Tungsten Bronze-type Structure Research Articles

Crystal Structure of the Ba4CeNb10O30 Reduced Niobate with a TTB-Type Structure

The structure of the cation-deficient Ba4.0(1)Ce0.98(3)Nb10O30 barium cerium reduced niobate with a tetragonal tungsten bronze (TTB) type structure was refined from X-ray single crystal data (tetragonal, a=12.508(2) Å, c=3.9328(4) Å, S. G. P4/mbm, Z=1, R=0.019, Rw=0.023). It was found that rare earth substitution for Ba is accompanied by formation of vacancies in A sites. Vacancies were preferably formed in the A(1) cavities in the structure.

Investigations of the “tungsten–bronze”-type (Ba1–αSrα)6–xLa8+2x/3Ti18O54 (0⩽x⩽3) solid solutions

Abstract A study of the Ba/La/Sr ordering in the (Ba 1– α Sr α ) 6– x La 8+2 x /3 Ti 18 O 54 (0⩽ x ⩽3) solid solutions was carried out by X-ray diffractometry and dielectric measurements. The maximum of substitution is obtained for x =0 and α =0.33, i.e. for Ba 4 Sr 2 La 8 Ti 18 O 54 composition. The crystal structure is closely related to the tungsten–bronze-type structure with 3×3 octahedral units of perovskite columns (orthorhombic symmetry, s.g. Pnma, a ≈22.4 A, b ≈7.7 A, c ≈12.2 A). The A2 sites (pentagonal channels) and the A1 sites (rhombic channels within the perovskite-like columns) are occupied by Ba and La respectively. Sr always occupies the particular rhombic A1′ sites located at the junction of two perovskite-like columns which can also accept excess Ba and La. The A2 and A1′ sites may be cation deficient. The structure of Ba 4 (Sr 2 La 8 )Ti 18 O 54 with structural composition A2 4 (A1′ 2 A1 8 )Ti 18 O 54 , is fully ordered. The thermal behaviour of the permittivity and, for some compositions, the occurrence of a strong dispersion in a wide temperature range, would likely be connected both to a cationic disorder (Sr, Ba and/or La) and vacancies in the rhombic A1′ sites.

Cu1.1Ta11O26.2F4.8: a Tetragonal-Tungsten–Bronze-related structure with square planar coordination of copper

The crystal structure of Cu1.1Ta11O26.2F4.8 was determined by single crystal X-ray diffraction in combination with HRTEM. The unit cell is orthorhombic with a=17.7128(8), b=17.1832(7) and c=3.9412(1) Å (X-ray powder data), space group Cmmm, and R=0.0327 for 594 independent reflections. The structure is related to the tetragonal tungsten bronze type structure of KNb6O15F which has 50% of the five-sided tunnels transformed into pentagonal bipyramids. The composition of the framework is CuTa11(O,F)31, with Cu in square planar coordination linking to two pentagonal TaX7 bipyramids. The additional Cu atoms are located in the five-sided tunnels. The composition given to the compound was established by the X-ray refinement. The HRTEM study showed planar faults, twin and grain boundaries in the crystals. EDS-analysis indicated a somewhat higher Cu-content.

Growth and Dielectric and Pyroelectric Properties of Magnesium-Doped Potassium Lithium Niobate Single Crystal

Magnesium doped potassium lithium niobate single crystal (K 3 Li 2 Nb 5 O 15 :Mg, denoted as KLN:Mg) has been grown by modified Czochralski technique. It has tetragonal tungsten bronze type structure. At room temperature, the point group is 4 mm with the lattice constants a = 1.262 nm and c = 0.398 nm. Dielectric, pyroelectric properties of a and c plates were studied in the temperature range from 10 to 700 K. The frequency dependence of dielectric constant in the frequency range 5 × 10 2 to 5 × 10 8 Hz was measured. Results reveal a paraelectric-ferroelectric phase transition near 623 K and a ferroelectric-ferroelectric phase transition near 80 K.

