Refinement Parameters Research Articles

Optimizing high-pressure sliding process parameters for grain refinement and enhanced mechanical properties using response surface methodology approach

Lightweight technology has emerged as a crucial focus within transportation machinery manufacturing, driving the pursuit for materials with exceptional strength-to-weight ratios. To address this need, ultra-fine grain (< 500 nm) and nanostructured (< 100 nm) materials are being developed using severe plastic deformation (SPD) techniques, particularly in confined flat sheets. This study focuses on the Multi Pass Incremental Feed High-Pressure Sliding (MPIF-HPS) technique, which offers significant potential for industries such as aerospace and automotive by enhancing the mechanical properties of materials like AA 7075 alloy. This work investigates the development and characterization of ultrafine-grained materials through SPD, focusing on the correlation between ultrafine grain structures and their distinct properties. Utilizing MPIF-HPS processes and design of experiment (DoE) methodologies, the study evaluates the evolution of fine-grained microstructures and the enhancement of boundary characteristics with increasing strain in AA 7075 alloy. The grain size was refined from 600 µm to 6 µm, indicating significant microstructural improvement. Concurrently, mechanical properties were notably enhanced, with hardness increasing from 102 to 165 HV, yield strength from 250 to 605 MPa, and ultimate tensile strength (UTS) from 400 to 650 MPa. The study systematically optimized processing parameters, including pressure, sliding distance, and number of passes, to determine the ideal conditions for grain refinement and mechanical performance. These findings underscore the critical role of strain-induced boundary characteristics in determining the material's final properties, paving the way for tailored solutions to meet specific industrial requirements.

Contributon-Informed Approach to RPV Irradiation Study Using Hybrid Shielding Methodology

An important aspect of pressurized water reactor (PWR) lifetime monitoring is supporting radiation shielding analyses which can quantify various in-core and out-core effects induced in reactor materials by varying neutron–gamma fields. A good understanding of such a radiation environment during normal and accidental operating conditions is required by plant regulators to ensure proper shielding of equipment and working personnel. The complex design of a typical PWR is posing a deep penetration shielding problem for which an elaborate simulation model is needed, not only in geometrical aspects but also in efficient computational algorithms for solving particle transport. This paper presents such a hybrid shielding approach of FW-CADIS for characterization of the reactor pressure vessel (RPV) irradiation using SCALE6.2.4 code package. A fairly detailed Monte Carlo model (MC) of typical reactor internals was developed to capture all important streaming paths of fast neutrons which will backscatter the biological shield and thus enhance RPV irradiation through the cavity region. Several spatial differencing and angular segmentation options of the discrete ordinates SN flux solution were compared in connection to a SN mesh size and were inspected by VisIt code. To optimize MC neutron transport toward the upper RPV head, which is a particularly problematic region for particle transport, a deterministic solution of discrete ordinates in forward/adjoint mode was convoluted in a so-called contributon flux, which proved to be useful for subsequent SN mesh refinement and variance reduction (VR) parameters preparation. The pseudo-particle flux of contributons comes from spatial channel theory which can locate spatial regions important for contributing to a shielding response.

Smoothed Weighted Quantile Regression for Censored Data in Survival Analysis

In this study, we propose a smoothed weighted quantile regression (SWQR), which combines convolution smoothing with a weighted framework to address the limitations. By smoothing the non-differentiable quantile regression loss function, SWQR can improve computational efficiency and allow for more stable model estimation in complex datasets. We construct an efficient optimization process based on gradient-based algorithms by introducing weight refinement and iterative parameter estimation methods to minimize the smoothed weighted quantile regression loss function. In the simulation studies, we compare the proposed method with two existing methods, including martingale-based quantile regression (MartingaleQR) and weighted quantile regression (WeightedQR). The results emphasize the superior computational efficiency of SWQR, outperforming other methods, particularly WeightedQR, by requiring significantly less runtime, especially in settings with large sample sizes. Additionally, SWQR maintains robust performance, achieving competitive accuracy and handling the challenges of right censoring effectively, particularly at higher quantiles. We further illustrate the proposed method using a real dataset on primary biliary cirrhosis, where it exhibits stable coefficient estimates and robust performance across quantile levels with different censoring rates. These findings highlight the potential of SWQR as a flexible and robust method for analyzing censored data in survival analysis, particularly in scenarios where computational efficiency is a key concern.

