Solid-state transformation of nanocrystalline phyllomanganate into tectomanganate: influence of initial layer and interlayer structure

Synthetic vernadite was equilibrated at pH values ranging from 3 to 10 and its crystal structure elucidated using X-ray diffraction on fresh samples and on samples aged for up to 8 years. The main structural transformation with time is related to the migration of Mn³⁺ from the octahedral layer to the interlayer. For low pH samples, which initially contain a higher number of interlayer Mn³⁺, this transformation leads to a tunnel-like cryptomelane structure (2 × 2 tunnel size).