Permittivity and conductivity of triglycine sulfate films on Al/SiO2 and α-Al2O3 substrates

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/SiO2) and white sapphire (α-Al2O3) 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/SiO2) and 0.1 × 1.0 mm (α-Al2O3). 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, Tc. The low-frequency conductivity G in TGS/Al/SiO2 structures displays a frequency dispersion described by the relation G ∼ ωs (s ≈ 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 Tc, the low-frequency conductivity in TGS/α-Al2O3 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/α-Al2O3 films with a dispersion G ∼ ω0.5, which can be associated with domain-wall relaxation.