“…It results from the formation of water molecules preceding the decomposition. Prereactional effects have been evidenced by different experimental techniques, in a large temperature range before the dehydration temperature (570 K with PHZ0 = 1.73 torr) (Freund and Wengeler, 1980;Freund, Scheikh-01-Eslami and Gentsch, 1975). In particular, X-ray and neutron diffraction studies on powders and single crystals of Ca(OH), and Ca(OD), have already revealed structural discontinuities at different temperatures which depend on the water pressure conditions (Chaix-Pluchery, 1986; Chaix-Pluchery, Bouillot, Ciosmak, Niepce and Freund, 1983;Chaix-Pluchery, Pannetier, Bouillot and Niepce, 1987).…”