Rietveld Structure Refinement Research Articles

Structural analysis and Rietveld refinement of YCr1-xFexO3 (x=0, 0.5) perovskite samples calcined at two different temperatures

In the present work, we have synthesized polycrystalline YCr1-xFexO3 (x = 0, 0.5) perovskite samples using the traditional high-temperature solid-state reaction route (HT-SSRR) at two different temperatures for calcination (1000 °C as well as 1150 °C). The main objective of our investigation is to observe how these calcination temperatures impact the structural properties of the polycrystalline YCr1-xFexO3 (x = 0, 0.5) perovskite samples and reveal the comparative difference based on structural analysis and Rietveld refinement. The powder XRD analysis confirmed the presence of secondary phases, including Y2O3, Cr2O3, and Fe2O3, in the synthesized samples at both calcination temperatures. Notably, a higher calcination temperature (1150 °C) led to a reduction in the secondary phases and an increase in the crystalline size as determined by the Debye-Scherrer method (DSM). The FullProf software suite was used for performing a Rietveld refinement of the powder X-ray diffraction (PXRD) data. These findings suggest the crucial role of calcination temperature in tailoring the phase purity and crystallinity of YCr1-xFexO3 (x = 0, 0.5) perovskites.

Effect of cobalt and aluminum doping on the structural and magnetic properties of zinc oxide nanoparticles

A systematic study of the substitution effect of Co and Al on ZnO nanoparticles was carried out by x-ray diffraction (XRD) and transmission electron microscopy and using a superconducting quantum interference device magnetometer to study their structural, morphological, and magnetic properties. Zn1−xMxO (M = Co, Al) at different doping concentrations was prepared using a hydrothermal technique. The XRD results with structural Rietveld refinement reveal that the major phase of all samples had a hexagonal wurtzite crystal structure with a P63mc space group. Hysteresis loops with no magnetic saturation at high fields were analyzed at 2 K in all samples. Zero magnetic remanence and zero coercivity were also examined. The results demonstrated that the magnetic ground state at 2 K in all samples was magnetism with the coexistence of antiferromagnetic, ferromagnetic, and superparamagnetic phases. This behavior persisted at 100 and 300 K in the Al-doped sample, while Co-doped ones exhibited a paramagnetic state only. The role of non-magnetic doping, which leads to the appearance of magnetism in ZnO nanoparticles persisting at high temperatures, is discussed herein.

Synthesis and Crystal Structures of Two Crystalline Silicic Acids: Hydrated H-Apophyllite, H16Si16O40 • 8–10 H2O and H-Carletonite, H32Si64O144

Hydrated H-Apophyllite (HH-Apo) and H-carletonite (H-Car) were synthesized at 0 °C by leaching an apophyllite and a carletonite single crystal in a large surplus of 1.2 molar hydrochloric acid. The XRD powder patterns of HH-Apo and H-Car were indexed with space group symmetries of P4/ncc and I4/mcm and lattice parameters of a = 8.4872(2) Å, c = 16.8684(8) Å and a = 13.8972(3) Å, c = 20.4677(21) Å, respectively. The crystal structures were solved based on model building of the structures of the precursors and a physico-chemical characterization. Rietveld structure refinements confirmed the structure models. HH-Apo and H-Car are among the very few crystalline silicic acids whose structures have been determined and confirmed based on a structure refinement. The structure of HH-Apo contains thin silicate monolayers that can be regarded as constructed by rings of interconnected [SiO3OH] tetrahedra which form a puckered silicate layer. A sheet of water molecules is intercalated between the silicate layers. There are no direct hydrogen bonds between the silanol groups, but there are hydrogen bonds of different strengths between the terminal O atoms of the silicate layers and the intercalated water molecules. The 1H MAS NMR spectrum presents a strong signal at 4.9 ppm related to the aforementioned bonds and interactions between the water molecules, as well as a small signal at 22.5 ppm corresponding to an extremely strong hydrogen bond with d(O...O) ≈ 2.2 Å. The structure of H-Car is free of structural water and consists exclusively of microporous silicate double-layers with 4-connected [SiO4] and 3-connected [SiO3OH] tetrahedra in a ratio of 1:1 and a thickness of 9.2 Å. Neighboring layers are connected to each other by medium–strong hydrogen bonds with O...O distances of 2.56 Å. The structure of HH-Apo decays within several hours while H-Car is stable. A topotactic condensation reaction applied to H-Car forms an irregularly condensed silicate which still contains the layers in a distorted form as building blocks.

