Single crystals of
Cs6Ln2Ge11O28 (Ln = La,
Pr, and Nd) and Cs12Bi3Ge24O58F were grown from a CsCl/CsF flux. These compounds
crystallize in new structure types and are members of a new structural
family related to the Wadeite structure by polyhedral substitution.
Elucidation of this structural family, dubbed the superwadeites, allows
for the prediction of the existence and structure of Cs2Ge5O11. Density functional theory calculations
support that Cs2Ge5O11 is a stable
compound. Ultimately, this compound is grown via a solid-state reaction,
and its structure is refined via Rietveld refinement.
A series of alkali metal rare-earth borates were prepared via hightemperature flux crystal growth, and their structures were characterized by single crystal X-ray diffraction (SXRD). Na 3 Ln(BO 3 ) 2 (Ln = La-Lu) crystallize in the monoclinic space group P2 1 /n, the potassium series K 3 Ln(BO 3 ) 2 (Ln = La-Tb) crystallize in the orthorhombic space group Pnma, while the Ln = Dy, Ho, Tm, Yb analogues crystallize in the orthorhombic space group Pnnm. To demonstrate the generality of this synthetic technique, high-entropy oxide (HEO) compositions K 3 N d 0 . 1 5 ( 1 ) E u 0 . 2 0 ( 1 ) G d 0 . 2 0 ( 1 ) D y 0 . 2 2 ( 1 ) H o 0 . 2 3 ( 1 ) ( B O 3 ) 2 a n d K 3 Nd 0.26(1) Eu 0.29(1) Ho 0.22(1) Tm 0.14(1) Yb 0.10(1) (BO 3 ) 2 were obtained in single crystal form. Radiation damage investigations determined that these borates have a high radiation damage tolerance. To assess whether trivalent actinide analogues of Na 3 Ln(BO 3 ) 2 and K 3 Ln(BO 3 ) 2 would be stable, density functional theory was used to calculate their enthalpies of formation, which are favorable.
A new niobium-doped inorganic scintillating oxyfluoride, Rb4Ge5O9F6:Nb, was synthesized in single crystal form by high-temperature flux growth. The host structure, Rb4Ge5O9F6, crystallizes in the orthorhombic space group Pbcn with lattice parameters a = 6.98430(10) Å, b = 11.7265(2) Å, and c = 19.2732(3) Å, consisting of germanium oxyfluoride layers made up of Ge3O9 units connected by GeO3F3 octahedra. In its pure form, Rb4Ge5O9F6 shows neither luminescence nor scintillation but when doped with niobium, Rb4Ge5O9F6:Nb exhibits bright blue luminescence and scintillation. The isostructural doped structure, Rb4Ge5O9F6:Nb, crystallizes in the orthorhombic space group Pbcn with lattice parameters a = 6.9960(3) Å, b = 11.7464(6) Å, and c = 19.3341(9) Å. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements suggest that the niobium is located in an octahedral coordination environment. Optical measurements inform us that the niobium dopant acts as the activator. The synthesis, structure, and optical properties are reported, including radioluminescence (RL) measurements under X-ray irradiation.
As
part of our exploration of plutonium-containing materials as
potential nuclear waste forms, we report the first extended structure
Pu(V) material and the first Pu(V) borate. Crystals of Na2(PuO2)(BO3) were grown out of mixed hydroxide/boric
acid flux and found to crystallize in the orthorhombic space group Cmcm with lattice parameters of a = 9.9067(4)
Å, b = 6.5909(2) Å, and c = 6.9724(2) Å. Na2(PuO2)(BO3) adopts a layered structure in which layers of PuO2(BO3)2– are separated by sodium cations. Plutonium
is found in a pentagonal bipyramidal coordination environment, with
axial Pu(V)–O plutonyl bond lengths of 1.876(3) Å and
equatorial Pu–O bond lengths ranging from 2.325(5) to 2.467(3)
Å. We find that the Pu(V)–O plutonyl bond lengths are
approximately 0.1 Å longer than the reported Pu(VI)–O
plutonyl bond lengths and shorter by approximately 0.033 Å than
the corresponding U(V) uranyl bond lengths. Raman spectroscopy on
single crystals was used to determine the PuO2
+ plutonyl stretching and the equatorial breathing mode frequencies
of the pentagonal bipyramidal coordination environment around plutonium.
Density functional theory calculations were used to calculate the
Raman spectrum to help identify the Raman bands at 690 and 630 cm–1 as corresponding to the plutonyl(V) ν1 stretch
and the equatorial PuO5 breathing mode, respectively. UV–vis
measurements on single crystals indicate semiconducting behavior with
a band gap of ∼2.60 eV.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.