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Moscow, Russia

Richter D.,Clausthal University of Technology | Sakharov S.,Fomos Materials | Forsen E.,Danish Technological Institute DTI | Mayer E.,Albert Ludwigs University of Freiburg | And 2 more authors.
Procedia Engineering | Year: 2011

Wireless surface acoustic wave devices based on langasite allow sensor operation in high-temperature environments. While langasite shows piezoelectric behavior up to temperatures close to its melting point of 1470 °C, the stability of thin film electrodes for excitation of acoustic waves limits the application temperature. Different metal and ceramic based thin films are tested regarding their applicability as electrode materials for wireless surface acoustic wave devices at temperatures above 600 °C. The devices should withstand temperatures of 800 °C for at least several hours. The high-temperature stability of platinum, platinum-rhodium, iridium as well as lanthanum strontium manganite (LSM) based electrodes is characterized using electrical measurements, x-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) imaging. SAW devices with Ti/Pt thin film electrodes are operated up to temperatures of 800 °C. LSM/Pt films exhibit a good stability up to temperatures of 800 °C. Above 600 °C its resistance is comparable to platinum films. © 2011 Published by Elsevier Ltd. Source

Buzanov O.A.,Fomos Materials | Kozlova N.S.,National University of Science and Technology "MISIS" | Zabelina E.V.,National University of Science and Technology "MISIS" | Kozlova A.P.,National University of Science and Technology "MISIS" | Siminel N.A.,National University of Science and Technology "MISIS"
Russian Microelectronics | Year: 2011

The optical transmission spectra and electrical properties of langasite (La 3Ga 5SiO 14) and lan- gatate (La 3Ta 0.5Ga 5.5O 14) single crystals are studied experimentally in relation to the oxygen concentration in an argon-oxygen atmosphere of growth. The variation of langatate conductivity with temperature under a constant electric field is examined over the range 20 to 500°C. Its dependence on current-carrying material is investigated for an Ir, Au/Ti, or Ag/Cr coating. © Pleiades Publishing, Ltd., 2011. Source

Roshchupkin D.,Russian Academy of Sciences | Plotitcyna O.,Russian Academy of Sciences | Irzhak D.,Russian Academy of Sciences | Emelin E.,Russian Academy of Sciences | And 3 more authors.
IEEE International Ultrasonics Symposium, IUS | Year: 2013

A five-component crystal of lanthanum-gallium silicate group La 3Ga5.3Ta0.5Al0.2O14 (LGTA) was grown by the Czochralski method. The LGTA crystal possesses unique thermal properties and substitution of Al for Ga in the unit cell leads to a substantial increase of electrical resistance at high temperatures. The unit cell parameters of LGTA were determined by powder diffraction. X-ray topography was used to study the crystal structure perfection: the growth banding normal to the growth axis were visualized. Excitation and propagation of surface acoustic waves (SAW) were studied by the double crystal X-ray diffraction at the BESSY II synchrotron radiation source. The analysis of the diffraction spectra of acoustically modulated crystals permitted the determination of the velocity of acoustic wave propagation and the power flow angles in different acoustic cuts of the LGTA crystal. © 2013 IEEE. Source

Kozlova N.S.,National University of Science and Technology "MISIS" | Busanov O.A.,Fomos Materials | Zabelina E.V.,National University of Science and Technology "MISIS" | Kozlova A.P.,National University of Science and Technology "MISIS" | Bykova M.B.,National University of Science and Technology "MISIS"
Crystallography Reports | Year: 2016

The hypotheses about the nature of color centers in langasite family crystals that are discussed in the literature are analyzed. Optical transmission spectra in the wavelength range of 200–800 nm are recorded for langasite and langatate crystals grown in atmospheres of argon and argon mixed with oxygen in different concentrations, both in the initial state and after isothermal annealings at 1000°C in nitrogen, in air, or in vacuum. Dichroism is observed in langasite and langatate crystals, and spectral dependences of the degrees of dichroism are plotted. © 2016, Pleiades Publishing, Inc. Source

Spassky D.A.,University of Tartu | Spassky D.A.,Moscow State University | Brik M.G.,University of Tartu | Brik M.G.,Chongqing University of Posts and Telecommunications | And 6 more authors.
Journal of Luminescence | Year: 2016

Luminescent, optical and electronic properties of La3Ta0.5Ga5.5O14 single crystals grown in different atmospheres are presented. The absorption bands at 255, 290, 350 and 480 nm were detected; the intensity of bands increases with the concentration of oxygen in the growth atmosphere. It is shown that the shift of the fundamental absorption edge with the temperature obeys Urbach rule. The corresponding fitting allowed to estimate the slope coefficient σ=0.35, which implies self-trapping of excitons in La3Ta0.5Ga5.5O14. Calculations of the band structure, partial densities of states and reflectivity spectra were performed. The bandgap of La3Ta0.5Ga5.5O14 was determined as Eg=5.6 eV. The luminescence properties under UV, VUV and X-ray excitation were studied. Intrinsic emission band at 440-450 nm is attributed to the excitons self-trapped at TaO6 molecular complexes. Extrinsic emission bands at 410, 440 and 550 nm are attributed to the emission of excitons trapped by antisite defects, F-centers and oxygen deficient oxyanionic complexes. © 2016 Elsevier B.V. All rights reserved. Source

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