Synthesis and Characterization of Vanadium Doped Hexagonal Rubidium Tungsten Bronze

Attempts have been made to synthesize vanadium doped rubidium hexagonal tungsten bronzes with the nominal composition RbxVyW1-yO3 (x = 0.30, 0.25, and 0.0 ≤ y ≤ x). The samples were synthesized using the solid state synthesis method in a silica glass tube under vacuum at (10-2 Torr) 700°C. The X-ray diffraction measurements reveal that a pure hexagonal tungsten bronze (HTB) phase can be formed with a 60% replacement of W5+ by V5+. The systematic incorporation of vanadium into the HTB lattice, as well as the reduction of V/W-O bond lengths in the xy plane and the lengthening of these bonds in the crystallographic c direction, are also revealed by Rietveld structure refinement of XRD data. The XRD results are supported by FTIR absorption spectra of the oxidized phases. Furthermore, an absorption signature develops as a function of y and exhibits a considerable increase in intensity with the eventual replacement of W5+ by V5+, showing a large decrease in the metallic like contribution and revealing the compounds' nonmetallic nature. Elemental analysis indicates good agreement with nominal values, demonstrating that vanadium was systematically incorporated into the RbxVyW1-yO3 system. Dhaka Univ. J. Sci. 72(1): 77-84, 2024 (January)

Enhanced dielectrics, ferroelectric and optical properties of lithium niobate for high temperature applications using potassium oxide (K2O) additive

Dielectrics, Ferroelectric and Optical properties of Lithium Niobate has been examined using Potassium Oxide (K2O) as an additive on the samples prepared by solid state reaction method using high energy ball milling. The crystal structure analysis by Rietveld structure refinement confirms that the LiNbO3 (LN) with K2O additive also exhibit the rhombohedral structure with R3c space group. The SEM characterization of the microstructure reveals that the samples sintered at a temperature of 1050 °C, have regular and uniform grain morphology and better density. The average grain size decreases for the K2O added compositions in the beginning and increases later for higher concentration of additive. Thermal study with TGA suggests that as the activation energy is decreases, the polarization is enhanced and the LN composition with 2.72 wt% K2O additive shows the best thermal stability. The frequency and temperature dependent dielectric properties were investigated in a wide range of frequency and a substantial enhancement in the dielectric constant of LN is obtained by K2O addition. A useful enhancement in permittivity is obtained with increase of temperature. The band gap values for direct and indirect band gaps for the various compositions are also determined. The least direct band gap is discovered to be 2.36 eV for the composition with 2.72 wt% K2O additive. The composition-dependent photoluminescence (PL) emission studies reveal that the emission spectra for both the pure LiNbO3 and K2O added LiNbO3 compositions lies in the UV–visible region. All the investigated compositions exhibit distinct green, yellow, and red emission peaks. The LN with 2.72 wt% K2O additive shows the best dielectric, thermal stability and polarization response with maximum polarization Ps ∼1.16 μC/cm2. The present investigations suggest that properties of LN can be significantly improved by using K2O additive for sustainable, low cost, environmental friendly energy storage material for high temperature applications.

High-pressure study of a 3d-4f heterometallic CuEu-organic skeleton.

