GROWTH, OPTICAL IMAGING AND DIELECTRIC PROPERTIES OF FERROELECTRIC BETAINE PHOSPHITE AND TRIGLYCINE SULPHATE FILMS

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 E_act ∼ 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.

Keywords:

• ferroelectric films
• amino acid
• ferroelectrics
• dielectric properties
• phase transitions

ACKNOWLEDGMENTS

This work was partly supported by RFBR (Project N 07-02-01286 and 08-02-00112).