A One-Step Mechanochemical Route to Core−Shell Ca₂SnO₄ Nanoparticles Followed by ¹¹⁹Sn MAS NMR and ¹¹⁹Sn Mössbauer Spectroscopy

Calcium stannate (Ca 2 SnO 4 ) nanoparticles with an average size of about 15 nm were synthesized via single-step mechanochemical processing of binary oxide precursors at room temperature. High-resolution TEM studies revealed a nonuniform structure of mechanosynthesized Ca 2 SnO 4 nanoparticles consisting of an ordered core surrounded by a disordered surface shell region. The inner core of a Ca 2 SnO 4 nanoparticle possesses a fully ordered orthorhombic structure, and the surface shell exhibits the thickness of about 1.5 nm. The volume fraction of surface shell regions in the nanostructured mechanosynthesized stannate is estimated to be about 50%. Because of the ability of both solid-state 119 Sn MAS NMR and 119 Sn Mössbauer spectroscopies to probe the local environment of Sn nuclei, valuable complementary insight into the local structural disorder in mechanosynthesized Ca 2 SnO 4 was obtained. It was concluded that the near-surface layers of stannate nanoparticles are disordered because of broadly distorted geometry of SnO 6 octahedra. The octahedra are deformed in such a way that they become more regular.