Polycrystalline Samples Research Articles

Rapid microcantilever preparation for conditional fracture toughness evaluation

The Ga+ focused Ion Beam (FIB) or Xe+ Plasma FIB (PFIB) procedure has enabled the ability to make specimens where mechanical tests in the microscale regime can be achieved with high precision. Nevertheless, milling times can be long and shape optimization can be arduous collectively limiting the ability to readily make a sufficient number of test samples. In this work, we present a sample preparation technique for microscale cantilever fabrication which streamlines the milling procedures by using combined electropolishing and FIB milling. Specifically, the procedure mitigates extensive undercutting requirements which reduces the fabrication time for the microcantilever to more than half that time as compared to direct milling methods from making similar geometries directly from the bulk material. This process is discussed along with specific aspects related to the sample alignment of the cantilever to specific fracture planes for single crystals. In addition, we comment on the applicability of this method to polycrystalline samples.

Thermophysical properties of H2O and D2O ice Ih with contributions from proton disorder, quenching, relaxation, and extended defects: A model case for solids with quenching and relaxation.

Application of the coherent thermodynamic model [W. Holzapfel and S. Klotz, J. Chem. Phys. 155, 024506 (2021)] for H2O ice Ih to the more detailed data for D2O ice Ih provides better insight into the contributions from quenched proton disorder and offers a new basis for understanding the apparent differences between the data for thermal expansion measured with neutron diffraction on polycrystalline samples [A. Fortes, Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 74, 196 (2018) and A. Fortes, Phys. Chem. Chem. Phys 21, 8264 (2019)] and macroscopic dilatation measurements on single crystals [D. Buckingham et al., Phys. Rev. Lett. 121, 185505 (2018)]. The comparison points to contributions from defects effecting the two techniques in different ways. The uncertainties in thermodynamic data due to the contributions from proton disorder and additional defects are compared with the "reference data" [R. Feistel and W. Wagner, J. Phys. Chem. Ref. Data 35, 1021 (2006)] for H2O ice Ih.

Temperature-dependent evolution of micromagnetic structure of B20-type Fe1-xCoxGe studied by Mössbauer spectroscopy

The non-collinear magnetic structures hosted in magnets with broken central inversion symmetry, some of which are topologically non-trivial, have unique physical properties and application prospects. This paper presents a detailed study of the temperature evolution of the micromagnetic structures of B20-type Fe1-xCoxGe (x = 0, 0.05, 0.10) polycrystalline samples using 57Fe Mössbauer spectroscopy. We take the relatively weak electric quadrupole interaction as a perturbation of the hyperfine magnetic interaction to obtain the distribution of the hyperfine magnetic field Hhf (φ) in the plane perpendicular to the magnetic propagation vector ks. It is found that the geometric features of Hhf (φ) are sensitive to the relative orientation of ks regarding the electric field gradient at the iron nucleus, as well as to the spin texture. The temperature dependence of Hhf (φ) provides a distinct signal of first-order phase transition when ks shifts from [100] to [111]. The doping of cobalt atoms leads to out-of-plane component and in-plane component aggregation of the neighboring iron magnetic moments. These results are instructive for understanding the dynamical behavior of spiral magnets with long-periods.

Structural and superconducting properties of non-stoichiometric Nb1+xSe2

The composition-dependent crystal and defect structures, and superconducting properties of Nb1+xSe2 (0 ≤ x ≤ 0.09) polycrystalline samples were revealed by x-ray diffraction, electrical resistivity, magnetization and specific-heat measurements. Stacking-disordered structures were characterized by gradually broadened and weakened (h0l) reflections: disordered 2Ha structure for x ≤ 0.04 and 2Hb + 3R mixed-layer structure for x ≥ 0.05. Superconducting transition temperature (Tc) is 7.3 K in pristine NbSe2, which decreases with increasing the content of interstitial-Nb (Nbint), down to below 2 K in x = 0.09. The lowered Tc originates from the decreased electron-phonon coupling and density of states at the Fermi level EF. Upper critical field μ0Hc2 of all samples evidently exceed the Pauli limit except for pristine NbSe2. μ0Hc2, irreversible field μ0Hirr and critical current density Jc are all raised in slight-Nbint samples compared with NbSe2. The enhancements are due to the increase in charge carrier scattering and vortex pinning by Nbint impurity and stacking disorders. These results indicate that minor nonmagnetic impurity doping could improve the current-carrying capacity under the premise of small impact on Tc, which thus is a promising strategy to develop high-field superconducting magnets.

