Neutron Diffraction Investigation of Langanite Crystals
- PDF / 393,291 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 45 Downloads / 231 Views
URAL STUDIES Dedicated to the memory of B.N. Grechushnikov
Neutron Diffraction Investigation of Langanite Crystals G. M. Kuz’michevaa, I. A. Kaurovaa, V. B. Rybakovb, A. B. Dubovskyc, A. Coussond, and O. Zaharkoe a
Lomonosov State Academy of Fine Chemical Technology, Moscow, 119571 Russia email: [email protected] b Moscow State University, Moscow, 119992 Russia c Moscow State Open University, Aleksandrov, Moscow oblast, 601655 Russia d Laboratoire Leon Brillouin, Cea/Saclay, 91191 GifsurYvette Cedex, France e Laboratory for Neutron Scattering, ETZ Zurich & Paul Scherrer Institute, CH 5332 Villigen PSI, Switzerland Received July 7, 2010
Abstract—The upper and lower parts of a single crystal with a nominal composition La3Ga 5.5Nb0.5O14 grown by the Czochralski method (Ir crucible, 99%Ar + 1%O 2, 〈0001〉 growth direction) have been studied by neutron diffraction for the first time. The compositions of the upper and lower parts are found to differ ((La2.935(2)䊐0.065)(Ga0.450Nb0.550(3))Ga3(Ga1.965(4)䊐0.035)(O13.90(1)䊐0.10) and (La2.940(1)䊐0.060)(Ga0.590Nb0.410(2))Ga5(O13.82(1)䊐0.18), respectively), and microtwin formation was observed in the upper part, with two unit cells related by the translation 1/2Z. Based on a comparison of the refined crystal composition and optical transmission spectra, the absorption bands at 30 000, 24 500, and 20 500 cm–1 were ''', 3VOii) x , oxygen vacancies, and color centers, respectively. A relationship assigned to divacancies (2VLa between the crystal color and oxygen content is established. DOI: 10.1134/S1063774510060258
INTRODUCTION Lanthanum–gallium niobate La3Ga5.5Nb0.5O14 (langanite (LGN), La3(Ga0.5Nb0.5)Ga5O14, La3(Ga0.5Nb0.5)(1)Ga3(2)Ga2(3)O14) crystals belong to the langasite family (sp. gr. P321, Z = 1). In the crystal structure of lanthanum–gallium niobate La3(Ga0.5Nb0.5)(1)Ga3(2)Ga2(3)O14, which was first described in [1], lanthanum atoms are in the dodeca hedral position, while gallium atoms occupy the octa hedral (Ga,Nb)(1) position (occupied by half by nio bium atoms), the tetrahedral Ga(2) position, and the trigonal pyramidal Ga(3) position. These crystals are widely used in surface and bulk acoustic wave filters, in mobile and cellular communi cation systems, and in temperature and pressure sen sors (based on the direct piezoelectric effect). The great demand for LGN crystals is explained by the unique combination of their properties: the absence of temperature phase transitions, high permittivity (ε11/ε0 = 20.7 ± 0.5 and ε33/ε0 = 79.0 ± 1.0), and large piezoelectric moduli (d11 = 7.41 ± 0.2 C/N and d14 = ⎯6.16 ± 0.5 C/N) [2] when compared with langasite and langatate crystals.
All langanite crystals were grown by the Czochral ski method and had different colors: from yellow to dark red [3–11] (Table 1). In contrast to La3Ga5SiO14 (LGS) and La3Ga5.5Ta0.5O14 (LGT) crystals, colorless LGN specimens were absent. The nature of the LGN color is unknown, although in [10] the dark red color of the LGN crystals grown in a Pt–Rh crucible was related to possible rhodium
Data Loading...
