Cation Redistribution along the Spiral of Ni-Doped Phyllosilicate Nanoscrolls: Energy Modelling and STEM/EDS Study

Here, we study the stress-induced self-organization of Mg²⁺ and Ni²⁺ cations in the crystal structure of multiwalled (Mg_1-x ,Ni_x )₃ Si₂ O₅ (OH)₄ phyllosilicate nanoscrolls. The phyllosilicate layer strives to compensate size and surface energy difference between the metal oxide and silica sheets by curling. But as soon as the layer grows, the scrolling mechanism becomes a spent force. An energy model proposes secondary compensation of strain: two cations distribute along the nanoscroll spiral in accordance with preferable radii of curvature. To reveal this, we study synthetic (Mg_1-x ,Ni_x )₃ Si₂ O₅ (OH)₄ nanoscrolls by the scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDS) technique. For a number of scrolls, we have found indeed a change of Ni concentration with increase in distance from the nanoscroll central axis. The concentration gradient, according to our estimates, can reach 50 at.% over 25 nm of the wall thickness.