Dielectric properties and far infrared reflectivity of lanthanum aluminate–strontium titanate ceramics

LaAlO3–SrTiO3 [(1 − x) LAO–xSTO] ceramics were prepared by a conventional solid-phase reaction method using high-purity reagents. Far infrared reflectivity spectra for (1 − x) LAO–xSTO ceramics were measured and eigenfrequencies and damping constants of the transverse and longitudinal optical modes were estimated in order to analyze the dielectric properties and lattice vibration parameters. The observed reflectivity spectra were fitted by 4 or 6 IR active modes in order to estimate the vibration eigenfrequencies and damping constants. In the range of microwave frequency, the permittivity and temperature coefficient of resonant frequency gradually increased with the amount of STO. The permittivity increase was due to increase in number of vibration mode by STO addition. The Q × f value of the solid solution showed the maximum value at x = 0.2. The lattice vibrational analysis of the (1 − x) LAO–xSTO and the dielectric properties measured at the microwave frequency range indicate that the variation of Q × f value is related to the change in loss spectrum at the lower far infrared frequency with the amount of STO.