We prepared a 3d-4f heterobimetallic CuEu-organic framework NBU-8 with a density of 1921 kg m-3 belonging to the family of dense packing materials (dense metal-organic frameworks or MOFs). This MOF material was prepared from 4-(pyrimidin-5-yl)benzoic acid (HPBA) with a bifunctional ligand site as a tripodal ligand and Cu2+ and Eu3+ as the metal centres; the molecular formula is Cu3Eu2(PBA)6(NO3)6·H2O. This material is a very promising dimethylformamide (DMF) molecular chemical sensor. Systematic high-pressure studies of NBU-8 were carried out by powder X-ray diffraction, high-pressure X-ray diffraction and molecular dynamics simulation. The high-pressure experiment shows that the (006) diffraction peak of the crystal structure moves toward a low angle with increasing pressure, accompanied by the phenomenon that the d-spacing increases, and as the pressure increases, the (10-2) diffraction peak moves to a higher angle, the amplitude of the d-spacing is significantly reduced and finally merges with the (006) diffraction peak into one peak. The amplitude of the d-spacing is significantly reduced, indicating that NBU-8 compresses and deforms along the a-axis direction when subjected to uniform pressure. This is caused by tilting of the ligands to become more vertical along the c direction, leading to its expansion. This allows greater contraction along the a direction. We also carried out a Rietveld structure refinement and a Birch-Murnaghan solid-state equation fitting for the high-pressure experimental results. We calculated the bulk modulus of the material to be 45.68 GPa, which is consistent with the calculated results. The framework is among the most rigid MOFs reported to date, exceeding that of Cu-BTC. Molecular dynamics simulations estimated that the mechanical energy absorbed by the system when pressurized to 5.128 GPa was 249.261 kcal mol-1. The present work will provide fresh ideas for the study of mechanical energy in other materials.

Enhancement of magnetism by tailoring synthesis conditions in electron-doped superconducting nanoparticles.

A study on the effects of sample synthesis conditions on the particle size, structure, and magnetic properties of electron-doped cuprate superconductors of Eu1.85Ce0.15CuO4+α-δ (ECCO) nanoparticles has been carried out using transmission electron microscopy (TEM), X-ray diffraction (XRD) and the superconducting quantum interference device magnetometer (SQUID). The ECCO nanoparticles were prepared through the sol-gel method with various sintering and annealing temperatures. From TEM characterization, the average particle sizes are 87 nm and 103 nm for the sintering temperatures of 700 °C and 900 °C, respectively. The XRD results with structural Rietveld refinement reveal that the lattice constants and bond distance Cu-O change considerably compared to the bulk case. Reducing the particle and crystallite size to below 200 nm causes strong suppression in the superconducting state. From SQUID measurements it is found that none of the samples show superconducting behavior. An upturn in magnetic susceptibility below 10 K is observed in the sample when the crystallite size is in the range of 69 nm to 88 nm, indicating the existence of magnetism. The lower the sintering temperature of the sample synthesis, the higher the effective magnetic moment and Curie temperature. It suggests that the magnetic correlation is more developed in the smaller samples.

Quenching-driven advancements in functional properties of high-temperature lead-free Sc, Ga modified 0.67BiFeO3-0.33BaTiO3 relaxor ceramics

The processing method is one of the most important deciding factors in the fabrication of BiFeO3–BaTiO3 (BF-BT) based piezoceramics because of the Bi2O3 volatization. It significantly influences the functional properties, including the piezoelectric coefficients, dielectric properties, and microstructure. This study presents a significant advancement in the realm of high-temperature lead-free piezoelectric ceramics in terms of understanding effects of processing method on functional properties. In this light, a novel ceramic solid-solution, 0.67{Bi(Fe0.97Ga0.03)1-xScxO3}-0.33(BaTiO3) with x ≤ 0.07, incorporating Scandium (Sc) and Gallium (Ga) modifications, was meticulously designed and synthesized. Impact of two distinct sintering methods, namely air quenching (AQ) and closed sintering (CS) on the structure and properties of the developed materials are investigated. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analysis verified the formation of pure perovskite phases with successful incorporation of Sc and Ga into the 0.67BF-0.33BT lattice. The FTIR analysis revealed a sharp absorptive band in the 590-604 cm−1 range, corresponding to the signature of stretching and bending vibrations of (Ti/Fe)O6 octahedra. Rietveld structure refinement confirmed the coexistence of pseudocubic (Pm-3m) and rhombohedral (R3c) phases in AQ samples, with predominantly pseudocubic phase, while CS samples closely approximated the pseudocubic phase. The microstructure of the samples exhibits small average grain size distribution (<2 μm). Temperature-dependent dielectric measurements show strong frequency dispersion in the dielectric permittivity with broadened transition peaks. The ferroelectric studies reveal low Pr and Ec values. These observations suggest a ferroelectric relaxor-like behavior of the developed materials. Moreover, the permittivity peaks maxima (Tm) temperature corresponding to CS samples for 0.04<x < 0.07 is less than 390 °C at 10 Hz while it is above 400 °C for AQ samples. The results of our study reveal that AQ samples exhibit superior electrical and ferroelectric properties as compared to the CS samples. The AQ samples demonstrate improvements in Tm (>400 °C), d33(∼35 pC/N), Pr (∼4–11 μC/cm2), PS (∼8–21 μC/cm2), Ec (∼13–25 kV/cm) with reduced dielectric loss, and a better dielectric constant over a wide temperature range.

