a particularly noteworthy topic of study. Recent experiments have shown strain-induced ferroelectricity in SrTiO 3 (STO) films, and huge changes in the ferroelectric transition temperature T C in both STO and BaTiO 3 (BTO) films under strain. 1,2 Other notable results include large changes in the metal-insulator transition temperature of NdNiO 3 films under strain 3 and reports of increasing the transition temperature of La 2−x SrCuO 4 under compressive strain. [4][5][6] In this letter, we present a systematic investigation of structural and ferroelectric properties in epitaxial Bi 2 FeCrO 6 (BFCO) films with varying degree of compressive strain by using several commercially available single crystal substrates. * Corresponding author.X-ray diffraction (XRD) patterns collected on polycrystalline BFCO film (400 nm) deposited on amorphous SiO 2 (100 nm) on Silicon (100) by laser ablation were fitted with a rhombohedral R3 unit cell similar to that previously reported for BiFeO 3 (BFO). 7 The rhombohedral lattice parameter of this BFCO film is found to be around 5.56 Å which corresponds to a pseudo-cubic lattice parameter of ∼ 3.93 Å. Recently, Suchomel et al. reported the synthesis of high pressure BFCO bulk. 8 They claimed that BFCO bulk has a hexagonal R3c unit cell and the refined lattice parameters, obtained from the high resolution synchrotron XRD data are a = 5.5454 Å and c = 13.6952 Å. These values of latti...

No abstract