A One-Step Mechanochemical Route to Core−Shell Ca2SnO4 Nanoparticles Followed by 119Sn MAS NMR and 119Sn Mssbauer Spectroscopy
Vladimir epelk* and Klaus Dieter Becker, Ingo Bergmann‡ and Shigeru Suzuki, Sylvio Indris, Armin Feldhoff and Paul Heitjans, Clare P. Grey
Calcium stannate (Ca2SnO4) 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 Ca2SnO4 nanoparticles consisting of an ordered core surrounded by a disordered surface shell region. The inner core of a Ca2SnO4 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 119Sn MAS NMR and 119Sn Mssbauer spectroscopies to probe the local environment of Sn nuclei, valuable complementary insight into the local structural disorder in mechanosynthesized Ca2SnO4 was obtained. It was concluded that the near-surface layers of stannate nanoparticles are disordered because of broadly distorted geometry of SnO6 octahedra. The octahedra are deformed in such a way that they become more regular.