CRYSTAL-STRUCTURE OF SODIUM BERYLLIUM BORATE FLUORIDE

An important use of nonlinear optical (NLO) materials is in vacuum ultraviolet (VUV) applications, and no crystal except KBe2BO3F2 (KBBF) can be used in the VUV region thus far. In this paper, the crystal structure of a new monoclinic VUV NLO crystal, sodium beryllium borate fluoride, NaBe2BO3F2(NBBF), is reported. The crystal structure has been determined by single crystal X-ray diffraction, and the final R value for 612 unique reflections with I>3.00 sigma(I) is 5.6%. The compound has the same polyanions as KBe2BO3F2. All the B atoms are nearly triangularly coordinated in the plane, while all the Be atoms are tetrahedrally coordinated. The structure is characterized by infinite sheets [Be2BO3F2], which may be described in terms of six-membered rings of [Be2BO6F2] composed of one [BO3] and two [BeO3F] with edges in common. Its large, nonlinear optical (NLO) coefficients, short absorption edge, and moderate birefringence show that it will also be a promising VUV NLO material.