Doped Strontium Barium Niobate Research Articles

Photoconduction of Polar and Nonpolar Cuts of Undoped Sr0.61Ba0.39Nb2O6 Single Crystals

In the last two decades, variably doped strontium barium niobate (SBN) has attracted a lot of scientific interest mainly due to its specific non-linear optical response. Comparably, the parental compound, i.e., undoped SBN, appears to be less studied so far. Here, two different cuts of single-crystalline nominally pure strontium barium niobate in the composition Sr0.61Ba0.39Nb2O6 (SBN61) are comprehensively studied and analyzed with regard to their photoconductive responses. We present conductance measurements under systematically varied illumination conditions along either the polar z-axis or perpendicular to it (x-cut). Apart from a pronounced photoconductance (PC) already under daylight and a large effect upon super-bandgap illumination in general, we observe (i) distinct spectral features when sweeping the excitation wavelength over the sub-bandgap region as then discussed in the context of deep and shallow trap states, (ii) extremely slow long-term relaxation for both light-on and light-off transients in the range of hours and days, (iii) a critical dependence of the photoresponse on the pre-illumination history of the sample, and (iv) a current–voltage hysteresis depending on both the illumination and the electrical-measurement conditions in a complex manner.

Feasibility of electron and hole injection in heavily doped strontium barium niobate (SBN50) Sr0.5Ba0.5Nb2O6 for thermoelectric applications

Undoped and heavily doped (K, Y, Zr, Mo) strontium barium niobate Sr0.5Ba0.5Nb2O6 (SBN50) materials have been prepared by co-precipitation. X-ray diffraction shows the formation of a single-phase product and that 10% and 12.5% of the Nb sites can be occupied by Zr and Mo, respectively. K can enter 40% of the Sr sites, while the maximum Y substitution is also around 40%. The starting stoichiometry is effective in driving the substitutions to the desired sites. X-ray Absorption Spectroscopy (XAS) at the Nb-K edge shows the presence of Nb(V) independent of doping. A pre-edge 1s-4d transition surprisingly indicates the hole injection with Y doping and the electron injection with Zr doping. Chemical reduction does not affect the stability of the structure, except for a small decrease of maximum Y solubility, while the Nb(V) oxidation state and the XAS pre-edge feature are unmodified. The oxidized samples are insulators, the reduced samples show electrical conductivity, and doping significantly enhances thermopower and electrical conductivity. The Y doped sample shows a power factor ∼30 times larger than that of the undoped sample.

Optical induction of non-diffracting discrete photonic lattice

The triangle lattices was optically induced in an externally biased cerium doped strontium barium niobate (SBN) photorefractive crystal using a mask with three holes or six holes, respectively. Numerically, the transmittance function of the amplitude mask and its Fourier-transform function were given out instead of treating each hole as a simple point source. Experimentally, the differences between the two lattices were analyze by phase distribution, far-field diffraction pattern, Brillouin-zone spectroscopy. And the three-dimensional (3D) images by computer simulation are also used to study their differences. In addition, the anisotropy lattices are presented by designing the amplitude mask properly.

Growth peculiarities and non-linear properties of profiled doped strontium-barium niobate crystals

The nominally pure and doped with Ce, Cr, Co strontium-barium niobate crystals of SBN:61 were grown by modified Stepanov technique. The specific features of the technique were studied and growth conditions for obtaining the high homogeneous SBN crystals in bulk-profiled configuration were optimized. The photorefractive and non-linear properties of SBN pure and doped with Ce, Cr and Co were investigated. It was shown that SBN:Ce crystal is an excellent medium for high efficiency holographic information recording. SBN:Cr and SBN:Co crystals are promising photorefractive materials with short response time. The as-grown SBN crystals were also used to demonstrate the diffuse noncollinear second harmonic generation emitted by a random domain SBN structure and Stimulated Raman Scattering and two-photon absorption associated with cubic nonlinear susceptibility of the materials.