Understanding the mechanism of bimodal texture evolution and DRX behavior of AZ31 magnesium alloy during shear deformation

Shear deformation in commercial magnesium alloys frequently resulted in an additional atypical texture where the basal plane aligned nearly parallel to the extrusion direction, affecting the alloy's mechanical anisotropy. This study prepared AZ31 magnesium alloys with both typical shear texture and atypical texture using a two-stage shear method at 250 °C, 290 °C, and 340 °C. The formation mechanism of the bimodal texture and their relationship with dynamic grain refinement and deformation parameters were comprehensively investigated. While temperature-dependent activation of <c+a> slip usually contributed to the atypical texture, this study identified a {101¯2} twin associated microstructure that reinforced the abnormal texture at lower processing temperature. It was found that the abundant nucleation of the multi-orientation {101¯2} twin bands in the initial stage and their differential slip activations facilitated the evolution of an alternating banded structures characterized by bimodal texture. These microstructures inherited the grain boundary rotation axis of {101¯2} twin and was potentially assimilated into specialized θ[112¯0] symmetric tilt grain boundaries with lower interface energy during continuous shear, stabilizing the bimodal texture. During shear deformation, grain nucleation strengthened the [101¯0]−[112¯0] fibers with bimodal texture by generating ∼30°[0001] grain boundaries through the preferential accumulation of prismatic dislocations. However, more continuous dynamic recrystallization, discontinuous dynamic recrystallization, and micro-shear bands facilitated the nucleation of grains with dispersed basal orientations via dominant non-prismatic dislocations, weakening the overall texture. Besides, the mechanical anisotropy of the alloys was comprehensively influenced by atypical texture and microstructure. At higher deformation temperatures, the reduction in twinning bands and the increase in dynamic recrystallization level relieved the alloy’s tension-compression asymmetry, but deprived its yield strength. This study supplemented the formation mechanisms of bimodal texture during shear deformation, providing valuable insights for optimizing wrought magnesium alloys with superior mechanical properties.

Resurgence of Refined Topological Strings and Dual Partition Functions

We study the resurgent structure of the refined topological string partition function on a non-compact Calabi-Yau threefold, at large orders in the string coupling constant $g_s$ and fixed refinement parameter $\mathsf{b}$. For $\mathsf{b}\neq 1$, the Borel transform admits two families of simple poles, corresponding to integral periods rescaled by $\mathsf{b}$ and $1/\mathsf{b}$. We show that the corresponding Stokes automorphism is expressed in terms of a generalization of the non-compact quantum dilogarithm, and we conjecture that the Stokes constants are determined by the refined Donaldson-Thomas invariants counting spin-$j$ BPS states. This jump in the refined topological string partition function is a special case (unit five-brane charge) of a more general transformation property of wave functions on quantum twisted tori introduced in earlier work by two of the authors. We show that this property follows from the transformation of a suitable refined dual partition function across BPS rays, defined by extending the Moyal star product to the realm of contact geometry.

