Irreversible Thermochromic Pb2Sn2O6·xH2O: Competition between Weak Ligand H2O and Lone-Pair Electrons

Abstract

Many post-transition-metal based compounds have been reported as thermochromic materials. However, the thermochromic effect of crystalline water induced competition between sp3 non-equivalent hybridized O2s and O2p orbitals and lone-pair electrons from post-transition-metal oxides have not been elucidated. Here, we provide a new model compound Pb2Sn2O6·xH2O to realize the dynamic competition at the bottom of the conduction band minimum in thermochromic process. Two different hydrothermal methods have been applied to synthesis the Pb2Sn2O6·xH2O samples. These materials all exhibited a color evolution from light yellow to reddish brown, and had color mutations due to dehydration at different temperature points. The difference in the color mutation temperature point is attributed to the different lattice energy and water content of the two, and it is an irreversible thermochromic material due to dehydration. However, due to the strong coupling between the crystal structure and electronic structure, the 6s2 lone pair of electrons repel each other due to heating, resulting in a decrease in the distance between Pb and O, and the Pb6s–O2p hybrid anti-bonding state is promoted to a higher energy, and the effective band gap decreases, thereby reducing the energy required for charge transfer. Therefore, our work not only provides a new dehydration-type inorganic irreversible thermochromic material, but also fully elucidates the interaction mechanism and band gap relationship between lone pair electrons and oxygen. It also provides a new idea to adjust the thermochromic rate and color mutation temperature point by changing the lattice energy and water content, which is conducive to the development of a new generation of inorganic thermochromic materials.