Metastable cubic Cu₃SbS₃: a facile solution-phase access to a kinetic polymorph.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nanotechnology

Background:

• Controlling inorganic solid properties relies on polymorphism, but stabilizing high-energy phases is difficult.
• The ternary copper chalcogenide Cu₃SbS₃ has diverse structures, yet its metastable cubic polymorph (space group I4̄3m) remains elusive in pristine form.

Purpose of the Study:

• To achieve room-temperature stabilization of the metastable cubic Cu₃SbS₃ phase.
• To investigate the structural, thermal, and electronic properties of the stabilized cubic Cu₃SbS₃ nanocrystals.
• To explore the potential of nanoscale synthesis for accessing novel material phases.

Main Methods:

• Low-temperature solution-phase synthesis of Cu₃SbS₃ nanocrystals.
• Structural and spectroscopic analysis (e.g., X-ray diffraction, spectroscopy).
• Thermal studies (high-temperature powder X-ray diffraction, positron annihilation spectroscopy).

Main Results:

• Phase-pure cubic Cu₃SbS₃ nanocrystals were successfully synthesized and stabilized at room temperature.
• The cubic phase is kinetically stable up to ~623 K, transforming irreversibly thereafter.
• Nanocrystals exhibit p-type semiconducting behavior, a band gap of ~1.86 eV, and ultralow thermal conductivity (~0.77 W m⁻¹ K⁻¹).

Conclusions:

• Nanoscale synthesis provides access to previously inaccessible metastable polymorphs.
• The low thermal conductivity is attributed to anharmonicity from Sb 5s² lone pairs and Cu coordination distortions.
• This work expands the accessible phase space of chalcogenides, enabling tailored optoelectronic and thermoelectric applications.