Body-centered Tetragonal Structure Research Articles

Neutron imaging for metallurgical characteristics of iron products manufactured with ancient Korean iron making techniques

This paper demonstrates the possible nondestructive analysis of iron artifacts’ metallurgical characteristics using neutron imaging. Ancient kingdoms of the Korean Peninsula used a direct smelting process for ore smelting and iron bloom production; however, the use of iron blooms was difficult because of their low strength and purity. For reinforcement, iron ingots were produced through refining and forge welding, which then underwent various processes to create different iron goods. To demonstrate the potential analysis using neutron imaging, while ensuring artifacts’ safety, a sand iron ingot (SI–I) produced using ancient traditional iron making techniques and a sand iron knife (SI–K) made of SI–I were selected. SI–I was cut into 9 cm2, whereas the entirety of SI–K was preserved for analysis. SI–I was found to have an average grain size of 3 μm, with observed α-Fe (ferrite) and pearlite with a body-centered cubic (BCC) lattice structure. SI–K had a grain size of 1–3 μm, α-Ferrite on its backside, and martensite with a body-centered tetragonal (BCT) structure on its blade. Results show that the sample’s metallurgical characteristics can be identified through neutron imaging only, without losing any part of the valuable artifacts, indicating applicability to cultural artifacts requiring complete preservation.

A holistic approach to optical characterizations of vacuum deposited Cu2ZnSnS4 thin film coatings for solar absorbing layers

This article aimed at making a good absorber layer of Cu2ZnSnS4 thin film coatings deposited onto glass substrates via spin coating technique with different rotational speeds. Three sets of Cu2ZnSnS4 thin film coatings were prepared at rotations of 3000, 3500, and 4000/min. The thickness of the thin film coatings was measured using a surface profilometer, and the coating thickness shows good rpm dependence i.e., the thickness of the coatings decreased with increasing rpm. The thicknesses of the coatings were in the nanometer (nm) range for all samples. The structural, morphological, and optical properties of the as coated thin films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and ultraviolet–visible (UV–Vis) absorption spectroscopy. The XRD pattern confirmed the body-centered tetragonal lattice structure with Kesterite Cu2ZnSnS4 phase having good crystallinity. The average crystallite size increases while lattice strain, dislocation density, and crystallite number are decreased with increasing thicknesses of the Cu2ZnSnS4 coatings. SEM micrographs represent the homogeneous, agglomerated surface without any cracks and pores. The average optical band-gap of the coatings was found to be 1.5 eV. Dielectric parameters such as refractive index, high-frequency dielectric constant, and static dielectric constant were declined with increasing thickness of Cu2ZnSnS4 thin film coatings. These characteristics would allow the Cu2ZnSnS4 thin film coatings to be suitable for an absorber layer used in photovoltaic devices.

Morphology and Optical Properties of Thin Cd3As2 Films of a Dirac Semimetal Compound

Using atomic-force microscopy (AFM) and wide-band (0.02–8.5 eV) spectroscopic ellipsometry techniques, we investigated the morphology and optical properties of Cd3As2 films grown by non-reactive RF magnetron sputtering on two types of oriented crystalline substrates (100)p-Si and (001) α-Al2O3. The AFM study revealed the grainy morphology of the films due to island incorporation during the film growth. The complex dielectric function spectra of the annealed Cd3As2/Al2O3 films manifest pronounced interband optical transitions at 1.2 and 3.0 eV, in excellent agreement with the theoretical calculations for the body centered tetragonal Cd3As2 crystal structure. We discovered that due to electronic excitations to the Cd(s) conical bands, the low-energy absorption edge of the annealed Cd3As2 films reveals a linear dependence. We found that for the annealed Cd3As2 films, the Cd(s) conical node may be shifted in energy by about 0.08–0.18 eV above the heavy-flat As(p) valence band, determining the optical gap value. The as-grown Cd3As2 films exhibit the pronounced changes of the electronic band structure due to the doping effect associated with Cd non-stoichiometry, where fine-tuning of the Cd concentration may result in the gapless electronic band structure of Dirac semimetals.