Sintering behavior and dielectric properties of Ce doped strontium barium niobate ceramics with silica sintering additive

Sr0.5Ba0.5Nb2O6 ceramics with and without CeO2 dopant were prepared by a partial co-precipitation method and a liquid phase sintering process. The cooperative effects of Ce doping and silica sintering additive on the sintering behaviors and the dielectric properties of Sr0.5Ba0.5Nb2O6 ceramics was investigated. It was observed that the lattice parameters of a-axis and c-axis of Sr0.5Ba0.5Nb2O6 ceramics decrease with the increase of Ce dopant, namely contraction of crystal cell volume occurs. Amorphous silica used for sintering additive can effectively restrain abnormal grain growth and prevent the rise of sintering activation energies caused by Ce doping, but Ce doping has more effect on the average size of the grains and the dielectric properties than the silica sintering additive when the Ce dopant and the silica sintering additive are introduced. Both the Curie temperatures and the maximum of dielectric constant at Tc decrease as the Ce3+ concentration increases.

2D infrared self-focusing in bulk photorefractive SBN

We experimentally demonstrate the possibility of photorefractive 2D self-focusing in bulk Cerium doped Strontium Barium Niobate (SBN:Ce) directly at telecommunications wavelengths (1.06 μm and 1.55 μm). Although the electro-optic coefficient of SBN is smaller at infrared wavelengths, 2D infrared self-trapping is observed and analyzed versus different parameters such as the laser beam intensity, the external applied electric field and time.

Characterization of Er 3+ and Nd 3+ doped Strontium Barium Niobate glass ceramic as temperature sensors

Temperature sensor is a vast group of the commercially approachable optical sensors. Recently has appeared a new kind of these devices using the fluorescence intensity ratio (FIR) with a very good sensitivity. The FIR technique has been carried out in Strontium Barium Niobate (SBN) glass ceramic sample to extend the knowledge of this kind of matrix. The samples has been doped with Erbium and Neodymium ions (2.5 mol%). The thermalized level 4S 3/2 ( 2H 11/2) of Er 3+ ions was studied in a wide temperature range from 300 K to 700 K with a maximum sensitivity of 0.0017 K −1 for 600 K. In these ions the FIR technique has been applied to the transitions 2H 11/2 → 4I 13/2 and 4S 3/2 → 4I 13/2 at 800 nm and 850 nm, respectively. The weak overlap between these thermalized emission bands is an important factor to reduce the error in the measurements. In the Nd 3+ doped sample, the emission bands corresponding to the 4F 5/2 → 4I 9/2 and 4F 3/2 → 4I 9/2 transitions were analyzed as a function of the temperature from 300 K to 700 K with a maximum sensitivity of 0.0015 K −1 for 600 K. These results are compared with other optical devices using FIR technique.

Phase formation, microstructure and dielectric properties of Sr 0.53Ba 0.47Nb 2− xTa xO 6 ceramics

Ta 5+ doped strontium barium niobate (SBN) ceramics were synthesized by conventional oxide-mixed method. The phase structure, microstructure and dielectric properties of the ceramics with different Ta 5+ contents and sintering temperatures were investigated. The X-ray diffraction patterns show that pure tungsten bronze structure can be obtained in all the ceramics. The ceramics with high relative density and a uniform and fine-grained microstructure could be obtained at 1430 °C. The grain size of Sr 0.53Ba 0.47Nb 2− x Ta x O 6 decreased with increasing the Ta 5+ content. The relaxor behavior observed in SBNT ceramics should be attributed to a cationic disorder induced by B-site substitutions, which was proved by linear fitting of the modified Curie–Weiss law. All samples are proved to be relaxor ferroelectric. It is also found that Curie temperature T c and maximum dielectric constant ɛ m both decrease with increasing Ta 5+ content.

Formation of Nd 3+ doped Strontium Barium Niobate nanocrystals by two different methods

The study of two different methods to obtain Strontium Barium Niobate nanocrystals has been carried out. Previously, Nd 2O 3 doped SrO–BaO–Nb 2O 5–B 2O 3 glasses were fabricated using the melt quenching process. In the first method, a thermal treatment in an electrical furnace at 620 °C was used to obtain glass ceramic samples. In the second one, the nanocrystals were obtained under continuous Ar laser irradiation in a localized zone in the glass sample. The X-ray diffraction patterns confirmed the formation of SBN nanocrystals in both cases. The optical measurements indicate the incorporation of Nd 3+ ions into the nanocrystals which produces an increment of the luminescence intensity. Moreover, a calibration with the temperature has been carried out for the ratio of the Nd 3+ emissions. This result could let to control the temperature of the laser irradiated zone.

