Distribution Of Nb Research Articles

Fine structural analysis of calcium–niobium–gallium garnet (CNGG) by single-crystal anomalous X-ray scattering

Single-crystal anomalous X-ray scattering (AXS) experiments were conducted to investigate the cation distribution of calcium–niobium–gallium garnet (CNGG). AXS measurements suggested an ordered distribution of Nb at the octahedral site, and further structural refinement allowed us to obtain the structural formula Ca3Nb1.703(0) Ga3.162(2)O12. Ca was only located in the dodecahedral site, while Ga was distributed in the octa- and tetrahedral sites. The tetrahedral site had a significant number of vacancies at a ratio of one vacancy per unit cell, and the Nb/Ga occupation ratio at the octahedral site results in non-stoichiometric chemical composition of CNGG and its unique broad absorption wavelength.The findings of this study can contribute to device fabrication, property optimization, and quality control processes related to CNGG.

Control of sintering characteristics and gyromagnetic properties of LiZn-based microwave ferrite ceramics by Nb2O5 doping

In this study, a new strategy of trace amounts of Nb2O5 doping was employed to control microwave loss of Ti-Mn-Bi co-substituted LiZn-based ferrite ceramics sintered at 890 °C. The results revealed the distribution of doped Nb in the spinel ferrites. Partial Nb5+ ions entered the lattices and induced the generation of Fe2+ ions, resulting in a decrease in the magnetocrystalline anisotropy linewidth (ΔHa). The rest of Nb2O5 remained at grain boundaries and formed high resistance layers, which contributed to lowering the dielectric loss (tanδε). Due to the particular distribution of Nb, a dual-structure and higher densification were observed, and thus the porosity-induced line broadening contributions (ΔHp) was reduced. Notably, by doping with 0.15 wt.% Nb2O5, the LiZn-based ferrites presented excellent magnetic properties (ΔH = 87 Oe, tanδε = 3.24 × 10-4, 4πMs = 3799 Gauss, Br/Bs = 0.9), which shows promising potential for low-loss microwave ferrite devices.

Numerical simulation of microstructure evolution in molten pool of nickel-based superalloy during selective laser melting

The competitive growth and the evolution of grain/dendrite structures of IN718 superalloy in the molten pool during selective laser melting (SLM) were investigated with the finite element method (FEM) coupling the phase-field model (PFM). The thermal evolution was solved by the FEM and then the results were input into the PFM model to simulate the microstructure evolution involving grain nucleation, grain epitaxial growth and grain competition. Based on the analysis of microstructure evolution of the transverse and longitudinal sections of the molten pool, the mechanism of dendrite competitive growth in the SLM process was discussed and the concentration distribution of the solute element Nb in the molten pool was quantitatively calculated. The results show that the dendrite competitive growth is affected by both the temperature gradient and the crystallographic orientation. The unfavorable orientation grain with a high misorientation (>22.5°) will be eliminated by the favorable orientation grain quickly.

The effect of different C contents on the microstructure evolution and mechanical properties of Ti45Al6Nb alloy

The content of C element and in-situ Ti2AlC phase is adjusted to reduce the content of B2 phase in the TiAl matrix, ultimately improving the compressive properties of TiAl alloys. Results show that there is a high content of B2 phase inside the lamellar colony, and the Nb content in the B2 phase is higher than that dissolved in matrix. The addition of C element results in the formation of a round rod like reinforcing phase and refining the lamellar colony. As the C content increases from 0 to 3.0 at. %, the content of in-situ Ti2AlC reinforcing phase increases from 0 to 17.8 vol. %, the content of B2 phase decreases from 10.4 to 1.4 vol. %, and the size of the lamellar colony decreases from 161.3 to 19.5 μm. The decrease in the content of B2 phase is due to the preferential formation of Ti2AlC reinforcing phase in the liquid, Nb will preferentially dissolve in it, resulting in a more uniform distribution of Nb in the solidified structure and reducing the segregation of Nb. Then, Ti2AlC particles act as heterogeneous nucleation, increasing the nucleation sites in the alloy melt and refining the microstructure. According to the results of the compression test, as the C content increases from 0 to 2.5 at. %, the compressive strength increases from 1186.9 to 2154.5 MPa, and the compressive strain increases from 6.5 to 20.2 %. Therefore, the precipitation strengthening effect of Ti2AlC, the grain boundary strengthening effect of refined microstructure, and the decrease in the content of B2 phase jointly contribute to the improvement of the compressive properties at room temperature.

