Unconventional vapor–liquid–solid mechanism of ultra-long Ba6Mn24O48 whiskers growth from chloride fluxes

Isothermal growth in evaporating salt fluxes allowed the reproducible and high-yield synthesis of unique submicron-thick and millimeter-long manganese-rich Ba6Mn24O48 whiskers with a composite tunnel crystal structure. The crystals morphology and growth conditions suggest that the whiskers proliferate by an unusual mechanism based on a transport reaction of MnCl2 vapor, its oxidation into manganese oxides and interaction with a BaCl2-containing melt film wetting the whisker bodies. Thin fibers of Ba6Mn24O48 were found to grow mostly in the [001] direction parallel to their structural tunnels. A simple acid leaching splits the whiskers into flexible 20–50 nm thick nanofibers and converts them simultaneously into a protonated form favoring one-dimensional ionic conductivity.