Search Results (22)

Nioboixiolite-(□) is a new mineral found in a carbonatite sill from the Bayan Obo mine, Baotou City, Inner Mongolia, China. It occurs as anhedral to subhedral grains (100 to 500 μm in diameter) that are disseminated in carbonatite rock composed of dolomite, calcite, magnetite, apatite, biotite, actionlike, zircon, and columbite-(Fe). Most of these grains are highly serrated, with numerous inclusions of columbite-(Fe). The mineral is gray to deep black in color; is opaque, with a semi-metallic luster; has a black streak; and is brittle, with an uneven conchoidal splintery. The Mohs hardness is 6–6½, and the calculated density is 6.05 g/cm³. The reflection color is gray with a blue tone, and there is no double reflection color. The measured reflectivity of nioboixiolite-(□) is about 10.6%~12.1%, close to that of ixiolite (11%–13%). Nioboixiolite-(□) is non-fluorescent under 254 nm (short-wave) and 366 nm (long-wave) ultraviolet light. The average chemical analysis results (wt.%) of twelve electron microprobe analyses are F 0.01, MnO 0.12, MgO 0.15, BaO 0.62, PbO 0.91, SrO 1.49, CaO 2.76, Al₂O₃ 0.01, TREE₂O₃ 1.58, Fe₂O₃ 3.57, ThO₂ 0.11, SiO₂ 1.69, TiO₂ 3.68, Ta₂O₅ 13.95, Nb₂O₅ 47.04, and UO₃ 21.56, with a total of 99.25. The simplified formula is [Nb⁵⁺, Ta⁵⁺,Ti⁴⁺, Fe³⁺,□,]O₂. X-ray diffraction data show that nioboixiolite-(□) is orthorhombic, belonging to the space group Pbcn (#60). The refined unit cell parameters are a = 4.7071(5) Å, b = 5.7097(7) Å, c = 5.1111(6) Å, V = 138.31(3), and β = 90(1) °Å³ with Z = 4. In the crystal structure of nioboixiolite-(□), all cations occupy a single M1 site. In these minerals, edge-sharing M₁O₆ octahedra form chains along the c direction. In this direction, the chains are connected with each other via common vertices of the octahedra. The strongest measured X-ray powder diffraction lines are [d in Å, (I/I0), (hkl)]: 3.662(20) (110), 2.975(100) (111), 2.501(20) (021), 1.770(20) (122), 1.458(20) (023). A type specimen was deposited in the Geological Museum of China with catalogue number M16118, No. 15, Yangrou Hutong, Xisi, Beijing 100031, People’s Republic of China. Full article

Textured microstructures and anisotropic properties are key factors for the optimization of magnetic materials. Only for high texture grades can the remanence J_r and the maximum energy product (BH)_max be maximized. In additive manufacturing such as laser powder bed fusion (PBF-LB), methods to achieve texture have to be developed. In this work, anisotropic (CoCuFeZr)₁₇Sm₂ sintered magnets have been used as a substrate in experiments featuring single laser tracks to study the relationships between crystallographic orientation of the substrate grains and crystallographic orientation of grain growth in the melt-pool. The <0001> crystal direction (c-axis) of the substrate has been systematically varied with respect to the orientation of the laser scan track on the specimen surface. Crystallographic orientations of the melt-pool and the substrate have been analyzed using electron backscatter diffraction (EBSD). It is found that if the c-axis is oriented perpendicular to the temperature gradient in the melt-pool, grains grow with orientation similar to that of the substrate grain. If the c-axis and the temperature gradient are oriented in the same direction, the grains grow with high misorientation to the substrate. The highest anisotropy in the melt-pool is achieved when the substrate’s c-axis is oriented along the laser scan track. Under these conditions, 98.7% of the melt-pool area shows a misorientation <45° compared to the substrate orientation. The texture grade of the melt-pool area is comparable to that of the substrate magnet, at 91.8% and 92.2%, respectively. Full article