Temperature-sensing characteristics of NaGd(MoO4)2: Sm3+, Tb3+ phosphors

In this study, Sm3+/Tb3+-co-doped NaGd(MoO4)2 phosphors were prepared via the hydrothermal method, with sodium citrate used as a chelator. X-ray diffraction confirmed the structure of the samples, and the test outcomes showed that the phosphors exhibited a body-centered tetragonal structure. Field-emission scanning electron microscopy results showed that the specimen morphology changed with the change in the Cit3−/Re3+ molar ratio. Moreover, the measured temperature-dependent emission spectra showed that Sm3+ and Tb3+ had different quenching trends; thus, the fluorescence intensity ratio can be used to represent temperature. In addition, the outcome of this experiment revealed that the temperature-sensing sensitivity of the phosphors gradually increased with the increasing Cit3−/Re3+ ratio, and the highest sensitivity value was 0.346 K−1 (at 503 K, Cit3−/Re3+ = 2). When the temperature was 298–369 K, the temperature-sensing relative sensitivity increased with increasing Cit3−/Re3+, but in the range 374–503 K, the relative sensitivity decreased with increasing Cit3−/Re3+. The highest relative sensitivity value of the sample was 2.7% K−1 (404 K, Cit3−/Re3+ = 0). Additionally, the Commission International del’Eclairage chromaticity coordinates displayed that the luminous colors of Sm3+/Tb3+-co-doped specimens continuously changed from green to red as the temperature changed.

Deposition of Thin Alumina Films Containing 3D Ordered Network of Nanopores on Porous Substrates.

Self-supporting thin films containing nanopores are very promising materials for use for multiple applications, especially in nanofiltration. Here, we present a method for the production of nanomembranes containing a 3D ordered network of nanopores in an alumina matrix, with a diameter of about 1 nm and a body centered tetragonal structure of the network nodes. The material is produced by the magnetron sputtering deposition of a 3D ordered network of Ge nanowires in an alumina matrix, followed by a specific annealing process resulting in the evaporation of Ge. We demonstrate that the films can be easily grown on commercially available alumina substrates containing larger pores with diameters between 20 and 400 nm. We have determined the minimal film thickness needed to entirely cover the larger pores. We believe that these films have the potential for applications in the fields of filtration, separation and sensing.

Internal Residual Stress Originated from Bain Strain and its Effect on Hardness in Fe-Ni Martensite

To further understand the internal residual stress that is microscopically generated via martensitic transformation in steels, the origin of internal strain attributed to Bain correspondence between face-centered cubic (fcc) and body-centered cubic (bcc) was evaluated from macro- and micro-viewpoints and its effect on hardness was investigated in an interstitial free Fe-16%Ni martensite. Neutron diffractometry and electron backscatter diffraction analysis showed that the as-quenched martensite had a body-centered tetragonal (bct) crystal structure with small tetragonality, even in martensitic steels without solute carbon, and that the [001]bct of bct martensite tended to be parallel to fcc of prior fcc austenite. In addition, the combination of micro-scale focused ion beam (FIB) and high-precision digital image correlation techniques revealed that a micropillar fabricated by FIB processing within a martensite block was anisotropically deformed by the release of the residual strain distributed in as-quenched martensite in correspondence with the orientation of the bct crystal structure. These results prove that a small part of the Bain strain remained as an internal elastic residual strain and was microscopically distributed among Bain groups in lath martensite after martensitic transformation. Furthermore, the residual strain generated a hydrostatic internal stress, and therefore, the nanohardness decreased considerably by the micropillar fabrication accompanied by the release of the internal stress. This means that the internal residual stress in martensite among Bain groups influences the mechanical properties of martensitic steel.