Investigation of structural, electrical, and magnetic variations of Ni-Zn-Co ferrites by substituting rare earth Ho3+ for high-frequency applications

The investigation of structural, magnetic, and electrical properties of Ni0.6Zn0.3Co0.1HoxFe2−xO4 (NZCHF, 0 ≤ x ≤ 0.2) ferrites, synthesized through the sol–gel autocombustion method, has been undertaken. The refined x-ray diffraction (XRD) analysis was performed for XRD data analysis using Fullprof Suite software and it confirmed a single-phase cubic spinel structure, with the determination of crystallite size, refinement parameters and lattice constants. The bulk density of the samples consistently remained lower than the x-ray density, with densities increasing proportionally to the enhancement of Ho concentration. FTIR analysis corroborated the presence of metal-oxygen bonds within the ferrite possessing a spinel cubic structure. 57Fe Mossbauer spectroscopy showed that the hyperfine magnetic field of tetrahedral (A) and octahedral (B) sites decreased with the substitution of Ho3+ ions that preferentially occupy the B site. The impedance analyzer and vibrating sample magnetometer (VSM) were utilized to measure the real and imaginary parts of the complex permeability and magnetic properties of the samples, respectively. Complex impedance plots were scrutinized to discern the contributions of grain and grain boundary resistances, providing insights into the electrical behavior of the ferrite samples. Furthermore, the introduction of Ho concentration led to alterations in other key properties of the ferrites, including coercivity (H c ), retentivity (M r ), anisotropy constant (K), and magnetic moment (μ B ).The impact of the rare-earth content on the magnetic features of the prepared NiZnCo ferrite microspheres was investigated by analyzing magnetic-hysteresis (M-H) loops, which showed soft ferrimagnetism. Concurrently, the dielectric constant and dielectric loss tangent of the studied samples exhibited a decrease with the rise in Ho3+ concentration. The expected reduction in tan loss in the prepared samples is attributed to the increase in ac resistivity associated with the higher Ho3+ content.

Ostwald ripening of gas bubbles in porous media: Impact of pore geometry and spatial bubble distribution

We study pore-scale gas bubble ripening in porous media by combining a mass transfer method based on chemical potential differences with a level-set method for updating the gas/liquid configurations. We examine the impact of pore geometry and initial gas bubble distribution on the evolution, as well as the effect of mesh refinement and numerical parameters controlling the adaptive time steps in the model. Our results show that the pore geometry has a significant impact as it determines the rate of bubble pressure change with volume, while the area for mass transfer influences the time scale of the evolution. Simulations with different spatial patterns of bubbles with high and low pressures yield different ripening behaviors, classified as local and global ripening regimes. Simulations on sandstone with volumetrically similar bubble distributions display different ripening paths depending on the initial bubble locations, emphasizing the importance of capturing displacement history before ripening investigations.

Strategic design of a rare trigonal symmetric luminescent covalent organic framework by linker modification

We designed a trigonal symmetric imine-linked covalent organic framework (COF), TFPC-DAB, with control over the angularity of the building units, where a bent C2-symmetric diamine, such as 1,3-diaminobenzene (1,3-DAB or DAB), with an exo-angle of 120° was used instead of those with an exo-angle of 180°, in combination with a C3-symmetric trialdehyde, such as tri(4-formylphenoxy)cyanurate (TFPC). Its synthesis was accomplished by reacting the building units in a mixture of mesitylene/dioxane/6 M acetic acid under solvothermal conditions. The phase purity, thermal stability, and porosity of TFPC-DAB were established by various analytical techniques. Utilizing the Density Functional Tight Binding (DFTB+) simulation and Pawley refinement, the best fit of the small angle x-ray pattern was found to have an AA stacking of TFPC-DAB in the trigonal space group P3 with low refinement parameters. Such smart materials are in huge demand to detect hazardous corrosive chemicals, such as HCl and NH3. The dual features of electron deficient π-acidic triazine moiety and heteroatoms (N/O) from TFPC and electron rich phenyl units from DAB embodied in the framework enhance its luminescent property and thereby make it suitable for solvent-based HCl and NH3 sensing. The detection limits for HCl and NH3 in methanol were found to be 14 and 82 ppb, respectively. The effect of solvent polarity on the sensing studies was observed with much lower detection limits in dioxane: 2.5 and 11 ppb for HCl and NH3, respectively. A detailed theoretical calculation using density functional theory and configurational bias Monte Carlo modules was conducted for understanding interactions between the COF and HCl or NH3 analytes.

