High-pressure Raman studies on laurionite-type hydroxides Ba(OD)X (X = Cl, Br, I) and Sr(OD)2

Abstract

High-pressure Raman studies on Sr(OD)2 and laurionite-type barium hydroxide halides Ba(OD)Cl, Ba(OD)Br, and Ba(OD)I were performed under hydrostatic compression up to 5 GPa using a diamond anvil cell. The pressure evolution of the OD stretching vibrations of the isostructural Ba(OD)X and Sr(OD)2 is discussed with respect to the different behaviours of the respective hydrogen bond systems. The OD stretching modes slightly increase (dνODdp = 4cm−1 GPa−1) with increase in pressure if the respective ions are not involved in hydrogen bonds as in the case of Ba(OD)I and OD(2) of Sr(OD)2 (lattice repulsion effect). The wavenumbers of OD stretching modes of ions involved in hydrogen bonds, as OD(1) of Sr(OD)2, decrease due to a strengthening of the respective bonds with increasing pressure. A discontinuous decrease of νOD is observed for Ba(OD)Br indicating transition from a weakly hydrogen-bonded structure to a more strongly bonded one via reorientation of the OD− ions. In the case of Sr(OD)2, it is confirmed that one of two crystallographically different hydroxide ions is involved in hydrogen bonding but the other is not.