SrxBa1 xNb2O6 Research Articles

Structural and relaxor characteristics of Ca0.18Sr0.226Ba0.594Nb2O6

Abstract Polycrystalline Ca0.18Sr0.226Ba0.594Nb2O6 (CSBN18) was synthesized via the solid-state reaction route. X-ray structural studies confirmed it belonged to the tetragonal tungsten bronze family. Rietveld refinement of the X-ray data has been carried out for CSBN18 where the atomic positions and site occupancy factors for A-sites have been determined. The dielectric properties of CSBN18 ceramic were studied as a function of temperature in the 100 Hz–1 MHz frequency range. The dielectric relaxation followed the Vogel–Fulcher relation wherein E a = 37.4 meV; T f = 131.5 °C and ω 0 = 4.31 × 109 rad s−1. A high pyroelectric coefficient of ∼ 250 μC m−2.K was obtained around the transition temperature (∼150 °C). This is significantly higher than that reported for polycrystalline Sr x Ba1-xNb2O6 (SBN). However, the piezoelectric coefficient (d 33) of the title composition was as low as 6 pC N−1.

A critical evaluation of reactive templated grain growth (RTGG) mechanisms in highly [001] textured Sr0.61Ba0.39Nb2O6 ferroelectric-thermoelectrics

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Thermoelectric power factor enhancement of textured ferroelectric SrxBa1–xNb2O6–δceramics

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Spectral Ellipsometry Study of SBN Single Crystals in Visible and Ultraviolet Region

The pseudo-dielectric function <ϵ>(E) = <ϵ1>(E) + i<ϵ2>(E) of strontium-barium niobate single crystals, Sr x Ba1-x Nb2O6 (SBN), was studied at room temperature for five nominal compounds indices x (x = 0.40, 0.55, 0.61, 0.65, 0.75) by spectroscopic ellipsometry using the synchrotron light ellipsometer in the photon energy range of 1.5– 10 eV. The spectra of <ϵ2>(E) obtained appear to be similar to the analogous spectrum of LiNbO3 crystal, where the NbO6 octahedral groups are responsible for the features of <ϵ2>(E). Differences in the dielectric function of SBN with various x have been found and analyzed. The nonlinear dependences of optical values on the compound index x have been found in SBN.

Synthesis, Ferroelectric and Electrooptic Properties of Transparent Crystallized Glasses with SrxBa1−xNb2O6 Nanocrystals

Crystallized glasses consisting of SrxBa1−xNb2O6 (SBN) nanocrystals (x=0.5, 0.61, and 0.62) with a tetragonal tungsten–bronze structure are synthesized using a conventional glass crystallization technique in xSrO–(32−x)BaO–32Nb2O5–36B2O3 glasses with x=16, 19.5, and 24. Nanocrystals of Sr0.5Ba0.5Nb2O6, Sr0.61Ba0.39Nb2O6, and Sr0.62Ba0.38Nb2O6 are found to have rod‐like shapes with an average diameter of 20–40 nm as determined from X‐ray diffraction analyses and transmission electron microscope observations and to exhibit ferroelectricities as deduced from the presence of hysteresis in polarization–electric field curves. Although the optical transparency of crystallized glasses in the visible region decreases along with the formation of SBN nanocrystals, optical transparencies (sample thickness: ∼1 mm, transmittance: ∼80%) are observed at the wavelength of 1.55 μm. Electrooptic activity was confirmed for the crystallized glasses with SBN nanocrystals, indicating that the present study would be a step for active optical device applications in glass‐related materials consisting of SBN nanocrystals.

Absorption spectroscopy and energy levels of rare earth impurity centres in Srx Ba1–xNb2O6 crystals

AbstractThe absorption spectra of Ce3+, Nd3+, Eu3+, Tb3+, Er3+, Tm3+ and Yb3+ rare earth (RE) impurity ions incorporated in Srx Ba1–x Nb2O6 (SBN) crystals were studied in a wide spectral range from the visible to the mid‐infrared. On the basis of the analysis of the Ce3+ absorption line shapes and their polarization properties the conclusion was drawn about the incorporation of multiple Ce3+ centres mostly in the position A1 of the crystal lattice of SBN. From the observed temperature dependence of the Ce3+ absorption line broadening the electron coupling strength (160 cm–1) and effective phonon energy (300 cm–1) were determined. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Reducing the positional modulation of NbO6-octahedra in Sr x Ba1–x Nb2O6 by increasing the barium content: A single crystal neutron diffraction study at ambient temperature for x = 0.61 and x = 0.34