Accelerating Electrocatalyst Innovation: High-Throughput Automated Microkinetic Modeling

To reduce energy-related emissions, we must create chemicals from carbon dioxide with renewable energy, instead of from petroleum. Designing such a process needs computer models that can describe all the chemical reactions that are happening, including those driven by electrochemistry. There may be thousands of such reactions, so we must build a tool to find them automatically. Our reaction mechanism generator for electrocatalysis will create detailed kinetic models for many electrochemical processes, but for this initial project we are targeting the reduction of carbon dioxide to produce propanol, a useful hydrocarbon product. The kinetic models will be used to simulate an electrochemical reactor, then analyzed both technically and economically to determine which catalyst materials and reactor designs are best. This will allow new catalyst materials to be discovered using powerful computers, instead of using very time-consuming and expensive experiments.Building on the state-of-the-art open-source Reaction Mechanism Generator (RMG) software [1,2], we are creating the first automated mechanism generator for electrochemical reactions on a catalyst. Supplied with a feedstock, catalyst, and conditions, it will propose a detailed kinetic model comprising hundreds of intermediate species and reactions. Reactor simulations will predict product yields as a function of feed, concentrations, and potential, allowing conditions to be optimized and the trade-off between conversion and selectivity to be investigated. In turn this could inform a detailed technoeconomic analysis, enabling catalyst materials to be screened in silico on an economic basis. Meanwhile sensitivity analysis of the simulations will select estimated parameters for refinement with DFT calculations.We must first extend RMG to allow charged species, and implement proton coupled electron transfer (PCET) reactions. We will at first use the computational hydrogen electrode model to determine the Gibbs energy of a species (and hence reaction) as a function of chemical potential. Potential-dependent kinetics will be estimated using a charge transfer coefficient model. In preliminary work with a framework like this we have constructed a reaction mechanism for carbon dioxide reduction on Cu(111) with 37 species and 292 reactions (23 of them electrochemical) [3]. The model discovered many key electrochemical pathways to reduce CO2 to experimentally observed products such as methane, methanol, formic acid, ethylene, and ethanol. Acknowledgements The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0001786. The authors thank Dr. David Farina Jr. for his significant contributions to the proof-of-concept.

Optimizing process parameters for hot forging of Ti-6242 alloy: A machine learning and FEM simulation approach

In this study, we investigated the hot deformation behavior of Ti–6Al–2Sn–4Zr–2Mo (Ti-6242) alloy and propose a method to derive optimal hot process parameters for grain refinement and avoidance of flow instability. Microstructural Risk Index (MRI) was introduced as a microstructural evaluation index consisting of grain size, standard deviation of grain size, and flow instability. The initial temperature of the material and the stroke speed of the die were selected as design variables. Finite element analysis (FEA) was used to calculate grain size and flow instability and determine MRI of the forgings. The grain size model coefficient and flow instability were calculated based on the flow stress curve and verified with optical microscope (OM) and electron backscatter diffraction (EBSD) analysis results. The Deep Neural Network (DNN) model was used to determine the optimal process parameters for the forging process. The MRI prediction accuracy of the trained DNN models showed excellent performance at 97.01 %. The MRI of the optimized process variables was improved by 7.95 % compared to the minimum MRI of the training data set. Optimized process parameters can improve the quality of forgings through grain refinement and avoidance of flow instability regions.

Site-occupancy factors in the Debye scattering equation. A theoretical discussion on significance and correctness.

