Circumventing Diffusion in Kinetically Controlled Solid-State Metathesis Reactions.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Inorganic Synthesis

Background:

• Solid-state diffusion often limits the synthesis of novel crystalline inorganic materials.
• Developing synthetic routes that bypass diffusion is crucial for accessing metastable compounds.

Purpose of the Study:

• To investigate solid-state metathesis reactions (MCl2 + Na2S2 → MS2 + 2 NaCl) for M = Fe, Co, Ni.
• To explore how different reactant preparation methods influence reaction pathways and product formation.

Main Methods:

• In situ synchrotron powder X-ray diffraction.
• Differential scanning calorimetry.
• Pair distribution function analysis.

Main Results:

• Air-free reactions showed diffusion-limited product formation with intermediate phases.
• Grinding reactants in air led to direct NaCl formation, displacing ions into an amorphous matrix.
• Heating the air-ground mixture resulted in direct nucleation of MS2, avoiding binary intermediates.

Conclusions:

• Grinding in air alters reaction pathways by forming NaCl, which dissipates lattice energy and facilitates direct MS2 nucleation.
• This method offers a route to bulk synthesis of various compounds, circumventing diffusion-limited binary intermediates.