On the Crystal Structure of Colloidally Prepared Metastable Ag2Se Nanocrystals

<p>Structural polymorphism is known for many bulk materials; however, on the nanoscale metastable polymorphs tend to form more readily than in the bulk, and with more structural variety. One such metastable polymorph observed for colloidal Ag₂Se nanocrystals has traditionally been referred to as the &ldquo;tetragonal&rdquo; phase of Ag₂Se. While there are reports on the chemistry and properties of this metastable polymorph, its crystal structure, and therefore electronic structure, has yet to be determined. We report that an anti-PbCl₂-like structure type (space group <em>P</em>2₁/<em>n</em>) accurately describes the powder X-ray diffraction and X-ray total scattering patterns of colloidal Ag₂Se nanocrystals prepared by several different methods. Density functional theory (DFT) calculations indicate that the anti-PbCl₂-like Ag₂Se polymorph is a dynamically stable, narrow-band gap semiconductor. DFT results reveal a dense theoretical Ag₂Se phase space with many low-energy polymorphs, which helps explain the large number of polymorphs reported in the literature.</p> <p>&nbsp;</p> <p>Analysis and calculation data are stored in the zip archive. The `ag2se-calcs.aiida.` contains the provenance of the calculations and can be imported into an AiiDA database instance. The <a href="https://zenodo.org/api/files/baed3fb2-a4d3-49f7-a5d1-cb8da7cdbf28/antiPbCl2like_Ag2Se_laboratory.cif?versionId=36c207de-c537-4217-9b96-1ae08c2b487e">antiPbCl2like_Ag2Se_laboratory.cif</a> file is the Reitveld refined Ag2Se structure starting from the PbCl₂ structure.<br> &nbsp;</p> <p>Also hosted on <a href="https://github.com/SMTG-UCL/ag2se-anti-pbcl2-paper">GitHub</a> with minor revisions.</p> <p>Published paper: <a href="https://doi.org/10.1021/acs.nanolett.1c02045">https://doi.org/10.1021/acs.nanolett.1c02045</a></p>