Metal Substitutions (M = Al, Ga, In; Sn, Ge; and Mn, Fe, Co) in ZnS: Sphalerite versus Wurtzite Formation.

A series of Zn1-xMxS polycrystalline samples were synthesized via a solid-state reaction in closed vessels to examine the solubility of foreign M cations within the wurtzite ZnS structure, employing quenching or slow cooling processes to favor specific polymorphs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses revealed diverse structural behaviors across different cations. Group 13 elements (Al and Ga) formed solid solutions with a wurtzite structure, while In showed complex layer stacking defects. For 3d magnetic cations (Mn, Fe, and Co), a broad solubility range in the hexagonal structure was noted for Mn, whereas Fe and Co more readily formed cubic structures, with solubilities similar to Mn in the sphalerite form. Despite structural differences, magnetic susceptibilities and spin freezing temperatures for Fe and Co were comparable. Group 14 elements showed varied behaviors: Sn was insoluble in ZnS, as attested by unchanged unit cell parameters and surface crystallite Sn, whereas Ge only formed in the cubic phase with a solubility limit of x ≈ 0.2. The study discusses these variations in solubility and structure in terms of oxidation states, ionic-covalent radius, and coordination preferences in sulfides.

Sr-substitution effects on crystal structure and thermoelectric properties of misfit layered cobaltate, [Ca2CoO3]pCoO2

Misfit-layered cobaltate [Ca2CoO3]pCoO2 is a promising thermoelectric (TE) material that can operate at high temperature in air. Partial substitution of Ca with Sr has been suggested to enhance TE properties. To comprehend the unresolved effects of Sr-substitution on the TE properties, we have prepared single-phase polycrystalline samples of Sr-substituted [Ca2CoO3]pCoO2, i.e., [(Ca1-xSrx)2CoO3]pCoO2, using a spark plasma sintering (SPS) method followed by O2 annealing. We analyzed the crystal structure by powder X-ray diffraction, evaluated the average valence state of Co ions by X-ray photoelectron spectroscopy, and measured temperature-dependent TE properties. Upon Sr-substitution, the average valence state of Co ions slightly increased. The electrical resistivity perpendicular to the SPS pressing direction increased, while that along the SPS pressing direction was almost unchanged. The Seebeck coefficient and the thermal conductivity were less affected by the Sr-substitution. The figure-of-merit zT perpendicular to the SPS pressing direction tended to decrease with Sr-substitution, reflecting the increase in electrical resistivity.

The magnetic and electronic properties of Ho6Fe23−xCox (x = 0, 1, 2, 3)

Magnetic and electronic properties of Ho6Fe23−xCox (x = 0, 1, 2, 3) compounds were investigated for the first time by experimental measurements on their polycrystalline samples combining with first-principles calculation. The samples of Ho6Fe23−xCox were successful prepared by a vacuum arc furnace. The XRD analysis and Rietveld refinement results show that Ho6Fe23−xCox crystallize in a face-centered cubic Th6Mn23-type structure with space group Fm3¯m (No.225), and their lattice parameters decrease with the increasing Co content. The M−T curves indicates that AFM-FM transition occurred at Neél temperature TN, the FM-PM transition occurred at Currie temperature TC for Ho6Fe23−xCox and the FM-PM transition belongs to a second-order transition. The Currie temperature and magnetic compensation temperature for all the samples increases with the increase of the content of Co. The maximum magnetic entropy change (-ΔSM) for the Ho6Fe23−xCox compounds under an applied magnetic field of 15 k Oe are 0.594, 1.023, 0.726 and 0.48 J kg−1 K−1 around their Currie temperature (TC = 542, 580, 622 and 654 K), respectively. This relatively large -ΔSM of Ho6Fe23−xCox occurred in a relatively high temperature region and under low applied magnetic field, pointing to the potential application as magnetic refrigeration materials using at higher temperature. The experimental results show that Co doping can regulate the magneto-thermal properties of the materials, so as to improve the magnetic entropy change of the existing magnetic refrigeration materials. The electronic properties of Ho6Fe23−xCox was studied by using the first-principle calculation. The band structures and density of states indicate that Ho6Fe23−xCox are good conductor.

