Physico-Chemical nanomaterials science

Investigations of Ca3TaGa3Si2O14 crystals properties changes under high temperature reducing annealing
Yu. Suhak 1, D. Sugak 2,3,  I.I. Syvorotka 2,3, A. Luchechko 4, Ya. Zhydachevskyy 2,5, D. Wlodarczyk 5, A. Suchocki 5,6, U. Yakhnevych 2, 
S. Ubizskii 2, H. Fritze 1
1 Institute of Energy Research and Physical Technologies, Clausthal University of Technology, 19B Am Stollen, Goslar, Germany 
2 Lviv Polytechnic National University, 12 Bandera st., Lviv, Ukraine.
E-mail: dm_sugak@yahoo.com
3 Scientific Research Company “Electron-Carat”, 202 Stryjska st., Lviv, Ukraine
4 Ivan Franko National University of Lviv, 107 Tarnavskoho st., Lviv, Ukraine
5 Institute of Physics PAS, 32/46 Al. Lotnikуw, Warsaw, Poland
6 Institute of Physics, University of Bydgoszcz, 11 Weyssenhoffa st., Bydgoszcz, Poland

The Ca3TaGa3Si2O14 (CTGS) single crystals are one of the most promising piezoelectric materials used, in particular, for nanogram-resolution mass balances and gas sensing applications. An important feature of the CTGS is the temperature stability of materials characteristics up to at least Т = 1300 оС [1]. At the same time, the behavior of the physical and chemical properties of CTGS in aggressive environments at high temperatures is only partially investigated. The current work focuses on changes in the properties of CTGS with different crystallographic orientation (X-, Y-, Z-), annealed for 168 hours at T = 1000 оC, in a mixture of 99.5% Ar + 0.5% H2, which corresponds to the oxygen partial pressure pO2 =10-19 bar. The research was carried out using X-ray diffraction, Raman scattering, X-ray and photoluminescence spectrophotometry, optical microscopy after completion of annealing in comparison with as-grown crystals and impedance spectroscopy method directly during annealing. The changes in the crystal structure of the CTGS surface layers after annealing are observed. Structural changes are also confirmed by investigations of the Raman spectra. The anisotropy of the Raman scattering is observed. Luminescence of annealed crystals undergoes significant changes. The thickness of the layers, in which changes of properties occurred, are estimated. The electrical conductivity of CTGS was found to increase at low oxygen partial pressure (pO2 ≤ 10-15 bar). The nature of the observed changes is discussed.

1. Suhak Yu., Johnson W.L., Sotnikov A., Schmidt H., Fritze H. Transport and Electromechanical Properties of Ca3TaGa3Si2O14 Piezoelectric Crystals at Extreme Temperatures // MRS Advances.- 2019.- 4.-. P. 515-521.