Polycrystalline Samples Research Articles

Resolving the Dependence of Aluminum Alloy Corrosion on Grain Orientation by Scanning Electrochemical Cell Microscopy

The study of grain-dependent corrosion behaviors of practical polycrystalline metals remains challenging due to the influences of other microstructural features, such as intermetallic particles and grain boundaries. In this work, we employed the oil-immersed scanning electrochemical cell microscopy (SECCM) to investigate the effect of grain orientations of a practical aluminum alloy AA7075-T73 on the surface electrochemical behaviors. Thousands of spatially resolved microscopic potentiodynamic polarization (PDP) measurements were performed, allowing the extraction of information only from grain interior areas excluding intermetallic particles and grain boundaries. The differences in the corrosion behaviors between grains were revealed. Cathodic currents exhibited a strong grain orientation dependence with a decreasing order of {101} > {001} > {111}, agreeing with the prediction from the order of atomic planar density. By contrast, the dependence of anodic currents on grain orientation was weak, and pitting was independent of grain orientation, which could be due to the limited mass transport of ions within the surface oxide film. This work highlights the capability of oil-immersed scanning electrochemical cell microscopy in resolving small electrochemical differences, which will greatly promote the study of grain-dependent behaviors of practical polycrystalline samples.

X-ray study of glassy, glass-ceramic, and polycrystalline LiNaGe4O9

X-ray diffraction was used to study the phase compositions of lithium tetragermanate LiNaGe4O9 glass and states obtained through its heating and crystallization. LiNaGe4O9 glass was obtained by quenching the melt. The amorphous-crystalline samples were prepared by isothermal heat treating at the temperatures chosen between the glass transition Tg = 783 K and devitrification TC = 829 K points. The polycrystalline samples were obtained by heating the glass well above TC. It was shown that in the glassy samples amorphous phase occupied about 92% of the whole volume, whereas the rest (~8%) fell on regions with ordered structure. In the amorphous-crystalline samples, disordered and ordered regions each occupied about half of the volume. In the polycrystalline samples, ordered regions occupied near 96% of the sample volume. The average size of ordered regions in the glass and amorphous-crystalline samples was estimated about 35 nm. In the polycrystalline samples, crystallites notably grew and had linear size near 120 nm. The obtained data demonstrate that controlled glass crystallization represents an effective way to prepare nanometer size structured solids.

INFLUENCE OF ELECTRON IRRADIATION ON THE CRYSTAL STRUCTURE, SURFACE MICRORELIEF AND BANDGANP WIDTH OF THE TRIPLE CRYSTALS OF IRON DOPED MONOSELINIDE OF THALLIUM AND INDIUM

In this work, the effect of electron irradiation on the structure, surface morphology and band gap of single-and polycrystalsof iron-doped ternary crystals of thallium and indium monoselinides was investigated. It has been established that the synthesized polycrystalline samples, as well as the grown single crystals of thallium and indium monoselinides, are single-phase. The crystals have a tetragonal unit cell (space group I4/mcm) with the following lattice parameters: a ~ b = 8.12 Å, c = 6.88 Å, α=β=γ= 90°. Irradiation with electrons with an energy of 2 MeV and a beam current density of 0.085 μA/cm2leads to changes in the structure and properties of crystals in a complex manner depending on the electron fluence. Leads to a change in the parameters of the crystal lattice, an increase in the maximum value of the arithmetic mean deviation of the profile, as well as a decrease inthe height of the average surface roughness of the irradiated crystals. Irradiation of a powder sample with electrons with a fluence of 5x1016electron/cm2helps to increase the size of nanocrystallites from 32.50 nm to 43.33 nm.

Effects of pressure and doping on Ruddlesden-Popper phases Lan+1NinO3n+1

Recently, the discovery of superconductivity with a critical temperature Tc up to 80 K in Ruddlesden–Popper phases Lan+1NinO3n+1 (n = 2) under pressure has garnered considerable attention. Up to now, the superconductivity was only observed in La3Ni2O7 single crystal grown with the optical-image floating zone furnace under oxygen pressure. It remains to be understood the effect of chemical doping on superconducting La3Ni2O7 as well as other Ruddlesden–Popper phases. Here, we systematically investigate the effect of external pressure and chemical doping on polycrystalline Ruddlesden–Popper phases. Our results demonstrate that the application of pressure and doping effectively tunes the transport properties of Ruddlesden–Popper phases. We find pressure-induced superconductivity up to 86 K in La3Ni2O7 polycrystalline sample, while no signatures of superconductivity are observed in La2NiO4 and La4Ni3O10 polycrystalline samples under high pressure up to 50 GPa. Our study sheds light on the exploration of high-Tc superconductivity in nickelates.