Molecular beam epitaxy growth of nonmagnetic Weyl semimetal LaAlGe thin film

Here, we report a detailed method of growing LaAlGe, a non-magnetic Weyl semimetal, thin film on silicon(100) substrates by molecular beam epitaxy and their structural and electrical characterizations. 50 nm thick LaAlGe films were deposited and annealed for 16 hours in situ at a temperature 793 K. As-grown high-quality films showed uniform surface topography and near ideal stoichiometry with a body-centered tetragonal crystal structure. Temperature-dependent longitudinal resistivity can be understood with dominant interband s-d electron-phonon scattering in the temperature range 5-40 K. Hall measurements confirmed the semimetallic nature of the films with electron dominated charge carrier density near 7.15*10^21 cm^-3 at 5 K.

Effect of cobalt doping on the electrochemical performance of trimanganese tetraoxide

Nanostructured transition metal oxides (TMO) are potential materials widely explored by researchers for energy storage applications. In this study, spinel trimanganese tetraoxide (Mn3O4) and cobalt doped trimanganese tetraoxide (Co-Mn3O4) was synthesized by using a simple solvent assisted hydrothermal route. Pure Mn3O4 and Co-Mn3O4 nanomaterials were characterized by an x-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), UV-diffuse reflectance spectroscopy (UV-DRS), field emission scanning electron microscope (FESEM), and high resolution transmission electron microscope (HRTEM). XRD analysis revealed the body centered tetragonal spinel structure of Mn3O4 and Co-Mn3O4 with a space group as l41/amd (141) and an approximate crystallite size of 45–33 nm. The presence of an Mn–O bond vibration was confirmed using FTIR and the band gap properties were analyzed through UV-DRS. Surface morphology and average grain size were examined using FESEM and HRTEM micrographs as nanosquares and nanospheres with diameter 126 nm and 118 nm, respectively. Electrochemical properties of Mn3O4 and Co-Mn3O4 were evaluated using cyclic voltammograms, charge–discharge curves, and electrochemical impedance spectra (EIS). Pure Mn3O4 showed a specific capacitance of 971 F g−1 at 0.1 A g−1 current density while Co-Mn3O4 achieved relatively higher specific capacitance of 1852 F g−1 at the same current density. It is observed that the increased specific capacitance of Co-Mn3O4 mainly arises from the doping effect. Electrochemical analysis shows that the Co doped Mn3O4 nanomaterials can be a promising electrode material for supercapacitor.

Linking constituent phase properties to ductility and edge stretchability of two DP 980 steels

Two DP 980 steels were characterized with multiple methods to determine its microstructure characteristics, tensile properties and edge stretchability. The first (DP980-B) is a commercial grade DP980 steel produced by AK Steel, while the second (DP980-T) is a modification of the first one by a tempering process. Both contain two individual phases: ferrite and martensite with body centered cubic (BCC) and tetragonal (BCT) crystal structure respectively. ASTM standard tensile tests were performed for both materials, revealing that DP980-B has higher work hardening and larger total elongation than DP980-T. Standard hole piercing and subsequent hole expansion and extrusion tests were also performed. The critical hole expansion ratio (HER) of hole pierced sheet at different nominal clearances, on the other hand, show an opposite trend: the HER of DP980-T almost doubles that of DP980-B. This indicates the tensile ductility and edge stretchability are determined by different mechanisms due to different deformation modes. The ductility of sheet metal during uniaxial tension is determined by deformation instability, i.e. necking, due to less constraint at the region of deformation and fracture will occur quickly after necking. The contribution of post-necking deformation to the total elongation is insignificant for the high strength grades such as DP980 steels. The ductility during hole-expansion, however, is mainly determined by material fracture behavior that is dependent on phase property disparity and material intrinsic fracture parameters. With the individual phase properties for both DP steels determined by in situ tensile tests under high energy X-ray diffraction, the results show that DP980-T steel has lower property disparities between the two phases than DP980-B steel, due to the tempering process. This explains why the DP980-T steel has higher HER than DP980-B steel: lower phase disparity will lead to less local deformation during loading. The higher work hardening rate for DP980-B steel contributes to its higher uniform elongation compared with DP980-T steel based on the maximum load condition of deformation instability. An integrated finite element simulation framework for studying hole expansion is also presented here, based on the calculated individual phase properties from the combined high energy x-ray diffraction (HEXRD) and elastic plastic self-consistent modeling. The simulation results correlate well with the experimental results on the HER difference between the two materials.

