Juarez-Arellano Erick A, Rosales Ivonne, Oliver Alicia, Ruvalcaba Jose Luis, Carbonio Raul E, Bucio Lauro, Orozco Eligio
Instituto de Física, Universidad Nacional Autónoma de México, AP 20-364, 01000 México DF, Mexico.
Acta Crystallogr C. 2004 Feb;60(Pt 2):i14-6. doi: 10.1107/S0108270103029056. Epub 2004 Jan 17.
A new indium holmium digermanate, In(1.06)Ho(0.94)Ge(2)O(7), with a thortveitite-type structure, has been prepared as a polycrystalline powder material by high-temperature solid-state reaction. This new compound crystallizes in the monoclinic system (space group C2/c, No. 15). The structure was characterized by Rietveld refinement of powder laboratory X-ray diffraction data. The In(3+) and Ho(3+) cations occupy the same octahedral site, forming a hexagonal arrangement on the ab plane. In their turn, the hexagonal arrangements of (In/Ho)O(6) octahedral layers are held together by sheets of isolated diortho groups comprised of double tetrahedra sharing a common vertex. In this compound, the Ge(2)O(7) diortho groups lose the ideal D(3d) point symmetry and also the C(2h) point symmetry present in the thortveitite diortho groups. The Ge-O-Ge angle bridging the diortho groups is 160.2 (3) degrees, compared with 180.0 degrees for Si-O-Si in thortveitite (Sc(2)Si(2)O(7)). The characteristic mirror plane in the thortveitite space group (C2/m, No. 12) is not present in this new thortveitite-type compound and the diortho groups lose the C(2h) point symmetry, reducing to C(2).
通过高温固态反应制备了一种具有钪钇石型结构的新型锗酸铟钬In(1.06)Ho(0.94)Ge(2)O(7)，呈多晶粉末材料。这种新化合物结晶于单斜晶系（空间群C2/c，编号15）。通过粉末实验室X射线衍射数据的Rietveld精修对其结构进行了表征。In(3+)和Ho(3+)阳离子占据相同的八面体位置，在ab平面上形成六边形排列。反过来，(In/Ho)O(6)八面体层的六边形排列由由共享一个公共顶点的双四面体组成的孤立双正基团片层连接在一起。在该化合物中，Ge(2)O(7)双正基团失去了理想的D(3d)点对称性以及钪钇石双正基团中存在的C(2h)点对称性。连接双正基团的Ge - O - Ge角为160.2(3)度，而钪钇石(Sc(2)Si(2)O(7))中的Si - O - Si角为180.0度。这种新型钪钇石型化合物中不存在钪钇石空间群（C2/m，编号12）中的特征镜面，双正基团失去了C(2h)点对称性，降至C(2)。