Structural, dielectric and electrical transport properties of thermal stable (1-x)K0.5Bi0.5TiO3-xBaTiO3 ceramics

Polycrystalline samples of (1-x)K0.5Bi0.5TiO3 - xBaTiO3 [(1-x)KBT - xBT] were synthesized using a solid-state reaction pathway. X-ray diffraction analysis confirmed the presence of a single-phase perovskite structure. To explore relaxation and conduction mechanisms, complex impedance spectroscopy was employed. Reduction in Curie temperature was observed as BT content increased. The grain and grain boundary contributions to relaxation was examined through complex impedance and modulus plots and quantified via fitting experimental data to an equivalent circuit model. Examination of the Complex impedance spectra uncovered the existence of dielectric relaxation characteristic of a non-Debye nature. Furthermore, the activation energy determined suggests commonalities in governing the conduction and relaxation processes in relation to temperature-dependent conductivity and relaxation time. A negative temperature coefficient of resistance behaviour was obtained from the temperature-dependent conductive study. Dielectric spectra revealed that these ceramic capacitors are useful in reduction of signal interference, signal attenuation and impedance matching circuits applications.

Signature of Superconductivity in Pressurized La4Ni3O10

The discovery of high-temperature superconductivity near 80 K in bilayer nickelate La3Ni2O7 under high pressures has renewed the exploration of superconducting nickelate in bulk materials. The extension of superconductivity in other nickelates in a broader family is also essential. Here, we report the experimental observation of superconducting signature in trilayer nickelate La4Ni3O10 under high pressures. By using a modified sol-gel method and post-annealing treatment under high oxygen pressure, we successfully obtained polycrystalline La4Ni3O10 samples with different transport behaviors at ambient pressure. Then we performed high-pressure electrical resistance measurements on these samples in a diamond-anvil-cell apparatus. Surprisingly, the signature of possible superconducting transition with a maximum transition temperature (T c) of about 20 K under high pressures is observed, as evidenced by a clear drop of resistance and the suppression of resistance drops under magnetic fields. Although the resistance drop is sample-dependent and relatively small, it appears in all of our measured samples. We argue that the observed superconducting signal is most likely to originate from the main phase of La4Ni3O10. Our findings will motivate the exploration of superconductivity in a broader family of nickelates and shed light on the understanding of the underlying mechanisms of high-T c superconductivity in nickelates.

Detailed phase evolution analysis, electrical and ferroelectric properties of SrBi2Nb2O9–Bi4Ti3O12 intergrowth Aurivillius phase ceramics

A polycrystalline sample with 2–3 layered intergrowth SrBi2Nb2O9–Bi4Ti3O12 (SrBi6Nb2Ti3O21) ceramics was synthesized by solid-state reaction route using a two-step calcination process. The X-ray diffraction (XRD) analysis and structural refinement revealed pure SrBi6Nb2Ti3O21 phase formation that crystallized in an orthorhombic crystal structure with a ‘I2cm’ space group. The d-spacing values evaluated from HR-TEM were consistent with the standard XRD. Microstructural analysis using Scanning Electron Microscopy (SEM) justifies grain formation of average size ∼4.81 μm possessing plate-like morphology. The ε vs T curves showed two dielectric anomalies at ∼250 °C–350 °C and ∼600 °C–700 °C. The diffuse dielectric peaks depict the relaxor behavior of the ceramics. The conduction mechanism is found to follow the overlapping large polaron tunneling model (OLPT), which elucidates the temperature dependence of power-law exponent ‘s’ and ac conductivity. The relaxation mechanism follows the Maxwell-Wagner relaxation behavior. The ferroelectric hysteresis loop and Positive Up Negative Down (PUND) polarization test confirm the ferroelectric nature of SrBi6Nb2Ti3O21 intergrowth ceramics and the existence of a small value of intrinsic switchable polarization.

