Melanie John
Ludwig-Maximilians-Universität München, Germany
Title: Synthesis of (doped) ABO2 nanoparticles: Can this work at temperatures ≤ 90 °C without using an additional reducing agent?
Biography
Biography: Melanie John
Abstract
Delafossite (ABO2) is in focus of extensive research for its special magnetic, photo- and electrochemical as well as antiviral properties. Delafossite structures show a wide variability of chemistry (A = e.g. Cu, Ag and B = e.g. Fe, Mn, Cr, Co, Al) and are used for diverse technical applications including catalysis, p-type conduction oxide, solar cells, or as luminescent material. Many physical properties are directly related to grain size, but most of the common synthesis routes as solid-state reactions, sol-gel or hydrothermal techniques lead to crystals in micron size. With the Lt-delafossite process, a new synthesis route by precipitation and subsequent ageing, it is possible to gain pure nano-sized delafossite at temperatures ≤ 90 °C. The synthesized product exclusively consist of hexagonal, platy crystals with a diameter of less than 500 nm. The thickness increases with increasing ageing time from 5 to 200 nm. In case of CuFeO2, green rust (GR), precipitates first. Additional supply of OH- leads to the transformation of GR to delafossite. At the same time, GR acts as reducing agent for Cu2+. The ratio of 3R and 2H polytype is directly controllable by e.g. NaOH supply. The magnetic properties of CuFeO2 prepared by Lt-delafossite process deviate from both, natural delafossite and samples synthesized by other routes. A new approach is to produce doped delafossite. However, the incorporation of foreign ions is limited. Partly they are adsorbed on the surface and so hinder crystal growth especially in [001]. Moreover it promotes twinning of the crystals.