Low-temperature phase transition and magnetic properties of K₃YbSi₂O₇

Abstract

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.

Configuration of the dimolybdate in salt inclusion type of compounds, Cs2Mo2O7 ⋅ CsX (X=Cl, Br, and I)

“…However, the eclipsed conformation remains in this case as well. On the other hand, for cation‐rich compounds such as K 3 YbSi 2 O 7 , a phase transition from P 6 3 / mmc to Cmcm at ≈210 K has been reported which establishes a bent disilicate (≈164°) in an eclipsed conformation [20] . The scope of the present work is to investigate the influence of the halide in the hetero‐honeycomb lattice for the series Cs 2 Mo 2 O 7 ⋅ CsX with X=Cl, Br, and I with respect to the [Mo 2 O 7 ] 2− configuration by using low temperature X‐ray diffraction and Raman spectroscopy.…”