Zn-Zr induced structural and magnetic changes in strontium hexaferrite system

Polycrystalline samples of M-type Strontium hexaferrite having chemical composition SrZnxZrxFe12–2xO19 (with x = 0 and 1 and abbreviated as SFO and SZFO, respectively) were prepared successfully using solid state reaction route. The influence of calcination temperature (900 °C – 1300 °C) on the structural, microstructural, and magnetic properties of the SFO samples was explored. X-ray analysis reveals that the SFO sample is pure over the whole calcination range. The obtained X2 (goodness-of-fit; GoF) values are in the ≈ 1.02 - 1.16 range. At 1300 °C, the SFO sample develops preferred orientations along (006), (008) and (0014) crystallographic planes. The incorporation of preferred orientations leads to an improvement in the value of GoF from ≈ 4.72 to ≈ 1.16 (at 1200 °C). However, no preferred orientations are observed in the SZFO samples. Single phase Rietveld refinement is insufficient to explain the structural data. A four - phase and a three -phase refinement has been observed to be suitable in samples calcined at 1200 °C and 1300 °C, respectively. FESEM micrographs reveal a dramatic change in grain size and shape at 1300 °C in both types of samples. The best of magnetic properties has been observed at 1200 °C calcination in both types of samples. The best Mr, Ms and Hc values have been observed45.36, emu/g, 90.26 emu/g, 5032 Oe (in SFO sample) and 10.39 emu/g, 58.22 emu/g and 1181 Oe (in SZFO sample), respectively. The lower magnetic parameter values of SZFO samples can be attributed to magnetic dilution. Low temperature M-T measurements establishes the absence of magnetic nature of segregated phases in x = 1 sample.

Elucidating the Surface Properties of Sr3PbO Inverse‐Perovskite Topological Insulator: A First‐Principles Study

The emergence of robust surface electronic states in topological insulators such as bulk Sr3PbO inverse‐perovskite makes them suitable candidates for spintronic devices and solid‐state quantum computers. Herein, the atomic structure, surface energetics, and electronic properties of Sr3PbO inverse‐perovskite Sr2O (SO)‐terminated and SrPb‐terminated (001) surfaces are examined using density functional theory. A comparison of the computed structural properties of SO‐termianted and SrPb‐terminated (001) surfaces reveals maximum surface rumpling and changes in interlayer distances for the SrPb‐terminated surface of Sr3PbO. However, the calculated surface energies indicate that both SO‐termianted and SrPb‐terminated (001) surfaces of Sr3PbO are energetically feasible, indicating that these surfaces can coexist in a polycrystalline sample of this material. Due to the presence of Pb in Sr3PbO, a comprehensive examination of the electronic structure of bulk and supercell slab structures of Sr3PbO by taking spin–orbit coupling effects into consideration is conducted. Noninsulating nature of electronic structure for the two possible (001) terminations of Sr3PbO is found. The domination of Pb‐6p states at the Fermi energy and the hole screening observed at the SrPb‐terminated surface of Sr3PbO support the p‐type nature observed in the experiment.

Comparison of Laboratory Diffraction Contrast Tomography and Electron Backscatter Diffraction Results: Application to Naturally Occurring Chromites.

Understanding how minerals are spatially distributed within natural materials and their textures is indispensable to understanding the fundamental processes of how these materials form and how they will behave from a mining engineering perspective. In the past few years, laboratory diffraction contrast tomography (LabDCT) has emerged as a nondestructive technique for 3D mapping of crystallographic orientations in polycrystalline samples. In this study, we demonstrate the application of LabDCT on both chromite sand and a complex chromitite sample from the Merensky Reef (Bushveld Complex, South Africa). Both samples were scanned using LabDCT and Electron Backscatter Diffraction (EBSD), and the obtained results were rigorously evaluated using a comprehensive set of qualitative and quantitative characterization techniques. The quality of LabDCT results was accessed by using the "completeness" value, while the inaccuracies were thoroughly discussed, along with proposed potential solutions. The results indicate that the grain orientations obtained from LabDCT are comparable to that of 2D EBSD but have the advantage of collecting true 3D size, shape, and textural information. This study highlights the significant contribution of LabDCT in the understanding of complex rock materials from an earth science perspective, particularly in characterizing mineral texture and crystallography in 3D.

