GLASSY PROPERTIES OF THE RELAXOR FERROELECTRIC STRONTIUM BARIUM NIOBATE AT LOW-TEMPERATURES

Relaxer ferroelectrics are known to show a low-temperature behaviour t hat quantitatively resembles the features of canonical glasses. In ord er to get a comprehensive characterisation of the responsible low-ener gy excitations, single crystals of strontium barium niobate were inves tigated below 10 K. The density of localised states was obtained from heat capacity, and their coupling to phonons from sound velocity and t hermal conductivity. The presence of slowly relaxing systems could be estimated from heat release data, respectively. In contrast with struc tural glasses, however, SBN and further relaxer ferroelectrics show an energy dependent density of states and an upper limit of the relaxati on time spectrum. Considering these properties, which appear to be typ ical also for other glassy crystals, a modification of the standard tu nneling model is proposed.