Sr1-xBaxNb2O6 Research Articles

Chemical Vapor Deposition of Sr1−xBaxNb2O6 Thin Films Using Metal Alkoxide Precursors

A novel two-step metalorganic chemical vapor deposition process was used in this study to prepare Sr1−xBaxNb2O6 (SBN) thin films. Two thin layers of single-phase SrNb2O6 and BaNb2O6 were deposited alternately on a silicon substrate, and the solid solution of SBN was obtained by high-temperature annealing. The stoichiometry control of the SrNb2O6 and the BaNb2O6 thin films was achieved through deposition process control, according to the evaporation characteristics of double metal alkoxide. The evaporation behavior of double metal alkoxide precursors SrNb2(1-OC4H9)12 and BaNb2(1-OC4H9)12 was studied, and the results were compared with the evaporation of single alkoxide Nb(1-OC4H9)5.

Light-induced charge transfer and kinetics of the NIR absorption of Nb 4+ polarons in SBN crystals at low temperatures

Sr1-xBaxNb2O6 (SBN) crystals with open tungsten-bronze structure show enhanced photorefractive properties with doping of impurities such as Ce, Cr, Rh etc. Under illumination with Kr+ laser (647 nm) or Ar+ laser light (488 nm or 514 nm) or UV light at low temperature, pure and doped SBN crystals show a broad polaron absorption band around 0.7 eV (6000 cm-1). The first step of a theoretical model involves the excitation of electrons by illumination from Cr3+/Ce3+ to higher excited states or the conduction band. The excited electrons can then be trapped by Nb5+ to form Nb4+ polarons and further on can directly tunnel through or hop over the potential barrier (with a value Δ≈0.15±0.02 eV) to recombine with Cr4+/Ce4+ ions. The experimental intensity dependence, temperature dependence, and decay process of the light-induced Nb4+ polarons can be fitted with the help of this model. Small, but systematic, differences lead to the additional assumption of different recombination rates of polarons at distinct distances from the Cr4+/Ce4+ recombination centers and therefore many parallel decay channels are active where each decay channel obeys a monoexponential decay law. A stretched exponential decay function is employed to fit in this case the decay process of the Nb4+ polarons at different temperatures and under illumination with different intensities. Due to the high dielectric constant value (e33 and e11 have values in the 102-103 range) at low temperature, the long range Coulomb attraction (to Ce3+ Sr/Ba) or repulsion (from Cr3+ Nb) of the electronic polaron is suppressed. The leading role in the attraction and the following trapping of the electronic Jahn–Teller polaron, both on Cr3+ Nb and Ce3+ Sr/Ba centers, is played by the indirect dipole–dipole interaction via the soft TO-mode.

Optical properties of lead barium niobate (Pb1−xBaxNb2O6) crystals

PBN (Pb1−xBaxNb2O6) polycrystals have been grown by the vertical Bridgman method. Transparent, stoichiometric, striation-free single-crystal specimens of millimeter size were obtained. The ordinary and extraordinary refractive indices, no and ne, of crystals with compositions Pb0.50Ba0.50Nb2O6 and Pb0.57Ba0.43Nb2O6 were measured by the minimum deviation method using optically polished prisms. Neither no nor ne was found to be strongly dependent on crystal composition, in contrast to the case of SBN (Sr1−xBaxNb2O6), in which ne is strongly dependent on composition. Optical transmission spectra showed PBN to be transparent in the range from 0.4 to 5 μm except for the OH− absorption bands around 2.87 μm. The dependence of the integrated OH− absorption intensity on polarization showed that all of the O–H bonds lie either in the a-b plane or along the c axis, with a greater density of O–H bonds in the a-b plane than along the c axis.

STUDY OF RAMAN SPECTRA FOR FERROELECTRIC TUNGSTEN BRONZE-TYPE CRYSTALS SBN AND KNSBN

The Raman spectra of Sr1-xBaxNb2O6(SBN) and (K1-yNay)z(Sr1-xBax)l-zNb2O6(KNSBN) crystals have been obtained and discussed based on the space group theory and lattice dynamics. It provides scientific basic for an improvement on SBN and KNSBN by ion doping.

