Chemical and morphological modifications of filamentary crystals of the Ba6Mn24O48 manganite with a tunnel structure

Abstract

Filamentary crystals of the Ba 6 Mn 24 O 48 manganite with a tunnel structure are synthesized in the protonated form for the first time. The protonated form of the whiskers is characterized by the formation of labile Mn-OH bonds, an increased value of the average oxidation number of manganese, and an anisotropic compression of the lattice in the direction perpendicular to the direction of the structural tunnels. These processes are accompanied by substantial changes in the micromorphology of whiskers, specifically by the splitting of the whiskers into 20-to 50-nm-thick nanofibers.

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

“…According to the literature, 10,21 Mn-O-H protons in the H-forms of manganites are mobile enough to result in decent proton conductivity. A detailed study of the protonated Ba 6 Mn 24 O 48 phase by impedance spectroscopy and four-probe transport measurements revealed that it demonstrates mixed conductivity with both proton and electronic components reaching $10 À3 U À1 cm À1 at 24 C. 10 The protonated form of whiskers also demonstrates a much higher ability to intercalate lithium.…”

“…Manganese-containing complex oxides have attracted interest for long time because of intriguing physical properties associated with their particular crystal structure. 3,4,6,13,14,20 The recently discovered Ba 6 Mn 24 O 48 phase demonstrates an unusual composite tunnel structure and would be formed as crystalline inorganic fibers [8][9][10][11][12][13]20,21 but details of their growth mechanism have never been reported. Here, we suggest an effortless technique of Ba 6 Mn 24 O 48 whisker growth from low-cost, nontoxic alkali-metal chlorides (KCl and NaCl) followed by proton insertion in the structural tunnels of Ba 6 Mn 24 O 48 whiskers achieved by a simple acid-leaching procedure.…”