The new ambient-temperature hexagonal (space group P6₃/mmc) polymorph of tripotassium ytterbium(III) disilicate (β-K₃YbSi₂O₇) has been synthesized by the high-temperature flux method and subsequently structurally characterized. In the course of the temperature-dependent single-crystal diffraction experiments, a phase transformation of β-K₃YbSi₂O₇ to a novel low-temperature orthorhombic phase (β′-K₃YbSi₂O₇, space group Cmcm) has been observed at about 210 K. β-K₃YbSi₂O₇ is isostructural with K₃ErSi₂O₇, whereas β′-K₃YbSi₂O₇ adopts a new type of structure. Both compounds can be built up from a regular alternation of layers of two types, which are parallel to the (001) plane. In the octahedral layer, YbO₆ octahedra are isolated and linked by K1O₆₊₃ polyhedra. The second, slightly thicker sorosilicate layer is formed by a combination of Si₂O₇ dimers and K2O₆₊₃ polyhedra. The boundary between the layers is a pseudo-kagome oxide sheet based on 3.6.3.6 meshes. The phase transition is due to a tilt of the two SiO₄ tetrahedra forming a single dimer which induces a decrease of the Si—O—Si angle between bridging Si—O bonds from 180° (dictated by symmetry in space group P6₃/mmc) to ≃164°. Magnetic characterization indicates that K₃YbSi₂O₇ remains paramagnetic down to 2 K, showing no apparent influence of the phase transformation on its magnetic properties. Analysis of the magnetization data revealed the positions of the three lowest crystal field levels of the Yb³⁺ cations, as well as the corresponding projections of their angular momentum on the direction of the magnetic field.

中文翻译：

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K3YbSi2O7 的低温相变和磁性能

已经通过高温熔剂法合成了_三钾镱（III）二硅酸盐（β-K ₃ YbSi ₂ O ₇）的新的常温六方晶型（空间群P 6 ₃ /mmc）多晶型物，并随后对其进行了结构表征。在温度依赖性单晶衍射实验过程中，β-K ₃ YbSi ₂ O ₇相转变为新型低温正交晶相（β'-K ₃ YbSi ₂ O ₇，空间群Cmcm）具有在大约 210 K 观察到。 β-K ₃ YbSi ₂O ₇与K ₃ ErSi ₂ O ₇同构，而β'-K ₃ YbSi ₂ O _{7 则}采用新型结构。两种化合物都可以由平行于 (001) 平面的两种类型的层的规则交替构成。在八面体层中，YbO ₆八面体被K1O ₆₊₃多面体孤立和连接。第二个稍厚的硅酸盐层由 Si ₂ O ₇二聚体和 K2O ₆₊₃的组合形成多面体。层之间的边界是基于 3.6.3.6 网格的伪 kagome 氧化物片。相变是由于形成单个二聚体的两个 SiO ₄四面体的倾斜导致桥接 Si-O 键之间的 Si-O-Si 角从 180° 减小（由空间群P 6 ₃ / 中的对称性决定）mmc ) 到 ≃164°。磁性表征表明，K ₃ YbSi ₂ O ₇在低至 2 K 时仍保持顺磁性，表明相变对其磁性没有明显影响。对磁化数据的分析揭示了 Yb ³⁺的三个最低晶体场能级的位置 阳离子，以及它们的角动量在磁场方向上的相应投影。