Search Results (25)

High-permittivity Ba(Eu_1/5Sm_1/5Nd_1/5Pr_1/5La_1/5)₂Ti₄O₁₂ (BESNPLT) high-entropy ceramics (HECs) were synthesized via a solid-state route. The microstructure, sintering behavior, phase structure, vibration modes, and microwave dielectric characteristics of the BESNPLT HECs were thoroughly investigated. The phase structure of the BESNPLT HECs was confirmed to be a single-phase orthorhombic tungsten-bronze-type structure of Pnma space group. Permittivity (ε_r) was primarily influenced by polarizability and relative density. The quality factor (Q×f) exhibited a significant correlation with packing fraction, whereas the temperature coefficient (TCF) of the BESNPLT HECs closely depended on the tolerance factor and bond valence of B-site. The BESNPLT HECs sintered at 1400 °C, demonstrating high relative density (>97%) and optimum microwave dielectric characteristics with TCF = +38.9 ppm/°C, Q×f = 8069 GHz (@6.1 GHz), and ε_r = 87.26. This study indicates that high-entropy strategy was an efficient route in modifying the dielectric characteristics of tungsten-bronze-type microwave ceramics. Full article

Investigating the microwave dielectric properties of ceramics prepared through the conventional solid-state route, such as x[(Mg_0.6Zn_0.4)_0.95Co_0.05]_1.02TiO_3.02-(1−x)Ca_0.6(La_0.9Y_0.1)_0.2667TiO₃, reveals notable characteristics. [(Mg_0.6Zn_0.4)_0.95Co_0.05]_1.02TiO_3.02 shows a permittivity (ε_r) of approximately 20, a high quality factor (Q × f) ranging between 250,000 and 560,000 GHz, and a temperature coefficient of resonant frequency (τ_f) of approximately −65 ppm/°C. To enhance the temperature stability, Ca_0.6(La_0.9Y_0.1)_0.2667TiO₃ featuring a τ_f value of +374 ppm/°C was incorporated into the [(Mg_0.6Zn_0.4)_0.95Co_0.05]_1.02TiO_3.02 composition. τ_f demonstrated an increase with rising Ca_0.6(La_0.9Y_0.1)_0.2667TiO₃ content, reaching zero at x = 0.95. A ceramic composition of 0.95[(Mg_0.6Zn_0.4)_0.95Co_0.05]_1.02TiO_3.02-0.05Ca_0.6(La_0.9Y_0.1)_0.2667TiO₃, incorporating 3wt.% BaCu(B₂O₅) as sintering aids, exhibited outstanding microwave dielectric properties: ε_r~22.5, Q × f~195,000 (at 9 GHz), and τ_f~0.1ppm/°C, with a sintering temperature at 950 °C. This material is proposed as a prospective candidate for 6G band components and GPS antennas. Full article

The contents of 49 trace elements in sub-bituminous Pernik coals and their waste products from preparation and combustion processes were investigated. The studied coals have trace element contents higher than the respective Clarke values for brown coals and some of them may pose environmental concerns. The elements Li, Rb, Cs, Ba, Sc, Y, La, Ce, Nd, Sm, Eu, Er, Ga, Zr, Sn, V, Nb, Ta, W, F, Cu, Zn, In, Pb, Cr, Co, Ni, and Th in the feed coals have concentrations that exceed twice the Clarke values. Most element contents in bottom ash are enriched compared with those in feed coal. Some of the volatile elements are equal or significantly depleted including Sn, Mo, Sb, F, Bi, Cd, Ge, and Pb. Fly ash has higher contents of Ga, Zr, Hf, Sn, V, Nb, Mo, and F in comparison with bottom ash. Most elements have a significant positive correlation with ash yield, indicating their inorganic association. The mixed wastes (coal slurry, bottom ash, and fly ash) in the disposal pond are slightly depleted of most of the elements studied with the exclusion of Cl, Ba, and Br. The Pernik coals and their waste products are unpromising for the extraction of REY due to their low element contents. Full article

