Aging and non-ergodicity in superprotonic water non-stoichiometric phases of MzHy(AO4) (z plus y)/2•xH2O crystals

The evidence for the glass transitions were obtained in highly conducting disordered phases of Cs5H3(SO4)(4) . xH(2)O (x approximate to 0.5) (PCHS), Cs5H3(SeO4)(4) . xH(2)O (x < 0.4) (PCHSe) and K9H6(SO4)(8)H . xH(2)O (x < 0.2) (NKHS) single crystals by dielectric spectroscopy, calorimetric and ultrasonic techniques. Temperatures of glass transitions T-g were found at 210, 240 and 270 K for NKHS, PCHS and PCHSe, respectively. Aging and irreversibility of physical proper-ties were found above the glass-transition temperature. Both the dc- and ac-conductivity strongly depend on the history of investigated crystals which was changed by varying the cooling rate. Slow dynamics is also detected on acoustic and thermal properties. The power law gives a good fit of time evolution of different properties at T < T-g, but above T-g a long time behavior is more complicated. The role of crystalline water in the aging processes is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.