Abstract We report on the influence of the barium content on the modulation amplitude in Sr x Ba1–x Nb2O6 compounds by comparing Sr0.61Ba0.39Nb2O6 (SBN61) and Sr0.34Ba0.66Nb2O6 (SBN34). Our single crystal neutron diffraction results demonstrate that the amplitude of the positional modulation of the NbO6 octahedra is reduced with increasing barium content, indicating that the origin of the modulation is the partial occupation of the pentagonal channels by Sr and Ba atoms. By increasing the Sr content the bigger Ba atoms are replaced by the smaller Sr atoms, which leads to a larger deformation of the surrounding lattice and hence to a larger modulation amplitude. The more homogeneous the filling of these channels with one atomic type (Ba) the lower the modulation amplitude. Our results also show that the structure can be described with a two-dimensional incommensurate harmonic modulation. No second order modulation has been observed, both by single crystal diffraction measurements and q-scans. The positional modulation of the Nb atoms is much smaller than that of the oxygen atoms, such that the modulation can be seen as a rotational modulation of almost rigid NbO6-octahedra.

Growth of highly orientated strontium barium niobate thin films on Si substrates through the sol–gel process using a K: SBN template layer

We report the growth of highly C-axis orientation of Sr x Ba1−x Nb2O6 (SBN) thin films on p-type (100) Si substrates by using a potassium-substituted SBN template layer with the sol–gel method. The crystallization of SBN thin films was found closely related to the potassium ion doping concentration and the postannealing temperature of the K-SBN template layer. Secondary ion mass spectrometry analysis showed that potassium elements were accumulated at the interface of the template layer and silicon substrate. SBN films postannealed at 750 °C with K-SBN template layer has a smaller full width at half maximum of X-ray rocking curve of 2.45° than that of 5.40° for the pure SBN films. By introducing a template layer, the surface morphologies of SBN films fabricated on silicon substrate were greatly improved.

Investigation of two‐center holographic recording in SBN:Ce:Cr and SBN:Mn:Fe

Non-volatile holographic storage, based on two-centre holographic recording (TCHR) has been tested in analogy to successful attempts in LiNbO3:Fe:Mn, in doubly doped strontium barium Niobate (SBN) (SrxBa1–xNb2O6). Several tests with differently co-doped (Ce+Cr, Fe+Mn) crystals are carried out after various oxidation/reduction treatments and with several wavelengths for sensitising and recording. Up till now no non-volatile hologram storage in SBN could be observed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Kinetics of light‐induced polaron‐ and VIS‐centers in SBN:Ce single crystals at low temperature

The promising photorefractive crystal SrxBa1–xNb2O6 (SBN, congruent composition x = 0.61) can be doped with polyvalent ions like Ce to enhance photorefractive properties. Illumination with blue Ar+-laser light at low temperature creates light-induced NIR and VIS absorption bands. The NIR absorption has been identified as being due to Nb4+ electron polarons and their properties have been investigated in some detail. The VIS-Centers are less well understood and their nature is still under discussion. It has been shown by our previous measurements that illumination with red Kr+-laser light (647 nm) or red laser diodes (673 nm) leads to a dissociation of the VIS-Centers and a simultaneous build-up of a transient NIR-polaron absorption. We report here some new facts important for the simplified charge transfer model needed to describe quantitatively the equilibrium values and the dynamics of the NIR-polaron and VIS-center absorption. These features give new insight into the dynamic nature of these VIS-centers, which are currently being discussed as either bipolarons (in analogy to LiNbO3) or polarons trapped at charged centers, or charge transfer vibronic exitons (CTVEs) being trapped at charged centers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

X-ray diffraction study of cerium-and thulium-doped (Sr,Ba)Nb2 O6 single crystals

The structural models of cerium-and thulium-doped (Sr0.61Ba0.39)Nb2O6 solid solutions were established and refined on the basis of single-crystal X-ray diffraction data. The dopants were located, and their concentrations in the specimens were refined. The effect of the Sr/Ba ratio and doping with rare earth elements on the structural characteristics of (SrxBa1-x)Nb2O6 crystals was analyzed.

