Nanoparticle Size Effects on Phase Stability for Molybdenum and Tungsten Carbides

Transition-metal
carbides (TMCs) are important materials for a
variety of applications and industrial processes, in part because
of their variable crystal structures and surfaces. However, the synthesis
of TMCs often proceeds through metastable phases during particle growth,
the appearance of which cannot be described by traditional phase diagrams.
Here, we use density functional theory calculations and thermodynamic
analyses to construct particle size-dependent phase diagrams for Mo
and W carbides and reveal the relationships between phase stability
and TMC nanoparticle size. We compute size-dependent phase diagrams
for a wide range of Mo carbide and W carbide phases, determine predicted
crystallization pathways during synthesis, and compare model results
with experimental data. We provide insights for the influence of nanoparticle
size on TMC nucleation and growth during synthesis and provide a computationally
guided road map for navigating the synthesis of target TMC surfaces
and phases.