Спинтроника немагнитных хиральных сред на примере эффекта Зеебека

Spin transport in chiral materials is considered as the main direction for the spintronics development. Experimental work on the study of the spin Seebeck effect shows that in chiral materials it is possible to achieve effective generation of spin-polarized current at distances up to several millimeters. In the presented work, we develop a theoretical approach to describe the spin Seebeck effect based on the spin Hamiltonian for conduction electrons in a chiral medium. Taking into account this Hamiltonian, the equation of electron spin dynamics averaged over the polycrystalline sample is obtained. In the approximation of ideal Fermi-gas and local-quasi-equilibrium distribution, the spin density operator of conduction electrons is constructed. It is shown that averaging over randomly oriented crystallites does not destroy spin ordering at strong spin-orbit interaction, and the temperature gradient generates spin polarization directed predominantly along the temperature gradient. Spin polarization by the described in the paper mechanism does not require external magnetic fields and remanent magnetization and therefore does not interfere with the operation of micro- and nano-sized structures of spintronics. Since the spin Seebeck effect is reciprocal with the spin Peltier effect, the theoretical approach presented in this work can form the basis of new methods for controlling heat flow in spintronics systems.

2D Helium Atom Diffraction from a Microscopic Spot.

A method for measuring helium atom diffraction with micron-scale spatial resolution is demonstrated in a scanning helium microscope (SHeM) and applied to study a micron-scale spot on the (100) plane of a lithium fluoride (LiF) crystal. The positions of the observed diffraction peaks provide an accurate measurement of the local lattice spacing, while a combination of close-coupled scattering calculations and MonteCarlo ray-tracing simulations reproduce the main variations in diffracted intensity. Subsequently, the diffraction results are used to enhance image contrast by measuring at different points in reciprocal space. The results open up the possibility for using helium microdiffraction to characterize the morphology of delicate or electron-sensitive materials on small scales. These include many fundamentally and technologically important samples which cannot be studied in conventional atom scattering instruments, such as small grain size exfoliated 2D materials, polycrystalline samples, and other surfaces that do not exhibit long-range order.

High-pressure synthesis and magnetic properties of Gd2Rh3Al9 with a distorted honeycomb lattice

This study focuses on exploring new Gd-based intermetallic compounds with honeycomb structures to elucidate intriguing magnetic phenomena, particularly the presence of magnetic skyrmions. The compound Gd2Rh3Al9, synthesized via high-temperature and high-pressure methods, exhibits an orthorhombic structure characterized by a distorted Gd-honeycomb network. Comprehensive investigations of its temperature-dependent behavior in polycrystalline samples reveal sequential antiferromagnetic transitions occurring at T1 = 13.6 K and T2 = 4.1 K. These transitions arise from the antiferromagnetic interaction between the magnetic moments of Gd3+ (S = 7/2) situated within the distorted honeycomb layer. Despite not observing a skyrmion phase in this compound, the data provide valuable insights into the complex behavior of Gd-based intermetallic compounds and their potential as hosts for novel magnetic phases. Further research, particularly using single crystals, is needed to explore the possibility of forming a skyrmion phase in this compound.

Synthesis, Structure and Magnetic Properties of Some Copper(II) Complexes Supported by Pendant Calix[4]arene Ligands

