A Nd-doped BiFeO(3) thin film deposited on MgO substrate was studied by synchrotron diffraction. ... more A Nd-doped BiFeO(3) thin film deposited on MgO substrate was studied by synchrotron diffraction. The ferroelectric nature of the film is proven by in-plane remanent polarization measurement. The highest possible symmetry of the film is determined to be orthorhombic, within the Fm2m space group. Such a structure is rotated by 45° with respect to the substrate and is consistent with tilts of oxygen octahedra doubling the unit cell. This polar structure presents a rather unusual strain-accommodation mechanism.
The analysis of polarization diagrams for specular and scattered second harmonic generation (SHG)... more The analysis of polarization diagrams for specular and scattered second harmonic generation (SHG) was used for the structural characterization of submicron domain structures of thin (Ba,Sr)TiO3 (BST) films. It is shown that the lack of separation of these two contributions may lead to completely wrong conclusions about the domain orientation in these films. SHG studies of the thickness dependence of domain fractions (including 180° domains) reveal the presence of ferroelectric domains in ultrathin BST films (6 nm), although no domain structure was observed by atomic force microscopy. Thus the presence of ferroelectric ordering was demonstrated in perovskite films with a thickness down to 6 nm.
We have studied electric-field-induced symmetry lowering in the tetragonal (001)-oriented heteroe... more We have studied electric-field-induced symmetry lowering in the tetragonal (001)-oriented heteroepitaxial (Ba0.8Sr0.2)TiO3 thin film deposited on (001)MgO substrate. Polarized micro-Raman spectra were recorded from the film area in between two planar electrodes deposited on the film surface. Presence of c domains with polarization normal to the substrate was confirmed from polarized Raman study under zero field, while splitting and hardening of the E(TO) soft mode and polarization changes in the Raman spectra suggest monoclinic symmetry under external electric field.
... In this zone the dominating process of exci-tation of atoms and ions is inelastic impact by f... more ... In this zone the dominating process of exci-tation of atoms and ions is inelastic impact by fast electrons entering from the cathode area. The third discharge zone represents specificities of the sputtered particle transport across the rf discharge plasma. Fig. ...
ABSTRACT X-ray diffraction and Raman spectroscopy of epitaxial Nd-doped bismuth ferrite films on ... more ABSTRACT X-ray diffraction and Raman spectroscopy of epitaxial Nd-doped bismuth ferrite films on MgO substrates reveal their orthorhombic symmetry Fmm2 (a = 7.914 Å, b = 7.913 Å, and c = 7.937 Å).
ABSTRACT The results of X-ray diffraction study of a new promising magnetoelectric composite film... more ABSTRACT The results of X-ray diffraction study of a new promising magnetoelectric composite films with alternating layers of barium strontium titanate and bismuth ferrite with layer thicknesses d = 6–200 nm are presented. All films show epitaxial growth on the MgO single crystals substrates. The 00L profiles for thick layered films (d > 15 nm) consist of the two reflections corresponding to the separate coherent scattering regions of composite layers. The XRD patterns of thin layered films testify the formation of superlattice. The mean microstrain and mean size of coherent scattering regions were determined using the Willamson-Hall approach.
ABSTRACT The lattice parameters of epitaxial barium strontium titanate films with various thickne... more ABSTRACT The lattice parameters of epitaxial barium strontium titanate films with various thicknesses (from 6 to 960 nm) were measured as a function of temperature in the normal and tangential directions with respect to the film plane using x-ray diffraction. The films were grown through the layer-by-layer mechanism by rf cathode sputtering under elevated oxygen pressure. A critical film thickness (∼ 50 nm) was found to exist, below and above which the films are subjected to compressive and tensile stresses, respectively. As the temperature varies from 780 to 100 K, the films undergo two diffuse structural phase transitions of the second order over the entire thickness range. The transitions in the films under tensile stresses are likely to be transformations from the paraelectric tetragonal to aa phase and then to r phase, whereas the transitions under compressive stresses are transformations from the tetragonal paraelectric to ferroelectric c phase and then, with further decreasing temperature, to r phase. PACS numbers77.80.-e–64.70.Nd–77.55.+f
ABSTRACT Using submillimeter and infrared spectroscopies, the reflectance R(ν) and transmittance ... more ABSTRACT Using submillimeter and infrared spectroscopies, the reflectance R(ν) and transmittance T(ν) spectra of heteroepitaxial barium-strontium titanate films of different thicknesses on MgO substrates are taken for the first time in the frequency range 10 < ν < 3000 cm−1. By modeling the experimental spectra by the Fresnel formulas for layered media, the spectra of complex permittivity ɛ*(ν) = ɛ′(ν) + iɛ″(ν) of the films are determined. It is shown that when the film thicknesses decrease down to 10 nm, there appear tensile stresses in the direction parallel to the substrate surface. As a result, the dielectric contribution of a low-frequency soft mode becomes several times larger than before.
