HIGH-PRESSURE RAMAN STUDIES ON LAURIONITE-TYPE HYDROXIDES BA(OD)X (X=CL,BR,I) AND SR(OD)(2)

High-pressure Raman studies on Sr(OD)(2) and laurionite-type barium hy droxide halides Ba(OD)Cl, Ba(OD)Br, and Ba(OD)I were performed under h ydrostatic compression up to 5 cpa using a diamond anvil cell. The pre ssure evolution of the OD stretching vibrations of the isostructural B a(OD)X and Sr(OD)(2) is discussed with respect to the different behavi ours of the respective hydrogen bond systems. The OD stretching modes slightly increase (dv(OD)/dp = 4cm(-1) GPa(-1)) with increase in press ure if the respective ions are not involved in hydrogen bonds as in th e case of Ba(OD)I and OD(2) of Sr(OD)(2) (lattice repulsion effect). T he wavenumbers of OD stretching modes of ions involved in hydrogen bon ds, as OD(1) of Sr(OD)(2), decrease due to a strengthening of the resp ective bonds with increasing pressure. A discontinuous decrease of v(O D) is observed for Ba(OD)Br indicating transition from a weakly hydrog en-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 t wo crystallographically different hydroxide ions is involved in hydrog en bonding but the other is not.