Role of Nb elements in SiCf/SiC/(CoFeNiCrMn)100-xNbx/GH536 brazed joints: Joint residual stress transfer and pinning of dislocations

Brazing is a critical method to address the challenge of connecting composite materials to metals. This study joined SiCf/SiC composites and GH536 superalloy using (CoFeNiCrMn)100-xNbx high-entropy alloy filler with varying Nb element contents successfully. The microstructural evolution and mechanical property changes of brazed joints were systematically investigated. Notably, when the Nb element content in the filler reached 12 %, a diffuse distribution of Nb(s, s) emerged in the joint, playing a vital role in effectively transferring residual stress on the SiCf/SiC side. This effect is attributed to the disparity in thermal expansion coefficients between the Nb(s, s) and face-centered cubic (FCC) phases. The resulting joint exhibited remarkable room temperature and high temperature shear strengths of 89.7 MPa and 49.7 MPa, respectively. Furthermore, the presence of Nb(s, s) in the brazing seam proved to impede the movement of dislocations during joint fracture. This work introduces a new technical paradigm for aero-engine manufacturing.

Analysis of the Contributory Factors to Accidents at Signalized Intersections using Generalized Estimating Equation with Negative Binomial Distribution

Ensuring safety on roadways and controlling conflicting and merging streams of traffic at signalized intersections has become a major concern for transportation engineers and road users globally and locally. Many factors contribute to accident occurrence at road segments and intersections with driver behavior being the major contributor.  Other factors include those related to the vehicle and the road. The primary aim of this study is to understand the impact of different factors causing traffic accidents at signalized intersections.  It also include developing a descriptive study of traffic accident data to show the variation with different factors at both intersections and roadway segments. To achieve this objectives, 22 signalized intersections and all roadways in Duhok city/Iraq were selected.  Assessing the effects of geometric characteristics and driver behavior on safety performance of the sites have been achieved through observations of trends from graphs and use of appropriate advanced statistical analysis such as Generalized Estimating Equation (GEE) with NB distribution and log link function.  The results show that approach width, driver inattention, red light running and surface moisture condition are the significant contributors to accident occurrence. The study results highlight the importance of driver education, police enforcement and appropriate geometric design of intersections to the reduction of accident occurrence. &nbsp

A novel strategy for architecting low interfacial energy transition phase to enhance thermal stability in a high-entropy alloy

Alloys with high strength and thermal stability are attractive for crucial applications in aerospace and power-generation sectors. In this paper, based on the thermodynamics, the microstructure, hardness, and compressive properties of the (FeCoNiCrCu1.71)96Nb4 and (FeCoNiCrCu1.71)90Nb10 (at%) high-entropy alloys (HEAs) upon high-temperature aging were studied. The results indicate that the addition of Nb increases the amounts of the Nb-rich precipitates and concentration of Nb within the matrix, enhancing the hardness and yield strength. With prolonged aging time, the hardness and yield strength of the (FeCoNiCrCu1.71)96Nb4 and (FeCoNiCrCu1.71)90Nb10 HEAs remain almost unchanged, showing high thermal stability. It is discussed from the synergistic of high-density secondary Cu-rich precipitates and the low-energy Nb-rich precipitate/transition precipitate/matrix and Cu-rich precipitate/matrix interfaces. From a thermodynamical point of view, the free energy of the matrix is decreased to be lower than that of the Nb-rich precipitates, changing the diffusion direction of Nb and forming a gradient distribution of Nb. It provides a convenient strategy to architect an fcc metastable transition precipitate linking Nb-rich precipitates and Cu-depleted matrix, reducing interface energy. Moreover, Cu and the coherent interfaces with low interfacial energy effectively retard the coarsening of the Nb-rich precipitates. It may serve as guidance for the future alloy design strategy of high-entropy superalloys with high thermal stability.