Piezoelectricity in tungsten bronze crystals

The range of piezoelectric properties available in tungsten bronze crystals reviewed includes both longitudinal and shear mode responses. Specific crystal compositions investigated include Sr1-xBaxNb2O6 (SBN), Ba2-xSrxK1-yNayNb5O15 (BSKNN), K3Li2Nb5O15 (KLN), (Ba, Sr)6Ti2Nb8O30 (BSTN), Sr2-x-CaxNaNb5O15 (SCNN), Sr2KNb5O15 (SKN) and Pb1-xBaxNb2O6 (PBN). SBN, SCNN and SKN exhibit large piezoelectric d33 coefficients, while BSKNN, PBN:60 and KLN have large d15 shear coefficients. In La3+ -modified SBN:60, d33 can exceed 1000 pC/N, although its relaxor character increases with increasing La3+ content. The role of dopants in the 12-, 9- and 6-fold coordinated crystallographic sites is described with respect to the relaxor character of SBN crystals. The high piezoelectric and dielectric constants in these single crystals suggest their use in high frequency ultrasonic tomography. Both piezoelectric and electrostrictive options would appear to be available in the bronzes and the very high perfection of the available crystals could permit the generation of composite ultrasonic senders and receivers at scales which would be impossible in conventional polycrystalline piezoelectric ceramics.

Low temperature dielectric relaxation phenomena in relaxor ferroelectric strontium barium niobate single crystals

Abstract Low temperature (15∼300K) dielectric permittivities of tungsten bronze Sr1–xBaxNb2O6 (SBN(1–x)%, 1–x=0.50, 0.61, and 0.75) single crystals were studied using dielectric spectrum techniques. Two distinct dielectric relaxation features were observed in all three crystal compositions. The dielectric anomaly at temperature range ∼(150K–300K) is presumably associated with the incommensurate (ICS) superlattice transformation identified by high resolution TEM (Bursill and Lin)1 No experimental evidence of phase transition was found in the measurement regime for the dielectric anomaly observed at temperature below 150K. Dielectric properties of the poled crystals indicate that the ICS related dielectric anomaly is strongly dependent on the polarization-strain coupling along the c-direction, while the second low temperature relaxation is associated to the polarization fluctuation in the a-b plane related to the relaxor nature of the SBN solid solution system. The experimental results further substantiate ...

Thermal focussing and optical bistability in ferroelectrics

Abstract A discussion is presented of thermal focussing in ferroelectrics near T c. Three materials are described: Ba2NaNb5O15 (BNN), Sr1-xBaxNb2O6 (SBN) and PbMg1/3Nb2/3O3 (PMN). Emphasis is on: 1) determining critical indices β and δ; 2) extracting Landau-Devonshire coefficients in the free-energy expression; 3) quantitative explanation of the temporal and spatial patterns; 4) criteria for optical bistability; 5) adiabatic and isothermal responses; 6) application to flow-rate and pressure sensors.

Low temperature properties of Tb-doped Sr1-xBaxNb2O6 (SBN) crystals

Tb-doped SBN crystals were prepared by the Czochralski technique. Their dielectric, ferroelectric, and pyroelectric properties were studied. A low temperature phase transition between two polar phases was revealed by the anomalies of the dielectric and pyroelectric properties; the polar axis changes its direction during this transition. The point group of the low temperature phase may be mm2, m or l.

Growth of ferroelectric tungsten bronze crystals and thin films

Abstract In this paper, we review the state-of-art for the growth of ferroelectric tungsten bronze single crystals in optical quality and large size. The Czochralski technique has been optimized for various bronze solid solution crystals such as Sr1−xBaxNb2O6 (SBN), Ba2−xSrxK1−yNayNb5O15 (BSKNN) and Sr2−xCaxNaNb5O15 (SCNN) with properties specifically tailored for electro-optic, pyroelectnc and more recently for photorefractive applications. SBN solid solution crystals are found to be easiest to grow in series up to 1′′ in diameter with excellent transverse electro-optic effects; whereas BSKNN crystals, which exhibit excellent longitudinal electro-optic effects are more difficult to grow in large sizes and optical quality. BSKNN crystals exhibit ferroelectric and optical properties similar to perovskite BaTiO3 and are found to be particularly useful for photorefractive applications. The SCNN solid solution crystals are orthorhombic at room temperature and are much more difficult to grow; currently, crysta...

