Ruzica Djenadic

Multicomponent equiatomic rare earth oxides

ABSTRACT Multicomponent rare earth oxide (REO) nanocrystalline powders containing up to seven equiatomic rare earth elements were successfully synthesized in a single-phase CaF2-type (Fm-3 m) structure. The addition of more than six elements resulted in the formation of a secondary phase. Annealing at 1000°C for 1 h led to the formation of a single-phase (Ia-3) even in the 7-component system. In the absence of cerium (Ce4+), secondary phases were observed irrespective of the number of cations or the extent of thermal treatment indicating that cerium cations played a crucial role in stabilizing the multicomponent REOs into a phase pure structure. GRAPHICAL ABSTRACT IMPACT STATEMENT Multicomponent equiatomic rare earth oxides pioneer a new group of materials that crystallize into a single-phase structure with the dominant role of a single element instead of entropy.

Chemical Vapor Synthesis of Nanocrystalline Oxides

The generation of nanoparticles in the gas phase by Chemical Vapor Synthesis (CVS) may be described from the point of view of chemical engineering as a sequence of unit operations among which reactant delivery, reaction energy input, and product separation are key processes which determine the product characteristics and quality required by the applications of nanoparticles and powders. In case of CVS, the volatility of the reactants (precursors) may severely limit the possible type of products as well as the production rate. It is shown that these limits can be lifted by use of a laser flash evaporator which also enables the use of precursor mixtures for the production of complex oxides as shown for Co-doped ZnO and the pulsed operation to influence powder characteristics. The mode in which energy is supplied to the particle synthesis reactor has also substantial influence on particle and powder characteristics as is shown for TiO\(_{2}\) using different time-temperatureprofiles.

Chemical vapor synthesis of nanocrystalline perovskites using laser flash evaporation of low volatility solid precursors

One key requirement for the production of multinary oxide films by chemical vapor deposition (CVD) or nanocrystalline multinary oxides particles by chemical vapor synthesis (CVS) is the availability of precursors with high vapor pressure. This is especially the case for CVS where much higher production rates are required compared to thin films prepared by CVD. However, elements, which form low valent cations such as alkaline earth metals, are typically only available as solid precursors of low volatility, e.g., in form of beta-diketonates. This study describes laser flash evaporation as precursor delivery method for CVS of nanocrystalline perovskites. Laser flash evaporation exploits the nonequilibrium evaporation of solid metal organic precursors of low vapor pressure by absorption of the infrared radiation of a CO(2) laser. It is shown that stoichiometric, nanocrystalline particles consisting of SrZrO(3) and SrTiO(3) can be formed from corresponding mixtures of beta-diketonates which are evaporated nonselectively and with high rates by laser flash evaporation.