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Two series of new lanthanide thiophosphates with partial Ca occupancy of the Ln sites, Cs0.3(Ca0.3Ln0.7)PS4 (Ln = Ce, Pr, Nd, Sm, Gd, Tb, and Dy) and Cs0.5(Ca0.5Ln0.5)PS4 (Ln = Pr, Nd, Sm, Gd, and Tb), were synthesized using a CsI flux and structurally characterized. The first series with an idealized formula of Cs0.3(Ca0.3Ln0.7)PS4 crystallizes in the Rm space group and belongs to a new structure type that consists of a channel containing [(Ca0.3Ln0.7)PS4]0.3− framework, where the channels are occupied by severely disordered Cs+ cations. A second new series with formula Cs0.5(Ca0.5Ln0.5)PS4 crystallizes in the monoclinic C2/c space group and exhibits a layered structure consisting of [(Ca0.5Ln0.5)PS4]0.5− layers with Cs+ cations located between the layers for charge balance. Together with the parent structure type, LnPS4, these three structure types illustrate how the LnPS4 structure changes with Cs+ cation incorporation, reducing its dimensionality from 3D to 2D. The magnetic properties of Cs0.3[(Ca0.3Ce0.7)PS4] and Cs0.3[(Ca0.3Pr0.7)PS4] were studied and revealed no magnetic transition down to 2 K.

Four new cesium-containing cobalt oxide complexes were reported. Cs(Co0.5Si0.5)SiO4 (1), Cs1.29(5)Co0.69(5)Ge1.81(5)O5 (2), and its ordered analogue Cs2CoGe4O10 (3) were synthesized using a mixed CsCl–CsF flux at 850 °C or 900 °C. The structure of (1) closely resembles that of known zeolite and feldspar structures, and (1) crystallizes in the noncentrosymmetric monoclinic space group Im with lattice parameters of a = 8.9926(4) A, b = 5.4599(2) A, c = 9.3958(6) A, and β = 91.5928(18)°. Complexes (2) and (3) crystallize in the same new structure with a highly porous three-dimensional framework in the tetragonal space group I with lattice parameters of a = 7.4239(14) A and c = 13.169(3) A for (2) and a = 7.3540(6) A and c = 13.1122(11) A for (3). The formation of (2) vs. (3) can be controlled based on slight variations in the quantities of the starting materials. Single-crystal-to-single-crystal ion exchange of (1) in a molten RbNO3 bath resulted in 14% Cs exchange with Rb, affording the composition Cs0.86Rb0.14(Co0.5Si0.5)SiO4 (4). First-principles density functional theory calculations were performed to elucidate the electronic and magnetic properties and stabilities of (1) and (3) at 0 K.

Single crystals of two new germanates, [(Rb6F)(Rb4F)][Ge14O32] and [(Rb6F)(Rb3.1Co0.9F0.96)][Co3.8Ge10.2O30F2], were synthesized via high temperature RbCl/RbF flux growth. Both compounds crystallize in the cubic space group F3m and possess the germanium framework of the previously reported salt inclusion material (SIM), [(Cs6F)(Cs3AgF)][Ge14O32], related to the Ge7O16 zeolitic family. These materials demonstrate the ability to accommodate a variety of salt-inclusions, and exhibit chemical flexibility enabling modifications of the framework through incorporation of Co. Alteration of the salt-inclusion led to intrinsic luminescence of [(Rb6F)(Rb4F)][Ge14O32] while modification of the framework resulted in an unanticipated Rb/Co salt/inclusion in [(Rb6F)(Rb3.1Co0.9F0.96)][Co3.8Ge10.2O30F2]. Fluorescence measurements were performed on [(Rb6F)(Rb4F)][Ge14O32]. First-principles calculations in the form of density functional theory (DFT) were performed for [(Rb6F)(Rb3.1Co0.9F0.96)][Co3.8Ge10.2O30F2] to elucidate its electronic and magnetic properties, and stability at 0 K.