Structural changes induced on strontium barium niobate glass by femtosecond laser irradiation

Localized modification of the optical properties of erbium doped strontium barium niobate (SBN) glass has been performed using femtosecond laser irradiation. The samples, with composition SrO–BaO–Nb2O5–B2O5 and doped with 5%mol of Er3+, were fabricated using a melt-quenching method. The samples were irradiated with different number of pulses per spot (1–50 pulses) at two different laser fluences (2.6 and 5.6 J/cm2) by using an fs laser amplifier operating at 800 nm and generating pulses with a duration of 120 fs.

Three-dimensional optically induced reconfigurable photorefractive nonlinear photonic lattices

We experimentally investigate the formation of reconfigurable three-dimensional (3D) nonlinear photonic lattices in an externally biased cerium doped strontium barium niobate photorefractive crystal by a spatial light modulator-assisted versatile simplified single step optical induction approach. The analysis of the generated 3D nonlinear photonic lattices by plane wave guiding, momentum space spectroscopy, and far field diffraction pattern imaging is presented, which points to the embedded potential of these 3D structures as reconfigurable platform to investigate advanced nonlinear light-matter interaction in periodic structures.

Localized desvitrifiation in Er3+-doped strontium barium niobate glass by laser irradiation

Localized desvitrifiation in strontium barium niobate glass doped with Er3+ under laser irradiation has been carried out. The samples of this study have been fabricated by the melt quenching method and doped with 5% mol of Er3+. A 1.5-W cw Ar laser was focused on the sample to obtain desvitrifiation of the glass. Evidence of the changes induced by the Ar laser has been observed through the analysis of the photoluminescence of the Er3+ ions. The transitions corresponding to 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 have been studied to analyze structure changes. Microluminescence measurements have been carried out to spatially select positions inside and outside the irradiated area. We have observed changes in the emission bands corresponding to these transitions. The emission bands from Er3+ ions in the irradiated zone show a resolved structure while they are broadened outside that area. These changes in the optical properties of the Er3+ ions indicate that the Ar-laser irradiation has produced a change in the local structure of the material. These results show that a localized desvitrifiation has been produced after the laser action and the transition from glass to glass ceramic has been completed.

Laser irradiation in Nd3+ doped strontium barium niobate glass

A local nanocrystalline formation in a neodymium doped strontium barium niobate (SBN) glass has been obtained under argon laser irradiation. The intense emission around 880 nm, originated from the F43/2 (F45/2) thermalized level when the glass structure changes to a glass ceramic structure due to the irradiation of the laser beam, has been studied. The intensities and lifetimes change from this level inside and outside the irradiated area made by the laser excitation. They have been analyzed and demonstrated that the desvitrification process has been successfully achieved. These results confirm that nanocrystals of SBN have been created by the laser action confirming that the transition from glass to glass ceramic has been completed. These results are in agreement with the emission properties of nanocrystals of the bulk glass ceramic sample. The present study also suggests that the SBN nanocrystal has a potential application as temperature detector.

Thermal properties of calcium doped strontium barium niobate crystal

Calcium doped strontium barium niobate is a tungsten-bronze ferroelectric crystal with a tetragonal unit cell. Thermophysical properties including specific heat, thermal expansion, and thermal diffusion were performed on a single crystal (Ca0.28Ba0.75)0.25(Sr0.60Ba0.40)0.75Nb2O6 (CSBN25) to determine thermal behaviors along the a and c axes. Negative thermal expansion was observed along the c axes below the Curie temperature. Isotropic thermal behavior (thermal diffusion and thermal conductivity) was observed around Curie temperature. The abnormal thermal behaviors are considered as arising due to the geometry of the dope-affected crystal.

