High-pressure behaviour of Cs2_{2}V3_{3}O8_{8} fresnoite

Crystal structure of Cs2V3O8 fresnoite (P4bm, Z=2) has been studied using single-crystal X-ray diffraction in a diamond anvil cell to 8.6 GPa at room temperature. Cs2V3O8 undergoes a reversible first-order phase transition at about 4 GPa associated with anomalies in the pressure dependencies of the lattice parameters and unit-cell volume but without any symmetry change. Both structures consist of layers of corner-sharing V5+O4 tetrahedra and V4+O5 tetragonal pyramids separated by the Cs+ cations located between the layers. At low pressures, the compression has little effect on the polarity of the structure. Above 4 GPa, the pseudosymmetry with respect to the corresponding centrosymmetric space group P4/mbm abruptly increases. The effects of external pressure and of the A+ cation substitution in the vanadate fresnoites A2V3O8 (A+: K+, Rb+, NH4+, Cs+) are discusse

Trivalent Cation-Controlled Phase Space of New U(IV) Fluorides, Na\u3csub\u3e3\u3c/sub\u3eMU\u3csub\u3e6\u3c/sub\u3eF\u3csub\u3e30\u3c/sub\u3e (M = Al\u3csup\u3e3+\u3c/sup\u3e, Ga\u3csup\u3e3+\u3c/sup\u3e, Ti\u3csup\u3e3+\u3c/sup\u3e, V\u3csup\u3e3+\u3c/sup\u3e, Cr\u3csup\u3e3+\u3c/sup\u3e, Fe\u3csup\u3e3+\u3c/sup\u3e): Mild Hydrothermal Synthesis Including an in Situ Reduction Step, Structures, Optical, and Magnetic Properties

A series of new, complex U(IV) fluorides, namely, Na3MU6F30 (M = Al3+, Ga3+, Ti3+, V3+, Cr3+, and Fe3+), containing trivalent transition- and main-group metal cations were synthesized via an in situ reduction step of U(VI) to U(IV). Single crystals of the series were grown in high yield under mild hydrothermal conditions and were characterized by single-crystal X-ray diffraction. The reported compounds crystallize in the trigonal space group P3̅c1 and exhibit complex crystal structures with a three-dimensional (3-D) framework composed of corner- and edge-shared UF9 polyhedra. The arrangement of U2F16 dimers forms two types of hexagonal channels, where MF6 polyhedra and sodium atoms are located. The most interesting structural feature is the presence of the 3-D framework that can accommodate various transition-metal ions in low oxidation states, indicating that the framework acts as an excellent host. Trivalent transition metal ions, even reduced Ti3+and V3+, were stabilized by both the rigid framework and by our synthetic conditions. Utilizing ionic radii of transition metal ions, a phase boundary was investigated, suggesting that there exists a size limit for the M site in the crystal structure. The valence state of uranium was studied by U 4f X-ray photoelectron spectroscopy, which confirmed the presence of U4+. Temperature-dependent magnetic susceptibility measurements yielded effective magnetic moments of 3.50 and 3.35 μB for Na3MU6F30 (M = Al3+ and Ga3+), respectively. For the other compounds, combined effective magnetic moments of 8.93, 9.09, 9.18, and 10.39 μB were obtained for Ti, V, Cr, and Fe members, respectively. In all cases, large negative Weiss constants were observed, which are indicative of the existence of a spin gap in U4+. Field-dependent magnetic property measurements at 2 K for Na3FeU6F30 demonstrated that U4+ attains a nonmagnetic singlet ground state at low temperature. Optical and thermal properties were measured and are reported

Mild Hydrothermal Crystal Growth, Structure, and Magnetic Properties of Ternary U(IV) Containing Fluorides: LiUF\u3csub\u3e5\u3c/sub\u3e, KU\u3csub\u3e2\u3c/sub\u3eF\u3csub\u3e9\u3c/sub\u3e, K\u3csub\u3e7\u3c/sub\u3eU\u3csub\u3e6\u3c/sub\u3eF\u3csub\u3e31\u3c/sub\u3e, RbUF\u3csub\u3e5\u3c/sub\u3e, RbU\u3csub\u3e2\u3c/sub\u3eF\u3csub\u3e9\u3c/sub\u3e, and RbU\u3csub\u3e3\u3c/sub\u3eF\u3csub\u3e13\u3c/sub\u3e

Single crystals of several ternary alkali uranium fluorides, LiUF5, KU2F9, K7U6F31, RbUF5, RbU2F9, and RbU3F13, have been obtained in a mild hydrothermal process using UO2(CH3CO2)2(H2O)2 as the uranium source. Their crystal structures were determined by single crystal X-ray diffraction. The uranium in the starting reagent was successfully reduced from U6+ to U4+ in a dilute hydrofluoric acid environment, aided by the presence of a copper salt. All materials exhibit highly complex crystal structures that range from two-dimensional to three-dimensional. The U4+ cations are found in high (UF8 and UF9) coordination environments. The magnetic susceptibility measurements yielded effective magnetic moments of 3.01–3.83 μB for the U4+cations. The temperature dependent magnetic susceptibility measurements confirmed that the U4+cation exhibits a nonmagnetic singlet ground state at low temperatures. No long-range magnetic order was observed for any of the above compositions down to 2 K. Optical and thermal behaviors of the fluorides were also investigated