Estimation and Distribution of Some Heavy Metals in Urban Soils at Kufa, Najaf Governorate: An Environmental Geochemistry Research

Kufa, considered one of the important cities in Iraq, is facing a rapid increase in population proportion and urban development in buildings and industry. Therefore, the concentration of several hazardous heavy metals is the main focus of this study. It presents the distribution and Estimation of heavy metals in urban lands in the Kufa area as an environmental geochemical study. Twenty samples of urban surface soils were collected in many sites to determine concentrations, distribution, and contamination of elements Cu, Zn, Co, Ni, Th, U, Pb, Hf, Nb, and Fe. The mean concentrations of heavy metals were compared with the local studies, UCC guidelines, and the world reference. To distinguish anthropogenic pollution, EF and Igeo guides were calculated. The obtained results established that contamination in Kufa soil land was slightly polluted by U (2.83ppm) and Nb (10.81ppm) and moderately polluted by Pb (31.7ppm) and Hf (9.75ppm). The research revealed that the reason for the elevation in the lead in the Kufa soil is that it often suffers from severe vehicle overcrowding during religious occasions.

Polyphase deformation-controlled giant Renli Nb–Ta deposit, South China: Constraints from systematic structural analysis

The Early Cretaceous Renli Nb–Ta deposit was recently discovered near the southern margin of the Late Jurassic–Early Cretaceous Mufushan composite granitic batholith, central Jiangnan Orogenic Belt, and represents the largest known rare metal deposit in South China. Substantial breakthroughs have been made in prospecting the pegmatite-dike-type of Nb–Ta mineralization in the deposit, especially from the perspective of geochemical exploration. However, there is still a lack of systematic structural studies in this area which has seriously hindered the in-depth understanding of the emplacement of pegmatite dikes and the distribution patterns of Nb–Ta ore bodies. In order to shed new light on this key issue, this study presents new and detailed structural data from the Mufushan region. The results indicate that the Renli and adjacent areas have experienced several deformational events, including D1 Neoproterozoic NE–SW contraction and upright-folding, D2 latest Late Jurassic to Early Cretaceous regional extension accompanied by granitic magma intrusion, and D3 Early Cretaceous brittle normal faulting and fracturing with granitic magma emplacement and Nb–Ta mineralization. The D1 event, corresponding to the Jiangnan Orogeny, formed regional-scale NW–SE-striking upright folds with ubiquitous subvertical S1 cleavages and subhorizontal L1 crenulation lineations. The D2 event represented orogenic exhumation and produced a domal structure cored primarily by gneissic/mylonitic rocks and granites and mantled by schists, which dominated the bulk structural architecture of the Mufushan area. This was followed by the D3 event which controlled the formation of numerous extension fractures in the study area. The Nb–Ta-bearing magmatic-hydrothermal fluids migrated along the pre-existing D2 shear zone and subsequently filled in the widespread D3 extension fractures to form pegmatite dikes. The D2 to D3 phases can be considered as a progressive exhumation event from plastic to brittle regimes. The D2 and D3 structures dictate the spatial distribution of Nb–Ta ore bodies.

Distribution of Li, Ga, Nb, and REEs in coal as determined by LA-ICP-MS imaging: A case study from Jungar coalfield, Ordos Basin, China