In-Situ synchrotron investigation of elastic and tensile properties of oxide dispersion strengthened EUROFER97 steel for advanced fusion reactors

The augmentation of mechanical properties of reduced activation ferritic martensitic steels through the introduction of creep resistant nano-oxide particles produces a class of oxide dispersion strengthened steels, which have attracted significant interest as candidates for first wall supporting structural materials in future nuclear fusion reactors. In the present work, the effect of temperature on the elastic properties and micro-mechanics of 0.3 wt% Y2O3 oxide dispersion strengthened steel EUROFER97 is investigated using synchrotron high energy X-ray diffraction in-situ tensile testing at elevated temperatures, alongside the non-oxide strengthened base steel as a point of comparison. The single crystal elastic constants of both steels are experimentally determined through analysis of the diffraction peaks corresponding to specific grain families in the polycrystalline samples investigated. The effect of temperature on the evolving dislocation density and character in both materials is interrogated, providing insight into deformation mechanisms. Finally, a constitutive flow stress model is used to evaluate the factors affecting yield strength, allowing the strengthening contribution of the oxide particles to be assessed, and correlation between the thermally driven microstructural behaviour and macroscopic mechanical response to be determined.

Copper(II) complexes of 1,3-dimethyl-(5-(8′-quinolinylazo)-6-aminouracil: Structures, magnetism and biological activity

Two Cu(II)-complexes were synthesized using 1,3-dimethyl-5-(8′-quinolinylazo)-6-aminouracil (H2L) ligand in combination with thiocyanide (SCN−) and azide (N3−) pseudohalides as co-ligands. The thiocyanide (SCN−) co-ligand guided to form monomeric aquo-isothiocyanato-Cu(II) complex, [CuII(HL)(NCS)(H2O)] (1) of H2L. Under similar reaction condition, the azide (N3−) co-ligand led to form polymeric azido-Cu(II) complex, [CuII(L′)(N3)]n, (2) of HL′, where HL′ was an in-situ generated new ligand, 1,3-dimethyl-(5-(8′-quinolinylazo)-6-hydroxouracil (HL′) from H2L. Both are tridentate ligands with different uracil-donor sites (H2L: NqNaNu, HL′: NqNaOu). The complexes are monoclinic with space groups C2/c (Z = 8) and P21/n (Z = 4) for 1 and 2, respectively. They possess slightly distorted square-pyramidal coordination around CuII ions with elongation at the axial sites (Cu1-O3 (water) bond is 2.2698(13)Å for 1 and Cu1-Oμ-uracil bond is 2.5525(13)Å for 2). The polymeric nature of 2 is availed through one of the exocyclic-C = O groups of HL′, making Cu…Cu spacing to 7.9973(3)Å. Direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 1 and 2 were carried out in the temperature range 1.8-300 K. The 1 is devoid of any significant interaction between the mononuclear units. Magnetic properties show weak ferromagnetic exchange coupling within the chain (J = 0.61 cm−1) in 2. The TD-DFT study reveals that ILCT, LMCT and d-d types of electronic transitions are involved in both the complexes. The evaluated biological efficacy of the compounds against plant pathogens it is revealed that the complex 1 has an antibacterial and complex 2 has antifungal properties.

Microstructure and texture control of Ni-Mn-Ga magnetic shape memory alloys manufactured by laser powder bed fusion

The Laser Powder Bed Fusion (LPBF) process was used to manufacture Ni-Mn-Ga polycrystalline samples. The initial powders with a fine particle size of about 20 µm were firstly prepared by a ball milling from melt-spun ribbons. The microstructure and texture evolution of Ni-Mn-Ga alloy manufactured by LPBF were investigated employing SEM, TEM, and synchrotron radiation diffraction. Using two different scanning strategies, optimization of laser parameters and post-processing heat treatment, a homogeneous microstructure with a strong crystallographic texture was obtained. The localized heating/cooling conditions allow obtaining a layered structure with preferred <100> fiber orientations along the growth direction. The crystal structure and crystallographic texture drastically change when the laser oscillation mode is chosen. The strong crystalline anisotropy and layered-type microstructure have a significant impact on twining flow behavior giving rise to an anisotropic mechanical response. The variant reorientation during mechanical training is realized by the so-called orthogonal shearing. It is also shown that the resulting crystal structure and characteristic transformation temperatures are strongly dependent on chemical composition related to Mn losses and internal stresses along with chemical order creating metastable phases due to the extremely high cooling rate upon the 3D printing. Therefore, all the above parameters are thoroughly monitored during the three-stage fabrication process.

