Microwave absorption in single crystals of lanthanum aluminate

Abstract

A very sensitive dielectric resonator technique is employed to measure loss tangent tan δ and relative permittivity εr of lanthanum aluminate (LaAlO3) single crystals at 4–300 K and 4–12 GHz. A variety of single crystals grown by different techniques and purchased from different suppliers are considered. For T>150 K the loss tangent tan δ is almost sample independent with linear frequency dependence and monotonous temperature variation from 8×10−6 at 300 K to 2.5×10−6 at 150 K and 4.1 GHz. In this temperature range the experimental data are explained by a model based on lifetime broadened two-phonon difference processes. The loss tangent below 150 K is characterized by a peak in tan δ(T) at about 70 K. The height of this peak is frequency and strongly sample dependent. This leads to a variation of the loss tangent from 10−6 to 1.5×10−5 at 77 K and 8.6 GHz, the lowest values are generally achieved with Verneuil grown crystals and approach the intrinsic lower limit predicted by the phonon model. The peak is explained by defect dipole relaxation (local motions of ions). The activation energy of the relaxation process is determined from the measured data to be 31 meV. This low value indicates that the defect dipoles are associated with interstitials, possibly impurities in interstitial positions. Considering absorption due to phonons and due to defect dipole relaxation the loss tangent is calculated for a wide frequency range.

Nonlinear dielectric microwave losses in MgO substrates

“…The same mechanism was attributed to the linear, T-dependent, microwave response of LaAlO 3 [24]. In Fröhlich's model,…”

Effect of annealing on the temperature-dependent dielectric properties of LaAlO3 at terahertz frequencies

“…[3][4][5][6] The microwave (4 GHz -12 GHz) absorption of single crystal LAO at different temperatures (4 K -300 K) have been investigated by Zuccaro et al. 7 They pointed out that the dielectric loss in LAO is due to microwave absorption by phonons and relaxation of dipoles brought about by defects in the crystal. Room-temperature absorption spectra were also studied at terahertz (THz) frequencies which contain information of large molecule and intermolecular vibrations.…”

Recent developments in the characterization of superconducting films by microwaves

“…Present efforts aim at understanding the different microwave properties of bulk and thin film SrTiO 3 for device applications. Another example is the observation of dielectric relaxation in LaAlO 3 or MgO, which cause non-monotonic temperature and field dependences of the loss tangent and hence the quality factor of microwave devices [31][32][33]. inhomogeneities, the existence of a small gap value.…”