Previous studies on modes of occurrence of Li, Ga, and Nb in coal are primarily based upon statistical analyses due to the low concentrations of these elements and the lack of methods of direct analysis. Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) can be used for the in-situ determination of trace elements in minerals. The strong heterogeneity and diversity of macerals lead to a lack of suitable internal calibration elements required for LA-ICP-MS-based analysis of trace elements in coal, making the determination of trace elements in organic matter in coal challenging. In this study, the previously investigated high-Al and Li-Ga-Nb enriched No. 6 coal in the Haerwusu Mine of the Jungar Coalfield, Ordos Basin, China, was chosen for revealing the distribution and modes of occurrence of Li, Ga, Nb, and rare earth elements (REEs; REY if Y included) in coal, using the LA-ICP-MS method of mapping (imaging) technology. The results indicate that the majority of Ga and Nb present within the coal was concentrated within a specific collotelinite layer. Gallium and Nb have an organic association and are rare within minerals (i.e., clay minerals and boehmite). Lithium is homogeneously distributed throughout the clay minerals in the collodetrinite. Most of the La and Ce in the coal are concentrated in La- and Ce-enriched minerals, including monazite, bastnaesite, and lanthanite. The other REEs are concentrated in the Ga- and Nb-enriched collotelinite, along with small amounts of La and Ce. A similar characterization processing may be used to determine the modes of occurrences of trace elements in other organic-rich rocks or fine-grained sediments.

Bayesian Inference for the Negative Binomial-Quasi Lindley Model for Time Series Count Data on the COVID-19 Pandemic

In statistical models, the generalized linear model (GLMs) plays a role in studying to describe a response variable as a function of 1 or more predictor variables. Computational methods and mixed distributions are frequently used to build predictive models to perform time-to-event data analysis. To develop a statistical model so that the model can make predictions appropriately and accurately, it starts with developing a suitable distribution for the nature of the actual data. This paper proposes a new mixed negative binomial distribution for count data with over-dispersion, the so-called negative binomial-quasi Lindley (NB-QL) distribution. A new GLMs framework for the NB-QL model to build the time series count data model is introduced, and its application is carried out based on the actual data sets of the COVID-19 epidemic in Thailand. The models are related to GLMs as they are linear relationships between outcome variables and covariates. Where the response variable was in the form of time series count data under the exponential family distribution function, with the random components and link functions. In this study, we study the factors that affect the number of COVID-19 death cases in Thailand and provide the predictive modeling of the number of the COVID-19 death cases from 1 January 2020 to 31 December 2020, for which this data set has the observed sample of 366 days. In contrast, a model with an NB-QL distribution and NB has approached the uniform. Based on the deviance, DIC, and the probability integral transform histogram, we can see that the proposed model is also suitable for forecasting the number of the COVID-19 death cases daily in Thailand, indicating that the NB-QL time series model was another efficient alternative to modeling count data that has an over-dispersion problem. According to the NB-QL time series model about the number of the COVID-19 death cases daily in Thailand, it is indicated that the average number of daily COVID-19 deaths is influenced by the number of the COVID-19 death cases in the previous 3 days. The average number of COVID-19 death cases in Thailand is also influenced by the previous 2 days. At the same time, the number of infected cases daily in Thailand is influenced by the number of the COVID-19 death cases daily. In addition, there are also the components interventions of internal covariate effects due to the data, as there was a surge in the number of the COVID-19 death cases daily in Thailand at the time. HIGHLIGHTS A new mixture NB distribution to be a flexible alternative to analyze count data with over-dispersion. The new distribution is a mix of the NB and QL distributions; a name is Negative Binomial-Quasi Lindley A new mixed negative binomial distribution for time series count data with over-dispersion, and the Bayesian approach is the method used to estimate the parameters of the proposed model. We will apply the GLMs framework to build the time series count data The new mixed NB distribution in this study is an extremely effective alternative for modeling count data in the context of over-dispersion GRAPHICAL ABSTRACT

Continental-scale distribution of niobium and tantalum in catchment sediments throughout China: Prospecting implications from the China geochemical Baselines project