The Debye scattering equation (DSE) [Debye (1915). Ann. Phys. 351, 809-823] is widely used for analyzing total scattering data of nanocrystalline materials in reciprocal space. In its modified form (MDSE) [Cervellino et al. (2010). J. Appl. Cryst. 43, 1543-1547], it includes contributions from uncorrelated thermal agitation terms and, for defective crystalline nanoparticles (NPs), average site-occupancy factors (s.o.f.'s). The s.o.f.'s were introduced heuristically and no theoretical demonstration was provided. This paper presents in detail such a demonstration, corrects a glitch present in the original MDSE, and discusses the s.o.f.'s physical significance. Three new MDSE expressions are given that refer to distinct defective NP ensembles characterized by: (i) vacant sites with uncorrelated constant site-occupancy probability; (ii) vacant sites with a fixed number of randomly distributed atoms; (iii) self-excluding (disordered) positional sites. For all these cases, beneficial aspects and shortcomings of introducing s.o.f.'s as free refinable parameters are demonstrated. The theoretical analysis is supported by numerical simulations performed by comparing the corrected MDSE profiles and the ones based on atomistic modeling of a large number of NPs, satisfying the structural conditions described in (i)-(iii).

Doping-induced structural and optical modifications in γ-CuI nanocrystals

This study investigates the structural and optical properties of doped CuI nanocrystals synthesized using a facile chemical method. Cadmium (Cd) and iron (Fe) were used as dopants, resulting in CuI–Cd and CuI–Fe samples. X-ray diffraction (XRD) was employed to characterize the crystal structure and phase purity. Rietveld refinement of the XRD data provided significant refinement parameters. The Williamson-Hall and Size-strain methods were applied for further analysis, yielding consistent size and strain values. X-ray photoelectron spectroscopy (XPS) was utilized to investigate the electronic states and dopant incorporation in CuI nanocrystals. The undoped and doped CuI samples exhibited distinctive morphologies, with pure CuI displaying an irregular shape, CuI–Cd showcasing a hexagonal morphology, and CuI–Fe featuring a triangular morphology. The average crystallite sizes of the nanocrystals were determined to be 96.67 nm, 70.57 nm, and 54.10 nm for pure CuI, CuI–Cd, and CuI–Fe, respectively. Energy-dispersive X-ray (EDX) analysis confirmed the presence of Cd and Fe in the doped samples. Optical bandgap energies estimated using Tauc's plot were 4.1 eV (CuI), 4.0 eV (CuI–Cd), and 4.0 eV (CuI–Fe).

Erbium substituted baddeleyites (ErxZr(1-x)O2): Structural, ferroelectric, magnetic and electrochemical analysis for supercapacitors electrodes using walnut shells charcoal

The fabrication of ErxZr(1-x)O2 (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) is carried out with solid-state method at 1200 °C temperature for 4-hrs to get the desired monoclinic structure. The structural, ferroelectric magnetic and electrochemical properties are investigated with X-ray diffractometer, ferroelectric, magnetic, cyclic voltametric, charging/discharging and electrochemical impedance respectively. The XRD and refinement parameters shows the formation of monoclinic symmetry. The low value of R-factors ensures the structural stability. The vista and diamond software are used to determine the different physical properties. The characteristic band at 665 and 721 cm−1 confirms the monoclinic identity of ZrO2 with ATR-FTIR. The SEM graphs show that the average particle size is present in 127-122 nm range. The decreased particle size is associated with the enhanced Csp due to the incease of surface-to-volume ratio. The ferroelectric analysis revealed the centrosymmetric alignment of tetrahedron sites having the 4-faces, 6 edges and 4-vertices. The magnetic analysis exposed the soft-diamagnetic feature. The high value of coercivity (Hc < Mr/2) gives the direction towards energy storage application. The CV graphs gives the good 389.8 F/g Csp which correlated with the GCD and EIS data. The highest 396.1 F/g Csp is measured using the charge/discharge curve and 309.75 F/g is calculated using the frequency-dependent EIS spectra. These high aggregates of specific capacitance values make them eligible for supercapacitors application.