Preparation and characterization of sol–gel derived potassium lithium niobate films

Potassium lithium niobate K 3Li 2Nb 5O 15 (KLN) films have been deposited on SiO 2/Si by sol–gel method using the ethoxides of K, Li, and Nb as starting materials. XRD and Raman studies have revealed that tetragonal tungsten–bronze-type structure could be achieved if the films were annealed at 700°C. The film had smooth and crack-free surface. Optical guiding measurement indicated that the film has a refractive index of 2.1443 at 632.8 nm.

Effect of Yb 3+ content on purity and crystal growth of Ba 2NaNb 5O 15

Growth by the micro-pulling-down technique (μ-PD) of homogeneous and crack-free fiber single crystals with composition Ba 2Na 1− x Yb x Nb 5O 15 ( 0<x<0.08) is reported. The effect of Yb 3+ addition to barium sodium niobate (BNN, x=0), having the tungsten bronze-type structure, was examined by room temperature X-ray powder diffraction and differential thermal analysis coupled to thermogravimetry. In the region of the monophased field the structure is tetragonal from x=0.02 to 0.16. Volume change is mainly by variation of the a-axis length. Addition of Yb 3+ to BNN could be effective for the production of high optical quality, crack-free, bulk crystals by the Czochralski technique.

Raman and Infrared Spectra of Nd-Doped Barium Sodium Niobate Crystals

Neodymium-modified barium sodium niobate (Ba2Na)1-xNdxNb5O15(BNN:Nd), with x = 0.025, crystallizes with a filled tungsten bronze (TB) type structure in the tetragonal system, conforming to the space group P4bm and Z = 2. The lattice constants are a = 1.2446(1) and c = 0.3991(1) nm at room temperature. Tc = 537 +- 2 °C. The experiments show that the Nd-ions effectively improve crystal structural quality. The lattice vibrational spectrum, studied by Raman and infrared reflectivity spectroscopy, shows that the crystal microscopic structure and lattice dynamics, thereby the microstrain and microstress, are very stable in a temperature range from 22 to approaching 500 °C.

Tungsten Bronze-Type Solid Solutions Ba6−3xSm8+2xTi18O54(x=0.3, 0.5, 0.67, 0.71) with Superstructure

Structural parameters of tungsten bronze-type compounds Ba6−3xSm8+2xTi18O54(x=0.3, 0.5, 0.67, and 0.71) were refined in a space groupPbnmby the Rietveld method using high-resolution synchrotron radiation powder diffraction data. All the specimens crystallized in the orthorhombic system with a superstructure having the doubledcaxis of the reported orthorhombic tungsten bronze-type structure. Unit-cell parameters (in Å) area=12.1715(5),b=22.3772(3),c=7.67523(9) forx=0.3,a=12.1568(1),b=22.3253(2),c=7.66301(7) forx=0.5,a=12.1472(1),b=22.2972(2),c=7.65338(6) forx=0.67, anda=12.1452(1),b=22.3029(2),c=7.65007(6) forx=0.71, andZ=2. The use of two wavelengths allowed the determination of cation and vacancy distributions over two pentagonal and five tetragonal tunnels in the structure. In the compounds withx=0.3 and 0.5, pentagonal tunnel sites were fully occupied by Ba, and the remaining Ba partially substituted Sm at two of five tetragonal tunnel sites. No evidence was found for the substitution of Sm for Ba at the pentagonal sites, and thus vacancies were formed at the pentagonal sites forx=0.71. An amplitude of periodic modulation along thecaxis, which caused superstructure, was increased with increasingxin the compositional range examined. A relationship between observed and calculated intensities of superstructure reflections suggests the presence of local lattice distortion, which takes its minimum atx=0.67.

