17O NQR Study of the Antiferroelectric Phase Transition in TlH2PO4

Abstract

The temperature dependence of the 1 7O NQR spectra in TlH2PO4 has been measured using a proton‐1 7 O nuclear quadrupole double resonance technique. The results show that the protons in the short one‐dimensionally linked O1–H1‐‐O1 and O2–H2‐‐O2hydrogen bonds are moving between two equilibrium sites above T c and freeze into one of the off‐center sites below T c . The protons in the asymmetric O3–H3‐‐O4hydrogen bonds are static and ordered above and below T c .