Re∞ectance Spectroscopy of Ba3+xZn1+yNb2O9 Perovskites

Complex perovskites in the Ba3+xZn1+yNb2O9 family were studied via re∞ectance spectroscopy for photon energies between 0.006 and 1eV. These materials are of interest as potential dielectric resonator materials which require large †1 (to enable device miniaturization), large Q … †1=†2 (for selectivity) and small temperature dependence of optical functions (for device stability). The dielectric functions were modeled by fltting the re∞ectance spectra to both Lorentz oscillator and factorized dielectric functions in order to get a sense of the uncertainty in extrapolating the measured far-infrared dielectric function to the microwave (MW) region (300GHz). Both models suggest that for the stoichiometric composition †1 … 40 while the extrapolated value of †2 has much more uncertainty. The extrapolated value of Q … 2000 at room temperature at MW frequency for Ba3ZnNb2O9 and Q is largest near stoichiometric composition. †1 is only weakly composition dependent, except for the sample furthest from stoichiometric composition (Ba2:7ZnNb2O9). Comparison of the present data for Ba3ZnNb2O9 with previous work reveals that the phonon scattering rates and low frequency †2 are much higher in the present samples yielding lower Q values, which were prepared at somewhat higher temperature than previous workers. It is possible that microstructure | which depends strongly on sample preparation temperature | is in∞uencing †2 in the microwave region more strongly than deviation from ideal stoichiometry Ba3ZnNb2O9.