A new Center for Radiopharmaceutical Cancer Research was established at the Helmholtz-Zentrum Dresden-Rossendorf in 2017 to centralize radionuclide and radiopharmaceutical production, as well as enable chemical and biochemical research. Routine production of several radionuclides was put into operation in recent years. We report on the production methods of radiopharmaceutical radionuclides, in particular ¹¹C, ¹⁸F, and radio metals like ⁶¹Cu, ⁶⁴Cu, ⁶⁷Cu, ⁶⁷Ga, ¹³¹Ba, and ¹³³La that are used regularly. In the discussion, we report typical irradiation parameters and achieved saturation yields. Full article

The present work elucidates the fabrication of Barium Lanthanum Oxide nanosheets (BaLa₂O₄ NSs) via a simple one-pot precipitation method. The acquired results show an orthorhombic crystal system with an average crystallite size of 27 nm. The morphological studies revealed irregular-shaped sheets stacked together in a layered structure, with the confirmation of the precursor elements. The diffused reflectance studies revealed a strong absorption between 200 nm and 350 nm, from which the band-gap energy was evaluated to be 4.03 eV. Furthermore, the fluorescence spectrum was recorded for the prepared samples; the excitation spectrum shows a strong peak at 397 nm, attributed to the ⁴F_7/2→⁴G_11/2 transition, while the emission shows two prominent peaks at 420 nm (⁴G_7/2→⁴F_7/2) and 440 nm (⁴G_5/2→⁴F_7/2). The acquired emission results were utilized to confirm the color emission using a chromaticity plot, which found the coordinates to be at (0.1529 0.1040), and the calculated temperature was 3171 K. The as-prepared nanosheets were utilized in detecting latent fingerprints (LFPs) on various non-porous surfaces. The powder-dusting method was used to develop latent fingerprints on various non-porous surfaces, which resulted in detecting all the three ridge patterns. Furthermore, the as-synthesized nanosheets were used to degrade methyl red (MR) dye, the results of which show more than 60% degradation at the 70th minute. It was also found that there was no further degradation after 70 min. All the acquired results suggest the clear potential of the prepared BaLa₂O₄ NSs for use in advanced forensic and photocatalytic applications. Full article

This study investigated the impact of samarium and lanthanum fluorides (SmF₃ and LaF₃) on the physical and mechanical properties of Tl_0.8Hg_0.2Ba₂Ca_2−xR_xCu₃O_9−δ−yF_y superconducting phases (specifically the (Tl, Hg)-1223 phase), where R = Sm and La, with $0.00\hspace{0.17em}\le \hspace{0.17em}x \hspace{0.17em}\le \hspace{0.17em}0.10$. The superconducting samples were synthesized using the solid-state reaction method. X-ray diffraction (XRD) verified the formation of the (Tl, Hg)-1223 phase without altering its tetragonal structure. Scanning electron micrographs (SEM) reveal the improvement of the grain size and inter-grain connectivity as Sm and La contents increased up to $x=0.025$. The electrical properties of (Tl, Hg)-1223 were studied using I-V and electrical resistivity measurements. Improved superconducting transition temperature (T_c) and transport critical current density (J_c) were observed up to $x=0.025$, beyond which they decreased substantially. Vickers microhardness (H_v) measurements were performed at room temperature to investigate their mechanical performance with various applied loads ($0.49–9.80$ N) and times ($10–90$s). For both substitutions, the mechanical properties were enhanced up to an optimal value at $x=0.025$. All samples exhibited normal indentation size effect (ISE) behavior. The proportional sample resistance (PSR) model best explained H_v values among five theoretical models. Dislocation creep was the primary creep mechanism in the samples, according to indentation creep studies. Full article

Multiphase fluoride polycrystalline eutectics pRF₃ × qMF₂ forming in the MF₂–RF₃ (M = Ca, Sr, Ba; R = La–Nd) binary systems were synthesized by the directional crystallization technique from a melt. The phase composition, morphology, and temperature dependences of fluorine ionic conductivity in fabricated composites were studied in detail. The pRF₃ × qMF₂ (p and q are the mole percentages of components) eutectic composites consist of both extremely saturated fluorite-type structure M_1−xR_xF_2+x solid solutions and the tysonite-type R_1−yM_yF_3−y ones. Microsized growth blocks with a fine lamellar structure are typical for synthesized composites. The thinnest (from 3 μm) and longest lamellae are observed in the 68LaF₃ × 32BaF₂ composition. The ionic conductivity values of pRF₃ × qMF₂ composites are determined by the phase composition, practically do not depend on their morphological features, and reach 10⁻³–10⁻² S/cm at 500 K (with an ion transport activation enthalpy of about 0.5–0.6 eV). Crystallized eutectics are superior to any single-phase M_1−xR_xF_2+x solid solutions and ball-milling R_1−yM_yF_3−y nanoceramics in terms of ion-conducting properties. These fluoride materials represent an alternative to widely applied tysonite-type ceramic composites in various electrochemical devices and require further in-depth studies. Full article

