Electromechanical coupling effects on the dielectric properties and feerroelectrpc phase transition in lithium thallpum tartrate

Dielectric, piezoelectric and elastic properties of LiTlC4H4O6 · H2O have been studied over the temperature range 4.2 to 300°K. It has been shown that at low temperature the dielectric constant K11 is very sensitive to the mechanical boundary conditions. At 10°K, close to the Curie point, the free dielectric constant Kx11 is ∼ 5 × 103, whilst the clamped constant Kx11 is only ∼ 30. Both the elastic compliance sE44 and the piezoelectric constant d14 become exceedingly large close to Tc and appear to have the highest magnitude yet measured in any ferroelectric. An analysis of the Helmholtz free energy shows that the unusually large electromechanical coupling effect plays an important role in stabilizing the ferroelectric phase at lower temperature.