The β-modification of trizinc borate phosphate, Zn3(BO3)(PO4)

Crystals of β-Zn3(BO3)(PO4) have been grown by the Kyropoulos method. The asymmetric unit contains three Zn sites, three B-atom sites (all with symmetry 3), two P sites (both with m symmetry) and nine O-atom sites (four with m symmetry). The fundamental building units of the title structure are isolated BO3 triangles and PO4 tetra­hedra, which are bridged by ZnO4 tetra­hedra or ZnO5 trigonal bipyramids through common O atoms, leading to a three-dimensional framework structure. Some significant structural differences between the β-polymorph and the α-polymorph are discussed

Crystal structures of spinel-type Na2MoO4and Na2WO4 revisited using neutron powder diffraction

Time-of-flight neutron powder diffraction data have been collected from Na2MoO4 and Na2WO4 to a resolution of sin ([theta])/[lambda] = 1.25 Å-1, which is substanti­ally better than the previous analyses using Mo K[alpha] X-rays, providing roughly triple the number of measured reflections with respect to the previous studies [Okada et al. (1974). Acta Cryst. B30, 1872-1873; Bramnik & Ehrenberg (2004). Z. Anorg. Allg. Chem. 630, 1336-1341]. The unit-cell parameters are in excellent agreement with literature data [Swanson et al. (1962). NBS Monograph No. 25, sect. 1, pp. 46-47] and the structural parameters for the molybdate agree very well with those of Bramnik & Ehrenberg (2004). However, the tungstate structure refinement of Okada et al. (1974) stands apart as being conspicuously inaccurate, giving significantly longer W-O distances, 1.819 (8) Å, and shorter Na-O distances, 2.378 (8) Å, than are reported here or in other simple tungstates. As such, this work represents an order-of-magnitude improvement in precision for sodium molybdate and an equally substantial improvement in both accuracy and precision for sodium tungstate. Both compounds adopt the spinel structure type. The Na+ ions have site symmetry .-3m and are in octa­hedral coordination while the transition metal atoms have site symmetry -43m and are in tetra­hedral coordination

Stimulated Raman Scattering in Melilite‐Type Crystals Ca2MgSi2O7 and Ca2Ga2SiO7

χ(3)‐nonlinear optical interactions in two melilite‐type stimulated Raman scattering (SRS)‐active non‐centrosymmetric crystals, Ca2MgSi2O7 and Ca2Ga2SiO7, formerly known as Nd3+‐laser media, are presented. Under picosecond pumping at 1.064 and 0.532 µm cascaded and cross‐cascaded effects occur in these tetragonal silicates. Besides the SRS‐promoting phonon modes with energy of ωSRS1 ≈ 908 cm−1 and ωSRS2 ≈ 668 cm−1 for Ca2MgSi2O7, and ωSRS1 ≈ 720 cm−1 and ωSRS2 ≈ 550 cm−1 for Ca2Ga2SiO7, respectively, combined phonon modes are observed. For Ca2MgSi2O7 new data in a broad wavelength range of refractive indices and their dispersion are given as well. The observed χ(3)‐nonlinear properties expand the functionality of the studied silicates and foreshadow their use in self‐frequency Raman laser converters (self‐SRS lasers)