Abstract
(NaCN(KCN mixed crystals with concentrations x=0.85 and 0.59 have been investigated by elastic and inelastic neutron scattering, x-ray diffraction, and dielectric techniques. Both crystals exhibit neither quadrupolar nor dipolar long-range order down to the lowest temperatures. However, the slowing down of the dipolar and the quadrupolar relaxation behaves very differently in the two samples investigated. In (NaCN(KCN the freezing-in of the quadrupolar degrees of freedom is a cooperative effect which is dominated by strain-mediated interactions. The resulting low-temperature state is characterized by frozen-in orientational correlations and frozen-in lattice strains. In (NaCN(KCN the experimental results on the dynamics of the quadrupolar freezing are indicative of single-ion behavior where the slowing down of the molecular reorientations is completely due to thermal activation across the hindering barriers of the crystal field set up by the neighboring and ions. Consequently the low-temperature state for x=0.59 is characterized by quenched quadrupolar disorder, i.e., independently frozen-in single ions. An analysis of the static dielectric susceptibilities demonstrates that dipolar interaction forces are negligible in (NaCN(KCN while significant deviations from a Curie-type behavior exist in (NaCN(KCN indicating the onset of short-range electric order near 70 K.
- Received 13 February 1986
DOI:https://doi.org/10.1103/PhysRevB.34.1238
©1986 American Physical Society