A Nd-doped BiFeO(3) thin film deposited on MgO substrate was studied by synchrotron diffraction. ... more A Nd-doped BiFeO(3) thin film deposited on MgO substrate was studied by synchrotron diffraction. The ferroelectric nature of the film is proven by in-plane remanent polarization measurement. The highest possible symmetry of the film is determined to be orthorhombic, within the Fm2m space group. Such a structure is rotated by 45° with respect to the substrate and is consistent with tilts of oxygen octahedra doubling the unit cell. This polar structure presents a rather unusual strain-accommodation mechanism.
The analysis of polarization diagrams for specular and scattered second harmonic generation (SHG)... more The analysis of polarization diagrams for specular and scattered second harmonic generation (SHG) was used for the structural characterization of submicron domain structures of thin (Ba,Sr)TiO3 (BST) films. It is shown that the lack of separation of these two contributions may lead to completely wrong conclusions about the domain orientation in these films. SHG studies of the thickness dependence of domain fractions (including 180° domains) reveal the presence of ferroelectric domains in ultrathin BST films (6 nm), although no domain structure was observed by atomic force microscopy. Thus the presence of ferroelectric ordering was demonstrated in perovskite films with a thickness down to 6 nm.
We have studied electric-field-induced symmetry lowering in the tetragonal (001)-oriented heteroe... more We have studied electric-field-induced symmetry lowering in the tetragonal (001)-oriented heteroepitaxial (Ba0.8Sr0.2)TiO3 thin film deposited on (001)MgO substrate. Polarized micro-Raman spectra were recorded from the film area in between two planar electrodes deposited on the film surface. Presence of c domains with polarization normal to the substrate was confirmed from polarized Raman study under zero field, while splitting and hardening of the E(TO) soft mode and polarization changes in the Raman spectra suggest monoclinic symmetry under external electric field.
... In this zone the dominating process of exci-tation of atoms and ions is inelastic impact by f... more ... In this zone the dominating process of exci-tation of atoms and ions is inelastic impact by fast electrons entering from the cathode area. The third discharge zone represents specificities of the sputtered particle transport across the rf discharge plasma. Fig. ...
ABSTRACT X-ray diffraction and Raman spectroscopy of epitaxial Nd-doped bismuth ferrite films on ... more ABSTRACT X-ray diffraction and Raman spectroscopy of epitaxial Nd-doped bismuth ferrite films on MgO substrates reveal their orthorhombic symmetry Fmm2 (a = 7.914 Å, b = 7.913 Å, and c = 7.937 Å).
ABSTRACT The results of X-ray diffraction study of a new promising magnetoelectric composite film... more ABSTRACT The results of X-ray diffraction study of a new promising magnetoelectric composite films with alternating layers of barium strontium titanate and bismuth ferrite with layer thicknesses d = 6–200 nm are presented. All films show epitaxial growth on the MgO single crystals substrates. The 00L profiles for thick layered films (d > 15 nm) consist of the two reflections corresponding to the separate coherent scattering regions of composite layers. The XRD patterns of thin layered films testify the formation of superlattice. The mean microstrain and mean size of coherent scattering regions were determined using the Willamson-Hall approach.
ABSTRACT The lattice parameters of epitaxial barium strontium titanate films with various thickne... more ABSTRACT The lattice parameters of epitaxial barium strontium titanate films with various thicknesses (from 6 to 960 nm) were measured as a function of temperature in the normal and tangential directions with respect to the film plane using x-ray diffraction. The films were grown through the layer-by-layer mechanism by rf cathode sputtering under elevated oxygen pressure. A critical film thickness (∼ 50 nm) was found to exist, below and above which the films are subjected to compressive and tensile stresses, respectively. As the temperature varies from 780 to 100 K, the films undergo two diffuse structural phase transitions of the second order over the entire thickness range. The transitions in the films under tensile stresses are likely to be transformations from the paraelectric tetragonal to aa phase and then to r phase, whereas the transitions under compressive stresses are transformations from the tetragonal paraelectric to ferroelectric c phase and then, with further decreasing temperature, to r phase. PACS numbers77.80.-e–64.70.Nd–77.55.+f
ABSTRACT Using submillimeter and infrared spectroscopies, the reflectance R(ν) and transmittance ... more ABSTRACT Using submillimeter and infrared spectroscopies, the reflectance R(ν) and transmittance T(ν) spectra of heteroepitaxial barium-strontium titanate films of different thicknesses on MgO substrates are taken for the first time in the frequency range 10 < ν < 3000 cm−1. By modeling the experimental spectra by the Fresnel formulas for layered media, the spectra of complex permittivity ɛ*(ν) = ɛ′(ν) + iɛ″(ν) of the films are determined. It is shown that when the film thicknesses decrease down to 10 nm, there appear tensile stresses in the direction parallel to the substrate surface. As a result, the dielectric contribution of a low-frequency soft mode becomes several times larger than before.
Uploads