School of Earth, Atmosphere and Environment, Monash University, 9 Rainforest Walk, Clayton 3800, Victoria, Australia.
Geosciences, Museums Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2022 Feb 1;78(Pt 1):20-32. doi: 10.1107/S2052520621013032. Epub 2022 Jan 16.
Synthetic and naturally occurring forms of tricopper orthotellurate, CuTeO (the mineral mcalpineite) have been investigated by 3D electron diffraction (3D ED), X-ray powder diffraction (XRPD), Raman and infrared (IR) spectroscopic measurements. As a result of the diffraction analyses, CuTeO is shown to occur in two polytypes. The higher-symmetric CuTeO-1C polytype is cubic, space group Ia3, with a = 9.537 (1) Å and V = 867.4 (3) Å as reported in previous studies. The 1C polytype is a well characterized structure consisting of alternating layers of CuO octahedra and both CuO and TeO octahedra in a patchwork arrangement. The structure of the lower-symmetric orthorhombic CuTeO-2O polytype was determined for the first time in this study by 3D ED and verified by Rietveld refinement. The 2O polytype crystallizes in space group Pcca, with a = 9.745 (3) Å, b = 9.749 (2) Å, c = 9.771 (2) Å and V = 928.3 (4) Å. High-precision XRPD data were also collected on CuTeO-2O to verify the lower-symmetric structure by performing a Rietveld refinement. The resultant structure is identical to that determined by 3D ED, with unit-cell parameters a = 9.56157 (19) Å, b = 9.55853 (11) Å, c = 9.62891 (15) Å and V = 880.03 (2) Å. The lower symmetry of the 2O polytype is a consequence of a different cation ordering arrangement, which involves the movement of every second CuO and TeO octahedral layer by (1/4, 1/4, 0), leading to an offset of TeO and CuO octahedra in every second layer giving an ABAB* stacking arrangement. Syntheses of CuTeO showed that low-temperature (473 K) hydrothermal conditions generally produce the 2O polytype. XRPD measurements in combination with Raman spectroscopic analysis showed that most natural mcalpineite is the orthorhombic 2O polytype. Both XRPD and Raman spectroscopy measurements may be used to differentiate between the two polytypes of CuTeO. In Raman spectroscopy, CuTeO-1C has a single strong band around 730 cm, whereas CuTeO-2O shows a broad double maximum with bands centred around 692 and 742 cm.
已通过三维电子衍射（3D ED）、X 射线粉末衍射（XRPD）、拉曼和红外（IR）光谱测量对合成的和天然存在的三铜正碲酸盐，CuTeO（矿物名称为 mcalpineite）进行了研究。衍射分析的结果表明，CuTeO 存在两种多型体。高对称的 CuTeO-1C 多型体为立方晶系，空间群 Ia3，a = 9.537 (1) Å，V = 867.4 (3) Å，这是以前的研究中报道的。1C 多型体是一种结构特征明确的结构，由交替的 CuO 八面体层和 CuO 和 TeO 八面体层以拼凑方式组成。本研究首次通过 3D ED 确定了低对称的正交 CuTeO-2O 多型体的结构，并通过 Rietveld 精修验证。2O 多型体在空间群 Pcca 中结晶，a = 9.745 (3) Å，b = 9.749 (2) Å，c = 9.771 (2) Å，V = 928.3 (4) Å。还收集了 CuTeO-2O 的高精密 XRPD 数据，通过 Rietveld 精修来验证低对称结构。得到的结构与 3D ED 确定的结构相同，晶胞参数 a = 9.56157 (19) Å，b = 9.55853 (11) Å，c = 9.62891 (15) Å，V = 880.03 (2) Å。2O 多型体的低对称性是由于阳离子排列方式不同所致，这种方式涉及到每个第二个 CuO 和 TeO 八面体层沿（1/4, 1/4, 0）移动，导致每个第二层的 TeO 和 CuO 八面体发生偏移，形成 ABAB*堆叠排列。CuTeO 的合成表明，低温（473 K）水热条件通常会产生 2O 多型体。XRPD 测量结合拉曼光谱分析表明，大多数天然 mcalpineite 是正交的 2O 多型体。XRPD 和拉曼光谱测量都可用于区分 CuTeO 的两种多型体。在拉曼光谱中，CuTeO-1C 在约 730 cm 处有一个强单峰，而 CuTeO-2O 显示出一个宽的双峰，中心位于 692 和 742 cm 处。
