Abstract: Topochemical ion-exchange reactions between solid micro- and nanostructured metal chalcogenides and aqueous salt solutions are generally used for formation of composite structures based on initial metal chalcogenides and products of their ion-exchange transformation. However, ion exchange has promises as a route to obtaining both composites and solid solutions based on the initial and the end chalcogenide phases. With the help of the ion-exchange technique, single-phase films of Pb_1-xSn_xSe substitutional solid solutions with a tin content up to ～2 at.%, which are promising for mid- and long-wavelength infrared radiation (IR) optoelectronics, have been obtained at the interface between PbSe polycrystalline thin films and SnCl₂ aqueous solutions containing sodium citrate. It has been shown that the pH value and temperature of the reaction system play an important role in the ion-exchange process. Incubation of lead selenide (PbSe) films in a tin(II) salt aqueous solution also leads to their modification with oxygen-containing tin compounds to a depth of ～3 nm. Differences in the film structure, such as changes in the coherent scattering region sizes and orientation of crystallites along the [220] direction, which arise during the contact with citrate-containing SnCl₂ solutions, have also been revealed. For the first time, an idea of the existence of a relatively wide reaction zone of an intragranular topochemical ion-exchange reaction in an aqueous solution, within which substitutional solid solutions can form in micro- and nanostructured systems, has been set forth.

Key words: Ion-exchange synthesis, Thin films, Lead selenide, Tin selenide, Substitutional solid solutions, Topochemical reaction