Transport and Electromechanical Properties of Ca 3 TaGa 3 Si 2 O 14 Piezoelectric Crystals at Extreme Temperatures
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.16
Transport and Electromechanical Properties of Ca3TaGa3Si2O14 Piezoelectric Crystals at Extreme Temperatures Yuriy Suhak1, Ward L. Johnson2, Andrei Sotnikov3, Hagen Schmidt3, Holger Fritze1 1
Clausthal University of Technology, Am Stollen 19B, Goslar, 38640, Germany.
2
National Institute of Standards and Technology, 325 Broadway St., Boulder, CO 80305, U.S.A.
3
Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, Dresden, 01069, Germany.
ABSTRACT
Transport mechanisms in structurally ordered piezoelectric Ca3TaGa3Si2O14 (CTGS) single crystals are studied in the temperature range of 1000-1300 °C by application of the isotope 18 O as a tracer and subsequent analysis of diffusion profiles of this isotope using secondary ion mass spectrometry (SIMS). Determined oxygen self-diffusion coefficients enable calculation of oxygen ion contribution to the total conductivity, which is shown to be small. Since very low contributions of the cations have to be expected, the total conductivity must be dominated by electron transport. Ion and electron conductivities are governed by different mechanisms with activation energies (1.9±0.1) eV and (1.2±0.07) eV, respectively. Further, the electromechanical losses are studied as a function of temperature by means of impedance spectroscopy on samples with electrodes and a contactless tone-burst excitation technique. At temperatures above 650 °C the conductivity-related losses are dominant. Finally, the operation of CTGS resonators is demonstrated at cryogenic temperatures and materials piezoelectric strain constants are determined from 4.2 K to room temperature.
INTRODUCTION Piezoelectric components have broad potential for applications at extreme temperatures. For example, the mass sensitivity of resonant sensors at high temperatures
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offers advantages for sensing gases or soot particles and thus supports the increase in efficiency and environmental compatibility of energy conversion processes [1]. However, application of piezoelectric materials at elevated temperatures faces many challenges, including thermal instability of the dielectric, piezoelectric and electromechanical properties, increased damping, and chemical instability (decomposition, oxidation). Additionally, the applicability of these materials for low temperature operation properties is of particular importance. Piezoelectric crystals of the langasite (LGS, La3Ga5SiO14) family are recognized as excellent candidates for low and high temperature applications as these crystals can be piezoelectrically excited from cryogenic temperatures to 1300 °C or more. They have been shown to have a high degree of thermal stability [2,3], which enables their application as gravimetric senso
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