Abstract

Hydrogen has been inserted into a γ-MnO₂ (CMD type) characterised by approximately 70% de Wolff disorder and a low amount of microtwinning. 22 compounds were prepared covering the range 0 < s < 0.88 where s is the value in MnO_1.944H_s. XRD and FTIR studies showed homogeneous insertion up to s = 0.56 and heterogeneous insertion above this level. The results have been compared with those published in a companion paper where the host γ-MnO₂ had 40% de Wolff disorder. For both materials, the onset of heterogeneous insertion occurred when the a lattice dimension, derived from the ramsdellite portions of the intergrowths, had increased, in the homogeneous region, to its value in the final product. An important finding was the evidence that insertion took place uniformly in both portions of the intergrowths and not preferentially into the ramsdellite parts. Another important finding was the sudden location of all inserted H to form OH bonds in the middle of the homogeneous insertion region. This contrasted with the absence of OH bond formation for s < 0.36 and thereby strengthens the hypothesis of independent mobility of protons and electrons in regions where OH bond formation was absent. The concept of hinging again proved useful in interpreting the data and allowed the calculation of lattice parameters of the pyrolusite/manganite portions of the intergrowth from XRD data interpreted in terms of the ramsdellite/groutite portions of the intergrowth. Hinging is here defined as the equal clockwise and anti-clockwise rotation of two edge-shared octahedral chains about the c-directed axis connecting them.