Heteroanionic
materials are a burgeoning class of compounds that
offer new properties via the targeted selection of anions. However,
understanding the design principles and achieving successful syntheses
of new materials in this class are in their infancy. To obtain mechanistic
insight and a panoramic view of the reaction progression from beginning
to end of the formation of a heteroanionic material, we selected BiOCuSe,
a well-known thermoelectric compound, and utilized in situ synchrotron powder diffraction as a function of temperature and
time. BiOCuSe is a layered material, which crystallizes in a common
mixed anion structure type: ZrSiAsFe. Two reactions of starting materials
(Bi2O2Se + Cu2Se and Bi2O3 + Bi + 3Cu + 3Se) were studied to determine the effect
of precursors on the reaction pathway. Our in situ investigation shows that the ternary–binary Bi2O2Se + Cu2Se reaction proceeds without intermediates
to directly form BiOCuSe, while the binary–elemental Bi2O3 + Bi + 3Cu + 3Se reaction generates many intermediates
before the final product forms. These intermediates include CuSe,
Bi3Se4, Bi2Se3, and Cu2Se. While the stoichiometric loading of the precursors necessarily
dictates the identity of the first intermediates, kinetics also plays
a contributing role in stabilizing unexpected intermediates such as
CuSe and Bi3Se4. Understanding and establishing
a link between the selection of precursors and the reaction pathways
improves the potential for rational synthesis of heteroanionic materials
and solid-state reactions in general.
Solid-state synthesis has historically focused on reactants and end products; however, knowledge of reaction pathways, intermediate phases and their formation may provide mechanistic insight of solid-state reactions. With an increased...
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