Measurement setup for Nernst and Seebeck effect at high temperatures and magnetic fields tested on elemental bismuth and full-Heusler compounds.

In this work, a measurement setup to study the Seebeck and Nernst effect at high temperatures and high magnetic fields is introduced and discussed. The measurement system allows for simultaneous measurements of both thermoelectric effects up to 700K and magnetic fields up to 12T. Based on theoretical concepts, measurement equations are derived that counteract constant spurious offset voltages and, therefore, inhibit systematic errors in the measurement setup. The functionality is demonstrated on polycrystalline samples of elemental bismuth as well as various full-Heusler materials, exhibiting an anomalous Nernst effect. In all samples, the measured Seebeck and Nernst coefficients align excellently with the reported values. This allows future research to substantially extend the measured temperature and field intervals, commonly limited to temperatures below room temperature. For the first time, the thermoelectric and thermomagnetic properties of these materials are reported up to temperatures of 560K.

Synthesis and Characterization of the Electrical and Energy Storage Properties of New Barium Titanate - Europium Titanate Solid Solution

In the present work, the investigation of the structural, dielectric, ferroelectric and energy storage properties of polycrystalline samples of (1-x)BaTiO3 – xEuTiO3 (BT-ET) solid solution materials prepared by conventional solid-state reaction method has been carried out. X-ray diffraction analyses have revealed the formation of a single-phase tetragonal structure with the P4mm space group. Furthermore, the temperature dependence of the dielectric constants marked the presence of the following sequence of structural phase transitions, namely from rhombohedral to orthorhombic, from orthorhombic to tetragonal and from tetragonal to cubic phase transitions with the increase of temperature. A diffuse phase transition has been observed from the dielectric permittivity peak and has been analyzed using the modified Curie-Weiss law and the degree of diffuseness is found to be in the range of 1.16 - 1.76 due to the existence of different states of polarization. A phase diagram has been established based on the temperature-dependent dielectric permittivity studies. The room temperature ferroelectric properties point to a coercive field larger than that of BaTiO3 ceramics. Broad dielectric peaks associated with diffuse phase transition appear in a wide temperature range (40 - 100 °C) with the highest dielectric permittivity ε’ = 6498 found in the x = 0.05 ceramics. Moreover, an improved energy storage performance is obtained in the 0.95BaTiO3-0.05EuTiO3 ceramic with a recoverable energy density of Wrec = 0.797 J/cm3, coupled with an efficiency η = 73% at 170 kV/cm and the highest storage energy density of Wst = 1.571 J/cm3 is obtained for 0.90BaTiO3-0.10EuTiO3, which is superior to other lead-free BT-based ceramics. All these features demonstrate that the BT-ET ceramics can be widely used in energy storage applications and also in high-temperature multilayer capacitors for automotive, aerospace and related industries.

Laue microdiffraction on polycrystalline samples above 1500 K achieved with the QMAX-µLaue furnace.

X-ray Laue microdiffraction aims to characterize microstructural and mechanical fields in polycrystalline specimens at the sub-micrometre scale with a strain resolution of ∼10-4. Here, a new and unique Laue microdiffraction setup and alignment procedure is presented, allowing measurements at temperatures as high as 1500 K, with the objective to extend the technique for the study of crystalline phase transitions and associated strain-field evolution that occur at high temperatures. A method is provided to measure the real temperature encountered by the specimen, which can be critical for precise phase-transition studies, as well as a strategy to calibrate the setup geometry to account for the sample and furnace dilation using a standard α-alumina single crystal. A first application to phase transitions in a polycrystalline specimen of pure zirconia is provided as an illustrative example.

