Dielectric resonance and magnetic properties of Fe-3% doped BaSnO3 thin films grown by pulsed laser deposition
TL;DR: In this article, two Fe-3% doped BaSnO3 thin films were grown on (2 0 0) n-type Si substrates by pulsed laser deposition, and the measured values of the resonant frequency and the surface resistivity showed a strong dependence on the thickness and the crystalline character of the thin films.
Abstract: Fe-3% doped BaSnO3 thin films of good crystalline quality with lattice constant a = 4.053 A were grown on (2 0 0) n-type Si substrates by pulsed laser deposition. Micro Raman spectra of the thin films showed the presence of strain-induced Raman modes with reference to that of the bulk polycrystalline Fe-3% doped BaSnO3. The films exhibited dielectric resonance in the frequency range 20 – 60 MHz and it is explained qualitatively based on the phenomenon of electromechanical piezoelectric resonance. The measured values of the resonant frequency and the surface resistivity showed a strong dependence on the thickness and the crystalline-character of the thin films. Magnetic measurements were performed selectively for the two films having (2 0 0) preferred orientation. It was found that both of them possess ferromagnetic ordering at 300 K and 1.8 K. At 300 K, the inherent diamagnetism of the undoped BaSnO3 was found to be dominating for higher applied magnetic field.
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TL;DR: The first-time growth of bulk BaSnO3 single crystals from the melt by direct solidification, their basic electrical and optical properties as well as their structural quality are presented, surpassing those single crystals that were reported in the literature.
Abstract: We present the first-time growth of bulk BaSnO3 single crystals from the melt by direct solidification, their basic electrical and optical properties as well as their structural quality. Our measurement of the melting point (MP) of BaSnO3 amounts to 1855 °C ± 25 K. At this temperature an intensive decomposition and non-stoichiometric evaporation takes place as the partial pressure of SnO(g) is about 90 times higher than that of BaO(g). X ray powder diffraction identified only the BaSnO3 perovskite phase, while narrow rocking curves having a full width at half maximum of 26 arcsec and etch pit densities below 106 cm−2 confirm a high degree of structural perfection of the single crystals. In this respect they surpass the structural properties of those single crystals that were reported in the literature. The electrical conductivity of nominally undoped crystals depends on the growth conditions and ranges from insulating to medium n-type conductivity. After post-growth annealing in an oxidizing atmosphere undoped crystals are generally insulating. Doping the crystals with lanthanum during growth results in a high n-type conductivity. For a La doping concentration of 0.123 wt.% we measured an electron concentration of 3.3 × 1019 cm−3 and an electron mobility of 219 cm2 V−1 s−1. Based on optical absorption measurements we determined an energy of 3.17 ± 0.04 eV at 5 K and of 2.99 ± 0.04 eV at 297 K for the indirect band gap of BaSnO3.
27 citations
TL;DR: In this article, Fe3+ doped BaSnO3 was synthesized by the modified Pechini method, with calcination between 300 and 800oC/4 h. The powder precursor was characterized by thermogravimetry after partial elimination of carbon.
Abstract: In the last ten years, stannates with perovskite structure have been tested as photocatalysts. In spite of the ability of perovskite materials to accommodate different cations in its structure, evaluation of doped stannates is not a common task in the photocatalysis area. In this work, Fe3+ doped BaSnO3 was synthesized by the modified Pechini method, with calcination between 300 and 800oC/4 h. The powder precursor was characterized by thermogravimetry after partial elimination of carbon. Characterization after the second calcination step was done by X-ray diffraction, Raman spectroscopy and UV-visible spectroscopy. Materials were tested in the photocatalytic discoloration of the Remazol Golden Yellow azo dye under UVC irradiation. Higher photocatalytic efficiency was observed under acid media. As no meaningful adsorption was observed at this condition we believe that an indirect mechanism prevails. Fe3+ doping decreased the band gap and favored the photocatalytic reaction, which may be assigned to the formation of intermediate levels inside the band gap.
26 citations
TL;DR: Magnetic and optical characteristic effects in Cr doped BaSnO3 nanostructures, synthesized by chemical precipitation method, are presented in this article, where structural and phase formation is explained based on Rietveld refinements from X-ray analysis and confirming the crystal structure of centrosymmetric perovskite BasnO3 (BSO).
Abstract: Magnetic and optical characteristic effects in Cr doped BaSnO3 nanostructures, synthesized by chemical precipitation method is presented. Structural and phase formation is explained based on Rietveld refinements from X-ray analysis and confirming the crystal structure of centrosymmetric perovskite BaSnO3 (BSO). The internal and local structural disorder of the compounds is discussed from the Raman spectra. HR-SEM analysis revealed morphological changes from cuboidal to mixed rod-like shape indicating the doping level. DRS measurements delineated the decreasing tendency of forbidden energy gaps upon introduction of Cr ions into BSO lattice. EPR spectra showed the presence of unpaired electrons and oxygen vacancies upon doping. VSM studies elucidated a change in diamagnetic to ferromagnetic behaviour indicating the Cr incorporation in BSO lattice.
20 citations
TL;DR: In this paper, the effects of Co-doping on the crystallinity, the microstructure, and optical properties of BSCO films were investigated, and it was found that Co doping increased the film roughness and the grain size.
