RÉSUMÉ
We report the synthesis and optical properties of noncentrosymmetric (NCS) γ-Cs2I4O11 that was obtained through IO4 polyhedral rearrangements from centrosymmetric (CS) ß-Cs2I4O11. Trifluoroacetic acid (TFA) acts as a structure-directing agent and plays a key role in the synthesis. It is suggested that the function of TFA is to promote rearrangement reactions found in the organic synthesis of stereoisomers. γ-Cs2I4O11 crystallizes in the NCS monoclinic space group P21 (No. 4) and exhibits a strong second-harmonic-generation (SHG) response of 5.0 × KDP (KH2PO4) under 1064 nm laser radiation. Additional SHG experiments indicate that the material is type I phase matchable. First-principles calculations show that SHG intensity mainly comes from its d34, d21, and d23 SHG tensor components. The synthetic strategy of discovering γ-Cs2I4O11 provides a new way for designing novel NCS SHG materials.
RÉSUMÉ
Two apatite-related silicates compounds, Tb2Pb3Si3O12 (I) and Pb5SiP2O12 (II), were obtained in the crystalline forms. Structure and ELF calculated results reveal that the lone pair cation of Pb2+ preferentially occupies the Cs site, and the repulsion between the mutual lone pair stabilizes channels. Moreover, combining conductivity results this preference has the important implications of exclusion and blocking the movement of the oxide ion in the channel of apatite-related structures. Our findings provide an experimental foundation for further interpreting the conductivity decrease in lone-pair ions as dopants into apatite-related silicate materials.
RÉSUMÉ
A novel zinc-beryllium borate BaZnBe2(BO3)2F2 was grown by a high-temperature flux method for the first time. It crystallizes in P3[combining macron] with the cell parameters of a = b = 4.5998, c = 7.7037 and Z = 1, which is different from BaMBe2(BO3)2F2 (M = Mg, Ca). Interestingly, when Zn replaces Mg and Ca in BaMgBe2(BO3)2F2 and BaCaBe2(BO3)2F2, the structure retains the same anionic group but the symmetry is lowered. The title compound contains a flexible net structure [Be3B3O6F3]∞ in the a-b plane with Ba and Zn atoms located in the interlayers accordingly, which overcomes the structural instability problems of SrBe2B2O7 (SBBO). The structure evolution from SBBO to BaZnBe2(BO3)2F2 was discussed. This work is of great significance to the discovery of new materials and the modification of existing materials.
RÉSUMÉ
A layered fluorooxoborate, KNiB4 O6 F3 , contains a new (B4 O6 F4 )4- group built of one planar (BO3 )3- triangle and three tetrahedral (BO3 F)4- units. Those units are joined together by sharing the oxygen atoms to form a 2-dimensinal (BO3/2 F)3 BO3/2 )∞ layer. K+ and Ni2+ occupy on the sides with F- and O2- of the (BO3/2 F)3 BO3/2 )∞ layer with a high (positive charge) to high (negative charge) and low to low coordination. Such kind of charge-oriented ordering is found to be governed by the stabilization energy of Coulomb interaction of the cations in certain sites. It is hoped that this mechanism of ordering may provide an additional tool for designing new structures with favourable properties, such as ferroelectrics or nonlinear optical materials.
RÉSUMÉ
Magnetic cooling at low temperature has attracted intensive interest in cryogenics research, which may become important as cooling medium for long-wave photon detectors to support space exploration. Here, we report a Gd-based quaternary magnetic refrigerant material, Gd5 BSi2 O13 , containing chains of face-shared GdO9 polyhedra and geometrically frustrated OGd3 triangles. Magnetic measurements indicate that Gd5 BSi2 O13 exhibits a large magnetocaloric effect (MCE) about 1.74â times that of the practical magnetic refrigerant GGG (-ΔSm =67.0â J kg-1 K-1 ). We analyzed the origin of the large MCE by comparing GdIII -containing compounds with different structures and concentrations of GdIII .