Melilite-type borates Bi2ZnB2O7 and CaBiGaB2O7
Melilite-type borates Bi2ZnB2O7 and CaBiGaB2O7
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DOI：
10.1021/cm0503073
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发表时间：
2005-06-14
影响因子：
8.6
通讯作者：
Cranswick, LM
中科院分区：
文献类型：
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作者：
Barbier, J;Penin, N;Cranswick, LM
在650-825℃和1个大气压下，用固相反应合成了Bi2ZnB2O7和CaBiGaB2O7。这些化合物是黄长石家族中唯一的合成二硼酸盐A(2)XZ(2)O(7)，其中A阳离子层与XZ(2)O(7)四面体层交替。除CdBiGaB2O7外，其他取代硼酸铋黄长石的合成均未成功。用粉末X射线衍射法测定了Bi2ZnB2O7和CaBiGaB2O7的晶体结构，并用粉末中子衍射数据用Rietveld方法进行了修正。CaBiGaB2O7采用含有B2O7四面体二聚体的正四方黄长石结构(P$(4)在2(1)m空间群上，Z=2)。Ca~(2+)和Bi~(3+)层间阳离子分裂的八配位的细化表明存在额外的无序。Bi2ZnB2O7采用独特的正交黄长石超结构(Pba2空间群，Z=4)，同时含有四面体B2O7和三角形B2O5二聚体。比尔阳离子占据了两个不同的层间位置，具有强烈的不对称6倍配位环境。对粉末样品的二次谐波产生效率的初步测量得到了相对于KH_2PO_4标准的4.0(Bi2ZnB_2O_7)和1.6(CaBiGaB_2O_7)。
The bismuth borates Bi2ZnB2O7 and CaBiGaB2O7 have been synthesized by solid-state reactions at temperatures in the 650-825 degrees C range at 1 atm pressure. These compounds are the only synthetic diborate members of the melilite family, A(2)XZ(2)O(7), in which layers of A cations alternate with XZ(2)O(7) tetrahedral layers. Except for CdBiGaB2O7, the synthesis of other substituted bismuth borate melilites has been unsuccessful. The crystal structures of Bi2ZnB2O7 and CaBiGaB2O7 have been determined by powder X-ray diffraction and refined by the Rietveld method using powder neutron diffraction data. CaBiGaB2O7 adopts the regular tetragonal melilite structure (P $(4) over bar $2(1)m space group, Z = 2) containing B2O7 tetrahedral dimers. The refinement of split eight-coordinated sites for the Ca2+ and Bi3+ interlayer cations suggests the presence of additional disorder. Bi2ZnB2O7 adopts a unique orthorhombic melilite superstructure (Pba2 space group, Z = 4) containing both tetrahedral B2O7 and triangular B2O5 dimers. The Bill cations occupy two distinct interlayer sites with strongly asymmetric 6-fold coordination environments. The preliminary measurement of second harmonic generation efficiencies (d(eff)) of powder samples has yielded values of 4.0 (Bi2ZnB2O7) and 1.6 (CaBiGaB2O7) relative to a KH2PO4 standard.