K2Fe2B2O7: A transparent nonlinear optical crystal with frustrated magnetism

A new noncentrosymmetric ferroborate crystal, K2Fe2B2O7, has been grown from high temperature melt Structure solution from single crystal X-ray diffraction shows that the title compound crystallizes in a trigonal space group P321 with cell dimensions of a=8 7475(12) angstrom and c=8 5124(17) angstrom. In the structure. FeO4 tetrahedron shares its three basal oxygen atoms with BO3 triangles forming a two-dimensional layer in the ab plane and the layers are connected by the apical Fe-O bonds along the c direction The crystal is transparent in the visible and near infrared region from 500 to 2000 urn with three pronounced absorption bands ascribed to d-d transitions of tetrahedrally coordinated Fe3+ ions. Though. structurally analog to K2Al2B2O7, the further twisting of the BO3 groups between adjacent layers reduces its optical nonlinearity to a second-harmonic generation intensity of about 04 times that of KDP Spin-glass behavior is observed at 20 K which is probably clue to geometrically magnetic frustration of the triangular Fe net in the ab plane. (C) 2010 Elsevier Inc All rights reserved.