Tungsten bronze Sr1-xBaxNb2O6: A case history of versatility

Abstract We review the chronological development of ferroelectric tungsten bronze Sr1-x Ba x Nb2O6 (SBN) single crystals in terms of crystal growth and applications ranging from pyroelectric to surface acoustic wave (SAW) to nonlinear optics, with specific emphasis on the compositions SBN:60, SBN:75 and SBN:50. In addition to a number of bulk crystal applications, these crystals are also now being used as substrates for the growth of various lattice-matched thin films, including ferroelectric and superconducting oxide materials.

Development And Modification Of Photorefractive Properties In The Tungsten Bronze Family Crystals

The Sr1-xBaxNb2O6 (SBN) and Ba2-xSrxK1-yNayNb5O15 (BSKNN) tungsten bronze solid-solution systems are shown to be promising photo-refractive materials. Because of the versatility of the bronze structure, both the response time and spectral response can be controlled by altering the type of dopant and its crystallographic site preference. This paper reviews the current status of the tungsten bronze crystals SBN and BSKNN for photorefractive applications in terms of their growth, electro-optic character, and the role of cerium dopants. Ferroelectric morphotropic phase boundary (MPB) bronze materials are also discussed as potentially important for future development.

Growth and applications of ferroelectric tungsten bronze family crystals

Single crystal growth of several ferroelectric tungsten bronze compositions such as Sr1-x Bax Nb2O6 (SBN), Sr2KNb5O15 (SKN), Ba2xSrxK1-yNayNb5O15 (BSKNN) and K3Li2Nb5O15 (KLN), has been studied in detail. The results show that the smaller unit cell bronzes, e.g., SBN and SKN, have a cylindrical growth habit with 24 well-defined facets while the larger unit cell bronzes, e.g., BSKNN and KLN, grow in a square shape with 4 well-defined facets. Significant changes in the dielectric and piezoelectric properties can be obtained with changes in composition, and significant differences in the physical properties, e.g., k33, d33 and d15, can be observed between the small and large unit cell bronzes.

Glass-Like Behaviour of Sr1−xBaxNb2O6 (SBN) Single Crystals Demonstrated by Heat Capacity Measurements

Glass-Like Behaviour of Sr1−xBaxNb2O6 (SBN) Single Crystals Demonstrated by Heat Capacity Measurements

Optical radiation damage of SBN materials and pyroelectric detectors at 10.6 μm

Thermal damage of Sr1−xBaxNb2O6 (SBN) crystals and infrared pyroelectric detectors due to 10.6−μm CO2 laser radiation was investigated. Permanent damage in the form of cracking or charring was observed depending on the irradiation conditions. Threshold values of energy density for cracking and charring were determined for SBN crystals of typical detector dimensions as a function of irradiation time. These damage thresholds of SBN are about an order of magnitude larger than the corresponding thresholds previously measured in triglycine sulfate. The energy density thresholds for cracking are independent of irradiation time τ for short times and increase as τ for long times. The time dependence of the cracking thresholds under the particular experimental conditions investigated is described by the empirical equation E0=[3+2400τ/tan−1(82τ)1/2] J/cm2. The charring thresholds are given by the empirical equation E0= (8+470τ1/2) J/cm2. The theoretical models presented for thermally induced damage are in satisfactory agreement with the experimental data. The damage thresholds of commerical SBN pyroelectric detectors were measured and found to correspond to those for SBN crystals.

Investigation of the Electrical Properties of Sr1−xBaxNb2O6 with Special Reference to Pyroelectric Detection

The dielectric constants, electrical conductivity, specific heat, and pyroelectric coefficients of ferro-electric Sr1−xBaxNb2O6 (SBN) are investigated as a function of temperature in the range 10°–500°K, and as a function of the Sr/Ba composition of the material. A simple technique for measuring absolute pyroelectric coefficients and spontaneous polarizations of ferroelectrics is described. The electric field and frequency dependence of the dielectric properties are also investigated. The theory of pyroelectric detection is discussed from a materials point of view, and the experimental data are considered in terms of the usefulness of SBN as a pyroelectric detector of electromagnetic radiation.