Solution-phase synthesis and thermal conductivity of nanostructured CdSe, In₂Se₃, and composites thereof

The use of nanoparticle-in-matrix composites is a common motif among a broad range of nanoscience applications and is of particular interest to the thermal sciences community. To explore this morphological theme, we create crystalline inorganic composites with nanoparticle volume fractions ranging from 0 to ∼100% using solution-phase processing. We synthesize these composites by mixing colloidal CdSe nanocrystals and In₂Se₃ metal-chalcogenide complex (MCC) precursor in the solution-phase and then thermally transform the MCC precursor into a crystalline In₂Se₃ matrix. We find rich structural and chemical interactions between the CdSe nanocrystals and the In₂Se₃ matrix, including alterations in In₂Se₃ grain size and orientation as well as the formation of a ternary phase, CdIn₂Se₄. The average thermal conductivities of the 100% In₂Se₃ and ∼100% CdSe composites are 0.32 and 0.53 W m^-1 K^-1, respectively. These thermal conductivities are remarkably low for inorganic crystalline materials and are comparable to amorphous polymers. With the exception of the ∼100% CdSe samples, the thermal conductivities of these nanocomposites are insensitive to CdSe volume fraction and are ∼0.3 W m^-1 K^-1 in all cases. We attribute this insensitivity to competing effects that arise from structural morphology changes during composite formation. This insensitivity to CdSe volume fraction also suggests that very low thermal conductivities can be reliably achieved using this solution-phase route to nanocomposites.