Niobium (Nb) and tantalum (Ta), which are chemical twins with very similar geochemical properties, are critical mineral resources for emerging global industries. Owing to increasing demands, understanding their concentrations and distributions in the pedosphere is essential for assessing potential Nb and Ta resources in China. To address this, we used geochemical data obtained from the China Geochemical Baselines (CGB) project, which began in 2008 and has since then yielded continental-scale datasets. With a density of approximately-one sampling site per 3,000 km2, the CGB project involved catchment sediments from two horizons at each site: a top sample collected at a depth of 0–25 cm and a deep sample collected at a depth greater than 100 cm. In total, 3,394 samples each of top and deep catchment sediments were collected, and Nb and Ta concentrations were measured using inductively coupled plasma mass spectrometry under strict quality control conditions. The Nb concentrations in the top and deep sediment samples varied in the ranges 0.04–89.86 ppm with a median value of 12.71 ppm and 1.20–104.12 ppm with a median value of 12.41 ppm, respectively. Further, the Ta concentrations in the top samples ranged from 0.01 to 26.41 ppm with a median of 0.97 ppm, while those in the deep samples ranged from 0.14 to 26.41 ppm with a median of 0.96 ppm. Furthermore, both the top and deep samples had similar 2.5th, 25th, 50th, 75th, and 97.5th percentile Nb and Ta contents, indicating that Nb and Ta in the catchment sediments underwent similar and consistent formation processes. Our results also indicated that the concentrations of both elements varied widely across regions, and their distributions in the catchment sediments throughout China were predominantly governed by the parent rock, particularly granites and alkaline rocks. Mineralization and sedimentation properties also played roles at a regional scale. Overall, the spatial distributions of Nb and Ta in the top and deep catchment sediments were relatively consistent, with concentrations being higher in southeastern China and lower in northwestern China. Twelve large-scale geochemical Nb-Ta belts were delineated based on continuous anomalous point distributions wherein many well known Nb-Ta deposits are already located. These nationwide Nb and Ta concentrations and distributions provide foundational large-scale data for further exploration and geological studies.

Mechanical Properties and Microstructural Evolution of Ti-25Nb-6Zr Alloy Fabricated by Spark Plasma Sintering at Different Temperatures

High-energy ball milling and spark plasma sintering (SPS) are used to create high-strength Ti-25Nb-6Zr biomedical alloys with β structures. The Ti-25Nb-6Zr alloy microstructure and mechanical properties were examined as a function of the sintering temperatures. The results showed that as the sintering temperature was raised, the densification process was expedited, and the comprehensive mechanical characteristics increased at first, then dropped slightly. Moreover, under high temperatures, the fracture morphology of the Ti-25Nb-6Zr biomedical alloys exhibited more dimples, indicating enhanced plasticity of the material. Evaluating the mechanical properties of the Ti-25Nb-6Zr biomedical alloy sintered at 1623 K indicated a high compressive strength of 1678.4 ± 5 MPa and an elongation of 12.4 ± 0.5%. The strengthening mechanisms are discussed in terms of the formation and distribution of bcc-Ti in the matrix as well as the homogeneous distribution of Nb and Zr. This research presents a new method for fabricating Ti-25Nb-6Zr biomedical alloys with high strength and low modulus values. The theoretical grounds for the development of high-performance Ti-Nb-Zr alloys will be laid by detailed research of this technology and its strengthening mechanisms.

First Digits’ Shannon Entropy

Related to the letters of an alphabet, entropy means the average number of binary digits required for the transmission of one character. Checking tables of statistical data, one finds that, in the first position of the numbers, the digits 1 to 9 occur with different frequencies. Correspondingly, from these probabilities, a value for the Shannon entropy H can be determined as well. Although in many cases, the Newcomb–Benford Law applies, distributions have been found where the 1 in the first position occurs up to more than 40 times as frequently as the 9. In this case, the probability of the occurrence of a particular first digit can be derived from a power function with a negative exponent p > 1. While the entropy of the first digits following an NB distribution amounts to H = 2.88, for other data distributions (diameters of craters on Venus or the weight of fragments of crushed minerals), entropy values of 2.76 and 2.04 bits per digit have been found.

