Features of bismuth tantalate based high-entropy pyrochlores preparation

Abstract

A family of high-entropy solid solutions based on bismuth tantalate with a pyrochlore structure (sp. gr. Fd-3m) containing transition 3d-element atoms in equimolar quantities was obtained for the first time by the method of solid-phase synthesis. The composition of pyrochlores can be described by the stoichiometric formulas Bi2A1/6B1/6C1/6D1/6E1/6F1/6Ta2O9+Δ and Bi2A1/5B1/5C1/5D1/5E1/5Ta2O9+Δ, where A–F are atoms of certain 3d-elements (Сr,Mn,Fe,Co,Ni,Cu). In total, seven compounds were synthesized, one six-component (according to the number of 3d elements) – Bi2Cr1/6Mn1/6Fe1/6Co1/6Ni1/6Cu1/6Ta2O9+Δ and six five-component pyrochlores. The synthesis of pyrochlores was a multi-stage heat treatment process at the temperatures of 650–1050 °C for 60 h. The amount of impurity phase of triclinic bismuth orthotantalate BiTaO4 (sp. gr. P-1) depended on the chemical composition of the samples due to the content of ions of 3d-elements in the bismuth sublattice. The creation of vacancies in the bismuth sublattice made it possible to prevent the formation of impurities. The samples are characterized by a dense, low-porosity microstructure with an average grain size of ∼3.0 μm. The parameter of the pyrochlore unit cell varies in the range of 10.4815–10.5223 Å depending on the chemical composition. The obtained results are promising for targeted chemical assembly of complex multicomponent compounds for catalytic applications.