(485e) Computational Investigation Of Bismuth Pyrochlores

There is considerable interest in pyrochlore systems (A₂B₂O₇) for use in high-permittivity dielectrics, capacitors and high-frequency filter applications. Substitutions on both the A and B sites in the pyrochlore structures can be used to tune material properties. Recently several complex Bi-containing pyrochlores, such as (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O_6.92 (BZN), have been synthesized but the structure-property relationship is still not well understood. Atomistic simulations will be important in gaining insight into these materials. Due to the disorder in the substitutions, molecular dynamics (MD) provides the best method for examining these large systems. We have developed a shell model potential for several Bi-containing pyrochlores based on fitting to extensive first-principles calculations of ideal bismuth pyrochlores. MD results for Bi_3/2ZnTa_3/2O₇ (BZT), Bi_3/2MgNb_3/2O₇ (BMN), Bi_3/2MgTa_3/2O₇ (BMT) and BZN will be presented and compared to experimental IR and Raman spectra and pair distribution functions to understand the role of the atomic substitutions on the material properties.