Elimination of room-temperature brittleness of Fe–Ni–Co–Al–Nb–V alloys by modulating the distribution of Nb through the addition of V

Compared with Ti–Ni-based and Cu–Al-based alloys, Fe–Ni–Co–Al-based superelastic alloys have received great attention in recent years because of their low cost and excellent performance. However, the precipitation of brittle precipitates on grain boundaries in Fe–Ni–Co–Al-based polycrystalline alloys significantly reduces the mechanical properties. In this paper, the effects of V on the formation of brittle precipitates on both grain boundaries and inside grains and mechanical properties in Fe–Ni–Co–Al–Nb alloy were investigated systematically. The results show that γ′(Ni3Al) precipitate with L12 structure precipitate out on grain boundaries and inside grains in the Fe–Ni–Co–Al–Nb alloy during aging without V addition. The γ′ precipitate with L12 structure on the grain boundaries grew to form a heavily-coarsened L12 precipitate (HCLP γ′ precipitate) due to the accumulation of Nb on the grain boundaries, resulting in a significant decrease in elongation. With the addition of V, intragranular Nb and V can combine together with γ′ to form Ni3(Al, Nb, V) (nano-sized γ′ precipitate) composite precipitates, which improves the strength. More important, since the diffusion coefficient of V was larger than that of Nb, V preferentially occupied the lattice positions on grain boundaries, repelling Nb from the grain boundaries to the matrix. Thus, the coarsening of HCLP γ′ precipitate on the grain boundaries was reduced, and the elongation of Fe–Ni–Co–Al–Nb–V alloy was significantly improved.

The distribution and substitution mechanism of trace elements in cassiterites: Constraints from LA-ICP-MS U[sbnd]Pb dating, elemental mapping and in situ trace element analyses of the Gejiu tin polymetallic deposit, SW China

The tetragonal lattice structure enables cassiterites to incorporate dozens of elements within their crystal lattice (e.g., Fe, Ti, W, Zr, Hf, Ta, Nb, Mn, Sc, V and Sb). Thus, it is anticipated that variations of these elements should record information of potential elemental substitution mechanisms and precipitation environments of cassiterites. With moderate amounts of U and Pb, cassiterites can be dated with U-Pb geochronology. In this study we collected cassiterite grains from six different ore types within the Gejiu tin polymetallic deposit to perform LA-ICP-MS U-Pb dating, multiple element mapping and in-situ trace element analysis. Systematic U-Pb dating of such cassiterites yielded Tera-Wasserburg lower-intercepted ages ranging from 81.91 ± 0.62 to 85.7 ± 1.4 Ma, coinciding, within their respective analytical uncertainties, with zircon U-Pb ages of regional Late-Yanshanian granitoids. Such age coincidence, combined with spatial association, suggests that tin mineralization may be genetically related to the late Cretaceous granitic magmatism. Multi-elemental mapping shows that the distribution of Nb, Ta, and Ti in the cassiterite grains correlate well with the regular oscillatory zoning patterns in Cathodoluminescence (CL) images. The relatively high Fe, Ga, Sb, W and U concentrations control the dark luminescing domains in these cassiterite grains. The systematic variations in chemical compositions suggest that trace elements such as Sc, V, Fe and Ga incorporate in cassiterites via coupled substitutions of Sc3+ + V5+ ↔ 2 (Sn, Ti)4+, Fe3+ + Ga5+ ↔ 2 (Sn, Ti)4+ and Fe3+ + OH−↔ Sn4+ + O2− or Fe3+ + H+↔ Sn4+. The covariation of redox sensitive elements such as Fe, Sb, W and U indicates that only ‘tin-granite’-type cassiterites were formed under an oxidized state whereas cassiterites from other ore types were precipitated in a reducing environment.

Chemické složení křemene a světlé slídy z komplexu ortoruly, granitu, pegmatitů a křemenných žil v Přibyslavicích jako indikátor jejich příbuznosti

