ABSTRACT
Polycrystalline films of betaine phosphite (BPI) and triglycine sulphate (TGS) were grown by the evaporation method on different substrates (α-SiO2, α-Al2O3 and LiNbO3 with interdigital transducers, and Al/SiO2). Large (∼1 mm in BPI and ∼0.2 mm in TGS) single-crystalline blocks were visualized in a polarizing microscope in the reflection mode. Blocks are characterized by preferable in-plane orientation of the ferroelectric axis. Temperature dependences of the BPI and TGS film capacity at frequencies 120 Hz–1 MHz exhibit a strong maximum at the temperature of the ferroelectric phase transition of bulk crystals. The effect of a bias electric field on the dielectric constant and losses was studied. Description of dielectric properties is carried out using Landau-Ginsburg-Devonshire model with account of film-substrate interaction. Low frequency conductivity in BPI films is related to DC conductivity due to thermo-activation process with activation energy Eact ∼ 0.1 eV. AC conductivity associated with the hoping mechanism and the combination DC and AC conductivity was found in TGS films on Al/SiO2 substrates and α-Al2O3 substrates correspondingly.
ACKNOWLEDGMENTS
This work was partly supported by RFBR (Project N 07-02-01286 and 08-02-00112).