Crystal structure refinement, low- and high-temperature X-ray diffraction and Mössbauer spectroscopy study of the oxoborate ludwigite from the Iten'yurginskoe deposit.

This paper reports an investigation of the chemistry, crystal structure refinement and thermal behavior (80-1650 K) of ludwigite from the Iten'yurginskoe deposit (Eastern Chukotka, Russia). Its chemical composition was determined by electron microprobe analysis, giving an empirical formula (MgFeMn)(FeAlMg)O(BO). A refinement of the crystal structure from single-crystal X-ray diffraction data (SCXRD) was provided for the first time for ludwigite from this deposit (R = 0.

Investigation of thermal behavior of mixed-valent iron borates vonsenite and hulsite containing [OM] and [OM] oxocentred polyhedra by in situ high-temperature Mössbauer spectroscopy, X-ray diffraction and thermal analysis.

The investigation of elemental composition, crystal structure and thermal behavior of vonsenite and hulsite from the Titovskoe boron deposit in Russia is reported. The structures of the borates are described in terms of cation-centered and oxocentred polyhedra. There are different sequences of double chains and layers consisting of oxocentred [OM] tetrahedra and [OM] tetragonal pyramids forming a framework.

The novel borate LuBaBO with a new structure type: synthesis, disordered crystal structure and negative linear thermal expansion.

Single crystals of LuBaBO were obtained by cooling from a melt and polycrystals of the borate were prepared using a multi-step solid-state synthesis. The crystal structure was determined from single-crystal X-ray diffraction data. The borate crystallizes in a new structure type in the monoclinic crystal system in space group C2/c, with cell parameters a = 13.

Metal arrays in structural units based on anion-centered metal tetrahedra.

Structural units based on anion-centered metal tetrahedra (XA(4); X = O, N; A = metal) are described as eutactic metal fragments with anions in tetrahedral interstices. In this respect these units may be subdivided into fluorite derivatives and units based on stellae quadrangulae (tetrahedral stars). To describe the geometry of the metal arrays a set of tetrahedrally packed metal radii, r(tp), is derived for A = Cu, Pb, Bi, and some rare-earth metals from the systematic analysis of the A.