The effect of Co and Ce codoping in CuIn0.9CexCo0.1−xTe2

The codoped dilute magnetic semiconductor CuIn0.9CexCo0.1−xTe2 has been successfully prepared by arc melting and vacuum solid-state reaction technologies. CuIn0.9CexCo0.1−xTe2 crystallizes into body centered tetragonal structure with a space group of I4¯2d. The codoping of Co and Ce induces the room temperature ferromagnetism in CuIn0.9CexCo0.1−xTe2. The magnetization of CuIn0.9CexCo0.1−xTe2 are enhanced by codoping Ce and Co into CuInTe2, which is ascribed to the exchanging interaction between 4f electron of Ce and 3d electron of Co. Magnetic measurements show that Co influences mainly on the saturation magnetic moment of CuIn0.9CexCo0.1−xTe2. The high doping ratio of Co and Ce is beneficial for increasing saturation magnetization and the magnetic transformation temperature. Codoping Ce and Co into CuInTe2 can adjust the light absorption bandgap from 0.92 eV to 1.08 eV, which is slightly higher than that of CuInTe2. It shows that the light absorption bandgap can be refined by controlling Co/Ce ratio for the potential application of solar cell material.

Temperature, strain and charge mediated multiple and dynamical phase changes of selenium and tellurium.

Semiconducting selenium and tellurium in their 3D bulk trigonal structures consist of parallel and weakly interacting helical chains of atoms and display a number of peculiarities. We predict that thermal excitations, 2D compressive strain and excess charge of positive and negative polarity mediate metal-insulator transitions by transforming these semiconductors into different metallic crystal structures. When heated to high temperature, or compressed, or charged positively, they change into a simple cubic structure with metallic bands, which is very rare among elemental crystals. When charged negatively, they transform first into body-centered tetragonal and subsequently into the body-centered orthorhombic structures with increasing negative charging. These two new structures stabilized by excess electrons also have overlapping metallic bands and quasi 2D and 1D substructures of lower dimensionality. Since the external charging of crystals can be achieved through their surfaces, the effects of charging on 2D structures of selenium and tellurium are also investigated. Similar structural transformations have been mediated also in 2D nanosheets and free-standing monolayers of these elements. These phase changes assisted by phonons are dynamical, reversible and tunable; the resulting metal-insulator transitions can occur within very short time intervals and may offer important device applications.

Semi-classical electronic transport properties of ternary compound AlGaAs2: role of different scattering mechanisms

Using Rode’s iterative method, we have investigated the semi-classical transport properties of the n-type ternary compound AlGaAs2. Four scattering mechanisms have been included in our transport calculation, namely, ionized impurity, piezoelectric, acoustic deformation and polar optical phonon (POP). The scattering rates have been calculated in terms of ab initio parameters. We consider AlGaAs2 to have two distinct crystal geometries, one in tetragonal phase (space group: ), while the other one having body centered tetragonal crystal structure (space group: ). Higher electron mobility has been observed in the body centered tetragonal phase, thereby making it more suitable for high mobility device application, over the tetragonal phase. In order to understand the differences in electron mobility for these two phases, curvatures of the E-k dispersion of the conduction bands for these phases have been compared. At room temperature, the dominant contribution in electron mobility was found to be provided by inelastic POP scattering. We have also noted that mobility is underestimated in relaxation time approximation compared with the Rode’s iterative approach.