Large-scale irrigation of Cr3+ into different octahedra of zinc aluminate toward continual broadband near-infrared emission

Broadband near-infrared (NIR) phosphors, as key materials in NIR phosphor-converted light-emitting diodes (pc-LEDs) for emerging applications, have recently attracted considerable attention. Herein, by selecting a comprehensive engineering strategy of co-substituting [Al3+-Al3+] with [Mg2+-Ge4+] units and increasing Cr3+ concentration, a novel Cr3+-doped ZnAl1.16Mg0.4Ge0.4O4 (ZA(MG)0.4:2 at.%Cr3+) phosphor with continual broadband NIR emission was synthesized. The site occupation of Mg2+/Ge4+ in ZnAl2O4 is unraveled by Rietveld structure refinement and density functional theory (DFT) calculations. According to the photoluminescence behaviors, the formed defect clusters of ZnAl’-Cr3+-GeAl· and MgAl’-Cr3+-GeAl· can not only introduce shallow defects to serve as new traps to obtain long-persistent luminescence but can also enhance the emission intensity at ∼689 nm and ∼694 nm. The quantity and scale of Cr3+-Cr3+ pairs and Cr3+ in distorted sites, which can improve the thermal quenching resistance and emission intensity in the range of 700–800 nm, can be accurately regulated by varying the concentration of Cr3+. Under 387 nm excitation, the designed material exhibits intensive NIR emission from 685 to 750 nm with a wide full-width at half maximum (FWHM) of 95 nm. The electroluminescence spectrum and potential applications of the NIR pc-LED prepared using ZA(MG)0.4:2 at.%Cr3+ phosphor are also reported. The results promise a feasible strategy to develop NIR phosphors as NIR pc-LEDs lighting sources for applications in non-destructive detection and anti-counterfeiting.

Mössbauer spectral analysis and Rietveld structural refinement for cationic distribution of Cr-Co ferrites

Sol-gel autocombustion was used to prepare Chromium-substituted Cobalt ferrite nanoparticles with the chemical formulas CoCrxFe2-xO4, with x (0.1 to 0.5 in steps of 0.1).The samples were systematically examined for providing information related to their structural aspects X-ray diffractometry and energy dispersive spectrometry and for determination of accurate ionic distribution using Mössbauer spectrometry and Rietveld structural refinement. The patterns obtained from the energy dispersive spectra ensure that the elemental concentrations of the samples match well with the ionic proportions set in the empirical formulae. Cationic distributions were first made by Mössbauer spectral analysis using hyperfine fields and then by Rietveld analysis based on integrated intensity ratios and profile matching. The results of the study are explained in terms of the compositional variations, cationic inversion degree associated with the fine particle nature of the materials and the relevant cationic distributions as a result of chromium substituted cobalt ferrite.

