posted on 2021-09-07, 17:08authored byPaul K. Todd, Matthew J. McDermott, Christopher L. Rom, Adam A. Corrao, Jonathan J. Denney, Shyam S. Dwaraknath, Peter G. Khalifah, Kristin A. Persson, James R. Neilson
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” Na2CO3 precursor to
enable the metathesis synthesis of single-phase Y2Mn2O7: an outcome that was previously only accomplished
at extreme pressures and which cannot be achieved with closely related
precursors of Li2CO3 and K2CO3 under identical conditions. 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 Y2Mn2O7, 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.