Late Cretaceous granitoids are developed in the eastern and western districts of the Gejiu ore district, but tin deposits mainly occur in the eastern district, and the reasons for the difference in mineralization between the eastern and western districts are still controversial. Considering the main factors controlling granite Sn fertility, the whole-rock geochemical characteristics of granites on both sides are compared. LA-ICP-MS zircon U-Pb analyses of the Gejiu granites yielded two age periods: the early phase from 79.2 to 83.3 Ma and the later phase from 73.8 to 75.6 Ma. The western district granites have higher zircon ε_Hf(t), CaO/Na₂O, Ba, and Sr concentrations and lower Rb/Sr ratios than the eastern district granites, indicating that the western district granites have more mantle-derived materials in the source than the eastern district granites. Results of oxygen fugacity show that the western granites have a higher oxygen fugacity condition. More depleted Ba, Sr, P, Eu and Ti characteristics with obviously negative Eu anomalies in the eastern granites also have high Rb/Sr ratios and low Nb/Ta and Zr/Hf ratios, indicating that the eastern granites experienced highly magmatic differentiation, attributed to high volatile F contents that can reduce the viscosity and solidus of magma. Combined with the differences in field observations and structural styles, on the whole, the western district granites have higher oxygen fugacities and lower F contents and magmatic differentiation than those in the eastern district granites, indicating that the western district granites are not conducive to mineralization. Full article

High-quality, uniaxially oriented, and flexible PbZr_0.52Ti_0.48O₃ (PZT) films were fabricated on flexible RbLaNb₂O₇/BaTiO₃ (RLNO/BTO)-coated polyimide (PI) substrates. All layers were fabricated by a photo-assisted chemical solution deposition (PCSD) process using KrF laser irradiation for photocrystallization of the printed precursors. The Dion–Jacobson perovskite RLNO thin films on flexible PI sheets were employed as seed layers for the uniaxially oriented growth of PZT films. To obtain the uniaxially oriented RLNO seed layer, a BTO nanoparticle-dispersion interlayer was fabricated to avoid PI substrate surface damage under excess photothermal heating, and the RLNO has been orientedly grown only at around 40 mJ·cm⁻² at 300 °C. The prepared RLNO seed layer on the BTO/PI substrate showed very high (010)-oriented growth with a very high Lotgering factor (F(010) = 1.0). By using the flexible (010)-oriented RLNO film on BTO/PI, PZT film crystal growth was possible via KrF laser irradiation of a sol–gel-derived precursor film at 50 mJ·cm⁻² at 300 °C. The obtained PZT film showed highly (001)-oriented growth on the flexible plastic substrates with F(001) = 0.92 without any micro-cracks. The RLNO was only uniaxial-oriented grown at the top part of the RLNO amorphous precursor layer. The oriented grown and amorphous phases of RLNO would have two important roles for this multilayered film formation: (1) triggering orientation growth of the PZT film at the top and (2) the stress relaxation of the underneath BTO layer to suppress the micro-crack formation. This is the first time that PZT films have been crystallized directly on flexible substrates. The combined processes of photocrystallization and chemical solution deposition are a cost-effective and highly on-demand process for the fabrication of flexible devices. Full article

