Diffuse scattering and the mechanism for the phase transition in triglycine sulphate

Dynamics of Hydrogen Bonds in TGS Crystals Observed by Means of Measurements of Pyroelectric Currents Induced by Linear Changes of Temperature

“…Therefore, the only way to register such weak signals is to measure them in plane perpendicular to the polar axis b. Non-vanishing currents I x and I y measured in the mutually perpendicular directions perpendicular to polar b axis show that the listed hydrogen bonds are activated at different temperatures and these components of the induced polarization vectors have various orientations. We believe that our results are in agreement with the observations of Hudspeth [3] and Hudspeth et al [4]. Our method seems to be a good tool for the deeper disclosure of weak effects accompanying the phase transition in TGS.…”

“…Two glycine groups G2 and G3 are arranged almost perpendicular to the ferroelectric axis b. The length d 12 of the hydrogen bond H12 between glycines G1 and G2 and the length d 13 of the bond H13 between molecules G1 and G3 as well as the length d 23 of the bond H3 between G2 and G3 depend on temperature [3,4]. The lengths d 12 and d 13 increases, whilst d 23 decreases with growing temperature.…”

“…3. Possible configuration of hydrogen bonds between G1 and surrounding molecules and the short hydrogen bond between G2 and G3 in ferroelectric phase [3,4]. Looking from the left side: G1 respectively in right and in left position.…”

“…As a result, N1 atom may develop two equivalent bonds with oxygens O22 (bond H12) or O32 (bond H13). In the diffuse scattering of X-ray experiments, it was found that the position of H3 atom in G2-G3 bond is correlated with the orientation of G1 molecule [3,4]. In the case of the right position of NH 3 group, H3 atom is covalently bonded with O32 atom, and N1 is hydrogen bonded to O22.…”

“…Hudspeth [3] underlined that the dominant mechanism of interaction of G1 molecules is indirect via hydrogen bonds between G1 and G2 or G1 and G3, giving the zig-zag networks of interactions as illustrated in Fig. 6 of the papers by Hudspeth [3] and Hudspeth et al [4]. As a result, the mirror plane disappears, the TGS structure has space group symmetry P 21, and the crystal becomes polarized along the b axis.…”