Martensitic-like microstructures across the isostructural phase transitions in Cerium

The isostructural gamma–alpha phase transition in elemental cerium is an electronic transition caused by a delocalization of the 4f electrons. This affects the bonding properties of Ce atoms and leads to a large volume collapse reaching ∼17% in the low pressure regime (¡ 2 GPa). While great attention has been drawn on the electronic description of this transition, attempts to understand the mesoscale mechanisms of this structural transition and their consequences in terms of microstructure remain scarce. We have investigated this transition by means of combined X-ray Computed Tomography and Energy Dispersive X-ray Diffraction on polycrystalline samples. Our experimental observations reveal a platelet-shape microstructure across the transition and up to the critical point, which have been associated to displacive mechanisms. Based on continuum mechanics modeling and ab initio calculations, we propose that here, this microstructure is initiated by elastic instability and shear anisotropy in the ¡100¿ directions.

Developing techniques for crystal growth synthesis and characterization of rare earth-silicon-germanium magnetoresponsive alloys

A crystal growth technique was developed for the family of intermetallic, magnetoresponsive RE5(Si1-xGex)4 alloys in order to access the intrinsic and anisotropic properties. Initial bulk properties measured on polycrystalline samples alluded to the properties being obscured or averaged and high-quality, well-characterized, single crystals would clarify this. Successful crystal growth led to development of oriented sample preparation techniques specific for the crystal structures (monoclinic and orthorhombic) and mechanical properties (hard and brittle) of these alloys, and customized for the various measurement techniques undertaken. Here we describe our journey, sometimes circuitous, from crystal growth to sample preparation and cite the scientific discoveries that came about as a result.

Evolution of crystalline misorientations in polycrystalline samples of pure ice

There are few studies where the evolution of grain orientations and crystal misorientations of neighboring grains in a polycrystalline ice sample during grain growth are analyzed. In this work, crystal orientations and misorientations were studied in two ice cylinders obtained from bidistilled water using the techniques of plastic replicas and chemical etching pits. The cylinders were grown, one through fast freezing and the other through slow freezing. It was observed that the initial crystal orientations of the grains varied from one cylinder to the other, but this did not result in significant differences in the final crystal misorientations between neighboring grains. Such crystal misorientations could be special because they are related to a coincidence sites lattice (CSL), which could be associated with low-energy grain boundaries. Therefore, the decrease in grain boundary energy during grain growth could be influenced by these special crystal misorientations.

Electrical conductivity, luminescence, and deep acceptor levels in β-Ga2O3-In2O3 polycrystalline solid solution doped with Zr4+ or Ca2+ ions

Photoluminescence, luminescence excitation spectra, and electrical conductivity of β-Ga2O3-In2O3 solid solutions were studied. For this purpose, polycrystalline samples of unintentionally doped (UID) and doped with Ca or Zr β-Ga2O3-In2O3 solid solution with 20% In were synthesized and characterized. All samples were obtained by the high-temperature solid-phase method from appropriate oxides at 1300 °C at low and high oxygen partial pressure. It was established that UID and doped with Ca2+ or Zr4+ samples synthesized in an oxygen atmosphere were highly resistive, while the samples synthesized in an argon atmosphere had high conductivity. The conductivity was the lowest in the samples doped with Ca2+ and was 10−13 Ω−1 cm−1, while in the samples doped with Zr4+, the electrical conductivity was the highest and reached 10−3 Ω−1 cm−1. The broadband luminescence of β-Ga2O3-In2O3 solid solution is a superposition of three elementary bands with maxima in the violet 3.08 eV, blue 2.73 eV, and green 2.45 eV regions of the spectrum. Doping with Ca2+ or Zr4+ impurities and varying the synthesis atmosphere led mainly to a redistribution of intensities between the elementary luminescence bands. The luminescence arises from the radiative recombination of charge carriers through donor–acceptor pairs and self-localized holes. Donors and acceptors are formed by native defects such as (Gai, VGa, VGaVo) or doping impurities (Zr4+, Ca2+). Unlike the luminescence spectra, the luminescence excitation spectra change significantly when the synthesis conditions vary or when doping with divalent impurities. The excitation band at 4.46 eV is due to electron transitions from the VGa or VGaVO acceptor levels to the conduction band. Electron transitions from acceptor levels of Ca2+ impurities are manifested in the intense excitation band at 4.1 eV.

