Lanthanum – gallium tantalate crystal (La3Ta0.5Ga5.5O14, langatate, LGT) is well-known piezoelectric material, space group of symmetry - P321. Langatate crystals are grown by the Czochralski method in different atmospheres. The important advantages of langatate - the temperature stability of piezoelectric coefficients up to at least 600 °C and absence of phase transitions up to the melting point Tm=1510 °C. Due to these physical properties of LGT crystals is used in high-temperature devices on direct piezoelectric effect [1]. The production technology of these devices includes coating of the crystals’ surfaces with the thin layer of a metal conducting material (electrodes). In case of LGT electrodes are coated on polar cuts of the crystal, this leads to the degradation of crystals’ surfaces and decrease of devices’ lifetime even at room temperature.  With increase of temperature, these processes become more intense.   The investigation of electrophysical properties of the structure «electrode / LGT / electrode» is necessary to understand the processes of degradation. The objective of our work is investigation how the LGT growth atmosphere and materials of the conductive coating influence on the bulk and surface electrophysical properties of LGT crystals.   LGT crystals for this work were grown in (Ar), argon with oxygen (Ar+O2) and air. From these crystals we made samples in form of plates of polar cuts and covered their surfaces with following conductive coating materials: iridium (Ir), gold (Au), gold with а titanium sublayer (Au(Ti)), silver with а chromium sublayer (Ag(Cr)) and tantalum (Ta).   We investigated the thermal and the thermal-frequency dependences of langatate electrophysical parameters in direct and alternating electric fields. We revealed how values of frequency dependences of relative dielectric constant (ε11/ε0), admittance, tg δ depend on the growth atmosphere and material of the conductive coating. The langatate electrophysical properties in alternating electric field were analyzed by means of impedance spectroscopy method. We constructed the equivalent circuits, determined the parameters of this electrochemical cell “electrode-crystal- electrode” and the input of different near-electrode processes into electrophysical properties of LGT. We showed that the cause of the electromotive force in our case is the difference between the electrochemical potentials of the opposite surfaces of polar cuts. This phenomenon was previously described for other crystals [2]. The electrochemical interaction of the conductive coatings with the surfaces of the LGT crystal leads to the degradation of the conductive coatings. We studу this interaction with the method of current spectroscopy in the temperature range from 20 to 600 oC.