Effect of Al3+ substitution on the magnetodielectric properties of the one-dimensional frustrated Ca3Co2O6

Ca3Co2-xAlxO6 (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) were prepared via the conventional sol-gel method. The structure, magnetic, dielectric and magnetodielectric properties were investigated. The Rietveld structural refinement confirms the rhombohedral structure of the samples. The positive Curie-Weiss temperature θ and magnetic coupling exchange constants J indicate the dominant intrachain ferromagnetic interactions in the spin chains. The obvious inhibition effect to equally spaced magnetization steps demonstrates that Al3+ could release the magnetic frustration. With Al3+ substitution, both the magnetization intensity and the critical field of the ferrimagnetism to ferromagnetism transition decrease. The samples present obvious dielectric anomalies around the Curie temperature Tc and the freezing temperature Tf. Meanwhile, the magnetic field dependence of dielectric permittivity decreases suddenly at critical magnetic fields. These results reveal strong magnetodielectric coupling effect in Ca3Co2-xAlxO6. The same sign of Δεr and Δtanδ suggests that the magnetodielectric coupling effect is intrinsic.

Comparative crystal chemistry of monovalent cation-exchanged birnessite

Birnessite (ideally, Na0.54Mn2O4∙1.5H2O) is a layered manganese oxide mineral formed by edge-sharing of MnO6 octahedral sheets stacked in ∼7 Å spacing where variable amounts of water molecules and Na+ cations are occupied in a loosely disordered fashion. As such, the interlayer cations can be mixed with or substituted by other cations to contain diverse rare metals and chemical species to endow unique sensitivity on natural environments. To understand comparative crystal chemistry of birnessite as a function of interlayer cation substitution, a series of monovalent cation-exchanged forms, i.e., H-, Li-, K-, NH4-, Rb-, and Cs-exchanged birnessite, were produced from the original Na-birnessite under ambient conditions and analyzed using synchrotron X-ray powder diffraction, thermo-gravimetry, and X-ray photoluminescence spectroscopy. The (001) interplanar spacing generally expands as a function of ionic radius while it contracts as a function of the water content. Compared to the original Na-birnessite, MnO6 octahedral sheets of cation-exchanged forms become generally reduced and show higher MnIII to MnIV ratio, which affects the interlayer cation and water population. Based on the Rietveld structural refinements, the interlayer structural models are categorized into two groups depending on the distribution fashion of cations and water molecules, i.e., water molecules and cations in the Li-, K-, Rb-, Cs-birnessite models occupy separate interlayer sites whereas those are statistically mixed in the H-, Na-, NH4-birnessite models. The interlayer bonding between water molecules and oxygen atoms of the MnO6 layer appears to be a controlling factor for the interlayer spacing. The complex interplay among cation type, water content, Mn oxidation state, and related structural and chemical parameters are discussed to understand the comparative crystal chemistry of birnessite, which would serve as a basis to understanding its potential role in the geochemical cycle of cationic species in aqueous terrestrial environments.

Enhanced the yellow emission of Dy3+/Eu3+: Na5Lu9F32 fluoride single crystals by the introduction of inactive central Y3+ ions

High-quality Na5Lu9F32 single crystals incorporated with Dy3+, Dy3+/Eu3+, and Dy3+/Eu3+/Y3+ ions were successfully synthesized by a reformative Bridgman technique. A significantly enhanced 573nm yellow emission for the Dy3+/Eu3+ incorporated crystal by dopant of inactive central Y3+ ions was demonstrated upon excitation of 453nm. The broken of the Dy3+ clusters by addition of Y3+ dopant was probably the main reason for the enhancement of the yellow emission. The crystal still held the phase of Na5Lu9F32 although the doping level reaches to 1.5 mol% Y3+ while the peaks of X-ray diffraction (XRD) were slightly blue-shifted, and Y3+ ions replaced the Lu3+ lattices as consequence of Rietveld structure refinements of the crystals. The maximum excited absorption and emission cross-sections at 573nm were also computed to be ∼8.91×10−21 and ∼6.06×10−21 cm2 separately. Therefore, the Dy3+/Eu3+/Y3+ tri-doped Na5Lu9F32 single crystal was considered as a prospective yellow solid-state laser material for related optical devices.