Synthesis, characterization and optical tuning of Sm3+ doped NaZnPO4 phosphors for white LED technology

This study presents a comprehensive investigation into the synthesis, structural-spectroscopic characterization, and optical properties analysis of Sm3-activated NaZnPO4 phosphors with varied Sm3+-doping percentiles, aimed at developing tunable luminescent materials for white-light-emitting diode (WLED) applications. The polycrystalline samples NaZn(1-x) Smx3+ PO4 (x = 0.00, 0.05, 0.10 and 0.15) phosphors were synthesized via a solid-state reaction method. X-ray diffraction data analysis confirms single phase monoclinic lattice with space group P 1 21/c 1 for all compositions. The Rietveld procedure also confirms the single phase and monoclinic structure of synthesized phosphors. Fourier-transform infrared) spectroscopy confirms compositional homogeneity. FE-SEM micrographs show irregularly stacked microstructures and morphology for all compositions irrespective of Sm3+ doping percentage. While EDS and Elemental mapping confirm uniform incorporation of Sm3+ ions in phosphors lattice. Diffuse Reflectance Spectra studies show Sm3+ doping resulted in redshift and band gap narrowing. In Photoluminescence spectroscopies, excitation and emission spectra reveal that distinctive photoluminescence spectra with notable emission peaks at 402 nm (6H5/2 → 4F5/2) and 599 nm (4G5/2 → 6H5/2). CIE chromaticity coordinates demonstrated varied color purity and coordinates for different doping levels, with promising orange-red emissions and increased luminosity. The observed optical properties suggest the potential suitability of Sm3+-activated NaZnPO4 phosphors as promising candidates for enhancing WLED efficiency and color quality.

Distinctive Effects between Hydrothermal and Ultrasound Synthesized SnO2 Nanoparticles on Ceramic Bi1.6Pb0.4Sr2Ca2Cu3O10+δ Superconductor

The effect of additions of two series of SnO2 nanoparticles synthesized using two different methods on crystal structure and superconductivity of Bi1.6Pb0.4Sr2Ca2Cu3O10+δ (BPSCCO) superconductors was investigated. Two series of spherical SnO2 nanoparticles were synthesized independently by using ultra-sonication (US-SnO2) and hydrothermal (HT-SnO2) methods. Polycrystalline samples of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1−x(SnO2)x, where x ranged between 0, 0.002 and 0.004, were fabricated by the solid-state reaction method. X-ray diffraction patterns showed a decrease in the volume fraction of the Bi-2223 and an increase in that of the Bi-2212 phases. Scanning electron microscopy images presented the “needle-like blossom” on the surface of the US-SnO2 doped samples, while the phenomenon was not found on the HT-SnO2 doped samples. The Tc was decreased extremely with US-SnO2 doping while slightly HT-SnO2 nanoparticle-doped samples. The field dependence of Jc, Jc(B), showed the opposite tendencies on two series of samples: Jc(B) was enhanced on the HT-SnO2 nanoparticle-doped samples, and that was decreased on UT-SnO2 nanoparticle-doped samples. The application of the Dew-Hughes model to explore the flux pinning mechanism exhibited that the point-like pinning centers were dominant on the HT-SnO2 doped samples. On US-SnO2 doped samples, however, the additional pinning center type was not found and could be explained by the observed over-sized SnO2 nano-needle.&#x0D; &#x0D; &#x0D;

Анализ внутреннего спинового эффекта Холла в металлах для задач спинтроники

A method for estimating the transverse spin-Hall resistance for polycrystalline samples of pure metals has been proposed. The spin Hall effect coefficients for various metals of 3-6 periods, including rare-earth lanthanides, have been calculated. It is shown that the sign of the calculated spin-Hall resistance always coincides with the experimental one. For most of the considered metals the calculation result agrees with the experimental data. It is shown that the agreement of the calculation results with experiment can be significantly improved if the used approximations of strong coupling and effective charge are supplemented by the assumption that the interaction of collectivized conduction electrons in the construction of the self-consistent field can be taken into account by the introduction of the effective mass of the conduction electron in the Hamiltonian of the spin-orbit interaction. The reasons for the deviation for aluminum, copper, dysprosium, holmium, and gadolinium are discussed.