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Nine new rare earth magnesium-containing thiosilicates of the formula RE3Mg0.5SiS7 (Ln = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) were synthesized in an alkali halide flux using the boron chalcogen mixture (BCM) method. Crystals of high quality were produced, and their structures were determined by single-crystal X-ray diffraction. The compounds crystallize in the hexagonal crystal system in the P63 space group. Phase pure powders of the compounds were used for magnetic susceptibility measurements and for second harmonic generation (SHG) measurements. Magnetic measurements indicate that Ce3Mg0.5SiS7, Sm3Mg0.5SiS7, and Dy3Mg0.5SiS7 exhibit paramagnetic behavior with a negative Weiss temperature over the 2−300 K temperature range. SHG measurements of La3Mg0.5SiS7 demonstrated SHG activity with an efficiency of 0.16 times the standard potassium dihydrogen phosphate (KDP). 

Planar MO 3 (M = B, C, N) units have frequently been considered important structural components of novel birefringent crystal materials. An efficient approach for constructing new functional crystals is to simultaneously assemble multiple structural motifs together. Two compounds, Na 3 Rb 6 (CO 3 ) 3 (NO 3 ) 2 X·6H 2 O (X = Br and Cl), were synthesized by the integration of three kinds of anionic groups. More interestingly, the [CO 3 ] 2− and [NO 3 ] − groups in Na 3 Rb 6 (CO 3 ) 3 (NO 3 ) 2 X·6H 2 O are all coplanar with the aid of [NaO 7 ] 13− polyhedra, which can enhance the anisotropic polarizability. Na 3 Rb 6 (CO 3 ) 3 (NO 3 ) 2 X·6H 2 O have a large theoretical birefringence of ∼0.165 at 1064 nm and possess a short UV cut-off edge of ∼230 nm. Additionally, the two compounds exhibit good crystal growth habits. These properties illustrate that Na 3 Rb 6 (CO 3 ) 3 (NO 3 ) 2 X·6H 2 O are promising UV birefringent crystals. 

KBiNb 2 O 7 was prepared from RbBiNb 2 O 7 by a sequence of cation exchange reactions which first convert RbBiNb 2 O 7 to LiBiNb 2 O 7 , before KBiNb 2 O 7 is formed by a further K-for-Li cation exchange. A combination of neutron, synchrotron X-ray and electron diffraction data reveal that KBiNb 2 O 7 adopts a polar, layered, perovskite structure (space group A 11 m ) in which the BiNb 2 O 7 layers are stacked in a (0, ½, z ) arrangement, with the K + cations located in half of the available 10-coordinate interlayer cation sites. The inversion symmetry of the phase is broken by a large displacement of the Bi 3+ cations parallel to the y -axis. HAADF-STEM images reveal that KBiNb 2 O 7 exhibits frequent stacking faults which convert the (0, ½, z ) layer stacking to (½, 0, z ) stacking and vice versa , essentially switching the x - and y -axes of the material. By fitting the complex diffraction peak shape of the SXRD data collected from KBiNb 2 O 7 it is estimated that each layer has approximately a 9% chance of being defective – a high level which is attributed to the lack of cooperative NbO 6 tilting in the material, which limits the lattice strain associated with each fault.