THE STRUCTURE OF FULLY H-INSERTED GAMMA-MANGANESE DIOXIDE COMPOUNDS

Four materials forming a structural series of gamma-manganese dioxides were identified by an increasing proportion of microtwinning (17-100% ) and a nearly constant amount of de Wolff disorder (P-r similar or eq ual to 0.41) as determined from their XRD patterns, Chemical I-I-inser tion was performed in a nonaqueous environment and the structure of th e fully I-I-inserted compounds investigated by XRD, In contrast to the starting materials the I-I-inserted compounds had similar XRD pattern s which could be indexed on the basis that I-I-insertion caused expans ion predominantly in the b orthorhombic direction, The anisotropic exp ansion changed the angle of the 021 and 061 microtwinning planes and c aused strain along them, The demicrotwinning which resulted was the re ason for the similarity of the XRD patterns of the II-inserted compoun ds, The common endpoint of II-insertion into the structural series was delta-MnOOH, which is an unmicrotwinned intergrowth structure based o n groutite and manganite type layers reflecting the original intergrow th of ramsdellite and pyrolusite type layers in the original host stru ctures. (C) 1996 Academic Press, Inc.