Microwave dielectric properties of lanthanum aluminate ceramics and single crystal

Single crystal and ceramics of LaAlO3 were prepared by a Czochralski method and conventional solid phase reaction, respectively, using high purity reagents. Far infrared reflectivity spectra for single crystals and ceramics of LaAlO3 were measured and eigenfrequencies and damping constants of transverse and longitudinal optical modes were evaluated in order to discuss variations in the dielectric properties. The observed reflectivity spectra were fitted by four IR active modes (predicted by factor group analysis) in order to calculate the vibration eigenfrequencies and damping constants. Differences in dielectric loss were found between the two kinds of single crystals, having different crystal orientations. It was inferred that the difference in dielectric loss was due to difference in cut off frequencies of these single crystals. The loss obtained from the IR reflectivity of the ceramics was used to evaluate the extrinsic loss in the ceramics.