Nonlinear optical dynamics and Eu3+ spectral holeburning in strontium barium niobate thin film grown by pulsed laser deposition

Optical quality SrxBa1−xNb2O6 (SBN) thin films, both undoped and Eu3+-doped, of thickness less than 0.5 μm have been successfully grown on fused quartz substrates using a pulsed laser deposition technique. Optical properties of these films were characterized in high-resolution spectroscopic experiments in time and frequency domains. For undoped SBN thin films, broadband emission in the UV region extending to the visible was observed following excitation at 355 nm. This emission is attributed to exciton luminescence of the SBN film. Nonlinear optical response in the picosecond regime and the third-order nonlinear susceptibility, χ(3), were studied using degenerate four-wave-mixing methods. In transverse alignment, χ(3) is enhanced by two orders of magnitude in comparison with its bulk counterpart. A thermal annealing process, monitored via changes in spectral properties of Eu3+, was employed to convert the as-grown amorphous film into a polycrystalline film. High-resolution spectroscopic measurements in the frequency domain were conducted on a 200-nm-thick film of Eu3+-doped SBN. Our spectroscopic results suggest that Eu3+ ions may substitute for Nb, thereby occupying a normally six-fold coordinated lattice site. At liquid helium temperature, spectral holes in the F07–D05 optical transition were burned in the thermally annealed films. Typical observed hole widths were 70–100 MHz and hole depths were as large as 30% of the peak fluorescence intensity.

Local configuration instability as an origin of relaxor-type properties of ferroelectric solid solutions SBN, SCT and KLTN

A model of phase transitions (PT) in concentrated and diluted ferroelectric oxide solid solutions with iso-charged doping is considered on examples of SBN (SrxBa1−xNb2O6), x = 0.61 for congruent composition, of SCT (Sr1−xCaxTiO3) for x <<1, and of KLTN (K1−xLixTa1-yNbyO3) with weak (Nb5+) and strong (Li+) off-center impurities for x <<1, y<<1 cases. This nano-cluster model with taking into account in-cluster local configuration instability (LCI) can explain uncommon relaxor-type properties of these systems as well as the origin of active polar clusters. It is shown that cooperative mechanism of cluster polarization formation due to co-operative LCI can be important for SBN and for SCT. The model also explains strong suppressing of ferroelectric PT by Cr-impurities in SBN. While the SBN and the SCT are characterised by LCI which is induced by the chemical fluctuation field, KLTN consists in Nb-rich nano-clusters obey Li-impurities as cluster cores. Multi-mode soft dynamics with local in-cluster piezoeffect is responsible for the origin of long-range electric dipole-dipole interaction as well as for co-existence of ferroelectric and glass-like states with reentrant glass phenomenon. The former is a key effect in the phenomenon of small concentration impurity influence on the PT in KLTN. This model explains also an appearance of a new PT in KLTN with strong hysteresis and cusp-type susceptibility.

Synthesis and dielectric properties of Sr Ba1–Nb2O6 formed by YAG laser ablation

Abstract Tungsten-bronze type tetragonal SrxBa1–xNb2O6 (SBN) ceramics have been synthesized by pressure-less sintering at 1250°C through a mixed-oxide route. With increasing x value in the range from 0.3 to 0.6, the Curie temperature shifted to lower temperature, but the corresponding maximum dielectric constant increased. Further, Sr0.3Ba0.7Nb2O6 thin films have been formed by pulsed YAG laser deposition (PLD) technique using a selected SBN bulk target with various choices of the deposition parameters. When Pt-coated Si substrates were used for PLD, a preferential c-axis-ordered structure was observed in the films deposited using an energy density above 2.0 J/cm2, at a substrate temperature above 650°C, and in oxygen partial pressure below 7 Pa. The thin film yielded a rhomboidal P–E hysteresis loop, and showing a remanent polarization (Pr) of 3.1 μ C/cm2 and coercive field (Ec) of 1.28 kV/cm.

Light-induced VIS-absorption and light-induced charge transfer in pure and doped SBN crystals

