Impedance spectroscopy study of lanthanum-gallium tantalate single crystals grown under different conditions

Abstract

The effect of the growth atmosphere and the type of deposited current conductive coatings on the impedance/admittance of La3Ta0.5Ga5.5O14 lanthanum-gallium tantalate has been revealed. The lanthanum-gallium tantalate single crystals have been grown in argon and argon with admixture of oxygen gas atmospheres. Current conductive coatings of iridium, gold with a titanium sublayer, and silver with a chromium sublayer have been deposited onto the single crystals. The tests have been carried out taking into account the polarity of the specimens. The temperature and frequency dependences of the admittance of lanthanum-gallium tantalate have been measured in an alternating electric field at frequencies in the 5 Hz to 500 kHz range and temperatures from 20 to 450 °C. The specimens with gold current conductive coating have the lowest admittance. Analysis of the temperature and frequency functions of the dielectric permeability has shown the absence of any frequency dependence in the entire test range. Equivalent electric circuits have been constructed. Graphic-analytic and numeric analysis of the equivalent electric circuits of the electrode/langatate/electrode cells has shown that the admittance of the metal/langatate/metal cells is controlled by the electrochemical processes at the electrode/electrolyte/electrode interface. The absolute values of the impedance components depend on the langatate growth conditions and the type of the electrodes. Our measurements suggest that the material of the current conductive coating has a greater effect on the absolute values of the measured parameters than the growth atmosphere.