For permanent magnetic materials, anisotropic microstructures are crucial for maximizing remanence J_r and maximum energy product (BH)_max. This also applies to additive manufacturing processes such as laser powder bed fusion (PBF-LB). In PBF-LB processing, the solidification behavior is determined by the crystal structure of the material, the substrate, and the melt-pool morphology, resulting from the laser power P_L and scanning speed v_s. To study the impact of these parameters on the textured growth of grains in the melt-pool, experiments were conducted using single laser tracks on (CoCuFeZr)₁₇Sm₂ sintered magnets. A method was developed to quantify this grain shape anisotropy from electron backscatter diffraction (EBSD) analysis. For all grains in the melt-pool, the grain shape aspect ratio (GSAR) is calculated to distinguish columnar (GSAR < 0.5) and equiaxed (GSAR > 0.5) grains. For columnar grains, the grain shape orientation (GSO) is determined. The GSO represents the preferred growth direction of each grain. This method can also be used to reconstruct the temperature gradients present during solidification in the melt-pool. A dependence of the melt-pool aspect ratio (depth/width) on energy input was observed, where increasing energy input (increasing P_L, decreasing v_s) led to higher aspect ratios. For aspect ratios around 0.3, an optimum for directional columnar growth (93% area fraction) with predominantly vertical growth direction (mean angular deviation of 23.1° from vertical) was observed. The resulting crystallographic orientation is beyond the scope of this publication and will be investigated in future work. Full article

Mixed oxygen ion and electron-conducting materials are viable cathodes for solid oxide fuel cells due to their excellent oxygen transport kinetics and mixed electrical conductivity, which ensure highly efficient operation at low and medium temperatures. However, iron-based double perovskite oxides usually exhibit poor electrocatalytic activity due to low electron and oxygen ion conductivity. In this paper, Ca is doped in PrBaFe₂O_5+δ A-site to improve the electrochemical performance of PrBaFe₂O_5+δ. Results show that replacing Pr with Ca does not change the crystal structure, and the Ca doping effectively increases the adsorbed oxygen content and accelerates the migration and diffusion rate of O²⁻ to the electrolyte|cathode interface. The polarization resistance of the symmetric cell PC_0.15BF|CGO|PC_0.15BF is 0.033 Ω·cm² at 800 °C, which is about 56% lower than that of PBF, confirming the enhancement of the mixed conduction of oxygen ions and electrons. In addition, the anode-supported single cell has a peak power density of 512 mW·cm⁻² at 800 °C. Full article

PbF₂ single crystals are usually grown in the temperature gradient region by the Bridgman–Stockbarger method. Temperature distribution during the growth process is particularly important for the preparation of high-quality crystals. In this study, the temperature field during the growth of the PbF₂ single crystals was simulated based on the finite element method. The temperature distribution and temperature gradient changes in the crucible were investigated at different growth stages, including the seeding, shouldering, and iso-diameters stages. The calculated results show that as the crucible position continues downward during the growth process, the axial temperature gradient increases and then decreases from the bottom to the top of the crucible, with almost flat isotherms near the solid–liquid interface where the axial temperature gradient is larger. At the shoulder below the crucible, the solid–liquid interface was improved by adjusting the tilt angle. Furthermore, based on a novel design of the heat-insulating baffle, the concave solid–liquid interface in the iso-diameter stage can be effectively adjusted to realize a lower radial temperature gradient. This study provides theoretical guidance for the optimization of the growth of high-quality PbF₂ crystals by the Bridgman method. Full article

We present a low-noise (<10 µ$\mathrm{rad}/\sqrt{\mathrm{Hz}}$) broadband Faraday Rotation Spectroscopy method which is feasible for near-ultraviolet through near-infrared wavelengths. We demonstrate this in the context of a high-precision spectroscopy experiment using a heated Pb vapor cell and two different lasers, one in the UV (368 nm) and a second in the IR (1279 nm). A key element of the experimental technique is the use of a uniaxial single crystal CeF₃ Faraday modulator with excellent transmission and optical rotation properties across the aforementioned wavelength range. Polarimeter performance is assessed as a function of crystal orientation and alignment, AC modulation amplitude, laser power, and laser wavelength. Crystal-induced distortion of the ${\left(6p^2\right)}^3{P}_0\to {\left(6p^2\right)}^3{P}_1$ (1279 nm) and ${\left(6p^2\right)}^3{P}_1\to {\left(6p7s\right)}^3{P}_0$ (368 nm) spectral lines due to misalignment-induced birefringence is discussed and modeled using the Jones calculus. Full article