Structural and magnetic properties of nanoparticles of La3Ni2NbO9 double perovskite

The nanoparticles of La3Ni2NbO9 (LNNO) have been produced via the glycine-nitrate combustion technique followed by a process of calcination with an average crystallite size of ∼ 25 nm. The powder X-ray diffraction (XRD) pattern was analyzed for structure analysis by Rietveld structure refinement. Study on the XRD pattern reveals that LNNO crystallizes in the single phase of monoclinic crystal structure with P21/n space group. Analysis of temperature-dependent magnetization reveals that nanoparticles of LNNO undergo paramagnetic to antiferromagnetic phase transition at Neel temperature TN ∼ 43 K and antiferromagnetic to spin glass transition at Tg ∼ 31.45 K. Analysis of magnetic ac-susceptibility reveals that the LNNO nanoparticles follow Vogel-Fulcher and dynamic scaling power laws in the low-temperature region.

Efficient photocatalytic activity of chitosan/tin oxide nanocomposite for environmental remediation

In this study, tin oxide (A-SnO2) nanoparticles (NPs) and Chitosan-tin oxide (CS-SnO2) nanocomposite were synthesized using an ammonia solution and chitosan. Thermal stability and degradation are analyzed using TG-DTA. The structural analysis and Rietveld refinement analysis of both synthesized nanoparticles indicate the presence of pure SnO2 NPs. Further, morphological analysis is used to identify the samples as spherical shapes. The UV spectra of both nanoparticles show that CS-SnO2 has a lower band gap energy than A-SnO2, increasing its photodegradation efficiency. The chemical bonding of the Sn-O-Sn functional groups and their valence state are confirmed by FT-IR absorption peaks and XPS spectrum. CS-SnO2 nanocomposite have the highest photodegradation efficiency of approximately 95 %, which is due to the role of chitosan as a biopolymer in SnO2 nanoparticles. In addition, the effect of pH, and the stability of the catalyst are also tested. Thus, this study reveals the potential of A-SnO2 and CS-SnO2 for practical applications in wastewater cleaning and environmental remediation using visible-light-driven photocatalysis. The combination of Chitosan-tin oxide (CS-SnO2) can improve the degradation rate of organic dyes. This strategy provides a good application prospect for dye degradation.

Lithium‐Filled Skutterudites by Intercalation at Ambient‐Temperature

AbstractThe incorporation of lithium as a filler species in Co1‐2xFexNixSb3 skutterudites was accomplished by intercalation at 60 °C, using n‐BuLi as a reducing agent. Solid state 7Li NMR and ICP‐MS analysis confirm the presence of lithium in the product phases and provide an estimate of the lithium content. The maximum uptake of lithium increases as cobalt is progressively substituted by an equimolar mixture of iron and nickel. Difference Fourier maps, calculated during Rietveld structure refinement using powder neutron diffraction data, locate the lithium cations at the 2a (0,0,0) sites within the cavities of the skutterudite framework. The intercalation of lithium results in reductions in thermal conductivity of up to 47 %, indicative of phonon glass electron crystal (PGEC) type behaviour. Charge transfer from lithium to the framework that accompanies intercalation results in a substantial decrease in electrical resistivity in lithiated phases and a more metal‐like temperature dependence. The increased carrier concentration also decreases the Seebeck coefficient, with the consequence that modest increases in the figure of merit occur, despite the reduced thermal conductivity.

Growth, structure and spectroscopic properties of Er:YSr3(PO4)3 disordered crystal for mid-infrared laser applications

Mid-infrared lasers in the ⁓ 3 µm region activated by Er3+ ion has attracted considerable attention due to their important applications. Herein, a heavy concentration (30 mol%) Er3+ ion doped YSr3(PO4)3 (Er:YSP) single crystal with a high crystalline quality was grown through the Czochralski pulling method. The structure of single crystal was ascertained to be cubic system with the point group 4¯3m using the powder X−ray diffraction and Rietveld structural refinement methods. Furthermore, the band structure and density of states of the crystal were analyzed by the first principal calculations. The absorption and fluorescence spectra were also investigated. An intense absorption band located at 974 nm with a full width half-maximum of 18 nm, where the absorption cross section was obtained to be 3.72 × 10−21 cm2. The full width half-maximum value of emission band centered at about 3090 nm is up to be 140 nm, which is very suitable for realizing ultrashort pulses and tunable lasers. In addition, the fluorescence lifetime of the upper 4I11/2 and lower 4I13/2 levels were obtained to be 0.65 ms and 5.37 ms, respectively. All the results show that the disordered structure crystal Er:YSP could potentially serve as a laser medium for the ⁓ 3µm region.

