A sensitive dielectric resonator technique was used to measure the tangent loss and relative permittivity of single crystals at 4 to 300K and 4 to 12GHz. At temperatures greater than 150K, the tangent loss was almost sample-independent, with a linear frequency dependence and a monotonic temperature variation. The tangent loss below 150K was characterized by a peak at about 70K. The height of the peak was frequency- and sample-dependent. The peak was attributed to defect dipole relaxation. The activation energy for the relaxation process was deduced to be 0.031eV. This low value indicated that the defect dipoles were associated with interstitials.

C.Zuccaro, M.Winter, N.Klein, K.Urban: Journal of Applied Physics, 1997, 82[11], 5695-704