Structural Change of Cu(HCOO) 2 ·4H 2 O Associated with the Antiferroelectric Phase Transition

Abstract

An accurate x-ray crystal structure analysis and an incoherent inelastic neutron scattering measurement of Cu(HCOO) 2 4H 2 O have been performed above and below the antiferroelectric phase transition temperature T t = 235.5 K. We confirmed the water layer is disordered above T t but could not find the reported hydrogen site called H(6). The obtained structure below T t can be understood by the condensation of the disordered structure above T t . We conclude that the structural change at T t is induced by the hindered rotation of water molecules about the two kinds of the ordered O-H bonds.