Effect of local dipole moments on the structure and lattice dynamics ofK0.98Li0.02TaO3

Abstract

We present high energy x-ray (67 keV) and neutron scattering measurements on a single crystal of K1−xLixTaO3 for which the Li content (x = 0.02) is less than xc = 0.022, the critical value below which no structural phase transitions have been reported in zero field. While the crystal lattice does remain cubic down to T = 10K under both zero-field and field-cooled (E 4 kV/cm) conditions, indications of crystal symmetry lowering are seen at TC = 63K where the Bragg peak intensity changes significantly. A strong and frequencydependent dielectric permittivity is observed at ambient pressure, a defining characteristic of relaxors. However an extensive search for static polar nanoregions, which is also widely associated with relaxor materials, detected no evidence of elastic neutron diffuse scattering between 300 K and 10 K. Neutron inelastic scattering methods were used to characterize the transverse acoustic and optic phonons (TA1 and TO1 modes) near the (200) and (002) Bragg peaks. The zone center TO1 mode softens monotonically with cooling but never reaches zero energy in either zero field or in external electric fields of up to 4 kV/cm. These results are consistent with the behavior expected for a dipolar glass in which the localmore » polar moments are frozen and exhibit no long-range order at low temperatures.« less