Spontaneous strain variations through the low temperature phase transitions of deuterated lawsonite

摘要: High resolution neutron powder diffraction has been used to determine lattice parameter variations of deuterated lawsonite across the Cmcm ↔ Pmcn and P 21 cn phase transitions, in temperature interval 1.6–505 K. The are reversible through heating cooling cycles. Strain analysis, based on a displacive model transitions with saturation temperatures describe temperature-independent behavior as T → 0 K, shows that data consistent tricritical transition at 271 ± 2 K second-order 155 1 Comparisons strains from published dilatation for natural (hydrogenated) sample highlight aspects most dependent protons structure. Replacing H by D causes low point be increased ~27 an anomaly strain evolution increase ~225 ~250 high-temperature remains same within ~2 We conclude proton ordering contributions both important transition, though component providing initial symmetry-breaking mechanism. Structural changes more or become ~20–50 below this. Strains driven single order parameter. values strain/order coupling coefficients calculation elastic anomalies due transitions.