Optical properties of Er 3+-doped strontium barium niobate nanocrystals obtained by thermal treatment in glass

Measurements of the optical properties of Er 3+ ions in strontium barium niobate glass and glass ceramics have been carried out. The glasses have been fabricated using a melt-quenching method, and the glass ceramic samples have been obtained from the glass precursor by a thermal treatment. The ceramic samples formed by a glassy phase, and a crystalline phase contains nanocrystals of Sr 1− x Ba x Nb 2O 6 (SBN) doped with Er 3+ ions with a mean size of ∼50 nm, as confirmed with XRD. Green up-conversion emission has been obtained under excitation at 800 nm, and the temporal evolution of this emission has been reported with the purpose of determining the involved up-conversion mechanism. These optical measures have confirmed that the Er 3+ ions have been incorporated into the SBN matrix, after a thermal treatment, which produced an increment of the up-conversion efficiency.

Time-resolved study electronic and thermal contributions to the nonlinear refractive index of Nd 3+:SBN laser crystals

The propagation of an optical beam through dielectric media induces changes in the refractive index, Δ n, which causes self-focusing or self-defocusing. In the particular case of ion-doped solids, there are thermal and non-thermal lens effects, where the latter is due to the polarizability difference, Δ α, between the excited and ground states, the so-called population lens (PL) effect. PL is a pure electronic contribution to the nonlinearity, while the thermal lens (TL) effect is caused by the conversion of part of the absorbed energy into heat. In time-resolved measurements such as Z-scan and TL transient experiments, it is not easy to separate these two contributions to nonlinear refractive index because they usually have similar response times. In this work, we performed time-resolved measurements using both Z-scan and mode mismatched TL in order to discriminate thermal and electronic contributions to the laser-induced refractive index change of the Nd 3+-doped Strontium Barium Niobate (Sr x Ba 1− x Nb 2O 6) laser crystal. Combining numerical simulations with experimental results we could successfully distinguish between the two contributions to Δ n.

Substrate Induced Pre-tilt in Hybrid Liquid Crystal/Inorganic Photorefractives

We report on the photorefractive properties of nematic liquid crystals sandwiched between windows of cerium doped strontium barium niobate (Ce:SBN). Unlike simple glass substrates, the Ce:SBN induces molecular pre-tilts that generate electric dipole moments in the liquid crystal through the flexoelectric effect. This enables the liquid crystal to become sensitive to the sign of the space-charge field and leads to an increase in the optical amplification when the cell thickness is decreased.

Determination of large nematic pre-tilt in liquid crystal cells with mechanically rubbed photorefractive Ce:SBN windows

We report on the determination of liquid crystal pre-tilt inside cells fabricated using single crystal birefringent and dichroic windows of cerium doped strontium barium niobate. We show that the average pre-tilt is significantly affected by the crystalline windows, leading to much larger values than those obtained with glass windows using identical fabrication methods. The same technique can be used to determine pre-tilts as large as 40 degrees, which is significantly larger than normally measurable using the cell rotation method.

Synthesis of Sm 3+-doped strontium barium niobate crystals in glass by samarium atom heat processing

New glasses giving the crystallization of Sm 3+-doped Sr x Ba 1− x Nb 2O 6 (SBN) ferroelectrics have been developed in the Sm 2O 3−SrO−BaO−Nb 2O 5−B 2O 3 system, and the formation of SBN crystal dots and lines by continuous wave Nd:YAG laser (wavelength:1064 nm, power: 1 W) irradiations, i.e., samarium atom heat processing, has been examined. The formation of Sm 3+-doped SBN non-linear optical crystals is confirmed from X-ray diffraction analyses, micro-Raman scattering spectra, second harmonic generations, and photoluminescence spectra. Sm 3+-doped SBN crystal dots with the diameters of 20–70 μm and lines with the widths of 20–40 μm are written at the surface of some glasses such as 10Sm 2O 3·10SrO·10BaO·20Nb 2O 5·50B 2O 3 (mol%) by Nd:YAG laser irradiations with the irradiation times of 20–70 s for the dots and with the scanning speeds of 1–5 μm/s for the lines. The present study suggests that the samarium atom heat processing has a potential for the patterning of optical waveguides consisting of ferroelectric SBN crystals in glass substrates.

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)