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锶镉硼酸盐体系中同质多晶化合物的探索与研究
张兴文
学位类型硕士
导师潘世烈
2015-05-20
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料工程
关键词同质多晶 硼酸盐 晶体结构 单晶衍射 粉末衍射
摘要

同质多晶作为结晶学领域一种重要的现象,在染料、食品、药剂等方面具有突出贡献,也对结晶过程和结构-性质关系研究具有特殊意义。本论文以研究同质多晶化 合物为目标,选择锶镉硼酸盐体系,通过传统的高温固相反应方法,成功合成出四种新型同质异晶化合物:β-Cd3B2O6,β-SrCdB2O5,β- Cd2B2O5,γ-Cd2B2O5。通过高温溶液法生长了小尺寸晶体,解析了晶体结构,并就固相合成、晶体结构、晶体生长、物化性质以及理论计算等方面 进行了研究。研究表明:在锶镉硼酸盐体系中,含有孤立硼酸盐阴离子基团的化合物更可能出现同质多晶现象,且一些同质异晶体是是亚稳相,可能较难通过传统的 高温固相合成方法得到粉末纯样。 1. 高温熔液法合成了β-Cd3B2O6化合物,其属于三斜晶系,空间群为 (No. 2),晶胞参数:a = 6.1114(5) ?,b = 6.1463(5) ?,c = 7.4232(6) ?,α= 76.521(3)°,β= 80.730(3)°,γ= 82.461(3)°,Z = 2,V = 266.34(4) ?3。β-Cd3B2O6的晶体结构是由孤立的平面BO3基团以及CdO5、CdO6基团组成,这三种基团通过共享氧原子相互连接形成了三维网络结构。用 高温固相反应法,在不同的温度梯度下合成Cd3B2O6样品,结合粉末X射线衍射技术,研究了Cd3B2O6的相转移过程。并结合差热-热重测试,确定了 精确的相变信息。另外也做了熔融前后实验,确定了Cd3B2O6的熔融行为。同时也对比了Cd3B2O6同质多晶体的结构,也分析了目前报道的其他硼酸镉 化合物的结构特点,例如CdB4O7, CdB2O4 和 Cd2B2O5。 2. 高温熔液法合成出正交晶系α-SrCdB2O5化合物和其同质多晶化合物单斜晶系的β-SrCdB2O5。使用X射线单晶衍射仪收集晶体信息,并对它们的 结构进行解析。对于α-SrCdB2O5,空间群为Pbca (No. 61),晶胞参数:a = 11.955(12) ?,b = 5.762(6) ?,c = 12.658(12) ?,V = 872.0(15) ?3, ρ = 4.595 Mg/m3。对于β-SrCdB2O5,空间群为C2/c (No. 15),晶胞参数:a = 7.639(7) ?,b = 10.183(10) ?,c = 11.140(10) ?,V = 855.2(14) ?3, ρ = 4.685 Mg/m3。在这部分工作中,主要研究了存在于SrCdB2O5同质多晶中的密度反常现象:高温相β-SrCdB2O5密度明显比低温相α- SrCdB2O5的密度大。通常情况下,应该是低温相的密度要比高温相的密度大,SrCdB2O5同质多晶中的这种情况比较少见。在SrCdB2O5同质 多晶结构中,不同的B2O5基团的二面角导致了不同的Sr-O层状结构,从而形成最终不同的晶体结构。依据他们不同的结构化学,分析了其密度反常现象的内 在原因。我们认为直接原因是Sr-O层间距的不同,在α-SrCdB2O5 中,Sr-O层间距是6.329 ?,而在β-SrCdB2O5中,Sr-O层间距是5.497 ?。另外,我们也通过高温固相方法和差热-热重测试研究了α- 和 β-SrCdB2O5之间的相转移过程。计算并比较了α- 和 β-SrCdB2O5的总能量差异,而这个差异也推动了我们研究Pb2+掺杂化合物PbxSr1-xCdB2O5 (x = 0.125, 0.25, 0.375, 0.5),这系列化合物均采取β-SrCdB2O5的结构构型。同时,我们也进行了理论计算,计算了β-SrCdB2O5的能带结构和态密度,结果也与从 UV-Vis-NIR漫反射光谱中得到的实验值吻合的很好。 3. 我们观察到化合物Pb1.13Ba7.87B18O36, Pb8Zn(BO3)6, Pb8Cd(BO3)6, Sr8MgB18O36的分子式都可以用M'8MBxOy来表示,我们受这一系列化合物的化学式的启发,又详细研究了它们的结构规律,最终设计并合成了两 个新化合物Sr8MB18O36 (M = Zn, Cd)。Sr8MB18O36 (M = Zn, Cd)都结晶在菱方 空间群,具有相同的结构构型。对于Sr8ZnB18O36,晶胞参数为a = 11.436(3) ?,c = 36.94(2) ?,Z = 6;对于对于Sr8CdB18O36,晶胞参数为a = 11.483(3) ?, c = 36.88(2) ?, Z = 6。在它们的结构中存在孤立的[B18O36]18-阴离子基团。化合物Sr8MB18O36 (M = Zn, Cd)与Pb1.13Ba7.87B18O36, Pb8M(BO3)6 (M = Zn, Cd), Sr8MgB18O36等系列化合物具有相似的规律,首先化学式中M':M的比例是8:1;其次在晶体结构中,M2+离子均占据在最高对称性的位置上;再 次,在这系列化合物中,M2+阳离子的离子半径均比M'2+阳离子的离子半径小。本项工作提供了一种设计并合成新化合物的思路。

其他摘要
ABSTRACT: Polymorphism, a very important phenomenon in crystallography field, has many practical applications not only in pharmaceuticals, pigments, foods, dyestuffs and so forth, but also for the research of structure-property relationship. This dissertation aims to research polymorphs in SrO-CdO-B2O3 system. Using traditional solid-state reaction techniques, we found four new borate polymorphs: β-Cd3B2O6,β-SrCdB2O5,β-Cd2B2O5 and γ-Cd2B2O5. Small single crystals of these polymorphs were grown from a high-temperature solution with flux systems in air. Their structures were solved by direct methods using SHELXS-97. Their crystal growth, crystal structures, powder synthesis, Powder X-ray Diffraction and some other physico-chemical properties have also been investigated. Our research suggests that some compounds with small anion groups are more likely to form polymorphs and some polymorphs are very hard to obtain by traditional solid-state reaction techniques. 