W. K. Cory

Progress in photorefractive tungsten bronze crystals

We review the current status of the photorefractive tungsten bronze family crystals in terms of their growth problems and applications, with special emphasis on the current results for the Sr1−xBaxNb2O6 solid-solution system. Ferroelectric morphotropic phase-boundary materials are discussed as an appropriate goal for future development.

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.

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.

Growth and optical properties of ferroelectric tungsten bronze crystals

Abstract The state of the art in the Czochralski growth of various optical-quality ferroelectric tungsten bronze single crystals is reviewed with respect to crystal structure, phase transitions and cationic make-up. Based on our growth of over 25 single crystal bronzes, we have classified these bronzes into four categories having distinctly different ferroelectric and optical characteristics. With the use of this classification, optimal bronzes can be chosen for specific electro-optic and photorefractive applications.

Ferroelectric tungsten bronze crystals and their photorefractive applications

Abstract The photorefractive properties of tungsten bronze ferroelectric crystals are reviewed with respect to host character and dopant. A classification into four groups is proposed for tungsten bronze materials based on their structural, ferroelectric and optical properties. The use of dopants is found to control the speed of response and coupling strength as well as spectral range. In particular, the availability of different crystallographic sites is shown to provide opportunities to separately adjust these properties. The best performance has been established for Ce3+ and Cr3+ doped SBN:60 crystals in the visible and IR regions, respectively.

Structural and dielectric properties of the phase Pb1−2xKxM3+xNb2O6, M = La or Bi

Abstract The Pb 1−2x K x M 3+ x Nb 2 O 6 , M = La or Bi, solid solutions have been prepared by solid state reaction and their structural and ferroelectric properties have been established. Complete crystalline solid solubility exists in both systems; in addition, three structurally related phases, namely, the ferroelectric orthorhombic and tetragonal tungsten bronze phases and the paraelectric tetragonal K. 5 La. 5 Nb 2 O 6 type phase, have been identified at room temperature. The composition ranges for three phases are 0.0 ≤ x ≤ 0.47, 0.48 ≤ x ≤ 0.85, 0.86 ≤ x ≤ 1.0, respectively. The ferroelectric phase transition temperature, T c , decreases with increasing concentration of K + and La 3+ or Bi 3+ in the orthorhombic tungsten bronze phase. A few compositions from each system exhibit excellent dielectric and piezoelectric characteristics, indicating that they could be future materials for piezoelectric and high frequency dielectric studies.