Rietveld Method Research Articles

Fabrication, structure, and physical properties of three-B-site perovskite Ba(Zr1–2xTixCex)O3

In this study, three-B-site perovskite Ba(Zr1–2xTixCex)O3 (x=0–0.2) materials with the co-substitution of Ti4+ and Ce4+ at the Zr-site of barium zirconate (BaZrO3) were successfully prepared. The analyses of XRD & Rietveld method, SEM, and TEM indicated that the substituted ions Ti4+ and Ce4+ entered the BaZrO3 lattice to form a single-phase solid solution, showing a conventional primitive cubic perovskite structure (Pm-3 m space group), and its lattice parameters gradually increased from 0.4192 nm to 0.4206 nm with x value. The sample with x=0.1 exhibited relatively optimal structural uniformity and densification, as well as comprehensive physical properties. The sample Ba(Zr0.8Ti0.1Ce0.1)O3 showed a minimum mean grain size of 1.50 μm. And due to the combined effect of solid solution formation and grain refinement, it displayed an apparent porosity of 1.42 % with a cold modulus of rupture (CMOR) of 123.8 MPa, and a thermal conductivity at ambient temperature of 2.197 W/mK. Furthermore, this three-B-site perovskite Ba(Zr1–2xTixCex)O3 exhibits excellent high-temperature stability. This study demonstrates the promising application of the dense, high-strength, and low-thermal conductivity Ba(Zr0.8Ti0.1Ce0.1)O3 perovskite material in the field of advanced refractory ceramics.

Microwave-assisted hydrothermal synthesis of carbonated apatite with calcium and phosphate resources derived from green mussel shell and bovine bone wastes

Resources recovery of calcium and phosphates from respective green mussel shells and bovine bones by calcination and chemically extracting are viable precursors for carbonate-rich apatite biomedical material applications. Because of their high osteoconductivity, carbonate-rich apatite bioceramics are being studied intensively for synthetic bone transplants. In the study, powder processing routes of calcination and following chemical dissolution in MgCl2 and H2SO4 were each for recovering calcium of mussel shells and phosphate of bovine bones yielding a crystal-forming solution feedstock for use in microwave-irradiated synthesis. FTIR spectra and XRD patterns validated the crystallinity and phase identification for as-synthesized powders. As a result, the presence of CO3, PO43-, and OH- bands in carbonate-calcium phosphate complexes were present in FTIR spectra. According to the XRD Rietveld method, the as-synthesized powder product contained brushite, carbonated hydroxyapatite (CHA), calcite, and gypsum. The recoverable CHA crystallites' size was 40 nm. This present study demonstrated that microwave irradiation synthesis of CHA powder with calcium and phosphates derived from mussel shells and bovine bones is the potential to yield a large amount of CHA for bioceramics and would aid in the design of a powder processing step for preparing the CHA powder precursor in biomedical applications.

Crystal Structure Parameter Analysis of Reduced Graphene Oxide (rGO) from Coconut Shell Charcoal

In this research, reduced graphene oxide (rGO) material from coconut shell charcoal was synthesized using the modified Hummer method. The reduction process of Graphene Oxide (GO) to rGO uses the reducing agent L-Ascorbic Acid (LAA) and is assisted by microwave radiation. The samples obtained were then characterized using XRD to analyze the crystal structure parameters of the rGO samples obtained. Based on the XRD results, the data obtained was then analyzed using the Scherrer and modified Scherrer equations to determine the crystal size in the sample. In addition, the Williamson-Hall equation is also used to analyze crystal size and lattice strain. This article also analyzes XRD data using the Rietveld method using Rietica software. The output from the Rietica software obtained lattice parameter values a ≠ b ≠ c and angle α = β = γ = 90° which indicates an orthorhombic crystal lattice structure. In the refinement process, Rietica's software affects the suitability parameters in the form of R and GOF indicator values. The sample obtained was also measured for the electrical conductivity value of the rGO sample using an LCR meter.

Study of the identity of the polymorphic form of API – dapagliflosin derivative and of its permanency structure under the influence of the tableting process

