Crystal Growth and Structure Determination of Oxygen-Deficient Sr6Co5O15

Large single crystals of oxygen-deficient Sr6Co5O15-δ compounds, i.e., Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36, were
obtained by using K2CO3 flux in the presence of additives of transition metal oxides. The single-crystal structure
determination shows that the structures of Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 crystallize in the space group R3̄
and can be described as one-dimensional face-sharing CoO3 polyhedral chains and Sr cation chains. Unlike the
other known 2H-perovskite-related oxides in which the polyhedral chains consist of octahedra (Oh) and trigonal
prism (TP), the structure of Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 contain Oh and intermediate polyhedra (IP) and can
be attributed to a general structure formula A6A‘2B3O15-δ, which is closely related to the known A6A‘B4O15 phases
by shifting of a B atom and the O3 triangle along the c axis. Further study on O3 reveals that this oxygen position
splits into two independent positions, corresponding to polyhedral geometry of IP and TP, respectively. Therefore,
the polyhedral chain in the structure should be more precisely described as a random composite of the 4Oh + TP
and 3Oh + 2IP. This model is used to interpret the magnetic properties, although not quantitatively. The 4-D
structure analysis was also conducted for both Sr6Co5O14.70 and Sr6Co4.9Ni0.1O14.36 with a commensurate modulated
structure in a 4-D superspace group, R3̄m(00γ)0s, γ = p/k = 3/5. By considering the same 4-D superspace
group R3̄m(00γ)0s but different t-phases, one can understand the structure relationship between Sr6Co5O14.70 and
Sr6Rh5O15.

通过在过渡金属氧化物添加剂的存在下使用K2CO3助熔剂，成功制备了氧缺陷的Sr6Co5O15-δ大单晶，即Sr6Co5O14.70和Sr6Co4.9Ni0.1O14.36。单晶结构分析表明，这两种物质的晶体结构均为R3̄空间群，并可描述为由一维共面共享的CoO3多面体链和Sr阳离子链构成。与已知的多面体链由八面体（Oh）和三角棱柱（TP）组成的2H-钙钛矿相关氧化物不同，Sr6Co5O14.70和Sr6Co4.9Ni0.1O14.36的结构中包含Oh和中介多面体（IP），并可归因于通式A6A‘2B3O15-δ，此通式与已知的A6A‘B4O15相通过沿c轴的B原子和O3三角形的位移密切相关。进一步对O3的研究发现，该氧位分裂成两个独立的位置，分别对应IP和TP的多面体几何形状。因此，结构中的多面体链应更精确地描述为由4Oh + TP和3Oh + 2IP的随机复合体。此模型被用于解释磁性质，尽管不是定量的。对Sr6Co5O14.70和Sr6Co4.9Ni0.1O14.36也进行了4-D结构分析，两者在4-D超空间群R3̄m(00γ)0s中具有相容的调制结构，γ = p/k = 3/5。通过考虑相同的4-D超空间群R3̄m(00γ)0s但不同的t相，可以理解Sr6Co5O14.70与Sr6Rh5O15之间的结构关系。