Reflectance spectroscopy of Ba3+xZn1+yNb 2O9 perovskites

Complex perovskites in the Ba3+xZn1+yNb 2O9 family were studied via reflectance spectroscopy for photon energies between 0.006 and 1eV. These materials are of interest as potential dielectric resonator materials which require large ε1 (to enable device miniaturization), large Q ≈ ε1/ ε2 (for selectivity) and small temperature dependence of optical functions (for device stability). The dielectric functions were modeled by fitting the reflectance 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 (300 GHz). Both models suggest that for the stoichiometric composition ε1 ≈ 40 while the extrapolated value of ε2 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. ε1 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 ε2 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 influencing ε2 in the microwave region more strongly than deviation from ideal stoichiometry Ba3ZnNb2O9.