AbstractThe synthesis and characterization of three new calix[4]arene ligands bearing two pendant acylhydrazone arms and some of their Cu2+ complexes, namely [Cu(L1‐2H)(MeOH)] (3), [Cu(L1’‐H)(Cl)(2‐hydroxy‐1‐naphthaldehyde)] (4), [Cu2(L2‐2H)2] (5) and [Cu4(L3‐2H)2(OH)2(ClO4)2] (6) are described. The ligands are obtained by simple imine condensation reactions between calix[4]arene‐1,3‐bis‐acyl‐hydrazides and the corresponding carbaldehydes. The Cu2+ ions are always situated in 5‐membered chelate rings, either in a deprotonated −O−CR=N−N=CHR (enolate) or a neutral O=CR−NH−N=CHR (keto) form. In 3 and 4 a 5‐membered chelate ring is formed through interaction of the Cu2+ ion with the naphtholato group. Additional MeOH, chlorido or naphthaldehyde ligands complete the planar (3) or square pyramidal (4) coordination spheres. The thiophenes in 5 do not interact with the Cu2+ ions and dimerization of [CuL] entities occurs to produce centrosymmetric 2 : 2 complexes with four‐coordinated Cu2+ ions. In 6, two dinuclear [Cu2(L3‐2H)(OH)] subunits are connected by μ1,3‐bridging ClO4− ions. The magnetic properties of polycrystalline samples of 5 and 6 were studied by variable temperature magnetic susceptibility measurements. The χ′′(T) vs T plots indicate antiferromagnetic exchange interactions. The exchange interactions in 6 (J=−4.8 cm−1) were found to be stronger than in 5 (J=−0.54 cm−1). This is also supported by broken symmetry DFT calculations.

Synthesis, crystal structure and optical properties of the first Hg-based polyselenide Ba2HgSe5

A new polyselenide, Ba2HgSe5 has been synthesized via conventional high-temperature solid state reaction. Single-crystal X-ray diffraction experiment reveals that the title compound crystallizes in the centrosymmetric space group Pnma of the orthorhombic system with a = 12.7123(7) Å, b = 8.9593(5) Å, c = 8.5470(5) Å and Z = 4. Its crystal structure consists of isolated dumbbell-shaped (HgSe2)2- and V-shaped Se32− ions. These molecular anions are charge-balanced by Ba2+. Diffuse reflectance spectrum demonstrates the semiconducting properties with a direct band gap of 1.75 eV. Electronic band structure calculation indicates that the band gap is defined by the 4p-orbitals of the selenium atoms of the Se32− groups. Moreover, the photocatalytic behavior of the polycrystalline sample was investigated by decomposing antibiotics tetracycline hydrochloride under visible right irradiation and the result indicates that the title compound displays moderate degradation rate of 60 % within 2 h. In addition, thermal analysis shows that Ba2HgSe5 has a good thermal stability up to 640 °C and exhibits incongruent melting behavior. These characteristics imply that Ba2HgSe5 may be a fascinating photoelectronic material and has potential applications in the future.

Suppression of ferromagnetism in La3CrAs5 via V substitution

In this work, we successfully synthesized a series of hexagonal La3Cr1-xVxAs5 (x = 0–0.8) polycrystalline samples under high-temperature and high-pressure conditions. A systematic study was carried out via the measurements of X-ray powder diffraction, temperature- and field-dependent magnetic susceptibility and magnetization. The X-ray diffraction data show that the lattice constant. a-parameter gradually increases, while c-parameter decreases with increasing V-doping level. In this series, the ferromagnetic behavior has been observed for x ≤ 0.3, and the Curie temperature TC decreases from 50 K for the parent compound to 20 K for x = 0.3, which indicates that the ferromagnetism is suppressed as the V-doped increases. For x = 0.4, the system begins to enter into a new magnetic state like spin glass at low temperature, and no magnetic order can be observed down to 2 K for x ≥ 0.8. In addition, the Weiss temperature Tϴ gradually decreases and changes to be negative for x = 0.6, which suggests that ferromagnetic interaction at first is weakened by the V substitution, and then transforms into anti-magnetic predominant interaction. The above results indicate that there is no quantum criticality occurred in the La3Cr1-xVxAs5 system.

Impact of hair-derived carbon substitution on structural and superconducting properties of MgB2

This study presents a comprehensive analysis of the effects resulting from the substitution of biowaste-derived carbon-dot (CD) from human hair on structural and superconducting properties of MgB2. Syntheses of polycrystalline samples were accomplished through a standard solid-state reaction route. X-ray powder diffraction results confirm the formation of MgB2 as a primary phase in all samples and show the successful substitution of carbon for boron in MgB2. The critical current density, determined at 20 K and 4.5 T, for carbon-substituted MgB2 synthesized at 850 °C was enhanced by more than four times compared with unsubstituted MgB2. The observed improvement is due to the formation of efficient pinning centers resulting from the incorporation of carbon substituting for boron in MgB2. Furthermore, x-ray photoelectron spectroscopy (XPS) confirmed the presence of carbon bonding to boron in MgB2 synthesized with biowaste-derived CDs, indicating successful incorporation into the structure. Ultraviolet photoelectron spectroscopy (UPS) results show that the carbon-substituted MgB2 can lead to changes in the electronic band structure and values of work function. These changes significantly impact the properties of MgB2 materials, including superconducting transition temperature, upper critical field, and critical current density. The XPS and UPS experimental results are in good agreement with density functional theory calculations for MgB2 with and without carbon substitution.

