Determination of the hydrogen-bond network and the ferrimagnetic structure of a rockbridgeite-type compound, [Formula: see text].

ABSTRACT

Applying neutron powder diffraction, four unique hydrogen positions were determined in a rockbridgeite-type compound, [Formula see text] [Formula see text]. Its honeycomb-like H-bond network running without interruption along the crystallographic [Formula see text] axis resembles those in alkali sulphatic and arsenatic oxyhydroxides. They provide the so-called dynamically disordered H-bond network over which protons are superconducting in a vehicle mechanism. This is indicated by dramatic increases of dielectric constant and loss factor at room temperature. The relevance of static and dynamic disorder of OH and HOH groups are explained in terms of a high number of structural defects at octahedral chains alternatingly half-occupied by [Formula see text] cations. The structure is built up by unusual octahedral doublet, triplet, and quartet clusters of aliovalent 3d transition metal cations, predicting complicate magnetic ordering and interaction. The ferrimagnetic structure below the Curie temperature [Formula see text]-83 K could be determined from the structure analysis with neutron diffraction data at 25 K.