HIGH-PRESSURE TRANSFORMATIONS OF NAOH

The structures of two high pressure modifications of NaOH have been de termined by in situ x-ray measurements with a diamond anvil cell. Ther modynamic data for the transformation are derived from the PT diagram. The structures are discussed and especially the influence of the H at oms on characteristic deformations. The compressibility of alpha-NaOH shows an anomaly, which can be explained by a continuous transformatio n to yet another new modification, which is isotypic with the low-temp erature form of NaOD.