Synthesis and crystal structure of the high-pressure iron borate α-FeB2O4

The high-pressure iron borate alpha-FeB2O4 was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 degrees C. The monoclinic iron borate crystallizes with eight formula units in the space group P2(1)/c with the lattice parameters a = 715.2(2), b = 744.5(2), c = 862.3(2) pm, and beta = 94.71(3)degrees. The compound is built up exclusively from corner-sharing BO4-tetrahedra, isotypic to the monoclinic phases beta-SrGa2O4, CaAl2O4-II, and CaGa2O4. Additionally, the structure is closely related to the orthorhombic compound BaFe2O4. The structure consists of layers of six-membered rings, which are interconnected to a three-dimensional network. The iron cations are coordinated by six and seven oxygen atoms. Next to synthesis and crystal structure of the new high-pressure borate, structural coherences to other structure types are discussed. (C) 2008 Elsevier Inc. All rights reserved.