Abstract:
Triglycine sulfate (TGS) films have been prepared by evaporation from a saturated aqueous solution on substrates of fused quartz coated by a layer of thermally deposited aluminum (Al/SiO$_2$) and white sapphire ($\alpha$-Al$_2$O$_3$) on whose surface interdigital electrodes have been deposited by photolithography. The TGS films have a polycrystalline structure made up of blocks measuring 0.1–0.3 mm (Al/SiO$_2$) and 0.1 $\times$ 1.0 mm ($\alpha$-Al$_2$O$_3$). The polar axis in the blocks is mostly confined to the substrate plane. The temperature dependences of the capacitance and dielectric losses normal to and in the film plane have maxima at the temperature coinciding with that of the ferroelectric phase transition in a bulk crystal, $T_c$. The low-frequency conductivity $G$ in TGS/Al/SiO$_2$ structures displays a frequency dispersion described by the relation $G\sim\omega^s$ ($s\approx$ 0.82). The conduction can be tentatively ascribed to the hopping mechanism involving localized carriers with a ground state energy of 0.8–0.9 eV. At temperatures above and below $T_c$, the low-frequency conductivity in TGS/$\alpha$-Al$_2$O$_3$ films operates through a thermally-activated mechanism with an activation energy of 0.9–1.0 eV. At the phase transition, an additional contribution to conductivity appears in TGS/$\alpha$-Al$_2$O$_3$ films with a dispersion $G\sim\omega^{0.5}$, which can be associated with domain-wall relaxation.
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