NEUTRON-DIFFRACTION STUDIES OF THE GEOMETRIC ISOTOPE EFFECT IN H-ORDERING TRANSITIONS

Neutron-diffraction studies have been carried out on PbHPO4 and its deuterated form PbDPO4 just above their respective H(D)-ordering phase transition temperatures, Tc, at atmospheric pressure. For PbDPO4, data have also been collected under pressure. The results are compared with a similar study of KH2PO4 and KD2PO4. In both systems, the large change in Tc on deuteration at atmospheric pressure appears to be attributable simply to the accompanying increase in δ, where δ is the separation between the two sites over which the H(D) atoms are disordered above Tc. © 1990, Taylor & Francis Group, LLC. All rights reserved.