The elastic stiffness constants and their hydrostatic pressure derivatives for TGS

Abstract

The thirteen adiabatic elastic stiffness moduli of triglycine sulphate (TGS) have been determined at room temperature from measurements of the ultrasound wave velocities. Results are used to describe the elastic behaviour of TGS. Accidental pure mode directions have been found at 9.4 ~ and 106.5 ~ A method has been developed for obtaining the hydrostatic pressure derivatives (aClj/~P) of the elastic constants of a monoclinic crystal from the hydrostatic pressure dependences of ultrasound wave velocities. This method has been applied to find the ~CIj/~P for TGS. There is no evidence for acoustic phonon mode softening under pressure.

Ultrasonic investigation of elastic properties and a phase transition in ferroelectric glycine phosphiteNH3CH2Deepthy1, Bhat2, Alex3 et al. 2000Phys. Rev. B220110View full textAdd to dashboardCite

“…[14][15][16] The velocities of all these 18 modes for GPI measured in the present experiments are listed in Table I The consistency of these internal checks ascertains the accuracy of the measured velocity values. Only three elastic constants, viz., C 22 , C 44 , and C 66 , are obtained directly from the measured wave velocities v 5 , v 8 , and v 2 , respectively, and are given below: Knowing these and the velocity v 11 , the value of elastic constant C 46 can be evaluated using the relation…”

Size-driven ferroelectric effects in TGS induced by high hydrostatic pressure

“…It is a reasonable statement, since in accordance with the theoretical data of Li et al [13] the limit of the critical size is strongly correlated with the dimension along of the spontaneous polarization direction. The lamellar structure of TGS [11] with the anisotropy of the unit cell compressibility [12] coincides with such a behavior at a high pressure.…”

“…The expansion and compressibility tensors [11,12] reveal high anisotropies below and above T C . It follows that the reduction of the correlation volume under pressure in TGS should lead to a vanishing ferroelectricity, as observed.…”

“…The sign of dT C dp changes from positive to negative above the pressure value is corresponding to this plateau. Some time ago, one of us has measured the components of the thermal expansion [11] and discussed the compressibility tensors [12] in TGS. It is likely that the sign of dT C dp is affected by the high anisotropies of these parameters at the phase transition temperature [13].…”

Dielectric properties of fine-grained triglycine sulphate (TGS)

“…In the uniaxial ferroelectrics like TGS, the anisotropy of the "correlation volume" [12] is related to the number of dipoles aligned along the P s direction. The expansion and compressibility tensors in TGS [24,25] reveal high anisotropies below and above T c . Reducing the sample size below the critical length parallel to the polar axis modifies the balance between long-and short-range forces.…”