Low-temperature phase transition in γ-glycine single crystal. Pyroelectric, piezoelectric, dielectric and elastic properties

Abstract

Temperature changes in the pyroelectric, piezoelectric, elastic and dielectric properties of γ-glycine crystals were studied in the range 100 ÷ 385 K. The pyroelectric coefficient increases monotonically in this temperature range and its value at RT was compared with that of other crystals having glycine molecules. A big maximum in the d14 component of piezoelectric tensor compared by maximum in attenuation of the resonant face-shear mode were observed at 189 K. The components of the elastic stiffness tensor and other components of the piezoelectric tensor show anomalies at this temperature. The components of electromechanical coupling coefficient determined indicate that γ-glycine is a weak piezoelectric. The real and imaginary part of the dielectric constant measured in the direction perpendicular to the trigonal axis show the relaxation anomalies much before 198 K and the activation energies were calculated. These anomalies were interpreted as a result of changes in the NH3+ vibrations through electron-phonon coupling of the so called “dynamical transition”. The anomalies of dielectric constant ε*11 and piezoelectric tensor component d14 taking place at 335 K are associated with an increase in ac conductivity caused by charge transfer of protons.