INFRARED REFRACTIVE-INDEXES OF LAALO3, AND LAGAO3, AND NDGAO3

We discuss the experimental and theoretical studies of the infrared op tical constants of three perovskite materials: LaAlO3, LaGaO3, and NdG aO3. These materials are commonly used as substrates for depositing hi gh-temperature superconducting films. The transmittance and the reflec tance are measured with a Fourier-transform infrared spectrometer. At frequencies from 1000 to 10 000 cm-1, for which the substrates are tra nsparent, the refractive index is extracted directly from the measured transmittance and reflectance. Kramers-Kronig relations are employed to yield the refractive index of these materials at frequencies from 1 00 to 1000 cm-1. We also use a Lorentz phonon oscillator model to obta in the refractive index by fitting the measured data to the model func tion. The advantages and limitations of each method are discussed. The refractive index for the LaAlO3 substrate is also obtained at 10 and 78 K with a cryogenic accessory. The results are compared with those r eported by other research groups. This research provides information n ecessary for the quantitative study of the optical properties of thin superconducting films.