1. Single crystal of β-Cd3B2O6 is grown by high temperature solution method. β-Cd3B2O6 crystallizes in triclinic space group (No.2)with lattice constants a = 6.1114(5) ?,b = 6.1463(5) ?,c = 7.4232(6) ?,α= 76.521(3)°,β = 80.730(3)°,γ = 82.461(3)°,Z = 2,V = 266.34(4) ?3. In the crystal structure of β-Cd3B2O6, BO3, CdO5 and CdO6 groups build up the three dimensional framework by sharing oxygen atoms. Polycrystalline samples of β-Cd3B2O6 were synthesized by traditional solid-state reaction techniques at different reaction temperatures to observe the phase transformation. The phase purity of the resultant solid was confirmed by powder XRD. The results of TG-DSC measurement show us the precise phase transformation information. The detailed structure comparison between Cd3B2O6 and other cadmium-containing borates, such as CdB4O7, CdB2O4 and Cd2B2O5 was also carried out. 2. Single crystals of α-SrCdB2O5 and β-SrCdB2O5 are grown by high temperature solution method. Their structures were measured by single crystal X-ray diffraction. α-SrCdB2O5 crystallizes in orthorhombic space group Pbca (No.61) with lattice constants a = 11.955(12) ?,b = 5.762(6) ?,c = 12.658(12) ?,V = 872.0(15) ?3, ρ = 4.595 Mg/m3. β-SrCdB2O5 crystallizes in monoclinic space group C2/c (No.15) with lattice constants a = 7.639(7) ?,b = 10.183(10) ?,c = 11.140(10) ?,V = 855.2(14) ?3, ρ = 4.685 Mg/m3. In this work, an unusual phenomenon that the density of high-temperature phase (β-SrCdB2O5) is obviously larger than that of the low-temperature phase (α-SrCdB2O5) has been investigated in detail. In the view of structure chemistry, we explain the reasons of this density phenomenon. We think that the different dihedral angles of B2O5 groups in α- and β-SrCdB2O5 result in different Sr-O layers and crystal structures. The direct reason why α-SrCdB2O5 possesses a smaller density than β-SrCdB2O5 is that the distance between the Sr-O layers in α-SrCdB2O5 (6.329 ?) is longer than that in β-SrCdB2O5 (5.497 ?). The phase transformation between α- and β-SrCdB2O5 was investigated by traditional solid-state reaction techniques and TG-DSC measurement. Furthermore, the comparison of total electronic energy between α- and β-SrCdB2O5 motivated us to substitute the Sr2+ cation for Pb2+ up to x = 0.5 successfully and the results suggest that Pb2+-doped can affect the stability of the high-temperature polymorph of SrCdB2O5. In addition, first-principles electronic structure calculation shows that the calculated band gap of β-SrCdB2O5 is in good agreement with the experimental one estimated from UV-Vis-NIR absorption spectrum. 3. In light of our detailed analysis about some compounds with formula M'8MBxOy, such as Pb1.13Ba7.87B18O36, Pb8Zn(BO3)6, Pb8Cd(BO3)6, Sr8MgB18O36, two new borate crystals, Sr8MB18O36 (M = Zn or Cd) with expected Sr : M (M = Zn or Cd) ratio of 8:1 were designed and successfully synthesized for the first time. They all crystallize in rhombohedral space group and possess isolated [B18O36]18- anionic group. The la
文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4241
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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张兴文. 锶镉硼酸盐体系中同质多晶化合物的探索与研究[D]. 北京. 中国科学院大学,2015.
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