Molten Alkali Halide Flux Growth of an Extensive Family of Noncentrosymmetric Rare Earth Sulfides: Structure and Magnetic and Optical (SHG) Properties

Abstract

Twenty new alkali rare earth thiosilicates and thiogermanates with the general formula ALnTS4 (A = alkali metal, Ln = lanthanide, and T = Si, Ge) were grown as X-ray diffraction-quality single crystals from molten alkali chloride fluxes. These include KNdSiS4, KPrSiS4, RbLnSiS4 (Ln = Ce, Pr, Nd, Gd, Tb, Dy, and Ho), RbLaGeS4, CsLnSiS4 (Ln = La, Pr, and Nd), and CsLnGeS4 (La, Ce, Pr, Nd, Eu, Gd, and Tb). Herein, we discuss the use of a molten chloride flux growth approach for the preparation of the title compounds and their structure determination via single-crystal X-ray diffraction. In addition, we comment on the magnetic properties of RbNdSiS4, CsNdSiS4, CsNdGeS4, and CsGdGeS4, which were found to be paramagnetic for T = 2–300 K and exhibited negative Weiss temperatures with no obvious antiferromagnetic transition down to 2 K. The optical properties of CsLaGeS4 and CsNdTS4(T = Si, Ge) were measured by UV–vis spectroscopy. Second harmonic generation measurements performed on CsLaGeS4 confirmed the crystallization of the compound in the noncentrosymmetric orthorhombic space group, P212121; CsLaGeS4 was found to be SHG-active with nearly half the intensity of α-SiO2 upon irradiation with a Nd:YAG 1064 nm laser, and a semiconductor exhibiting a band gap of 3.60 eV based on UV–vis diffuse reflectance measurements.

Two Mixed-Anion Units of [GeOSe3] and [GeO3S] Originating from Partial Isovalent Anion Substitution and Inducing Moderate Second Harmonic Generation Response and Large Birefringence

“…However, only the [GeO 2 Q 2 ] and [GeOS 3 ] units have been identified so far. The [GeOS 3 ] unit is found in Ae 2 MGe 2 S 6 O (Ae = Sr, Ba; M = Zn, Mn) compounds, which belong to the melilite-type sturcture. − The [GeO 2 Q 2 ] units appear in the compounds of AeGeOQ 2 (Ae = Ba, Sr; Q = S, Se), which crystallize ina noncentrosymmetric (NCS) structure ( P 2 1 2 1 2 1 ). The [GeO 2 Q 2 ] tetrahedra connect to each other via corner sharing of O atoms, forming unique 1∞[GeQ 2 O] 2– helical chains.…”

Two Rare‐Earth Molecular Ferroelectrics with High Curie Temperatures, Large Spontaneous Polarization, Switchable Second Harmonic Generation Effects, and Strong Photoluminescence

“…Rare‐earth elements have unique fluorescent and magnetic properties, because they possess unique outer‐shell electronic structures enabling diverse charge transfer such as D→F, H→P, F→L, etc., and containing a number of unpaired f orbit electrons. Furthermore, they possess large atomic radii and usually exhibit diverse coordination modes; for example, the coordination number can vary from 6 to 14 in similar coordinating compounds, offering a wide stage for constructing all kinds of compounds .…”

One-Dimensional Quaternary and Penternary Alkali Rare Earth Thiophosphates Obtained via Alkali Halide Flux Crystal Growth

“…For postreaction workup, methanol proved to be an effective solvent as it is sufficiently polar to dissolve the ionic alkali chloride fluxes and, at the same time, sufficiently water free to avoid degrading the product thiophosphate compounds . All compositions reported herein are stable for several days when stored in closed glass vials wrapped in Parafilm.…”

“…Klawitter et al reported on the first quaternary alkaline-earth rare earth thiophosphates, Ba 3 Ln 2 (PS 4 ) 4 (Ln = Gd – Er), utilizing BaCl 2 as the flux . For a long time, zur Loye and co-workers have utilized halide flux crystal growth approaches to prepare diverse complex oxides − and recently demonstrated that alkali halide fluxes are extremely effective as the solvent for the crystallization of complex chalcogenides. − The relative ease with which halide fluxes can be removed in postreaction workup and the fact that halide fluxes produce crystals of compounds in typically good yields and phase pure form make them an attractive flux.…”