A necessary criterion for obtaining accurate lattice parameters by Rietveld method

Synthesis of Petitjeanite Bi3O(OH)(PO4)2 Photocatalytic Microparticles: Effect of Synthetic Conditions on the Crystal Structure and Activity toward Degradation of Aqueous Perfluorooctanoic Acid (PFOA)

The discovery of synthetic Bi₃O(OH)(PO₄)₂ [BOHP] and its application toward photocatalytic oxidation of the water contaminant perfluorooctanoic acid (PFOA) have prompted further interest in development. Despite its high activity toward PFOA degradation, the scarce appearance in the literature and lack of research have left a knowledge gap in the understanding of BOHP synthesis, formation, and photocatalytic activity. Herein, we explore the crystallization of BOHP microparticles via hydrothermal syntheses, focusing on the influence of ions and organics present in the reaction solution when using different hydroxide amendments (NaOH, NH₄OH, NMe₄OH, and NEt₄OH). To better understand the unique structure-activity aspects of BOHP, the related bismuth oxy phosphate (BOP) structural family was also explored, including A-BOP (A = Na⁺ and K⁺) and M-BOP derivatives (M = Ca²⁺, Sr²⁺, and Pb²⁺). Results from materials characterization, including X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, indicated that the crystal structure, morphology, and atomic composition were significantly influenced by solution pH, inorganic metal cations (Na⁺, K⁺, Ca²⁺, Sr²⁺, and Pb²⁺), and organic amines. Experiments involving ultraviolet photocatalytic destruction of PFOA by a BOHP suspension revealed that catalytic activity was influenced by the choice of reagents and their variable effect on surface facet growth and crystal defects in the resulting microparticles. Together, this work provides a strategy for crystal facet and surface defect engineering with the potential to expand to other metal oxides within the hydrothermal system.

Specimen-displacement correction for powder X-ray diffraction in Debye-Scherrer geometry with a flat area detector

The effect of small changes in the speci-men-to-detector distance on the unit-cell parameters is examined for synchrotron powder diffraction in Debye-Scherrer (transmission) geometry with a flat area detector. An analytical correction equation is proposed to fix the shift in 2θ values due to speci-men capillary displacement. This equation does not require the use of an internal reference material, is applied during the Rietveld refinement step, and is analogous to the speci-men-displacement correction equations for Bragg-Brentano and curved-detector Debye-Scherrer geometry experiments, but has a different functional form. The 2θ correction equation is compared with another speci-men-displacement correction based on the use of an internal reference material in which new integration and calibration parameters of area-detector images are determined. Example data sets showing the effect of a 3.3 mm speci-men displacement on the unit-cell parameters for 25°C CeO₂, including both types of displacement correction, are described. These experiments were performed at powder X-ray diffraction beamlines at the National Synchrotron Light Source II at Brookhaven National Laboratory and the Advanced Photon Source at Argonne National Laboratory.

Hydrothermal Synthesis of Zinc Oxide Nanoparticles Using Different Chemical Reaction Stimulation Methods and Their Influence on Process Kinetics

The aim of this work was to study the effect of the applied chemical reaction stimulation method on the morphology and structural properties of zinc oxide nanoparticles (ZnONPs). Various methods of chemical reaction induction were applied, including microwave, high potential, conventional resistance heater and autoclave-based methods. A novel, high potential-based ZnONPs synthesis method is herein proposed. Structural properties-phase purity, grain size-were examined with XRD methods, the specific surface area was determined using BET techniques and the morphology was examined using SEM. Based on the results, the microwave and autoclave syntheses allowed us to obtain the desired phase within a short period of time. The impulse-induced method is a promising alternative since it offers a non-equilibrium course of the synthesis process in an highly energy-efficient manner.

Sol-Gel Synthesis and Characterization of the Cu-Mg-O System for Chemical Looping Application

A sol-gel technique was applied to prepare the two-component oxide system Cu-Mg-O, where MgO plays the role of oxide matrix, and CuO is an active chemical looping component. The prepared samples were characterized by scanning electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction analysis. The reduction behavior of the Cu-Mg-O system was examined in nine consecutive reduction/oxidation cycles. The presence of the MgO matrix was shown to affect the ability of CuO towards reduction and re-oxidation significantly. During the first reduction/oxidation cycle, the main characteristics of the oxide system (particle size, crystallization degree, etc.) undergo noticeable changes. Starting from the third cycle, the system exhibits a stable operation, providing the uptake of similar hydrogen amounts within the same temperature range. Based on the obtained results, the two-component Cu-Mg-O system can be considered as a prospective chemical looping agent.

Structural, diffuse reflectance and luminescence study of t-Mg2B2O5 nanostructures

We report here the structural, reflectance, photoluminescence and thermoluminescence study of t-Mg₂B₂O₅ nanostructures synthesized using optimized combustion method relatively at much lower temperature. The rietveld refinement of X-ray diffraction data confirms single-phase triclinic crystal structure of Mg₂B₂O₅ nanoparticles. The direct band gap determined using diffuse reflectance spectra (DRS) was 5.23 eV, which is contrary to earlier reports quoting Mg₂B₂O₅ as indirect band gap material. To elucidate the nature of band gap in Mg₂B₂O₅, we performed first principle calculations based on full potential linearized augmented plane-wave (FPLAPW) method, predicting the direct band gap of 5.10 eV in t-Mg₂B₂O₅ which is in good agreement with our experimental results. The t-Mg₂B₂O₅ nanoparticles were found to exhibit yellow-reddish photoluminescence peaking at 588 nm, attributed to various defects states. The combustion synthesized Mg₂B₂O₅ nanocrystals exhibited ultraviolet (254 nm) responsive thermoluminescence (TL). TL glow curve of Mg₂B₂O₅ comprises of one dominant peak around 417-428 K and less intense shoulder around 573-589 K which arouse possibility of various trapping sites or defects present in the sample. The TL analysis using general order Kitti's equations was performed to estimate the activation energies of trapping states. Owing to already well-known mechanical and thermal properties, the direct wide band gap nature and UV responsive thermoluminescence of combustion synthesized t-Mg₂B₂O₅ nanostructures can pave way for its use in luminescence-based applications and UV dosimetry. As an additional application of Mg₂B₂O₅, anti-biofilms activity of Mg₂B₂O₅ nanoparticles using pseudomonas aeruginosa bacterial cells was also performed which revealed 91 ± 2.7% inhibition of biofilms formed by P. aeruginosa, respectively, at 100 μg/ml after 24 h of treatment.

