Neutron Scattering Study on the Structural Phase Transition in KDCO₃

Abstract

Neutron coherent scattering study at the structural phase transition point of KDCO 3 crystal has been carried out. Strong quasielastic diffuse scattering is observed. From the detailed analysis of the intensity distribution in a wide range of the reciprocal space, we conclude as follows: (i) Even at T > T c , the individual dimer is already deformed by the self-trapping of deuterons, thus locally breaking the symmetry of the averaged lattice within the time interval determined by the energy resolution limit of the spectrometer (τ<0.8×10 -11 sec). (ii) The inter-dimer interaction takes place via the strain field induced by the deformed dimers in the self-trapped state. (iii) The structural phase transition is triggered mainly by the strain-mediated indirect interaction between the dimers.