Owing to its high reliability and accuracy, the ratiometric luminescent thermometer can provide non-contact and fast temperature measurements. In particular, the nanomaterials doped with lanthanide ions can achieve multi-mode luminescence and temperature measurement by modifying the type of doped ions and excitation light source. The better penetration of the near-infrared (NIR) photons can assist bio-imaging and replace thermal vision cameras for photothermal imaging. In this work, we prepared core–shell cubic phase nanomaterials doped with lanthanide ions, with Ba₂LuF₇ doped with Er³⁺/Yb³⁺/Nd³⁺ as the core and Ba₂LaF₇ as the coating shell. The nanoparticles were designed according to the passivation layer to reduce the surface energy loss and enhance the emission intensity. Green upconversion luminescence can be observed under both 980 nm and 808 nm excitation. A single and strong emission band can be obtained under 980 nm excitation, while abundant and weak emission bands appear under 808 nm excitation. Meanwhile, multi-mode ratiometric optical thermometers were achieved by selecting different emission peaks in the NIR window under 808 nm excitation for non-contact temperature measurement at different tissue depths. The results suggest that our core–shell NIR nanoparticles can be used to assist bio-imaging and record temperature for biomedicine. Full article

Geochemical baselines are crucial to explore mineral resources and monitor environmental changes. This study presents the first Laos geochemical baseline values of 69 elements. The National-scale Geochemical Mapping Project of Lao People’s Democratic Republic conducted comprehensive stream sediment sampling across Laos, yielding 2079 samples collected at 1 sample/100 km², and 69 elements were analyzed. Based on the results of LGB value, R-mode factor analysis, and scatter plot analysis, this paper analyzes the relationship between the 69 elements and the geological background, mineralization, hypergene processes and human activities in the study area. The median values of element contents related to the average crustal values were: As, B, Br, Cs, Hf, Li, N, Pb, Sb, Zr, and SiO₂, >1.3 times; Ba, Be, Cl, Co, Cr, Cu, F, Ga, Mn, Mo, Ni, S, Sc, Sr, Ti, Tl, V, Zn, Eu, Al₂O₃, Tot.Fe₂O_3, MgO, CaO, and Na₂O, <0.7 times; and Ag, Au, Bi, Cd, Ge, Hg, I, In, Nb, P, Rb, Se, Sn, Ta, Th, U, W, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and K₂O, 0.7–1.3 times. R-mode factor analysis based on principal component analysis and varimax rotation showed that they fall into 12 factors related to bedrock, (rare earth, ferrum-group, and major Al₂O₃ and K₂O elements; mineralization–Au, Sb, and As) and farming activities–N, Br, S, and C). This study provides basic geochemical data for many fields, including basic geology, mineral exploration, environmental protection and agricultural production in Laos. Full article

To investigate the effect of co-doping on the optical properties of Eu^(2+/3+) doped in Ba₀.₉₈SiO₃:0.02Eu, the series of Ba₀.₉₆SiO₃:0.02Eu, 0.02R^+/3+ (R⁺ = Li⁺, K⁺ or Na⁺, R³⁺ = La³⁺ or Y³⁺) phosphors were synthesized using a solid-state reaction method. The excitation efficiency due to the charge transfer band (CTB) was enhanced via co-doping of R⁺ and the emission intensity due to Eu³⁺ was thus increased by 3.7 times compared with that of the single-doped Ba₀.₉₈SiO₃:0.02Eu³⁺. However, the co-doping of R⁺ does not increase the emission intensity of Eu³⁺ via the direct ⁷F₀→⁵L₆ excitation of Eu³⁺, but rather decreases it. On the other hand, the emission intensities due to Eu²⁺ were decreased via the co-doping of R⁺ but increased via the co-doping of La³⁺. The present work reveals that the optical properties of Eu³⁺ or Eu²⁺ doped in BaSiO₃ depend not on the charge state (+ or 3+) of the co-doped ions, but on the co-doped element itself. Full article

The effects of K⁺ substitution at the Ba-site on the structural, magnetic, and electrical properties and magnetoresistance (MR) of La_0.7Ba_0.3−xK_xMnO₃ (x = 0 and 0.04) manganites prepared via the solid-state method were investigated. Rietveld refinement of X-ray diffraction data confirmed that both samples were crystallized in the rhombohedral structure with the R3$\overline{c}$ space group. In addition, the unit cell volume, V, and the average grain size also increased with K⁺ ions. Magnetization versus applied field (M–H) measurement was carried out, and the saturation magnetization (M_s) was found to increase from 1.81 ${\mu }_B$/f.u. (x = 0) to 4.11 ${\mu }_B$ /f.u. (x = 0.04), implying that K⁺ ions strengthened the ferromagnetic (FM) interaction. Furthermore, the metal–insulator transition temperature, T_MI, increased from 257 K (x = 0) to 271 K (x = 0.04). The observed behaviour may be related to the enhancement of double-exchange (DE) interaction due to the increase in Mn-O-Mn bond angle and electronic bandwidth (W), favouring the increasing rate of the e_g electron hopping process. The fitting of the electrical resistivity data in the metallic region describes the significance of residual resistivity, electron–electron and electron–magnon scattering processes to elucidate the electronic transport properties. Within the insulating region, variable range hopping (VRH) and small polaron hopping (SPH) models are proposed to describe the conduction mechanism. Full article