The complex of leucocratic granitoid rocks at Přibyslavice (Fig. 1), composed of muscovite-tourmaline orthogneiss, muscovite granite and several types of pegmatites, is well known for numerous finds of interesting minerals like large almandine crystals (Breiter et al. 2005b), Li-Fe-Mn phosphates (Povondra et al. 1987), nigerite (Čech et al. 1978), columbite and cassiterite (Šrein et al. 2004, Breiter et al. 2006), lepidolite (Šrein et al. 2004) and oxy-schorl (Bačík et al. 2013). Less attention has been paid so far to the petrology of orthogneisses, granite and pegmatites and their genetic relationships. This study aims, based on the chemical composition of quartz and muscovite, to assess possible genetic links among all these rocks of granitoid composition including an associated cassiterite-bearing quartz vein with a B, Ta-rich metasomatic halo. Major elements in micas were analyzed using electron microprobe, and trace elements in both quartz and mica were determined using laser ablation-ICP-MS according to methods described in Breiter et al. (2017, 2020). About 550 spot analyses of quartz and 220 spot analyses of mica allow reliable definition of the typical composition of quartz and mica from all types of studied rocks (Tables 2, 3). Some genetic relationships are visualized in Figs. 2 and 3. The Přibyslavice orthogneiss is geochemically more evolved than petrographically similar orthogneisses through entire Moldanubicum as expressed not only in bulk rock chemical composition but also in trace element composition of quartz (higher Al, Ge and Li contents, Fig. 2) and muscovite (higher Li, Nb, Ta, Sn and W contents, Fig. 3). Pegmatoids at Přibyslavice and nearby Březí, forming small nests in orthogneisses with a gradual mutual transition, are interpreted as in situ anatexites. The direct genetic link between the granite intrusion and the quartz vein with cassiterite and B, Ta-rich metasomatites (tourmaline + Ta-rutile) is supported by the Sn, Nb and Ta enrichment of granite. It is highlighted by the relative distribution of Nb and Ta, with Nb preferentially bonded to muscovite in granite and Ta segregated into a fluid (see e.g. Stepanov et al. 2014). Chemical and mineral similarity between the granites and the orthogneiss suggests a common source lithology located deep below the present surface. During the first melting of the protolith in the late Cambrian (Vrána – Kröner 1995), a boron-rich melt was formed, which extracted most boron from the source and facilitated the origin of tourmaline orthogneiss. The second, Variscan melting of the same or a very similar protolith produced a melt slightly enriched in F and Li. We assume that the Přibyslavice granite represents only a small proportion of this melt, strongly enriched in Sn, W, Nb and Ta due to fractionation. Chemistry and mineralogy of several types of associated pegmatites suggest their relation rather to the granite melt than to the anatexis of the orthogneiss. The difference in their chemical composition including the content of water, F, and Li reflects the timing of separation from the parental magma and the distance of the melt transport upwards. During the transport, internal fractionation culminated in the “Li-pegmatite” by crystallization of its quartz-lepidolite core.

The effects of Nb addition on magnetic property of Nd10.23Pr2.56Fe68.32Co13.08B5.81 ribbons through modification of the intergranular phase and grain refinement

The (Nd10.23Pr2.56Fe68.32Co13.08B5.81)100-xNbx (x = 0, 0.5, 1, 2, 3) ribbons were prepared by melt-spinning at a wheel speed of 15 m/s. The effects of Nb addition on the microstructure and the magnetic properties of the ribbons were investigated. The X-ray diffraction (XRD) patterns of the ribbons show that the Nd2(Fe, Co)14B (2:14:1) phase is observed in all samples indicating that Nb addition does not change the phase constitution. The transmission electron microscopy (TEM) images show that Nb addition can dramatically reduce the average grain size from 52 ± 5 nm of the Nb-free alloy to 12 ± 2 nm of the Nb-containing x = 3 alloy. Based on the atom probe tomography (APT) result, we identify different mechanisms for grain refinement at different Nb content. When x = 0.5, the distribution of Nb is uniform at the intergranular phase and Nb addition promotes the segregation of rare-earth Nd and Pr at the thick ferromagnetic intergranular phase (≈ 10 nm), which leads to decreasing the average grain size to 38 nm. With further increasing Nb addition to x = 2, the existence of Nb-rich precipitations (2–4 nm in width) at the grain boundaries effectively reduces the grain size to 16 nm. The remanence (Br) and the maximum energy product ((BH)max) are obviously increased by Nb addition and the maximum of the Br and the (BH)max is obtained in the (Nd10.23Pr2.56Fe68.32Co13.08B5.81)98Nb2 (x = 2) alloy. The values of the Br and the (BH)max are 0.90 T and 138 kJ/m3, 8.4% and 22.1% higher than that of the Nb-free alloy. It ascribes to the grain refinement, the changes of the distribution and the composition of the ferromagnetic intergranular phase by Nb addition. Our findings provide a new method of designing prospective permanent alloys with increased magnetic properties by reducing the grain size and tuning the distribution and chemical composition of the intergranular phase.