Epitaxial Growth of Sr0.3Ba0.7Nb2O6 Thin Films Prepared by Sol-Gel Process

AbstructWe succeeded in the preparation of strontium-barium niobate (Sr0.3Ba0.7Nb2O6 : SBN30)that have a tetragonal tungsten bronze type structure thin films on SrTiO3 (100), STO, or La doped SrTiO3 (100), LSTO, single crystal substrates by a spin coating process. LSTO substrate can be used for electrode. A homogeneous coating solution was prepared with Sr and Ba acetates and Nb(OEt)5 as raw materials, and acetic acid and diethylene glycol monomethyl ether as solvents. The coating thin films were sintered at temperature from 700 to 1000°C for 10 min in air. It was confirmed that the thin films on STO substrate sintered above 700°C were in the epitaxial growth because the 16 diffraction spots were observed on the pole figure using (121) reflection. The &lt;130&gt; and &lt;310&gt; direction of the thin film on STO were oriented with the c-axis in parallel to the substrate surface. However, the diffraction spots of thin film on LSTO substrate sintered at 700°C were corresponds to the expected pattern for (110).

Vibrational Spectra of a K0.30Na0.10Sr0.48Ba0.32Nb0.2O0.6 Single Crystal Studied by Raman and Infrared Reflectivity Spectroscopy

Potassium and sodium (K/Na)-modified strontium barium niobate (SBN) of the idealized formula (K x Na 1 x)0.4(SryBa1-y)0.8Nb2O6 (KNSBN). with x = 0.75. y = 0.60, a Curie temperature of (200 ± 2) C, and a laser damage threshold larger than 600 MW/cm 2 at 4 pps, crystallizes with a filled tungsten bronze (TB) type structure in the tetragonal system. The lattice constants are a = (1.2488 ± 0.0001) and c = (0.3955 ± 0.0001) nm at room temperature. There are five formulas per unit cell. The lattice vibrational spectrum of KNSBN, which arises mainly from internal vibrations of the Nb-O octahedra and studied by Raman and infrared reflectivity spectroscopy, typifies a tetragonal TB type structure. The results shown in Figs. 1 to 6 are typical for vibrational spectra, The NbO 6 clusters form the rigid Nb-O octahedra, and the rigidity of the lattice is mainl ascribed to five vibrations, as a non-degenerate symmetric Nb-O stretching vibration (v 1 ), a doubly degenerate symmetric O-Nb-O stretching vibration (v 2 ). >a >triply |>|>>degenerate >antisymmetric >Nb-O>stretching >vibration >(v 3 ). a triply degenerate antisymmetric O-Nb-O bending vibration (v 4 ), and a triply degenerate symmetric O-Nb-O bending vibration (v 5 ). The KNSBN crystals as well as the SRN crystals show good structural quality and mechanical properties, and large linear electro-optical and pyroelectric coefficients. Besides, the nonlinear optical property of KNSBN is better than that of SBN,

Structural and magnetic properties of the mixed fluoridesKMn1−xCoxFeF6

Magnetic substitution in ${\mathrm{KMnFeF}}_{6}$ with a tetragonal tungsten bronze-type structure has been performed. Structural characterization of the series of compounds has been carried out from x-ray powder patterns. It is seen that the lattice parameter $a$ decreases linearly with the increase in $x,$ whereas the parameter $c$ remains almost unaltered up to $x$=0.5 and then increases continuously till $x=1$. The unit-cell volume decreases in the range $0&lt;~x&lt;~0.6$ and then increases continuously in the range $0.6&lt;~x&lt;~1$. The bulk magnetic properties have been investigated in high magnetic fields as a function of cobalt concentration and temperature. These results show that the ferrimagnetic transition temperature ${T}_{\mathrm{N}}$ in ${\mathrm{KMnFeF}}_{6}$ decreases linearly with the increase in ${\mathrm{Co}}^{2+}$ concentration $(x)$ at the ${\mathrm{Mn}}^{2+}$ sites. However, the magnitude of the Curie-Weiss temperature which indicates the strength of the exchange interaction does not follow this behavior throughout the whole concentration range. The results suggest that the extent of magnetic frustration in the triangular cycles of the magnetic ions increases above $x=0.6$. Furthermore, the nature of ${\ensuremath{\chi}}_{\mathrm{M}}^{\ensuremath{-}1}$ vs $T$ curves clearly shows the coexistence of antiferromagnetic (AF) and ferromagnetic (F) short-range correlations above ${T}_{\mathrm{N}}$ in the samples with the concentration of the ${\mathrm{Co}}^{2+}$ ions lying in the range with $0.6&lt;~x&lt;1$. The $M\ensuremath{-}H$ curves below ${T}_{\mathrm{N}}$ in all the samples are analyzed by using the law of approach to saturation. These results show that the saturation magnetization decreases continuously with the increase in $x$. Furthermore, these results also indicate the existence of noncollinear magnetic structure in the mixed systems, below the magnetic ordering temperature.