Rietveld refinement and structural characterization of Mn0.5Zn0.5La0.09Fe1.91O4 nanocomposite

Mn0.5Zn0.5La0.09Fe1.91O4 composite has synthesized by adopting the solid-state reaction method. Chemicals like MnO2, ZnO, Fe2O3 and La2O3 were used for preparation of the powder sample of Mn0.5Zn0.5La0.09Fe1.91O4. As prepared composites were subjected to sintering for 5hrs at the temperature of 850 °C. The obtained sample was structurally characterized using XRD. The crystallite size was calculated using Debye Scherrer formula which came out to be 51.14 nm, 95.21 nm, 52.48 nm for phase A, B and C respectively. Further refinement of the XRD data was performed using Rietveld refinement method by using FullProf Suit. The refinement of XRD data for synthesized sample confirms the presence of three phases: phase A – periclase (Fe0.037Mg0.0963O) 1.7%, phase B – lanthanum (La) 0.3%, phase C – hetaerolite (Mn2O4Zn) 97.9%. The results obtained from XRD suggests that the nanoparticles in phase A are cubic in shape and the no. of space group is obtained as 225 with Laue class and point group m-3m. The Hermann-Mauguin symbol is Fm-3 m. The nanoparticles in phase B are found to be hexagonal in shape with the no. of space group is obtained as 194 with Laue class and point group 6/mmm. The Hermann-Mauguin symbol for phase B is P63/mmc. The XRD studies for phase C showed that it has tetragonal structure. From the Rietveld refinement, the no. of space group is obtained as 141 with Laue class and point group 4/mmm. The Hermann-Mauguin symbol is I 41/amd:1. In this paper the Rietveld refinement parameters like the goodness factor, Bragg R value, Rexp are also given.

A robust Freeman-Hill-inspired pulse protocol for ringdown-free T1 relaxation measurements

A new difference-spectroscopy method is introduced for measuring T1 relaxation times. It is inspired by the earlier work of Freeman and Hill and eliminates the need for recording signal intensities at thermodynamic equilibrium. The new method is termed SIP-R (Split-Inversion Pulse and Recovery) and reduces the number of refinable parameters in the curve fitting process of relaxation-delay-dependent signal intensities by using two instead of the three parameters typically used in the standard inversion-recovery sequence. The SIP-R method preserves the dynamic range of measurement of the standard inversion-recovery method but converts the rise-to-maximum mathematical functionality of the recorded data into a decay-to-zero functionality. The decay-to-zero functionality renders the SIP-R sequence advantageous for inverse Laplace transformation numerical optimizations. The new technique proves to be extremely robust with respect to pulse imperfections, pulse-power changes during the pulse sequence, pulse-width miscalibrations, resonance offsets, and radiofrequency field variations. It also compensates for acoustic ring-down effects and proves reliable for measurements with inhomogeneously broadened signals up to several kilohertz linewidth. 1H NMR experiments with methane gas at pressures up to 50 atm in toroid-cavity pressure vessel probes and in the presence of the methane-to-methanol conversion catalyst Cu-ZnO/Al2O3 are used to show the usefulness of the new method for relaxation time investigations under pressure, at strong radiofrequency field gradients, and in the presence of paramagnetic materials.

Lead free high Tc piezoelectric Sr2Nb2O7-La2Ti2O7 solid solution: A structural, dielectric ferroelectric and piezoelectric studies