LA–ICP–MS U–Pb Dating, Elemental Mapping and In Situ Trace Element Analyses of Cassiterites from the Gejiu Tin Polymetallic Deposit, SW China: Constraints on the Timing of Mineralization and Precipitation Environment

As a major constituent in magmatic–hydrothermal ore deposits, cassiterites, with moderate amounts of U and low Pb, can be dated with U–Pb geochronology. The tetragonal lattice structure makes cassiterites capable of incorporating dozens of elements within its crystal lattice (e.g., Fe, Ti, W, Zr, Hf, Ta, Nb, Mn, Sc, V, and Sb). Variations of these elements record information of potential elemental substitution mechanisms and precipitation environments of cassiterites. In this study, we collected cassiterite grains from four different ore styles of the Gejiu tin polymetallic deposit to perform LA–ICP–MS U–Pb dating, multiple element mapping, and in situ trace element analysis on these cassiterites. Systematic U–Pb dating yielded Tera–Wasserburg lower intercepted ages at around 85 Ma, coinciding with zircon U–Pb ages of regional Late Yanshanian granitoids, within their respective analytical uncertainties. Such age coincidence, combined with the spatial association, suggests that tin mineralization may be genetically related to the Late Cretaceous granitic magmatism. Multielemental mapping shows that the distribution of Nb, Ta, and Ti in the cassiterite grains correlates well with the regular oscillatory zoning patterns in cathodoluminescence (CL) images. The relatively high Sb, Fe, W, Ga, and U concentrations control the dark luminescing domains in these cassiterite grains. The systematic variations in chemical compositions suggest that trace elements such as Sc, V, Fe, and Ga incorporate in cassiterites via coupled substitutions of Sc3+ + V5+ ↔ 2 (Sn, Ti)4+, Fe3+ + Ga5+ ↔ 2 (Sn, Ti)4+ and Fe3+ + OH– ↔ Sn4+ + O2– or Fe3+ + H+ ↔ Sn4+. The covariation of redox sensitive elements such as W, U, Fe, and Sb indicates that the ”tin-granite” type of cassiterites were formed under an oxidized state whereas cassiterites from skarn, massive sulfide, and oxidized ore styles were precipitated in a reducing environment.

Correlation between thickness dependent nanoscale structural chemistry and superconducting properties of ultrathin epitaxial NbN films

NbN-based superconductors have attracted interest for superconducting circuits, quantum computation and high frequency devices. The superconducting properties of NbN films are predominately reliant on the microstructure, therefore, an atomic-level understanding of the structure-chemistry is required to achieve high quality epitaxial NbN films. Here, the thickness-dependent superconducting properties of NbN films (5, 10, and 50 nm) within NbN/AlN/Al2O3 heterostructures are investigated. NbN and AlN were epitaxially grown by an industrial scale physical vapor deposition technique. The role of nanoscale chemistry on the ultrathin NbN superconducting film is investigated at the atomic level for the first time via atom probe tomography, providing three-dimensional atomic distribution, chemical homogeneity, effect of impurities, specially, in secondary phase formations and interfacial abruptness. The NbN film with 5 nm of thickness demonstrates a superconducting transition temperature of 11.2 K as compared to 50 nm NbN films with a transition temperature of 15.3 K. These thickness dependent variation of superconducting properties are associated with the chemical inhomogeneity in terms of in-plane N:Nb distribution, secondary phase formations and NbN/AlN interfacial abruptness as a function of the NbN films thicknesses. The analysis depicts the interplay between the surface/interface and the superconducting properties of ultrathin NbN films. These results provide insights on material design and growth that will enable the development of optimized superconducting NbN films for quantum devices.