Spinel compounds, with the general chemical formula AB2O4, are a wide class of materials, where A and B can be a variety of cations, providing this structure with a great deal of functional flexibility and giving rise to its considerable scientific interest. Recently, a spinel with the general formula ABB′O4 has been predicted, increasing the possible usability of the spinels due to the higher cation diversity in the so-called double spinel structure. Here, we use density functional theory calculations to predict if double spinels can be formed between experimentally synthesized normal and inverse single spinels. Our computations reveal that 49 double spinels have negative mixing enthalpies and are thus thermodynamically stable, with most of the stable compounds being formed from one of two distinct cation orderings. We show that the 17 different cations that form the different double spinels have a preferred site, tetrahedral or octahedral, except for Mn, Fe and Co which can occupy both sites interchangeably. We also study the relation between mixing enthalpies and cation-specific properties, as well as ways to classify the double spinels into distinct types and spinel groups depending on the cation ordering and cation oxidation states, respectively. By applying the Sure Independence Screening and Sparsifying Operator (SISSO) approach on the coordination-dependent ionic radii of the elemental constituents, we show that an interplay of local strain and electrostatic dominated terms can be used to separate the double spinels into distinct structural types depending on the cation order and their oxidation states.

Experiments show that zeolites, such as Linde Type A (LTA), are promising materials for radioactive decontamination processes. In this work, the thermodynamic properties associated with alkaline earth ion (Ca2+, Sr2+ and Ba2+) exchange in pure silica LTA was studied using periodic first-principles calculations. The adsorption energies of alkaline earth ions compared with that of Na+ were investigated. The driving forces for alkaline earth exchange and related isotherms were calculated, and analyzed as a function of the electron chemical potential. The results demonstrate that Na+ in a pure silica LTA can completely be removed by Ba2+ and almost completely be removed by Sr2+ from a stream, but cannot be effectively exchanged by Ca2+. We also showed that electron-donating dopants should suppress Sr2+ and Ba2+ ion exchange, and that there is a substantial preference for incorporating Ba2+ over Sr2+. Lastly, the substantial difference between the adsorption energies of the ions in an assumed vacuum and those computed in water suggests that a solvation model is needed for accurate representation of ion adsorption in an LTA zeolite.

The novel phases Rb4NaU3O12−xFx (1), K4NaU3O12−xFx (2), and Rb2.1K1.9KU3O12−xFx (3) were synthesized by molten flux methods using mixed alkali fluoride melts. The oxyfluorides crystallize in the cubic space group Imm with a lattice parameters of 8.7472(2) A, 8.6264(2) A, and 8.8390(3) A, respectively. All three structures crystallize in a cubic perovskite structure, ABO3 (A4BB′3O12), where the A site is fully occupied by an alkali cation, and the B site is shared by the remaining smaller alkali cation and uranium in an ordered fashion such that the alkali cation on the B site is surrounded by square uranyl bipyramids. The structures were characterized by single crystal X-ray diffraction, energy dispersive spectroscopy, X-ray absorption near edge structure spectroscopy, X-ray photoelectron spectroscopy, magnetic susceptibility measurements, DFT calculations, thermogravimetric analysis, and UV-vis spectroscopy, all of which support the presence of U(V) in the three new materials.

Using first-principles DFT we systematically investigate the thermodynamic stability and off-stoichiometry in 108 nominal 19-electron half-Heusler (hH) compounds. We demonstrate unambiguously that considering a cation deficiency towards the off-stoichiometric valence balanced, VEC = 18 composition is necessary for explaining the stability of all previously reported nominal VEC = 19 compounds. This is understandable in terms of an energy benefit from valence balance considering the valence of each atom using Zintl chemistry that offsets the energy penalty of forming defects in nearly all cases. Thus, we propose a valence balanced rule to understand the ground state stability of half-Heuslers irrespective of stoichiometry and nominal electron count (8, 18 or 19). Using this generalized rule we (a) predict 16 previously unreported nominal 19-electron XYZ half-Heuslers and (b) rationalize the reports of giant off-stoichiometries in compounds such as Ti(1−x)NiSb which has been known for over 50 years. Of the 16 new compounds predicted here, Ti(1−x)PtSb was synthesized and the half-Heusler phase confirmed through X-ray studies. The flexibility in stoichiometry of the half-Heusler systems to attain a stable valence balanced composition by accommodating large defect concentrations opens up multiple dimensions for discovery of multi-component defective half-Heuslers based on intrinsic and extrinsic defects which compensate for the nominally non-18-electron count of the structure.