Alkaline rocks are generally enriched in rare metals (e.g., Nb, Ta, and Zr) and rare earth elements (REE), but the key factors controlling Nb-Ta-REE enrichment remain unclear. The Boziguoer Nb (Ta-Zr-Rb-REE) deposit in Southwest Tianshan (northern margin of Tarim Basin) is China’s largest, with reserves of 0.32 Mt Nb₂O₅ and 0.02 Mt Ta₂O₅. It is an alkaline felsic complex 4.45 km in length and 0.5–1.3 km in width, composed of alkalic granite and syenite, which can be subdivided into syenite I and syenite II. The main minerals in each lithofacies are the same (albite, K-feldspar, quartz, arfvedsonite and aegirine). The Nb in the deposit is mainly hosted in pyrochlore supergroup minerals, ubiquitous in alkalic granite and syenite of the Boziguoer deposit. The wide variation in cations (Ca, Na, REE, U, Th) in the A-site further classifies the Boziguoer pyrochlore supergroup minerals as fluornatropyrochlore, fluorcalciopyrochlore and fluorkenopyrochlore. All Boziguoer pyrochlore supergroup minerals are Nb-rich and Ta-poor at the B-site and dominated by F at the Y-site. These cation occurrence illustrate a new mechanism of substitution in the Boziguoer pyrochlore supergroup minerals (2Ca²⁺ +Ti⁴⁺ +4Ta⁵⁺ = REE³⁺ +A-V + 5Nb⁵⁺, where A-V is the A-site vacancy). This substitution mechanism is different from that in the pyrochlore supergroup minerals from other rocks such as carbonatite and nepheline syenite, which are dominated by the replacement of Ba (Rb, Sr) with Ca+ Na + A-V. In addition, the substitution of REE (mainly La, Ce) for Ca in the Boziguoer pyrochlore supergroup minerals is likely a result of either REE enrichment or a change in the REE partition coefficient during the evolution of the alkaline magma. Both the pyrochlore supergroup minerals and their host rocks display negative large ion lithophile element (LILE; K, Rb, Sr, and Ba) anomalies, positive high-field-strength element (HFSE) anomalies and light rare earth element (LREE) enrichment with negative Eu anomalies. This is consistent with the crystallization of the pyrochlore supergroup minerals from the magma rather than from hydrothermal fluids, suggesting a magmatic origin. These findings indicate that the mechanisms of pyrochlore supergroup minerals crystallization in alkaline magma may be significantly different from those in carbonatite and nepheline syenite, and that magmatic differentiation processes may have played a role in the enrichment of the Boziguoer deposit by Nb. Full article

The release of fission products and fuel materials from a molten-salt fast-reactor fuel in hypothetical accident conditions was investigated. The molten-salt fast reactor in this investigation features a fast neutron spectrum, operating in the thorium cycle, and it uses LiF-ThF₄-UF₄ as a fuel salt. A coupling between the severe accident code MELCOR and thermodynamical equilibrium solver GEMS, the so-called cGEMS, with the updated HERACLES database was used in the modeling work. The work was carried out in the frame of the EU SAMOSAFER project. At the beginning of the simulation, the fuel salt is assumed to be drained from the reactor to the bottom of a confinement building. The containment atmosphere is nitrogen. The fission products and salt materials are heated by the decay heat, and due to heating, they are evaporated from the surface of a molten salt pool. The chemical system in this investigation included the following elements: Li, F, Th, U, Zr, Np, Pu, Sr, Ba, La, Ce, and Nd. In addition to the release of radioactive materials from the fuel salt, the formation of aerosols and the vapor-phase species in the modeled confinement were determined. Full article