Local crystal chemistry, induced strain and short range order in the cubic pyrochlore (Bi_1.5-αZn_0.5-β)(Zn _0.5-γNb_1.5-δ)O_{(7-1.5α-β- γ-2.5δ)} (BZN)

Clear evidence (in the form of structured diffuse scattering) is found for short range ordering of metal ions and associated induced structural relaxation in two members of the cubic BZN pyrochlore (Bi_1.5-αZn _0.5-β)(Zn_0.5-γNb_1.5-δ)O _{(7-1.5α-β-γ-2.5δ)} solid solution. An average neutron powder diffraction structure refinement is carried out for one of these. Electron probe micro-analysis suggests that the primary mechanism for non-stoichiometry in cubic BZN is the removal of ZnO from the nominally fully occupied (Bi_1.5Zn_0.5)(Zn_0.5Nb _1.5)O₇ end-member. A detailed bond valence sum analysis of a recently reported average crystal structure is used to suggest possible local cation ordering schemes along with the induced displacive relaxation that is likely to accompany such local cation ordering. The observed diffuse distribution is qualitatively interpreted via Monte Carlo modelling.