| 英文摘要: |
hree compounds δ-CsB5O8, BaZn2B2O6 and RbCdB3O6 have been obtained in Cs2O-H3BO3, Rb2O-CdO-H3BO3 and BaO-ZnO-H3BO3 systems, respectively. Though, all the compounds crystalize in the centrosymmetric groups. The δ-CsB5O8 and BaZn2B2O6 compounds have their own polymorphisms. The RbCdB3O6 compound is isomorphic to KCdB3O6. In this thesis, the synthesis, crystal structures, crystal growth and properties of the above compounds are investigated. 1. Single crystal of δ-CsB5O8 is grown by high temperature solution method. δ-CsB5O8 crystallizes in orthorombic space group Pccn (No. 56) with lattice constants a = 21.028(6) ?, b = 10.415(3) ?, c = 13.294(4) ?, Z = 16, V = 2911.5(4) ?3. The 3D network consists of 21 helical chains analogous to DNA which are connected by BO4 units and three types of Cs+ ions filling in the space to balance the charge. And to the best of our knowledge, the FBB B10O19 has not been reported previously in any anhydrous and hydrated borates. 2. The relation and difference of ring structures in all the CsB5O8 polymorphs are discussed to show the exciting diversity of CsB5O8. The work provides an idea to the design and synthesis of new borate compounds. 3. Single crystal of BaZn2B2O6 is grown by high temperature solution method. BaZn2B2O6 crystallizes in monoclinic space group P21/n (No. 14) with lattice constants: a = 10.154(16) ?, b = 4.928(8) ?, c = 12.085(19) ?, β = 111.227(19) °. A layer of ∞[Zn2B2O6]2- which is composed of BO3 and ZnO4 exists in the structure. The layers are connected by the Ba2+ ions. 50 % of the Zn atoms in the structure are connected to each other through oxygen atoms by edge which contradicts the third Pauling’s Rules. 4. By comparison with the polymorphisms, the phase-transition is reconstruction phase change and the thermal analysis endothermic peaks are not obviously observed. The BSI and GII of both BaZn2B2O6 phases are calculated to compare their stability. The results show that BaZn2B2O6 belonging to the monoclinic system may be more stable. This result may be caused by the edge-sharing ZnO4 structure which is similar with KZnB3O6. 5. A novel mixed-borate RbCdB3O6 has been synthesized using Rb2CO3 and H3BO3 as the flux system due to its incongruent melting behavior. The crystal structure has been determined by single-crystal X-ray diffraction method. RbCdB3O6 crystallizes in monoclinic space group C2/c with lattice constants a = 7.357(2) ?, b = 13.315(4) ?, c = 12.702(4) ?, β = 106.711(3) °, Z=8. It is a layer-type structure composed of planar B3O6 rings, which are parallel to each other in the same layer but distributed discretely from layer to layer. The Rb and Cd atoms alternately occupy sites among the B3O6 rings in the same layer and combine the layers together by Cd-O and Rb-O bonds. The structure comparison among RbCdB3O6, α-BaB2O4 and β-BaB2O4 suggests that RbCdB3O6 may have a large birefringence, which consists with the calculated value (0.06 - 0.07 in the visible region). In addition, the diffuse reflectance spectrum shows that the absorption edge at about 295 nm. The first-principles theoretical calculation shows that the compound is direct-gap semiconductor with band gap of 3.97 eV, which is in good agreement with experimental value. 6. RbCdB3O6 is isomorphic to KCdB3O6. By the comparison bewteen RbCdB3O6 and KCdB3O6, both structures contain a layer of isolated B3O6 groups and one-dimentional CdO5 polyhedra chain. However, the connected atoms are different in the distance between layers and the coordination numbers of oygen atoms. The difference of cations radii leads to the diversities of tunnel size and denity of the compounds. All the changes make the GII value of RbCdB3O6 larger than that of KCdB3O6. |
