STABILIZATION OF DISORDERED SUPERPROTONIC PHASES IN CRYSTALS OF THE M5H3(AO(4))(4)CENTER-DOT-XH(2)O FAMILY

In order to clarify the nature of the suppression of the order-disorde r phase transitions and the stabilisation of the disordered highly-con ducting state, conductivity, thermal (TGA and DSC) and infrared spectr oscopic measurements have been carried out on single crystals of Cs5H3 (SO4)(4) . xH(2)O, Cs5H3(SeO4)(4) . H2O and K5H3(SO4)(4) . H2O. The pr oton dynamics and structural superprotonic phase transitions are brief ly reviewed for these compounds. Protonic conductivity is demonstrated and is shown to be due mainly to the acid protons. An opposite influe nce of the water content on the stability of poorly conducting and hig hly conducting phases was found, where a stoichiometric water content tends to stabilise, at low temperature, ordered phases with a low cond uctivity; whilst a loss of water through an increase in temperature le ads to stabilisation of superprotonic phases characterised by disorder ed acid hydro en bond networks and in which the phase transition from the superionic phase is suppressed.