J. R. Oliver

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 availa...

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.

A thermodynamic phenomenology for ferroelectric tungsten bronze Sr0.6Ba0.4Nb2O6 (SBN:60)

The tetragonal tungsten bronze ferroelectrics in the strontium barium niobate system have been extensively studied over many years. As for many of the bronzes, a crude interpretation of the experimental data has been attempted in the past using the simple Landau‐Ginsburg‐Devonshire expansion of the Gibbs free energy as a Taylor series in powers of the polarization, lumping all the temperature dependence into the lowest order term. In this paper new measurements are presented for the temperature dependence of dielectric polarization, permittivity, and the E‐field dependence of the permittivity. It is shown that for a realistic fitting of the data, the Taylor expansion must be taken to at least the eighth power term, and that the coefficients of terms up to the sixth power must be taken as functions of temperature. Since the phenomenology describes equilibrium behavior, it is the total static polarizability that is being explored in this treatment. The nature of this temperature dependence strongly suggests...

Ferroelectric and structural properties of the tungsten bronze system K2Ln3+Nb5O15'Ln = La to Lu

The K2Ln3+Nb5O15 system has been investigated for a range of rare-earth ions (La3+ to Ho3+, Y3+). The temperature-dependent dielectric properties indicate that all but the La3+-containing materials have a tungsten bronze orthorhombic structure. Two phase transitions occur above room temperature, one paraelectric:ferroelectric and the other ferroelectric:ferroelastic. These transitions shift toward higher temperatures as the size of the rare-earth ion decreases. The lattice constant determination for this system indicates that the larger ions (La3+ to Gd3+) predominantly prefer the 12-fold coordinated site, Tb3+ to Ho3+ are distributed over both the 12- and 9-fold coordinated sites, and the smaller rare-earths (Er3+ to Lu3+) do not yield the tungsten bronze phase. Because of their low dielectric constants, these bronzes appear to be promising for some optical and pyroelectric detector applications.

Ferroelectric properties of the tungsten bronze M2+6M4+2Nb8O30 solid solution systems

Abstract Ferroelectric compositions based on the chemical formula M 2+ 6 M 4+ 2 Nb 8 O 30 , where M 2+ = Ba, Sr or Ca and M 4+ = Ti, Sn or Zr, have been synthesized and their characteristics have been compared with the results of earlier work. X-ray diffraction and dielectric constant measurements show that Ba 2+ analogs are tetragonal at room temperature as previously reported, with one phase transition, while the Sr 2+ analogs are orthorhombic with two phase transitions. The orthorhombicity becomes pronounced on the addition of Ca 2+ into the Sr 2+ site and two phase transitions, paraelectric:ferroelectric and ferroelectric:ferroelastic, have been established. The solid solution between Ba 6 Ti 2 Nb 8 O 30 and Sr 6 Ti 2 Nb 8 O 30 was studied and found to exhibit a morphotropic phase boundary near the Sr 2+ rich side. The structural and ferroelectric properties of these various bronzes are described with respect to the M 2+ and M 4+ cations.

Ferroelectric properties of tetragonal tungsten bronze single crystals

Ferroelectric tetragonal tungsten bronze (T.B.) family single crystals, e.g., SBN, BSKNN, KLN, SKN and PBN, have been grown and their ferroelectric properties have been investigated. The results show that the dielectric, piezoelectric, and electromechanical coupling coefficients are significantly large for these crystals; however, they are markedly different when going from smaller to bigger unit cell T.B. crystals. For example, e33 and d33 are substantially larger for the smaller unit cell T.B. crystals, e.g., SBN and SKN, while e11 and d15 are dominant for bigger unit cell bronzes. However, these differences do not have such a significant effect on the respective electro-optic and pyroelectric properties.

Growth and ferroelectric properties of tungsten bronze Sr2−xCaxNaNb5O15 single crystals

Abstract The growth of ferroelectric Sr 2−x Ca x NaNb 5 O 15 , x = 0.1 or 0.2, solid solution crystal by the Czochralski technique has been successful. The orthorhombic crystals exhibit large and almost equal transverse and longitudinal effects. Two phase transitions are observed, one paraelectric/ferroelectric (T c ≅ 270°C), and the other ferroelectric/ferroelastic (T c ∼ 95 dg C). The spontaneous polarization and pyroelectric coefficient are found to be large at 40 μcoul/cm 2 and 9.2 × 10 −2 μ coul/cm 2 -°C, respectively. The electro-optic coefficients, r 3 3 and r 5 1 , are estimated to be 1325 × 10 −12 m/V and 1100 × 10 −12 cm/V with optical figures of merit substantially larger than the current leading tetragonal bronze crystals such as SBN, BSKNN and SKN. Ce 3+ -doped SCNN crystals also show strong fanning in the visible, indicating potential utility in photorefractive applications.

Growth and properties of tungsten bronze K3Li2Nb5O15 single crystals

Tetragonal tungsten bronze K/sub 3/Li/sub 2/Nb/sub 5/O/sub 15/(KLN) single crystals have been grown up to 8 - 10 mm diameter and 40 - 50 mm long using the Czochralski technique. Crystal growth was studied in various orientations with growth along and being relatively easier than along . Crystals grown along have a square cross-section similar to other bigger unit cell bronzes such as Ba/sub 2-chi/Sr/sub chi/K/sub 1-chi/Na/sub yNb/5/sub O/15(BSKNN). Like BSKNN, KLN crystals show strong longitudinal effects, such as {epsilon}/sub 11/, {kappa}/sub 15/, d/sub 15/ and r/sub 51/, indicating suitability for Surface Acoutic Wave (SAW), electro-optic and photorefractive applications.

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.