半水榴石型化合物Sr_6Sb_4M_3O_(14)(OH)_(10)(M=Co,Mn)的合成、结构与性质

在强碱性水热条件下合成了两种新化合物Sr6Sb4Co3O14(OH)10(SSC)与Sr6Sb4Mn3O14(OH)10(SSM).采用粉末X射线衍射数据,通过Rietveld方法进行了结构分析,讨论了金属离子的拓扑结构.两种化合物均为石榴石-水榴石相关结构,空间群I43d,晶胞参数a分别为1.30634(2)nm(SSC)和1.31367(1)nm(SSM).结构中,SbO6八面体与MO4(M=Co,Mn)四面体共顶点连接,Sb5+-M2+(M=Co,Mn)离子表现为ctn即C3N4型的拓扑结构.拓扑结构中,Sb5+为三连接,过渡金属离子M2+(M=Co,Mn)为四连接.Sb5+离子的拓扑结构为体心立方,而M2+(M=Co,Mn)分布呈类风扇状,相互连接形成thp型拓扑结构(即Th3P4中Th原子之间连接关系).过渡金属离子的分布与化合物表现出的磁性质密切相关,Co2+(Mn2+)间存在反铁磁相互作用.Sr6Sb4Co3O14(OH)10在低温下表现出反铁磁倾斜有序.Sr6Sb4Co3O14(OH)10和Sr6Sb4Mn3O14(OH)10在高温下发生分解,产物主相为双钙钛矿Sr2(Sb,M)2O6(M=Co,Mn).

Syntheses, Structures and Properties of Hemi-Hydrogarnet Sr6Sb4M3O14(OH)10(M=Co,Mn)

Two new compounds, Sr6Sb4Co3O14(OH)10 (SSC) and Sr6Sb4Mn3O14(OH)10 (SSM), were synthesized under hydrothermal conditions in an alkaline medium. Their structures were determined by powder X-ray diffraction using Rietveld analysis, and the topology of the metal cation network was discussed. These two isostructural compounds crystallize in a garnet-related or hydrogarnet-related structure with the space group I43d and the lattice parameters (a) are 1.30634(2) nm(SSC) and 1.31367(1) nm(SSM). The SbO6 octahedron and MO4 (M=Co, Mn) tetrahedron share corners with each other to formthe backbone of the structure. The topology of the Sb5+ andM2+ (M=Co,Mn) network is ctn, which is the C3N4network. The Sb5+ node is three-connected and that of M2+ (M=Co, Mn) is four-connected. The distribution of the M2+ (M=Co, Mn) cations in the structure is in a fanlike mode with a thp topology, i.e., a network of Th atoms in Th3P4. These two compounds are antiferromagnetic. Sr6Sb4Co3O14(OH)10 exhibits a net magnetic moment, which may be related to the canting ordering of Co2+ ions below 10 K. Sr6Sb4Co3O14(OH)10 and Sr6Sb4Mn3O14(OH)10 decompose above 300 ℃ and give rise to the perovskite-type compounds Sr2(Sb, M)2O6(M=Co, Mn) as the main phases in the products after treatment at 900 ℃ under atmospheric conditions.