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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Structure of the clinopyroxene-type compound CaCuGe2O6 between 15 and 800 K
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Structure of the clinopyroxene-type compound CaCuGe2O6 between 15 and 800 K

机译：15至800 K之间的斜茂铁型化合物CaCuGe2O6的结构

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摘要

CaCuGe2O6 shows a strongly distorted clinopyroxene-type structure with P2(1)/c symmetry at 298 K. The Cu2+ ion at the M1 site is coordinated by six O atoms forming an octahedron, which deviates significantly from ideal geometry. Individual M1 sites are connected via common edges to form an infinite zigzag chain parallel to the crystallographic c axis. The Ca2+ ion at M2 shows a sevenfold coordination. M2 sites are connected to the M1 chain via three common edges, thereby forming a metal layer within the bc plane. Besides the strong Jahn-Teller distortion of the Cu site, the structure of the title compound differs from `normal' clinopyroxenes by a distortion of alternate layers of Ge sites. While the Ge( A) site is fourfold coordinated by O atoms, forming infinite chains of corner-sharing chains parallel to the c axis, the Ge( B) site exhibits a fivefold coordination, thereby forming a true two-dimensional layer of edge-sharing GeO5 bipyramids. Decreasing the temperature causes a magnetic phase transition at 40 K, as monitored by a broad maximum in the magnetic susceptibility and by discontinuities in the lattice parameters. Increasing the temperature causes variations in bond lengths, edge lengths and bond angles. Most prominent is the increase of one bond length of the Ge( B) site and the increase of the tetrahedral bridging angle of the Ge( A) site. At 660 K a crystallographic phase transition is observed where the symmetry changes from P2(1)/c to C2/c. The transition is accompanied by large changes in the lattice parameters which are indicative of distinct topological changes of several structural building units. The high-temperature C2/c structure is similar to that of the germanate clinopyroxene CaMgGe2O6.
机译：CaCuGe2O6在298 K处显示出具有P2（1）/ c对称性的强烈变形的斜茂铁石型结构。M1处的Cu2 +离子由六个O原子形成一个八面体进行配位，这显着偏离了理想的几何形状。各个M1位点通过公共边缘相连，以形成平行于晶体c轴的无限之字形链。 M2处的Ca2 +离子显示出七重配位。 M2位点通过三个公共边连接到M1链，从而在bc平面内形成金属层。除了Cu位的强Jahn-Teller畸变外，标题化合物的结构与Ge交替层的畸变还不同于“正常”的斜py。 Ge（A）位点由O原子四重配合，形成了平行于c轴的角共享链的无限链，而Ge（B）位点则表现出五重配位，从而形成了边缘的真正二维层。共享GeO5双锥体。温度的降低会引起40 K的磁相变，这是由磁化率的广泛最大值和晶格参数的不连续性所监测的。温度升高导致粘结长度，边缘长度和粘结角度变化。最突出的是Ge（B）位的一个键长的增加和Ge（A）位的四面体桥接角的增加。在660 K处观察到结晶相变，其中对称性从P2（1）/ c变为C2 / c。过渡过程伴随着晶格参数的大变化，这些变化指示了几个结构建筑单元的明显拓扑变化。高温C2 / c结构类似于德国的斜茂铁茂CaMgGe2O6。

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