Lead-based halide perovskite semiconductors have demonstrated considerable potential in optoelectronic applications. However, the lack of high-quality crystals suitable for research has led to rare reports on CsPbF₃ single crystals. Good quality CsPbF₃ single crystals were successfully grown using the Bridgman method. The structure, luminescence, and electrical properties of crystals were investigated. At room temperature, the crystal structure was determined to be cubic perovskite, with a calculated bandgap of 3.68 eV. The measured emission spectrum showed one broad emission peak at approximately 400 nm. Three decay time constants were obtained from a sum of exponential functions fit to the fluorescence decay curve: 0.4 ns, 2.4 ns, and 15.0 ns for fast, middle, and slow decay times, respectively. The decay times excited by pulsed X-ray were measured to be 2.2 ns and 10.2 ns, indicating that CsPbF₃ is an ultrafast scintillator. Furthermore, the electrical properties demonstrated that CsPbF₃ exhibits high ion mobility, which is approximately 20 times that of electron mobility. Full article

Experiments on the preparation of the new mixed cations XeF₅M(AF₆)₃ (M = Cu, Ni; A = Cr, Nb, Ta, Ru, Rh, Re, Os, Ir, Pt, Au, As), XeF₅M(SbF₆)₃ (M = Sn, Pb), and XeF₅M(BF₄)_x(SbF₆)_3-x (x = 1, 2, 3; M = Co, Mn, Ni, Zn) salts were successful only in the preparation of XeF₅Ni(AsF₆)₃. In other cases, mixtures of different products, mostly XeF₅AF₆ and XeF₅A₂F₁₁ salts, were obtained. The crystal structures of XeF₅Ni(AsF₆)₃, XeF₅TaF₆, XeF₅RhF₆, XeF₅IrF₆, XeF₅Nb₂F₁₁, XeF₅Ta₂F₁₁, and [Ni(XeF₂)₂](IrF₆)₂ were determined for the first time on single crystals at 150 K by X-ray diffraction. The crystal structures of XeF₅NbF₆, XeF₅PtF₆, XeF₅RuF₆, XeF₅AuF₆, and (Xe₂F₁₁)₂(NiF₆) were redetermined by the same method at 150 K. The crystal structure of XeF₅RhF₆ represents a new structural type in the family of XeF₅AF₆ salts, which crystallize in four different structural types. The XeF₅A₂F₁₁ salts (M = Nb, Ta) are not isotypic and both represent a new structure type. They consist of [XeF₅]⁺ cations and dimeric [A₂F₁₁]⁻ anions. The crystal structure of [Ni(XeF₂)₂](IrF₆)₂ is a first example of a coordination compound in which XeF₂ is coordinated to the Ni²⁺ cation. Full article

Inorganic scintillators are of great significance in the fields of medical CT, high-energy physics and industrial nondestructive testing. In this work, we confirm that the Pb₄Lu₃F₁₇: Re (Re = Tb, Eu, Sm, Dy, Ho) crystals are promising candidates for a new kind of scintillator. Detailed crystal structure information is obtained by the Rietveld refinement analysis. Upon X-ray irradiation, all these scintillators exhibited characteristic 4f-4f transitions. The Ce and Gd ions were verified to be useful for enhancing the scintillation intensity via introducing energy transfer processes. The integrated scintillation intensity of the Pb₄Lu₃F₁₇: Tb/Ce is about 16.8% of the commercial CsI (Tl) single crystal. Our results manifested that Pb₄Lu₃F₁₇: Re has potential application in X-ray detection and imaging. Full article

