Effect of Sintering Atmosphere on Dielectric Properties of LaAlO3-SrTiO3 System

LaAlO3-SrTiO3 [(1-x) LAO-xSTO] ceramics were prepared by a conventional solid phase reaction method using high purity reagents. To investigate influence of the sintering atmosphere, the samples were sintered under oxygen partial pressures from 97.7% to 6.3%. The permittivity was rarely affected by the sintering atmosphere. However, Qf values of 0.6LAO-0.4STO and 0.5LAO-0.5STO were strongly affected by the atmosphere. Cathode luminescence examination showed that a low oxygen partial pressure introduced oxygen defects in these materials. It was confirmed by far infrared measurement that the oxygen defects barely affected the lattice vibration. The electrical conductivity of these two solid solutions was confirmed, and it was inferred that an oxygen defect introduced a conductive electron in their structures. The loss tangent calculated from the electrical conductivity was approximately in agreement with that obtained by microwave measurement in the 0.5LAO-0.5STO solid solution. The possibility that the induced electron may act like a small-radius polaron was shown by Ti XPS spectra. Further investigation is needed to clarify the character of the electron.