Energy state of Nd3+ doped in barium sodium niobate crystals

Nd-doped barium sodium niobate (Ba2Na)1−xNdxNb5O15 (BNN:Nd), with x=0.025 and a Curie temperature of 537±2 °C, crystallizes with a filled tungsten bronze-type structure in the tetragonal system. The lattice constants are a=b=1.2446(1) and c=0.3991(1) nm at room temperature. There are two formulas per unit cell. The five typical deep energy levels, formed by the Nd3+ ions doped in the A1 and A2 sites, are 2.36, 2.12, 1.68, 1.55, and 1.43 eV. Investigating the green and yellow second-harmonic generation shows that the BNN:Nd crystal can be expected as a useful material for the green, especially for the yellow laser radiation at room temperature.

Microwave Dielectric Properties of Ba 6- 3xSm 8+ 2xTi 18O 54 Solid Solutions with Sr Substituted for Ba

We have evaluated the effect of substituting Sr cations for Ba cations in solid solutions with a tungsten bronze-type structure used in microwave dielectric resonators. Instead of Ba6-3xSm8+2xTi18O54 solid solutions formula, the structure formula is presented as (Sm8+2xBa2-3x)(Ba4)Ti18O54 for the range of 0≤x≤2/3 and (Sm9.33+2(x-2/3))(Ba4-3(x-2/3))Ti18O54 for 2/3 ≤x ≤1. The quality factor Q \\cdotpf has been improved based on the substitution of 0.2 Sr ions for 0.2 Ba ions in perovskite blocks in (Sm9.2Ba0.2)(Ba4)Ti18O54 where x=0.6. This composition has the best dielectric quality in the solid solution series, because the substitution reduced the strain caused by the Ba ions. The relationship between the lattice parameters and the microwave dielectric properties is also presented.

Nonlinear single-crystal fibers of undoped or Nd 3+-doped niobates: growth by LHPG, spectroscopy and second harmonic generation

The renewal of second order non-linear crystals is very strong in laser materials optics. We are involved in the search of new systems based upon the highly non-linear niobate crystal family. Among these crystals, Ba 2NaNb 5O 15 (BNN) and K 3Li 2− x Nb 5+ x O 15+2 x (KLN, 0.15 < x < 0.5) with a tungsten bronze-type structure are very efficient materials for the obtention of, respectively, green and blue laser light by frequency doubling or by self-frequency doubling after doping by Nd 3+ ions. Unfortunately, BNN and KLN are difficult to grow by conventional techniques such as Czochralski without cracks caused by a strong lattice change occurring during cooling of the crystals. In addition, microtwins in BNN crystals and compositional inhomogeneities in KLN ones are often encountered. The obtention of good quality and crackless BNN and KLN single crystals doped with different amounts of Nd 2O 3 is reported. The crystals were grown by the laser heated pedestal growth (LHPG) technique. This method allowed to obtain good quality and homogeneous crystals of BNN and KLN overcoming the problems encountered with other growth techniques. More particularly, for BNN crystals, a structural transition between orthorhombic (space group: Pba2) and tetragonal symmetry (space group: P4bm) was found to occur for a Nd 3+ amount between 2 and 3 at% avoiding the microtwinning which disturbs the optical properties of the crystals. Low temperature spectroscopy revealed that Nd 3+ ions substitute both Ba 2+ and Na + ions in the pentagonal and square sites of the tungsten bronze-type structure of BNN whereas they substitute only K + ions in the pentagonal sites of that of KLN. Non-critical phase matching at room temperature was also investigated for both materials.