The photosynthetic reaction center of the purple bacterium Cereibacter sphaeroides with two site-directed mutations Ile-L177–His and M197 Phe–His is of double interest. The substitution I(L177)H results in strong binding of a bacteriochlorophyll molecule with L-subunit. The second mutation F(M197)H introduces a new H-bond between the C2-acetyl carbonyl group of the bacteriochlorophyll P_B and His-M197, which is known to enhance the stability of the complex. Due to this H-bond, π -electron system of P finds itself connected to an extensive H-bonding network on the periplasmic surface of the complex. The crystal structure of the double mutant reaction center obtained with 2.6 Å resolution allows clarifying consequences of the Ile L177 – His substitution. The value of the P/P⁺ midpoint potential in the double mutant RC was found to be ~20 mV less than the sum of potentials measured in the two RCs with single mutations I(L177)H and F(M197)H. The protein environment of the BChls P_A and B_B were found to be similar to that in the RC with single substitution I(L177)H, whereas an altered pattern of the H-bonding networks was found in the vicinity of bacteriochlorophyll P_B. The data obtained are consistent with our previous assumption on a correlation between the bulk of the H-bonding network connected with the π-electron system of the primary electron donor P and the value of its oxidation potential. Full article

Single crystals of Pb_1−3x▯_xNd_2x(MoO₄)_1−3x(WO₄)_3x (PNMWO) with scheelite-type structure, where ▯ denotes cationic vacancies, have been successfully grown by the Czochralski method in air and under 1 MPa. This paper presents the results of structural, optical, magnetic and electrical, as well as the broadband dielectric spectroscopy measurements of PNMWO single crystals. Research has shown that replacing diamagnetic Pb²⁺ ions with paramagnetic Nd³⁺ ones, with a content not exceeding 0.01 and possessing a screened 4f-shell, revealed a significant effect of orbital diamagnetism and Van Vleck’s paramagnetism, n-type electrical conductivity with an activation energy of 0.7 eV in the intrinsic area, a strong increase of the power factor above room temperature for a crystal with x = 0.005, constant dielectric value (~30) and loss tangent (~0.01) up to room temperature. The Fermi energy (~0.04 eV) and the Fermi temperature (~500 K) determined from the diffusion component of thermopower showed shallow donor levels. Full article

A new modification of PbF(IO₃) has been obtained as single crystals from hydrothermal synthesis, alongside the known centrosymmetric, Pb(IO₃)₂, as a second phase. Measured with the Kurtz-Perry SHG method, the new crystals are phase-matchable for YAG:Nd laser radiation and demonstrate strong SHG output. According to an X-ray diffraction analysis conducted on a single crystal at low temperature, the new crystals appear monoclinic, of space group Pn, as opposed to the known orthorhombic modification of the PbF(IO₃), of space group Iba2. The new crystals were also measured at room temperature, showing an orthorhombic disordered variant of the new phase (space group C2ma, standard Abm2). This variant presents an “average structure” with the mirror plane in the group. The low-temperature X-ray single-crystal experiment allowed us to find the correct structural model, where the mirror plane was found as a twin element in the real monoclinic Pn structure. A careful crystal chemical analysis led to a whole family of nonlinear optical crystals with a common formula, AX(IO₃), A = Bi, Ba, Pb, X = O, F, (OH), currently counting six representatives, including the well-known BiO(IO₃). All of them possess common central cationic layers similar to those known in Aurivillius-type phases, with anionic iodate layers attached above and below these layers instead of the perovskite-like, or halogens. The structure–property relationships are discussed with respect to the important role of the large cations: Pb²⁺, Bi³⁺ or Ba²⁺. A number of iodates with similar structures are also analyzed. Full article

A detailed study was carried out to gain a better understanding of the microstructural differences between Ti-6Al-4V parts fabricated via the conventional powder metallurgy (PM) and the laser powder bed fusion (L-PBF) 3D printing routes. The parts were compared in terms of the constituent phases in the microstructure and their effects on the micro- and nano-hardness. In L-PBF parts, the microstructure has a single phase of martensitic α′ with hcp crystal structure and acicular laths morphology, transformed from prior parent phase β formed upon solidification of the melt pool. However, for the sintered parts via powder metallurgy, two phases of α and β are noticeable and the microstructure is composed of α grains and α + β Lamellae. The microhardness of L-PBF processed Ti-6Al-4V samples is remarkably higher than that of the PM samples but, surprisingly, the nano-hardness of the bulk martensitic phase α′ (6.3 GPa) is almost the same as α (i.e., 6.2 GPa) in PM samples. This confirms the rapid cooling of the β phase does not have any effect on the hardening of the bulk martensitic hcp α′. The high microhardness of L-PBF parts is due to the fine lath morphology of α′, with a large concentration of low angle boundaries of α′. Furthermore, it is revealed that for the α phase in PM samples, a higher level of vanadium concentration lowers the nano-hardness of the α phase. In addition, as expected, the compacting pressure and sintering temperature during the PM process led to variations in the porosity level as well as the microstructural morphology of the fabricated specimens, which will in turn have a significant effect on the mechanical properties. Full article