Dielectric, Magnetic and Surface Analytical Study of Dy and Tb Doped (Bi, Pb)(Fe,Ti)O3 Multiferroic Ceramics

Polycrystalline samples of Bi0.8A0.1Pb0.1Fe0.9Ti0.1O3(where A = Dy and Tb) ceramics have been prepared through high temperature sintering technique. X-ray diffraction analysis showed that the ceramics possess perovskite phase with hexagonal crystal symmetry. Dielectric and electrical properties indicate that the Curie temperature shifted to higher temperature with Dy doping. AC conductivity of the sample increases with increase in temperature which confirms the negative temperature coefficient of resistance (NTCR) behaviour of material. Substitution of Dy and Tb ions at A-site suppress the spiral spin structure of BiFeO3 which is further responsible for the appearance of weak ferromagnetism atroom-temperature.Induced destruction of the spin cycloid due to the Dy and Tb substitution, these multiferroic properties are attributed because of the enhanced magneto-electric interaction.

Temperature dependent structural properties of Mn1.90M0.10O3 (M = Cr and Fe)

The polycrystalline samples of Mn1.90Cr0.10O3 (MCO) and Mn1.90Fe0.10O3 (MFO) have been investigated for their temperature dependent magnetic and structural properties. The Cr and Fe substitutions have significant effect on the magnetic and structural properties of Mn2O3. Like pristine Mn2O3, the Cr and Fe substituted samples MCO and MFO also exhibit two antiferromagnetic transitions; one at ∼77 K, ∼80 K, respectively and another at ∼40 K. Our room temperature synchrotron x-ray powder diffraction (SXRD) results confirm that both the MCO and MFO samples crystallize in cubic symmetry. The temperature dependent SXRD results demonstrate the cubic to orthorhombic structural transition for the studied samples. The pristine Mn2O3 shows cubic to orthorhombic transition around 310 K, whereas this structural transition shifted towards lower temperature side with these substitutions i.e. around 240 K for MCO and 260 K for MFO. Interestingly, the centrosymmetric Pcab to non-centrosymmetric Pca21 change in symmetry is also resolved at the ferroelectric ordering temperature for MCO.

Structural, Optical, Relaxor and Transport Properties of a Nanocrystalline Double Perovskite: Ba2(FeMo)O6

The paper presents a synthesis (solid-state. reaction) and characterization of a lead-free double perovskite oxide Ba2(FeMo)O6 ceramic. The initial analysis using X-ray diffraction revealed that the material has a cubic crystal symmetry with a micro-lattice strain of 0.000824 and an average crystallite size of 62[Formula: see text]nm. The microstructural features and elemental composition of the prepared polycrystalline sample were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The SEM micrograph, EDX spectrum and elemental mapping show distinctly grown grains with well-defined grain boundaries, purity and distribution pattern of the grains, respectively. Raman scattering spectroscopy is a valuable tool for studying the vibrational modes to get information about structural and chemical properties of materials. The optical properties of the material were investigated using UV–Vis spectroscopy, which provides various parameters including energy bandgap for different technological applications. The electrical behavior of the synthesized double perovskite was examined through frequency- and temperature-dependent dielectric measurements as well as impedance spectroscopy. The electrical conduction in the material followed Jonscher’s power law and is supported by a thermally activated conduction mechanism. The analysis of electrical resistance versus temperature confirms negative temperature coefficient of resistance nature and can be used as NTC thermistors. The study of polarization-electric field loop opens up the possibility of the ferroelectric nature of the studied sample and also measures energy storage density, energy loss density and efficiency for searching different potential applications related to sensors. Overall, the results suggest its potential for various technological applications, such as in sensors and devices requiring specific electrical behavior or ferroelectric properties.