1H NMR spin–spin relaxation in TlH2PO4 undergoing separated antiferroelectric and ferroelastic phase transitions

We have investigated hydrogen-bonded TlH2PO4 (TDP), undergoing separated antiferroelectric and ferroelastic phase transitions, by means of 1H nuclear magnetic resonance (NMR) spin–spin relaxation, which gave two distinct decay constants attributed to the lattice diffusion and dynamically disordered hydrogen bonds. A frustrated proton dynamics of the H-bond defects, with an increased activation energy, was identified in association with the ferroelastic phase transition in the system, throwing new light onto the microscopic nature of the phase transitions in the KH2PO4 (KDP)-type crystals.