Kavli Affiliate: Kristin A. Persson
| First 5 Authors: Paul K. Todd, Matthew J. McDermott, Christopher L. Rom, Adam A. Corrao, Jonathan J. Denney
| Summary:
In sharp contrast to molecular synthesis, materials synthesis is generally
presumed to lack selectivity. The few known methods of designing selectivity in
solid-state reactions have limited scope, such as topotactic reactions or
strain stabilization. This contribution describes a general approach for
searching large chemical spaces to identify selective reactions. This novel
approach explains the ability of a nominally "innocent" Na$_2$CO$_3$ precursor
to enable the metathesis synthesis of single-phase Y$_2$Mn$_2$O$_7$ — an
outcome that was previously only accomplished at extreme pressures and which
cannot be achieved with closely related precursors of Li$_2$CO$_3$ and
K$_2$CO$_3$. By calculating the required change in chemical potential across
all possible reactant-product interfaces in an expanded chemical space
including Y, Mn, O, alkali metals, and halogens, using thermodynamic parameters
obtained from density functional theory calculations, we identify reactions
that minimize the thermodynamic competition from intermediates. In this manner,
only the Na-based intermediates minimize the distance in the hyperdimensional
chemical potential space to Y$_2$Mn$_2$O$_7$, thus providing selective access
to a phase which was previously thought to be metastable. Experimental evidence
validating this mechanism for pathway-dependent selectivity is provided by
intermediates identified from in situ synchrotron-based crystallographic
analysis. This approach of calculating chemical potential distances in
hyperdimensional compositional spaces provides a general method for designing
selective solid-state syntheses that will be useful for gaining access to
metastable phases and for identifying reaction pathways that can reduce the
synthesis temperature, and cost, of technological materials.
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