Hydrogen bond as a trigger of ferroelectric-like phase transition in lithium-thallium tartrate monohydrate

The dielectric and pyroelectric properties have been investigated in lithium-thallium tartrate monohydrate crystals at 2-100 K. It is shown that ferroelectric-like transition at 10-12 K occurs only in the proton subsystem without changes in the symmetry of the unit cell, which is confirmed by polarized Raman spectroscopy. Similar behavior of dielectric properties was detected earlier in non-polar phase of a number of ferroelectrics after a sharp cooling below the Curie point, which created anisotropic thermoelastic stresses. In this case, the temperature anomalies of dielectric permittivity coincide with the specific points of the proton subsystem of OH center dot center dot center dot O hydrogen bonds.