A neutron diffraction study of the phase transition of fully deuterated triglycine sulphate (ND₂CD₂COOD)₃.D₂SO₄

Abstract

Using neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND2CD2COOD)3.D2SO4 is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below TC using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range — from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H‐bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long‐range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS – no low temperature anomalies were observed in the crystal structure.

Approaches to modelling thermal diffuse scattering in triglycine sulfate, (NH2CH2COOH)3·H2SO4

“…3c), the streaks still appear to be visible but are much weaker and more diffuse. These diffuse streaks were found to be due to short-range correlations in the G1 orien-tations parallel to the ferroelectric b axis developing as TGS passes through the ferroelectric phase transition (Hudspeth, research papers The (a) (0kl) and (b) (h0l) slices of reciprocal space for TGS from the X-ray diffuse scattering data collected on the 11-1D-B beamline at APS at 295 K. 2012; Hudspeth, Goossens, Gutmann & Studer, 2013). The onset of significant short-range order appears to occur between 40 and 30 K below T C (Hudspeth, Goossens, Gutmann & Studer, 2013;Hudspeth, Goossens, Welberry & Gutmann, 2013).…”

“…The short-range order in the G1 orientations close to T C was modelled using an Ising-type model in which the two G1 orientations were treated as spin up and spin down (Hudspeth, 2012;Hudspeth, Goossens, Gutmann & Studer, 2013). To model both the orientational and displacive short-range order, the occupancy file from the Ising-type MC simulation was read into ZMC, which was then used to model the correlated atomic displacements.…”

“…Many features are equally well modelled by the three approaches, so the qualitative comparison focuses on the diffraction features that are most sensitive to the different modelling approaches. To better explore the qualities of the different approaches, the modelling was undertaken using the MC method at all temperatures, with the parameters of the occupancy model (Hudspeth, Goossens, Gutmann & Studer, 2013) changed to reflect the changes in the ordering close to and far away from the phase transition.…”

“…Being able to accurately model the thermal diffuse scattering in TGS is important because any diffuse intensity arising from short-range order of the G1 orientations will be modulated by the thermal motions of the molecules. Hence, to understand the short-range order, and thus gain insight into the mechanism of the phase transition, modelling the thermal diffuse scattering is useful (Hudspeth, Goossens, Gutmann & Studer, 2013).…”

Triglycine sulphate and its deuterated analog in polyurethane matrix for thermal/infrared detection: A comparison

“…One of these is deuteration of TGS. 13 Use of DTGS crystals allows to extend temperature range of sensing by 5-12 C due to their higher Curie temperature, depending on the deuteration level. In fully deuterated TGS (FDTGS) with chemical formula (ND 2 CD 2 COOD) 3 .D 2 SO 4 , the H atoms in the CH 2 group will also be replaced by deuterium.…”