Anisotropy of Thermal Expansion of Oxoborate Warwickite

Abstract

In this paper, the transition metal oxoborate warwickite (Fe²⁺,Mg)Fe³⁺(BO₃)O is studied for the first time by low- and high-temperature X-ray diffraction in the temperature range from 93 to 513 K. The sharply anisotropic nature of its thermal expansion is revealed. A structural interpretation of the expansion mechanism is given both in terms of the contribution of cationic and oxocentered polyhedra.