High-pressure phase transition in lithium deuteroxide: a neutron powder diffraction and vibrational spectroscopic study

Abstract

Summary and Conclusions Raman spectra of deuterated and hydrogenated cyclohexane have been obtained over the pressure range 1 bar to 30 kbar at room temperature. Data were also collected in the low-temper- ature phase I1 and in the metastable phase. As pressure is in- creased from ambient, the phase sequence in both C&II2 and C6DIZ is I - I11 - IV - V. The monoclinic phase 11 was not obtained at room temperature up to 30 kbar. The general similarity of spectra in the region 5-300 K and ambient to 30 kbar suggests that the phase diagram topologies of these compounds are identical. A new phase (phase V) has been discovered in both materials but its structure remains unknown. The similarity of spectra in all phases suggests that there is only a small degree of molecular distortion accompanying these first-order transitions. Comparison of the metastable phase spectrum with those of the other phases suggests that it is most similar to the phase IV high-pressure polymorph,