The roméite-group is part of the pyrochlore-supergroup and comprises cubic oxides of A₂B₂X₆Y formula in which Sb⁵⁺ predominates in the B-site. The A and Y main occupants determine different minerals in the group and are important for the discovery of new mineral species. Two different roméite-group mineral samples were analysed by electron microprobe analysis (EMPA), Raman spectroscopy and single-crystal X-ray diffraction (XRD). The first sample is from Prabornaz Mine (locality of the original roméite), Saint Marcel, Valle d’Aosta, Italy, whereas the other one occurs in Kalugeri Hill, Babuna Valley, Jakupica Mountains, Nezilovo, Veles, Macedonia. Sample 1 was identified as fluorcalcioroméite, and sample 2 as hydroxycalcioroméite. Both samples belong to the cubic crystal system, space group Fd$\overline{3}$m, Z = 8, where a = 10.2881(13) Å, V = 1088.9(4) ų for sample 1, and a = 10.2970(13) Å, V = 1091.8(4) ų for sample 2. The crystal structure refinements converged to (1) R₁ = 0.016, wR₂ = 0.042; and (2) R₁ = 0.023, wR₂ = 0.049. Bond-valence calculations validated the crystal structure refinements determining the correct valences at each crystallographic site. Discrepancies observed in the Sb⁵⁺ bond-valence calculations were solved with the use of the proper bond valence parameters. The resulting structural formulas are (Ca_1.29Na_0.55□_0.11Pb_0.05)_Σ=2.00(Sb_1.71Ti_0.29)_Σ=2.00[O_5.73(OH)_0.27]_Σ=6.00[F_0.77O_0.21(OH)_0.02]_Σ=1.00 for sample 1, and (Ca_1.30Ce_0.51□_0.19)_Σ=2.00(Sb_1.08Ti_0.92)_Σ=2.00O_6.00[(OH)_0.61O_0.21F_0.18]_Σ=1.00 for sample 2. The Raman spectra of the samples exhibited the characteristic bands of roméite-group minerals, the most evident corresponding to the Sb-O stretching at around 510 cm⁻¹. Full article

An Er³⁺/Sc³⁺ co-doped 0.68Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ ferroelectric single crystal was grown by high-temperature flux method. The remnant polarization Pr is 27.97 µC/cm² and the coercive field Ec is 8.26 kV/cm for [100] oriented crystal. Green (524 and 551 nm) and red (654 nm) emission bands are generated at the 980 nm excitation, which corresponds to the ²H_11/2→ ⁴I_15/2, ⁴S_3/2→ ⁴I_15/2 and ⁴F_9/2→ ⁴I_15/2 transitions of Er³⁺, respectively. Judd–Ofelt theory has been applied to predict the spectroscopic characteristics of the as-grown crystals. The obtained J–O intensity parameters Ω_t (t = 2, 4 and 6) are Ω₂ = 0.76 × 10⁻²⁰ cm², Ω₄ = 1.0 × 10⁻²⁰ cm², Ω₆ = 0.55 × 10⁻²⁰ cm². Spectroscopic characteristics, including optical transition probabilities, branching ratio, and radiative lifetime of Er³⁺ in the crystal, are determined. The calculated radiative lifetimes of ⁴I_13/2 and ⁴I_11/2 energy levels are 2.82 ms and 2.61 ms, respectively. These investigations provide possibilities for the crystal Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃:Er³⁺/Sc³⁺ to be a new type of multifunctional crystal integrating electricity-luminescence. Full article