Abstract: Co doped BaSnO3 films [BaSn1 − xCoxO3(0 ≤ x ≤ 0.50), i.e., BSCO] have been grown on MgO single-crystal substrates via pulsed laser deposition. Effects of the Co-doping level on the crystallinity, the microstructure, and optical properties of the BSCO films are investigated. All the BSCO films are of high crystallinity and grown epitaxially on MgO substrates. The lattice parameter of the (200) plane drops linearly with the increase of the ‘x’ value. The Co doping is found to increase the film roughness and the grain size, and a RMS roughness of 8.33 nm and grain size up to 100 nm are observed in the film with x = 0.50. The low Co-doping level (x = 0.05, 0.1) has slight anti-reflection effects on the incident visible light, and the Co-doping level higher than 0.2 reduces the optical transmittance significantly. The optical bandgap shows a first-rising then falling trend with the increase of the Co content, and the lowest bandgap of 1.94 eV is realized in the BSCO film with x = 0.50.
13 citations
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TL;DR: It is shown that epitaxial strain from a newly developed substrate can be harnessed to increase Tc by hundreds of degrees and produce room-temperature ferro electricity in strontium titanate, a material that is not normally ferroelectric at any temperature.
Abstract: Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T(c)) is traditionally accomplished by chemical substitution-as in Ba(x)Sr(1-x)TiO(3), the material widely investigated for microwave devices in which the dielectric constant (epsilon(r)) at GHz frequencies is tuned by applying a quasi-static electric field. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees, which is detrimental to tunability and microwave device performance. An alternative way to adjust T(c) in ferroelectric films is strain. Here we show that epitaxial strain from a newly developed substrate can be harnessed to increase T(c) by hundreds of degrees and produce room-temperature ferroelectricity in strontium titanate, a material that is not normally ferroelectric at any temperature. This strain-induced enhancement in T(c) is the largest ever reported. Spatially resolved images of the local polarization state reveal a uniformity that far exceeds films tailored by chemical substitution. The high epsilon(r) at room temperature in these films (nearly 7,000 at 10 GHz) and its sharp dependence on electric field are promising for device applications.
1,861 citations
TL;DR: A review of recent results on transition metal doping of electronic oxides such as ZnO, TiO 2, SnO2, BaTiO 3, Cu2O, SrTiO3 and KTaO3 is presented in this article.
Abstract: A review of recent results on transition metal doping of electronic oxides such as ZnO, TiO2, SnO2, BaTiO3, Cu2O, SrTiO3 and KTaO3 is presented. There is interest in achieving ferromagnetism with Curie temperatures above room temperature in such materials for applications in the field of spintronic devices, in which the spin of the carriers is exploited. The incorporation of several atomic per cent of the transition metals without creation of second phases appears possible under optimized synthesis conditions, leading to ferromagnetism. Pulsed laser deposition, reactive sputtering, molecular beam epitaxy and ion implantation have all been used to produce the oxide-based dilute magnetic materials. The mechanism is still under debate, with carrier-induced, double-exchange and bound magnetic polaron formation all potentially playing a role depending on the conductivity type and level in the material.
527 citations
TL;DR: Ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase TiO2 thin film is investigated, using the magnetic circular dichroism (MCD) at the Co L(2,3) absorption edges to show that the ferromagnets are induced by a small amount of clustered Co.
Abstract: We investigated ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase ${\mathrm{T}\mathrm{i}\mathrm{O}}_{2}$ thin film, using the magnetic circular dichroism (MCD) at the Co ${L}_{2,3}$ absorption edges. The magnetic moment was observed to be $\ensuremath{\sim}0.1{\ensuremath{\mu}}_{B}/\mathrm{C}\mathrm{o}$ in the measurements, but the MCD spectral line shape is nearly identical to that of Co metal, showing that the ferromagnetism is induced by a small amount of clustered Co. With thermal treatments at $\ensuremath{\sim}400\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, the MCD signal increases, and the moment reaches up to $\ensuremath{\sim}1.55{\ensuremath{\mu}}_{B}/\mathrm{C}\mathrm{o}$, which is $\ensuremath{\sim}90%$ of the moment in Co metal. In the latter case, the cluster size was observed to be 20--60 nm.
354 citations
TL;DR: The participation of the normally inert A- site cation in the electronic structure near the Fermi level can be considered an inductive effect, as it utilizes substitution on the A-site to directly modify the electronic structures of the SnO(3)(2)(-) framework.
Abstract: Experimental and computational studies were performed to understand the electronic structure of ternary perovskites (ASnO3, A = Ca, Sr, Ba, Cd), pyrochlores (RE2Sn2O7, RE = Y, La, Lu; Cd2Sb2O7), and defect pyrochlore oxides (Ag2Sb2O6) containing the main group ions Sn4+ and Sb5+. In all compounds, the lowest energy states in the conduction band arise primarily from the antibonding Sn/Sb 5s−O 2p interaction. In the alkaline-earth stannate perovskites (BaSnO3, SrSnO3, and CaSnO3) the conduction bandwidth decreases strongly in response to the octahedral tilting distortion triggered by the decreasing size of the alkaline-earth cation. This in turn leads to a corresponding increase in the band gap from 3.1 eV in BaSnO3 to 4.4 eV in CaSnO3. The band gap of CdSnO3 is relatively small (3.0 eV) considering the large octahedral tilting distortion. The origin of this apparent anomaly is the mixing between the empty Cd 5s orbitals and the antibonding Sn 5s−O 2p states. This mixing leads to a widening of the conductio...
338 citations
238 citations