Ab initio investigation of physical properties of LaT2B2C (T=ir, Rh) compounds: A density functional theory approach

The structural, electronic, lattice dynamical, and electron-phonon interaction properties of LaIr2B2C and LaRh2B2C crystallised in body-centred tetragonal structure are investigated by using the generalised gradient approximation of the density functional theory and the planewave pseudopotential method. The structural results are in good accordance with previous experimental studies. The electronic studies show that the density of states at the Fermi level of both borocarbide compounds are dominated by the d states of transition metal Ir(Rh). Also it is observed that the electron-phonon interaction in LaIr2B2C and LaRh2B2C are mainly carried out by the low-frequency phonon modes. By integrating Eliashberg spectral function, the superconducting transition temperature for LaIr2B2C and LaRh2B2C are obtained as 0.22 K and 0.20 K, respectively.

Manganese hydrides and superhydrides at high pressure

Manganese hydrides and superhydrides have been studied from ambient up to high pressures by the ab initio random structure searching algorithm. At ambient pressure conditions and room temperature, the subhydride ${\mathrm{Mn}}_{2}\mathrm{H}$ (space group $P\overline{3}m1$) is the only compound found stable among those studied, since $\ensuremath{\epsilon}$-MnH (hcp structure, space group $P{6}_{3}/mmc$), although stable at 0 K, is destabilized by thermal effects. With increasing pressure, MnH is stabilized, and then hydrogen-rich hydrides appear: first ${\mathrm{MnH}}_{2}$ around 30 GPa, then ${\mathrm{MnH}}_{7}$ around 40 GPa, and finally ${\mathrm{MnH}}_{3}$ around 90 GPa. ${\mathrm{MnH}}_{8}$ is likely to become stable around 150 GPa. The body-centered tetragonal structure of ${\mathrm{MnH}}_{2}$ (space group $I4/mmm$) is identical to that of ${\mathrm{FeH}}_{2}$ and ${\mathrm{CoH}}_{2}$. ${\mathrm{MnH}}_{3}$ has an original body-centered tetragonal structure, with space group $I4/m$ and 4 formula units per primitive cell. It contains a structural unit ${\mathrm{H}}_{8}$ with rather short H-H distances. ${\mathrm{MnH}}_{7}$ is extremely stable at high pressure. ${\mathrm{MnH}}_{7}$ and ${\mathrm{MnH}}_{8}$ exhibit a mixed structure, with one hydrogen being under the molecular form (1/2 ${\mathrm{H}}_{2}$) and the other ones under an atomic (hydrided) form. Atomic charges computed by the Bader method confirm the electron transfer from Mn to H, with Mn oxidation increasing from MnH to ${\mathrm{MnH}}_{3}$, and then saturating beyond. At high pressure, nuclear quantum effects tend to stabilize ${\mathrm{MnH}}_{4}$ and increase the stability of ${\mathrm{MnH}}_{8}$.

Real time observation of martensite transformation for a 0.4C low alloyed steel by neutron diffraction

A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium-carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during quenching with and without the ausforming process. The fresh martensite exhibits a body-centered tetragonal structure when it forms immediately below the martensite start (Ms) temperature, and its c/a ratio decreases rapidly as time elapses. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. After ausforming, the data reveal that lattice parameters are larger in austenite whereas smaller in martensite compared with those in the non-ausformed case, which is ascribed to the introduced dislocations. Thus, the lattice defects affect the lattice parameter during martensite transformation. Ausforming also slightly raises the Ms temperature and increases the amount of retained austenite at room temperature as a result of different dislocation densities. The cutting-edge operant quantitative measurements with neutron diffraction for steel production is demonstrated.

Surface- and Strain-Mediated Reversible Phase Transformation in Quantum-Confined ZnO Nanowires.

The phase stability of ZnO in a quantum-confinement size regime (sub-2-nm) remains fiercely debated. Applying insitu (scanning) transmission electron microscopy, we present the atomistic view of the phase transitions from the original wurtzite structure to an intermediate body-centered tetragonal and h-MgO structure under tensile strain in quantum-confined ZnO nanowires. Strikingly, such structural transitions are reversible after releasing the stress. Further theoretical calculations mirror the transition pathway and provide basic insight into the overall landscape regarding surface- and strain-dependent phase transition behavior. Our results provide the critical piece to solve the puzzle in phase stability of ZnO, which may prove essential for advancing a variety of nanotechnologies, e.g., quantum-dot light-emitting devices.

