Real-time in-situ monitoring of the topotactic transformation of TlCu3Se2 into TlCu2Se2

•Topotactic transition from TlCu3Se2 to TlCu2Se2 followed in situ.•Synchrotron radiation X-ray powder diffraction enabled short scans.•Relative abundance of phases refined from powder data.•Opens up for studying similar systems in the same manner.

The solid state transformation of monoclinic TlCu3Se2 into tetragonal TlCu2Se2 by oxidative copper leaching in concentrated ammonia solution has been studied in situ by the use of synchrotron radiation. The diffraction patterns of parent and daughter phase are both sharp, indicating a strong topotactic relationship between them that effectuates a rapid change by “chimie douce” performed at +19 °C.The transformation rate is strongly connected to the access of oxygen from the surrounding air. The transformation was followed in a real-time mode, being almost complete after 2.5 h with 1 h incubation due to low oxygen content, as shown from refining the diffraction patterns by Rietveld profile technique.