Room-Temperature Solid-State Transformation of Na 4 SnS 4  ⋅ 14H 2 O into Na 4 Sn 2 S 6  ⋅ 5H 2 O: An Unusual Epitaxial Reaction Including Bond Formation, Mass Transport, and Ionic Conductivity

• Published in: Chemistry : a European journal Vol. 29; no. 1; p. e202202318
• Main Authors: Benkada, Assma, Hartmann, Felix, A Engesser, Tobias, Indris, Sylvio, Zinkevich, Tatiana, Näther, Christian, Lühmann, Henning, Reinsch, Helge, Adams, Stefan, Bensch, Wolfgang
• Format: Journal Article
• Language: English
• Published: Germany 02.01.2023
• Subjects: Infrared spectroscopy; Magic angle spinning NMR; Raman spectroscopy; AIMD simulations; Epitaxy; Ionic conductivity
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202202318

A highly unusual solid-state epitaxy-induced phase transformation of Na SnS  ⋅ 14H O (I) into Na Sn S  ⋅ 5H O (II) occurs at room temperature. Ab initio molecular dynamics (AIMD) simulations indicate an internal acid-base reaction to form [SnS SH] which condensates to [Sn S ] . The reaction involves a complex sequence of O-H bond cleavage, S protonation, Sn-S bond formation and diffusion of various species while preserving the crystal morphology. In situ Raman and IR spectroscopy evidence the formation of [Sn S ] . DFT calculations allowed assignment of all bands appearing during the transformation. X-ray diffraction and in situ H NMR demonstrate a transformation within several days and yield a reaction turnover of ≈0.38 %/h. AIMD and experimental ionic conductivity data closely follow a Vogel-Fulcher-Tammann type T dependence with D(Na)=6×10  m  s at T=300 K with values increasing by three orders of magnitude from -20 to +25 °C.