Mechanisms of the antiferro-electric ordering in superprotonic conductors CsH(SeO) and CsD(SeO).

Wide ranges of absorbance spectra were measured to elucidate a difference in the antiferro-electric (AF) ordering mechanisms below 50 and 168 K in CsH(SeO) and CsD(SeO), respectively. Collective excitations due to deuterons successfully observed at 610 cm exhibit a remarkable isotope effect. This indicates that the transfer state in the dimer of CsD(SeO) is dominated by a deuteron hopping in contrast to CsH(SeO), where a proton hopping makes a tiny contribution compared to a phonon-assisted proton tunneling (PAPT) associated with 440-cm def .