Dielectric and ferroelectric properties of Ba3NaLaNb10O30 crystal

Ba3NaLaNb10O30 crystal has been grown by the Czochralski technique. It has a tetragonal tungsten bronze type structure. At room temperature, the space group is P4/mbm with the lattice constants a=b=1.247nm, c=0.395nm. Dielectric, pyroelectric and ferroelectric measurements revealed a paraelectric-ferroelectric phase transition near 280K which is highly diffused with the diffuseness index γ=1.8. The low temperature ferroelectric phase belongs to point group 4mm.

Structure and properties of Ba6 − xLnxNb10O30, Ln = La, Ce and Nd compounds

Ba 6 − x Ln x Nb 10 O 30 compounds, Ln = La, Ce and Nd, with a tetragonal tungsten bronze-type structure have been synthesized and were characterized by X-ray powder diffraction and EDS analysis. The homogeneity regions of the obtained compounds were found to be 0 ≤ x ≤ 2 for La, and 0 ≤ x ≤ 1.5 for Ce and Nd. The crystal structures of Ba 5LaNb 10O 30 and Ba 4La 2Nb 10O 30 were refined using X-ray powder diffraction data. Refinement indicated the presence of vacancies in the Ba La positions. This observation was supported by oxidation studies of the La-substituted compounds. The temperature dependence of the normalized resistivity of the compounds showed a nonmetallic behavior. The increase in the R R 273 ratio with decreasing temperature is less distinct for the phases with the higher concentration of rare-earth cation.

Preparation and Crystal Structure of K2YNb5O15−δ

Single crystals of new reduced potassium yttrium niobate, K2YNb5O15−δwere prepared in a H2atmosphere at 1200°C. Potassium yttrium niobate crystallizes in the orthorhombic space groupCmmmwitha= 10.316(1),b= 15.257(1), andc= 3.914(1) Å,Z= 2, and the finalRfactors areR= 0.046 andRw= 0.047 for 1077 unique reflections. The crystal structure is built up by corner-sharing of NbO6octahedra and the three-dimensional framework formed by the Nb5O15units is same as that of the NaNb6O15F-type structure. The Y3+ion is located in a distorted perovskite-like cavity and the K+ion is in a pentagonal tunnel. Reduced potassium yttrium niobate, K2YNb5O15−δ, is oxidized without deterioration in crystallinity at about 450°C, and the oxidized phase, K2YNb5O15, transforms to the tetragonal tungsten bronze-type structure at 1150°C.

ChemInform Abstract: Novel Compounds ABnW3‐nO9 with a Hexagonal Tungsten Bronze Type Structure

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Frequency dependence of the complex dielectric permittivity of ferroelectric relaxors.

Ferroelectric relaxors belong to a class of materials which possess a local polarization until very high temperature and exhibit a wide frequency range dielectric dispersion around and below ${\mathit{T}}_{\mathrm{max}}$, the temperature of the dielectric maximum. By supposing an exponential-type distribution for the volume of the polar microdomains, we have modeled the dielectric behavior of ferroelectric relaxors. From this model, the low-frequency permittivity appears to follow a power law of ${\mathrm{\ensuremath{\omega}}}^{\mathit{n}}$ type with the exponent n inversely proportional to the width of the size distribution. By analyzing experimental data in two typical ferroelectric relaxors with perovskite-type and tungsten bronze-type structures, the temperature dependence of the exponent has been determined. It comes out that the size of nanodomains begins to strongly increase upon cooling through ${\mathit{T}}_{\mathrm{max}}$, giving rise to a peak of the permittivity which does not result from a true phase transition. The peak observed for the imaginary part of the permittivity corresponds to the temperature at which the dispersion of the real part attains maximum. The interval between the largest and smallest cluster sizes has been estimated. It is found that only a small variation in polar cluster size can lead to a wide dielectric dispersion covering several frequency decades.

K 3(Nb 3Ti 2)O 11F 4: un nouvel oxyfluorure de type ‘bronzes oxygénés de tungstène quadratiques’

A new oxyfluoride K 3(Nb 3Ti 2)O 11F 4 with a tetragonal tungsten bronze type structure has been prepared and characterized in the KNbO 3TiOF 2 system. The room temperature space group ( P4/ mbm) has been determined on a single crystal. The unit cell parameters are a = 12.453 Å and c = 3.972 Å.