金属硼酸盐、磷酸盐及硼酸磷酸盐新化合物的合成、结构及性能研究

The exploration of new borate and phosphate compounds has been a hot topic in recent years owing to their rich structural chemistry and a series of excellent optical performance. For example, it is benificial for these compounds to have a wide transparency range because of the large electronegativity of the atoms in B-O and P-O groups and the short bond length of B-O and P-O groups. These compounds have relatively stable physical and chemical properties. Because of the larger optical band gap of these compounds, they usually have larger optical damage threshold. Five compounds, Na2K2Ba(B9O15)2, APbPO4 (A = K, Rb, Cs), and LiPb4(BO3)(PO4)2, have been obtained in borate, phosphate, borate-phosphate systems, respectively. In this thesis, the crystal structures, syntheses, performance measurements and the electronic structures of the above compounds were investigated. 1. A new mixed-alkali- and alkaline-earth-metal quaternary borate, Na2K2Ba(B9O15)2, has been synthesized by spontaneous crystallization use K2CO3 and PbCl2 as flux. Na2K2Ba(B9O15)2 crystallizes in the monoclinic system, P21/c (No. 14) space group with a = 8.493(8) ?, b = 8.540(9) ?, c = 17.102(16) ?, β = 90.453(11)°, V = 1240(2) ?3, and Z = 2. In the structure, three [B3O7]5- groups form a [B9O19]11- group by sharing oxygen atoms, and the [B9O19]11- groups are further condensed into a 3D [B9O15]3- framework with the metal atoms filled in the pore space. The powder XRD pattern and the TG/DSC curves unambiguously demonstrates that Na2K2Ba(B9O15)2 is an incongruently melting compound. Therefore, the flux method is necessary for the purpose of its crystal growth. The calculated result shows that the optical properties of the compounds mainly depends on boron oxygen groups. 2. Three alkali metal lead orthophosphates, APbPO4 (A = K, Rb, Cs), have been synthesized by spontaneous crystallization. They crystallize in the same space group Pnma (No. 62), but they are not all isostructural. APbPO4 (A = K, Rb) are isostructural, and the three-dimensional (3D) structure of RbPbPO4 (representative) consists of [Pb1|Rb1O4]∞ chains connected by isolated PO4 tetrahedra, with the Pb2|Rb2 atoms filling in the pore space. The 3D structure of CsPbPO4 consists of another kind of [PbO4]∞ chains connected with isolated PO4 tetrahedra, and the Cs atoms reside in the channel. The UV-Vis-NIR diffuse reflectance spectra exhibit that the cut off edges of three compounds are below 250, 254 and 242 nm, respectively. 3. Analysis results show that through regulating the ratio of [M/(B+P)] is also an effective strategy to synthesize new borate-phosphates. And the first lithium lead borate-phosphate, LiPb4(BO3)(PO4)2, has been synthesized by regulating this ratio. It crystallizes in the orthorhombic space group Pbca (No. 61) with a = 12.613(13) ?, b = 6.551(7) ?, c = 25.36(3) ?, V = 2095(4) ?3, and Z = 8. It possesses a 3D structure with a corrugated 2D layer of [B2Pb8O18]∞ that is further connected by a [LiP2O8]∞ chain, both BO3 and PO4 were isolated. The calculated result of electronic structure and optical properties shows that LiPb4(BO3)(PO4)2 is a direct bandgap semiconductor with a relative large birefringence about 0.040~0.090 with the wavelength from 1064 to 350 nm.