Under illumination with Ar+-, Kr+-laser or UV light, SrxBa1−xNb2O6 (SBN):Ce, SBN:Cr and pure SBN crystals show a light-induced absorption band around 2.1eV (600nm) with a considerable dichroism. This light-induced VIS-absorption exhibits nonlinear intensity dependence with saturation at high illumination strength. The temperature dependence of the light-induced absorption of the VIS-center for a specific illumination intensity shows for temperatures T<200K a nearly constant value, which however decreases rapidly at higher temperatures T>200K. The decay of the light-induced VIS-centers after the illumination is switched off is non-monoexponential and strongly depends on temperature. The decay rate of the VIS-centers is nearly zero at low temperatures T<100K, increasing rapidly above T>140K. The absorption and therefore the concentration of Ce3+- or Cr3+-centers in SBN crystals have been found to decrease with increasing illumination intensity at T=2K. At low temperatures T<140K under illumination (with Ar+-, Kr+-laser, UV light), in addition to the VIS-center absorption, a strong absorption band because of Nb4+ polarons [1], similar to absorption bands observed in reduced SBN crystals [2], appears in the NIR spectral region (λmax about 1.6μm). The bandshape of this Nb4+ polaron absorption extends with its tail into the visible region, overlapping with the absorption of the VIS centers. The Nb4+ polaron absorption decays rapidly even at low temperatures, and above T>140K no NIR absorption of these centers could be detected any more. A light-induced charge transfer model is proposed to explain the experimental results of the light-induced NIR and VIS absorption and the possible origin of the light-induced VIS-centers.

Temperature induced red shift of the UV fundamental absorption edge in ferroelectric oxide crystals: effect of charge transfer vibronic excitons

A pronounced temperature induced red shift of the fundamental UV-absorption edge is observed in ferroelectric oxides at T > 300 K. The biggest shift value of—1.3 meV/K is found in tetragonal SBN (Sr x Ba1-x Nb2O6), where no peculiarities were detected in the region of the diffused phase transition (T c = 350 K). A model involving new in-gap states due to charge transfer vibronic excitons (CTVE) with a new correlated CTVE-phase is proposed to explain the experimental observations.

Study of the formation mechanism of sol-gel derived sen powders using raman spectroscopy and X-ray diffractometry

Sol-gel derived SrxBa1−xNb2O6(SBN) powders of different chemical composition (x = 0.3 to × = 0.75) were prepared at annealing temperatures ranging from 600 °C to 1400 °C. Their structural properties were studied by Raman spectroscopy (RS) and X-ray diffractometry (XRD). The annealing temperatures for fabrication of tetragonal tungsten bronze (TTB) type SBN are found to depend on the composition. Our results suggest that the development of TTB phase SBN with × ≠ 0.5 follows two parallel reaction routes. At low temperature, the TTB phase SBN50 (x = 0.5) and excess BN or SN were formed initially. Thereafter these two phases formed the solid solution of SBN at higher annealing temperature.

Observation of amplitude gratings in nonpoled strontium barium niobate crystals

We present the results of recording of amplitude gratings in SrxBa1-xNb2O6 (SBN) crystals. To eliminate the photorefractive effect we used nonpoled samples. A simple technique defined the susceptibility of doped SBN to amplitude gratings recording. It was shown that, of SBN crystals doped with Ce, Cr, and Co, SBN:Co is the most effective material for use in investigating the photochromic effect. This material has a strong dichroism in linear and photoinduced absorption. The steady-state and dynamic behavior of absorption gratings in nonpoled SBN:Co crystals was studied by the two-wave mixing technique. The study is important both for the optimization of doped SBN for photorefractive applications and for characterization of the electronic structure of defects in these materials.

Effect of the Strontium:Barium Ratio and Atmosphere on the Sintering Behavior of Strontium Barium Niobate

The sintering behavior of SrxBa1−xNb2O6 (SBN) (x= 0.5, 0.6, and 0.7) was studied. The densification rate increased and the evaluated activation energy of SBN decreased as the Sr:Ba molar ratio increased. Also, when SBN50 (SBN where x= 0.5) was sintered at &lt;1300°C, the densification rate decreased as the oxygen partial pressure increased, and, at 1300°C, the oxygen partial pressure had insignificant influence on the densification. The relationship of sintering behavior and structure of SBN has been discussed, and the niobium ion was suggested as being the rate‐limiting species when sintering SBN.

Nonisothermal Reaction Kinetics of SrNb2O6 and BaNb2O6 for the Formation of SrxBa1−xNb2O6

The solid‐state reaction of SrNb2O6 and BaNb2O6 to form SrxBa1−xNb2O6(SBN) at different temperatures and heating rates was investigated. The reaction kinetics were analyzed by X‐ray diffractometry for quenched samples, and the internal‐standard method was applied to quantify the extent of the reaction. A nonisothermal kinetic empirical model was proposed to evaluate the activation energy and rate constant of SBN with different Sr:Ba ratios. It was found that the kinetic form would change above and below a transition at a reaction fraction of ∼60%, which might be due to the change of the frequency factor. It was also verified that the model that was presented was more favorable to describe the nonisothermal reaction kinetics of SBN.