(Ca_(0.5),□_(0.5))BaCe_2(CO_3)_4F矿物晶体结构的测定

Crystal Structure of (Ca_(0.5),□_(0.5))BaCe_2(CO_3)_4F

(Ca0.5□0.5)BaCe2(CO3)4F属于六方晶系,晶胞参数为:a=b=5.093(6),c=23.017(6),r=120°,Z=2。用强功率四圆单晶衍射仪在2=2—65°范围内共收集到821个原始衍射强度数据。晶体结构主要靠重原子法解出,采用空间群P62C,根据344个独立衍射点经多轮最小二乘修正后,获得其全部原子的三维坐标、占位度、各向同性及各向异性温度因子等参数,最终的偏离因子R=0.05。

This paper deals with a fluor-carbonate mineral of Ca-Ba-REE(Ce-series) recently discovered in China by the authors, whose crystalstructure has been thoroughly studied. The data collection was completed on a RASA-5RP automatic four-circle single crystal diffractometer in our university (graphite monochromator, Moka, 50kV/150mA, 20=2—65°). The cell parameters refined on this device are a=b=5.093(6), c=23.017(6) and V=517~3. 821 reflections were collected, of which 344 show F>3σ(F). The structure was solved by threedimensional Patterson P(uvw)and the differential electron density map using space group P62c, Isotropic refinement led to the value R=0.06 for all 344 independent reflections, and anisotropic refinement to R=0.05. Atomic coordinates, site occupancies and isotropic thermal vibration parameters are given in Table 1. The structure has a layered feature (// c axis). All heavy atoms (Ba, Ce) and CO_3 group form a hexagonal base-centered net-like framework. At z=1/4 and z=3/4 the hexagonal layer consists of Ca and F atoms, in which each kind of atoms is also arranged in a hexagonal basecentered net-like framework. Those hexagonal layers of atoms are stacked along c axis in the sequence of Ba-Ce-Ca-Ce-Ba…. The plane of CO_3 group is normal to c axis.