An answer to the carbon cluster in low-temperature aged ferritic low-carbon steel

The morphology and crystal structure of the carbon cluster in a low-temperature aged low-carbon ferritic steel were clarified by performing conventional and in-situ TEM, and atomically-resolved ADF-STEM observation. The carbon cluster grow parallel to <001> direction of the matrix, whose morphology was presumed to be either disk or plate. Lattice constant of the carbon cluster was measured by peak fitting of atomic columns observed by ADF-STEM. The result clarified that the structure of the carbon cluster was martensite-like body-centered tetragonal (bct) structure. This martensite-like bct structure suggested that the carbon cluster was supersaturated with carbon atoms occupying specific octahedral sites.

Improvement in the wear resistance of a hypereutectoid rail via heat treatment

The rail, as the most important component in railways, needs to be routinely checked to maintain proper service conditions to prevent catastrophic accidents by any premature failure of the rail. The severe plastic deformation of rails due to cyclic wheel/rail contact forces forms a superficial deformed layer, referred to as the white etching layer, because of cementite decomposition and the formation of the carbon-supersaturated nanostructured ferrite phase. This supersaturated superficial layer is highly prone to the initiation and propagation of rolling contact fatigue cracks. However, it has been observed that transition carbides and cementite can precipitate when the first and third stages of tempering starts at approximately 150 and 400 °C, respectively, due to carbon ejection from the body-centered tetragonal structure. A controlled laboratory heat treatment was conducted on a used hypereutectoid rail at 200 and 500 °C. Then, the wear resistances of the heat-treated samples were compared with the as-received rail sample using pin-on-disc testing. A significant increase in the wear resistance of the sample treated at 200 °C confirmed the improvement in the wear resistance of used pearlitic rails, which is a great interest for railway industries.

Density functional theory calculations of the double gamma prime Ni3Ta phase under pressure: Structural, mechanical, and electronic properties

In this study, we investigated the structural, mechanical, and electronic properties of the γ′′-Ni3Ta (body-centered tetragonal structure) phase under various pressures using first-principles methods. The negative formation enthalpy indicated that γ′′-Ni3Ta is energetically stable when external pressure is applied. The elastic constant and polycrystalline elastic moduli were calculated using the stress–strain and Voigt–Reuss–Hill approximations methods. The results showed that γ′′-Ni3Ta is mechanically stable and ductile. The mechanical anisotropies of γ′′-Ni3Ta were measured using the elastic anisotropic indexes (AU, AB, and AG, and A1, A2, and A3) and the calculated results suggest that γ′′-Ni3Ta is anisotropic. In addition, the sound velocities and Debye temperatures were calculated. Finally, the electronic densities of states were investigated to determine the internal mechanisms responsible for the structural and mechanical properties of γ′′-Ni3Ta.

Coexistence of hcp and bct Phases during In Situ Superlattice Assembly from Faceted Colloidal Nanocrystals.

We study the in situ self-assembly of faceted PbS nanocrystals from colloidal suspensions upon controlled solvent evaporation using time-resolved small-angle X-ray scattering and X-ray cross-correlation analysis. In our bulk-sensitive experiment in transmission geometry, the superlattice crystallization is observed in real time, revealing a hexagonal closed-packed (hcp) structure followed by formation of a body-centered cubic (bcc) superlattice. The bcc superlattice undergoes continuous tetragonal distortion in the solvated state shortly after its formation, resulting in the body-centered tetragonal (bct) structure. Upon solvent evaporation, the bct superstructure becomes more pronounced with the still coexisting hcp phase. These findings corroborate the existing simulations of assembling cuboctahedral-shaped particles and illustrate that we observed the predicted equilibrium states. This work is essential for a deeper understanding of the fundamental forces that direct nanocrystal assembly including nanocrystal shape and ligand coverage.