The ferroelectric and piezoelectric properties of Sr2Nb2O7–La2Ti2O7 (SNB-LT) solid solution ceramics have been studied. The La and Ti ions were substituted into the Sr2Nb2O7 (SNB) lattice and their resultant phase of SNB-LT has lattice distortion. The Rietveld refinement parameters from the XRD patterns corroborate a solid solution of Sr2Nb2O7–La2Ti2O7. The addition of La3+ and Ti4+ dampens the SNB intra-structural phase. Raman spectroscopy confirmed the internal lattice relaxation due to the Ti(Nb)O6 octahedron in the lattice. At 2×106 Hz, the dielectric permittivity of SNB-LT-1, SNB-LT-2, and SNB-LT-3 is 17.2, 17.5, and 21.3, respectively, with σac conductivity in the order of 10−5 S/m. With an increase in Ti(Nb)O6 distortion, the piezoelectric coefficient of SNB-LT-1, SNB-LT-2, and SNB-LT-3 increases linearly as 6.3, 8.1, and 9.3 pC/N. The temperature-dependent ferroelectric polarization of SNB-LT-1, SNB-LT-2, and SNB-LT-3 has been tested, and a substantial rise in polarization has been demonstrated up to 120 °C. At 120 °C, the SNBLT solid solution showed a two-fold increase in remnant polarization.

High entropy effect on double exchange interaction and charge ordering in half doped Nd0.5Sr0.5MnO3 manganite

The entropy stabilized oxides i.e., the so-called high-entropy oxides are of great interest in recent time due to their intriguing physical properties. This new category of advanced materials is stabilized by the high configurational entropy of randomly mixed elements, where a specific lattice site is populated by five or more elements. The present study is devoted to explore the high entropy effect in well-known charge ordered manganite Nd0.5Sr0.5MnO3 where a delicate balance exists between the ferromagnetic double exchange and the antiferromagnetic superexchange interactions. Powder X-ray diffraction analyses confirm phase purity of the samples. FE-SEM imaging revealed the microstructure and elemental mapping confirmed the chemical homogeneity of the samples as well as nominal cationic composition. Bond valence sum (BVS) calculation using refinement parameters supports the expected cationic valence in all the samples. Replacement of Nd3+ by five trivalent cations as in (La0.1Pr0.1Nd0.1Gd0.1Bi0.1)Sr0.5MnO3 with larger average A-site ionic radius,<rA>and smaller size variance, σ2 compared with Nd0.5Sr0.5MnO3 dramatically suppressed the ferromagnetic double exchange interaction. This observation is in contrast with the expected variation in<rA>and σ2. In (La0.1Nd0.1Gd0.1Bi0.1Y0.1)Sr0.5MnO3 with smaller<rA> and marginally higher σ2 the ferromagnetic state ceases to exist. In both the multicationic compositions, a long-range antiferromagnetic state is evolved around 200 K with the retention of charge ordering. In the high entropy (La1/6Nd1/6Dy1/6Ca1/6Ba1/6Sr1/6)MnO3 composition with nominal<rA> and larger σ2 values the high temperature long-range ordering is completely suppressed and a new antiferromagnetic state is evolved at 45 K without manifestation of any charge ordering. This composition also avoids magnetic frustration unlike the dopant variant with larger σ2. The present investigation thus highlights the role of local lattice distortion or high entropy effect apart from the<rA>and σ2 in manganites.

Synthesis, Crystal Structure, and Electrical and Magnetic Characterizations of the Monoclinic Compounds Ln3Mo4+xSi1–xO14 (Ln = La, Ce, Pr, and Nd; x = 0 and 0.35) Containing Mo3 Clusters and Mo2 Dimers

Powder samples of the new monoclinic compounds Ln3Mo4SiO14 (Ln = La, Ce, Pr, and Nd) and single crystals of Pr3Mo4.35Si0.65O14 were obtained by the solid-state reaction. The crystal structure of Pr3Mo4.35Si0.65O14 was determined by single-crystal X-ray diffraction. Pr3Mo4.35Si0.65O14 crystallizes in the monoclinic space group P21/n with unit-cell parameters a = 5.6361 (2) Å, b = 17.5814 (8) Å, c = 10.9883 (4) Å, and Z = 4. Full-matrix least-squares refinement on F2 using 7544 independent reflections for 203 refinable parameters results in R1 = 0.0359 and wR2 = 0.0831. The structure contains chains of Mo3O13 clusters and chains of edge-sharing MoO6 octahedra with alternately short (2.508 Å) and long (3.161 Å) Mo-Mo distances running parallel to the a axis that are separated by 8- or 10-coordinate Pr-O polyhedra. Magnetic susceptibility measurements on the Ln3Mo4SiO14 (Ln = La, Ce, Pr, and Nd) are in agreement with a trivalent state of the rare earths for the Ce, Pr, and Nd compounds, while that on the lanthanum compound confirms the presence of one unpaired electron per Mo3 as expected. Resistivity measurements on a single crystal show that Pr3Mo4.35Si0.65O14 is a small band gap semi-conductor.