Synthesis, Crystal Structure, and Magnetic Properties of the Oxometallates KBaMnO\u3csub\u3e4\u3c/sub\u3e and KBaAsO\u3csub\u3e4\u3c/sub\u3e

Single crystals of KBaMnO4 and KBaAsO4 were grown using the hydroflux method and characterized by single crystal X-ray diffraction. Both compounds crystallize in the orthorhombic space group Pnma with a = 7.7795(4) Å, b = 5.8263(3) Å, and c = 10.2851(5) Å for the manganate and a = 7.7773(10) Å, b = 5.8891(8) Å, and c = 10.3104(13) Å for the arsenate. The materials exhibit a three-dimensional crystal structure consisting of isolated MnO43− or AsO43−tetrahedra, with the charge balance maintained by K+ and Ba2+. Each tetrahedron is surrounded by six K+ and five Ba2+, and shares its corner/edge with KO10 polyhedra and corner/edge/face with BaO9 polyhedra, respectively. The crystal growth, crystal structure and magnetic properties are discussed

Toughness behavior and deformation mechanisms in FCC-based Fe45Co30Cr10V10Ni5-xMnx high-entropy alloys: Insights from instrumented Charpy impact tests

This study investigated toughness properties of FCC-based Fe45Co30Cr10V10Ni5-xMnx high entropy alloys (HEAs). Ductile-dimpled rupture mode in all alloys and test temperatures complicated precise explanations on Charpy impact energy, but the instrumented Charpy test provided a breakdown of total energy (ET) into initiation energy (EI) and propagation energy (EP), offering critical insights into Mn-content- and temperature-related energy variations. Pmax and TP, reflecting maximum flow stress and time, respectively, until initiation of crack propagation from the notch tip, involved a transition of deformation mechanisms from slip to TWIP, then to BCC-TRIP, thereby inducing increased strain hardening and delaying plastic instability at the notch tip. At 25 °C, an increase in Mn content prompted a transition in deformation behavior from slip to TWIP and subsequently to BCC-TRIP, correlating well with increased Pmax and TP and consequently ET due to enhanced strain hardenability. At −196 °C, predominant BCC-TRIP activity in all alloys led to increased formation of BCC martensite, intensifying strain hardening and requiring higher Pmax for crack initiation than at 25 °C. Due to minimal slip line field formation associated with reduced plastic deformation, however, cracks initiated directly from the notch-tip center, representing fast initiation of crack propagation and consequently reduction in EI and ET. Thus, utilizing parameters from instrumented Charpy tests, including Pmax, TP, EI, EP, and ET, provided insights into fracture phenomena and their interrelations in the present HEAs

Crystal Growth, Structural Characterization, Cation–Cation Interaction Classification, and Optical Properties of Uranium(VI) Containing Oxychlorides, A\u3csub\u3e4\u3c/sub\u3eU\u3csub\u3e5\u3c/sub\u3eO\u3csub\u3e16\u3c/sub\u3eCl\u3csub\u3e2\u3c/sub\u3e (A = K, Rb), Cs\u3csub\u3e5\u3c/sub\u3eU\u3csub\u3e7\u3c/sub\u3eO\u3csub\u3e22\u3c/sub\u3eCl\u3csub\u3e3\u3c/sub\u3e, and AUO\u3csub\u3e3\u3c/sub\u3eCl (A = Rb, Cs)

Single crystals of five new alkali metal uranium oxychlorides, K4U5O16Cl2, Rb4U5O16Cl2, Cs5U7O22Cl3, RbUO3Cl, and CsUO3Cl, have been grown from molten chloride fluxes and structurally characterized by single crystal X-ray diffraction. All of the materials are monoclinic. The first three crystallize in the space group P21/n and exhibit a 2D layered structure with a novel layer topology, consisting of UO6, UO7, and UO4Cl2 polyhedra and cation–cation interactions (CCIs) within the plane of the uranyl sheet. A general cation–cation classification scheme is presented. RbUO3Cl and CsUO3Cl crystallize in the space group P21/m and exhibit 1D zipper-like chains of UO5Cl2 polyhedra. The lattice parameters of the new oxychlorides are: K4U5O16Cl2, a = 9.9574(4) Å, b = 6.9766(3) Å, c= 14.3920(6) Å, and β = 105.7690(10)°; Rb4U5O16Cl2, a = 10.2164(4) Å, b = 7.0160(3) Å, c= 14.4930(5) Å, and β = 103.8290(10)°; Cs5U7O22Cl3, a = 10.6214(5) Å, b = 18.1071(8) Å, c= 16.0857(7) Å, and β = 102.9850(10)°; RbUO3Cl, a = 7.3602(6) Å, b = 4.1127(3) Å, c = 8.5556(7) Å, and β = 104.602(2)°; CsUO3Cl, a = 7.7768(4) Å, b = 4.1245(2) Å, c = 8.7701(5) Å, and β = 105.4680(10)°. The materials were further characterized by UV-vis reflectance spectroscopy and fluorescence spectroscopy