Recent breakthrough of novel hierarchic materials, orchestrated through oriented attachment of crystal subunits, opened questions on what is the mechanism of their self-assembly. Using rutile-type TiO₂, synthesized by hydrothermal reaction of Ti(IV)-butoxide in highly acidic aqueous medium, we uncovered the key processes controlling this nonclassical crystallization process. Formation of complex branched mesocrystals of rutile is accomplished by oriented assembly of precipitated fibers along the two low-energy planes,i.e.{110} and {101}, resulting in lateral attachment and twinning. Phase analysis of amorphous material enclosed in pockets between imperfectly assembled rutile fibers clearly shows harmonic ordering resembling that of the adjacent rutile structure. To our understanding this may be the first experimental evidence indicating the presence of electromagnetic force-fields that convey critical structural information through which oriented attachment of nanocrystals is made possible.

Platinum copper alloy nanoparticle catalysts supported on graphitized carbon with and without partial crystal ordering were synthesized and tested for oxygen reduction and methanol oxidation reaction for potential use in direct methanol fuel cells and proton exchange membrane fuel cells. The activity enhancement by at least a factor of 2 is possible when Pm-3m phase is present in the nanoparticle with respect to the pure Fm-3m phase. A significance of Pt-skin type catalysts concept is explained for lowering the platinum content