Mn2+ doped LiBaF3 fluoride perovskite single crystal with broadband infrared luminescence pumped by blue LED

In this study, Mn2+ ions doped lithium barium fluoride single crystals (LiBaF3: Mn2+) with perovskite structure were successfully prepared by a reformative Bridgman technique. A near-infrared (NIR) emitting broadband of the single crystal with a peak wavelength of 767 nm and a full width half maxima (FWHM) of 77 nm is owing to the 4T1g(4G)→6A1g(6S) transition of the Mn2+ ions in strong crystal field. Mn2+ ions replace the lattices of Li+ ions from the results of Rietveld structure refinements of the crystals performed by General Structure Analysis System (GSAS) program. A high internal quantum efficiency (41.4%) can be obtained in the synthesized single crystal upon excitation of 494 nm, and the emission intensity of this single crystal at 473 K remains at 42.9% of that at 298 K. Therefore, the LiBaF3: Mn2+ single crystal is a promising candidate for NIR solid-state light-emitting material due to its effective broadband NIR emission. This work offers a novel route to rational design of efficient broadband NIR luminescence and provides a new insight into Mn2+ luminescence and its applications.

Crystal growth and phase formation of high‐entropy rare‐earth monoclinic aluminates

AbstractFor the first time, high‐entropy rare‐earth monoclinic aluminate crystals were grown via directional solidification using the micro‐pulling‐down method. Five high‐entropy compositions were formulated with a general formula RE4Al2O9, where RE is an equiatomic mixture of five rare‐earth elements. The rare‐earth elements included were Lu, Yb, Er, Y, Ho, Dy, Tb, Gd, Eu, Sm, Nd, and La. High‐temperature powder X‐ray diffraction and Rietveld structure refinement indicated that all crystals were a single monoclinic phase and that rare‐earth average ionic radius did not affect phase purity. At room temperature, the refined lattice parameters increased consistently with increasing average ionic radii of the five compositions. One of the crystals had a typical high‐temperature phase transition of single‐RE RE4Al2O9 in the range of 1100–1150°C, which consisted of a lattice contraction upon heating. Differential scanning calorimetry indicated a thermal event corresponding to that phase transition. Electron probe microanalysis revealed Al‐rich inclusions on the surface of the crystals. Crystals containing Tb had dark surface features that became lighter after annealing in a reducing atmosphere, which indicated that Tb4+ may be responsible for the dark features.

Influence of graphene oxide on the dielectric properties of biogenically synthesized ZnO nanoparticles

This study presents a novel and biogenic route to synthesize zinc oxide (ZnO) nanoparticles using Phoenix dactylifera fruit extract as a plant-mediated reducing agent. Graphene oxide (GO) was synthesized using the improved Hummer's method, and a series of GO-ZnO nanocomposites were produced by the ultrasonic-dispersion method. The structural and optical properties of the nanocomposites have been analyzed using XRD, TEM, FESEM-EDX, UV-vis. DRS, and FTIR spectroscopy. The results indicate that ZnO nanoparticles are deposited over GO sheets in the nanocomposites. The structural analysis and Rietveld refinement confirmed the successful synthesis of crystalline single-phase ZnO nanoparticles with a hexagonal-wurtzite structure. The influence of GO on the dielectric properties of green-synthesized ZnO nanoparticles was analyzed in the frequency range 20 Hz-2 MHz at ambient temperature. The results showed a significant increase in the dielectric constant and ac conductivity with growing GO content in the nanocomposites compared to that of pristine ZnO. Complex impedance analysis revealed the non-Debye type relaxation and a decreasing trend in the complex impedance value with increasing GO content. This novel biogenic synthesis approach is energy-efficient and environment-friendly, which can provide an effective route for low-cost and scaled-up production of nanocomposites for several applications.