Investigation on structural, magnetic and optical properties of Sm–Co Co-substituted BiFeO3 samples

Abstract Sol–gel derived Sm–Co co-substituted BiFeO3 ceramics (Bi1–x SmFe1–x Co x O3 with x = 0.0, 0.01, 0.02 and 0.03; named as BFO, BSFCO-1, BSFCO-2 and BSFCO-3, respectively) were investigated for structural, vibrational, magnetic and optical properties. Distorted perovskite rhombohedral structure with R3c crystal symmetry has been established in X-ray diffraction (XRD) patterns analysis by Rietveld refinement and detailed structural parameters like lattice constants, unit cell volume, bond angles, bond length etc. have been evaluated. Raman spectra further confirmed typical rhombohedral structure of BiFeO3 by exhibiting 13 clear Raman active phonon (9E + 4A) modes along with second order modes in the wave number range 50–1500 cm−1. Fourier Transform Infrared (FTIR) spectra showed the presence of Fe–O and Bi–O bands and the calculated Fe–O bond length was in good agreement with that obtained from Rietveld analysis. Room temperature magnetization versus magnetic field (M–H) measurement using Vibrating Sample Magnetometer (VSM) showed enhancement of ferromagnetic ordering parameters with increasing Sm–Co content in BiFeO3 samples. The maximum magnetization values increased from 0.237 emu g−1 for BFO sample to 1.167 emu g−1 for BSFCO-3 sample along with increase in remnant magnetization values. The optical property of Bi1–x SmFe1–x Co x O3 samples was investigated by estimating the energy band gap using UV–Visible spectroscopy. The calculated values of energy band gap were varied in the range 2.46 eV–1.81 eV indicating tuning of energy band gap with Sm–Co co-substitution in BiFeO3 sample.

Structural, dielectric, magnetic and magnetoelectric studies of (1-x) BaFe12O19-x BiFeO3 composites

The synthesis of multiferroic (1-x) BaFe12O19-x BiFeO3; (x = 0.05, 0.08, 0.10) composites was carried out with solid state reaction. The XRD data confirmed the formation of the composites with phases of both compounds. The low values of Rietveld refinement parameters along with modified lattice parameters of both hexaferrite and multiferroic phase reconfirmed the amalgamation of phases. FESEM with EDX were utilized for morphological study and elemental compositional analysis in the composites. The dielectric constant and tanδ both parameters showed typical low frequency dispersion. A mild anomaly in dielectric constant and tangent loss is quite noticeable near to magnetic transition temperature (TN) of BiFeO3 suggests the possible occurrence of magnetoelectric effect in prepared composite system. The fitting of AC conductivity data suggested the OLPT (overlapping large polaron tunneling) conduction process in the composite system. The saturation magnetization (Ms) showed a decreasing trend with increment of BiFeO3 content in composites owing to substituted Fe3+ ion in spin-up state. Coercivity (Hc) found in good agreement with magnetocrystalline anisotropy of hexaferrite phase. The improvements in magnetoelectric coupling coefficient of barium hexaferrite were clearly noticeable with the introduction of BiFeO3 phase owing to piezoelectric coefficient and magnetostriction of ferroelectric and ferrite phases respectively.