Cutting Edge of High-Entropy Alloy Superconductors from the Perspective of Materials Research

High-entropy alloys (HEAs) are a new class of materials which are being energetically studied around the world. HEAs are characterized by a multicomponent alloy in which five or more elements randomly occupy a crystallographic site. The conventional HEA concept has developed into simple crystal structures such as face-centered-cubic (fcc), body-centered-cubic (bcc) and hexagonal-closed packing (hcp) structures. The highly atomic-disordered state produces many superior mechanical or thermal properties. Superconductivity has been one of the topics of focus in the field of HEAs since the discovery of the bcc HEA superconductor in 2014. A characteristic of superconductivity is robustness against atomic disorder or extremely high pressure. The materials research on HEA superconductors has just begun, and there are open possibilities for unexpectedly finding new phenomena. The present review updates the research status of HEA superconductors. We survey bcc and hcp HEA superconductors and discuss the simple material design. The concept of HEA is extended to materials possessing multiple crystallographic sites; thus, we also introduce multisite HEA superconductors with the CsCl-type, α-Mn-type, A15, NaCl-type, σ-phase and layered structures and discuss the materials research on multisite HEA superconductors. Finally, we present the new perspectives of eutectic HEA superconductors and gum metal HEA superconductors.

Multi-Technique Characterization of a Fine Fraction of CDW and Assessment of Reactivity in a CDW/Lime System

This study analysed the fine particle (<5 mm) waste generated during siliceous or calcareous (depending on the composition of the original aggregate) concrete waste crushing. In the absence of industrial applications, such waste is amassed in open-air stockpiles on construction and demolition wastes (CDW) management plant grounds. The aim pursued was to find an outlet for that material in the cement industry. The starting waste, sourced from six Spanish management facilities, was characterised for its chemical and mineralogical composition, physical properties and pozzolanicity. The mineralogical phases in the CDW/lime system and their variations during the pozzolanic reaction were likewise identified. The findings showed that the fine waste consisted primarily in quartz, calcite, micas and feldspars, with smaller fractions of kaolinite and cement anhydrous phases. No portland cement hydration phases were identified. All six types analysed exhibited medium to low pozzolanicity, with the highest values recorded for the siliceous waste. Ettringite, C–S–H gels and calcium aluminate hydrates (C4AH13, C4AcH12) were identified during the pozzolanic reaction in CDW/lime system. Therefore, this type of waste can be reused as supplementary cementitious material with low-medium pozzolanic activity.

The Impact of the Composition Effect on Ferromagnetic Properties of Tb2Co2Ga

The ferromagnetic properties of Tb2Co2Ga, crystallizing into an orthorhombic W2CoB2-type structure, were investigated by preparing 11 polycrystalline samples with different starting atomic compositions. We found that Tb2Co2Ga possesses a homogeneity range in the ternary phase diagram. The Curie temperature TC is sensitive to the atomic composition and ranges rather widely, i.e., from 75 to 145 K. For the samples with a TC above 90 K, the nearest Tb–Tb and the Tb–Co distances would be important factors deciding TC, considering the RKKY interaction through the hybridization between Tb and Co atoms. An anisotropic change of two kinds of Co–Tb–Co angles in the octahedron formed by two Tb and four Co atoms occurs in the samples with a TC lower than 90 K. Such a change of octahedral parameters seems to be related to a difference of shapes in the ac magnetization anomaly at TC between the samples in the lowest TC (~ 75 K) group and those in the other groups.

The influence of X-ray diffraction pattern angular range on Rietveld refinement results used for quantitative analysis, crystallite size calculation and unit-cell parameter refinement

This article reports a detailed examination of the effect of the magnitude of the angular range of an X-ray diffraction (XRD) pattern on the Rietveld refinement results used in quantitative phase analysis and quality assurance/quality control applications. XRD patterns from 14 different samples (artificial mixtures, and inorganic and organic materials with nano- and submicrometre crystallite sizes) were recorded in 2θ interval from 5–10 to 120°. All XRD patterns were processed using Rietveld refinement. The magnitude of the workable angular range was gradually increased, and thereby the number of peaks used in Rietveld refinement was also increased, step by step. Three XRD patterns simulated using CIFs were processed in the same way. Analysis of the results obtained indicated that the magnitude of the angular range chosen for Rietveld refinement does not significantly affect the calculated values of unit-cell parameters, crystallite sizes and percentage of phases. The values of unit-cell parameters obtained for different angular ranges diverge by 10−4 Å (rarely by 10−3 Å), that is about 10−2% in relative numbers. The average difference between the calculated and actual phase percentage in artificial mixtures was 1.2%. The maximal difference for the crystallite size did not exceed 0.47, 5.2 and 7.7 nm at crystallite sizes lower than 20, 50 and 120 nm, respectively. It has been established that these differences are statistically insignificant.