Dielectric Properties of Betaine Phosphite-Betaine Phosphate in Improper Ferroelastic Phase

Abstract

The temperature dependences and electric field effect on dielectric constant of BPI-BP solid solutions in improper ferroelastic phase are studied. The temperature dependences of ϵ⁻¹ in the improper ferroelastic phase of BPI_xBP_{1 − x} (0.9 ≤ x ≤ 1) and the effect of electric field on dielectric constant are described within phenomenological model taking into account biquadratic coupling of nonpolar order parameter for improper ferroelastic phase transition and polarization with a negative coupling coefficient.

Keywords:

• Betaine compounds
• ferroelectric and improper ferroelastic phase transitions

Acknowledgments

This study was supported by the RFBR (project no. 01-02-17873), the Ministry of Industry, Science and Technology of Russia (Sc.S-2168.2003.2) and the Department of Physics Sciences of RAS.