Structure and dielectric properties of rf sputtered Bi2O3-MgO-Nb2O5 pyrochlore thin films

The cubic pyrochlore Bi1.5MgNNb2.5−NO8.5−1.5N (BMN) thin films with various compositions were deposited on Pt coated sapphire substrates by rf magnetron sputtering. Crystal structures of the BMN thin films by X-ray diffraction exhibited nearly pure cubic pyrochlore phase in a wide range of chemical substituents. The dielectric properties were systematically studied and discussed. The dielectric constant was found to increase with increasing Mg2+ content, while the dielectric loss changed little with the Mg2+ concentration and remained in a low level of ∼0.006. The BMN thin films with a composition of Bi1.5Mg1.0Nb1.5O7 demonstrated a tunability of 20% at applied bias filed of 1.0 MV/cm. The insufficient Mg2+ content decreased the tunability of the BMN thin films. However, the BMN thin films with excess Mg2+ content also did not exhibit enhanced tunable performance. These results indicated that the appropriate Mg2+ content and stoichiometric composition were of significance for improving the tunability of BMN thin films.