The aim. To investigate the polymorphic structure of the API – Dapagliflozin propanediol monohydrate and to reveal the absence of an effect of the tabletting process on the polymorphic structure of the API in model compositions of tablets. Materials and methods. Model mixtures of API - dapagliflozin propanediol monohydrate and excipients were studied. The research used the method of designing pharmaco-technological parameters of solid dosage forms, the method of quantum-chemical modelling of the mechanical properties of polymorphic modifications of APIs, the modelling of shear deformation, the nanoindentation method, the Rietveld method for calculating X-ray patterns, X-ray structural analysis of API and selected model compositions of tablets. Results. The polymorphic structure of API - dapagliflozin propanediol monohydrate and its polymorphic structure in selected model compositions of tablets produced by the pressing method were studied and analyzed. An X-ray structural study was carried out, and the qualitative and phase composition of samples and polymorphic modifications of API and model series of tablets were determined. According to the results of the X-ray structural analysis, it was established that there is no polymorphic transition and that the polymorphic structure of API is invariant under the influence of pressing pressure, which ensures the quality of the tablet form. Conclusions. The design of an experimental study was determined based on the application of the QbD concept, design of experiments – DoE, for designing and ensuring a high-quality technological process – tabletting of API - Dapagliflozin propanediol monohydrate and excipients. To manage a critical technological parameter - the stability of the polymorphic structure of the API, which guarantees the quality of the tablet form, its bioavailability and bioequivalence, it is necessary to use a set of methods for studying structural changes and polymorphic modifications of the API during the tableting process. According to the results of the X-ray structural study of API and selected model compositions of tablets, it was established that during the process of tabletting under pressure, the structure of the polymorphic modification of dapagliflozin propanediol monohydrate does not change, and no polymorphic transition is observed

Obtaining of disordered highly ionic conductive Ag7+x(P1−xSix)S6 single crystalline materials

For the first time, bulk single crystals of the Ag7+x(P1−xSix)S6 solid solution were obtained via directional crystallization from the melt. The crystal structure of the Ag7+x(P1−xSix)S6 solid solution was determined by the Rietveld method. It was demonstrated that Ag7+x(P1−xSix)S6 solid solutions crystallize in two crystal systems—cubic and orthorhombic, and different SG: P213, F-43m and Pna21. The grown crystals were studied by SEM and EDS methods. The electrical parameters of Ag7+x(P1−xSix)S6 were studied in wide frequency and temperature ranges. Established that Ag7+x(P1−xSix)S6 solid solutions exhibit an increase in ionic conductivity compared to the initial compounds. Among the studied solid solutions, the Ag7.25P0.75Si0.25S6 sample demonstrated the highest conductivity with values reaching σion = 2.9 × 10−2 S/cm. The lowest activation energy value (Ea(ion) = 0.2 eV) is also observed for the given composition of solid solutions. The mechanism of ion transport is considered within the context of limiting distances and position occupancy.

Production of dense forsterite with ultra low dielectric loss using ZrO2 additive

Forsterite was synthesized with MgCO3 and SiO2 powders using a solid-state method at 1200–1300°C. The ceramic specimen with the highest forsterite phase content was sintered with the ZrO2 sintering aid at mass fractions of 0.5, 1.0, and 1.5 wt% at 1400°C for 4 h. The dielectric constant and loss tangent were also measured via the waveguide method at 8–12 GHz. The formation of enstatite and cristobalite was minimized through precise synthesis temperature control. Phase measurement by the Rietveld method showed that specimen F28 contained more than 99.8% forsterite. It was found that ZrO2 reduced the pore volume percent and increased the density even at low mass fractions. A liquid phase on the grain boundaries was demonstrated. The solid ceramic specimen F28-15Z showed a dielectric constant of 6.5 and high quality factor of 189000.

Ternary intermetallic compounds R23Ru7In4 (R[dbnd]Ce, Pr): Synthesis, crystal structure and physical properties

Two novel ternary intermetallic compounds Ce23Ru7In4 and Pr23Ru7In4 were synthesized by arc melting of components and subsequent annealing at 600 °C. Both compounds crystallize in a hexagonal cell, with structure type Pr23Ir7Mg4, space group P63mc (№ 186), Pearson symbol hP68, Z = 2, the cell parameters: a = 9.861(5) Å, c = 22.520(12) Å (Ce); a = 9.9260(7) Å, c = 22.4109(2) Å (Pr). The structure of Ce23Ru7In4 was determined by single-crystal X-ray diffraction and the structure of Pr23Ru7In4 was determined by the Rietveld method using powder X-ray diffraction pattern. Compound Ce23Ru7+xIn4-x exist in the homogeneity range 0 ≤ x ≤ 3. An essential feature of compound Ce23Ru7In4 is the presence of abnormally short distances Ce–Ru (2.637 Å, 2.735 Å). The compound Pr23Ru7In4 melts incongruently and compound Ce23Ru7In4 melts congruently at temperatures 756 and 683°С respectively. The Pr23Ru7In4 compound is characterized by the presence of a magnetic transition at 12 K. The observed magnetic transition is most likely indicative of a transition to the spin glass state.

Polar orientation and extension in a novel crystallographic model for PbTiO3-based perovskites explaining the experimental ferroelectric thermal anomalies

PbTiO3-based ferroelectric solid-solution ceramics have been widely used for electromechanical devices. However, it is still challenging to separate and control the contributions to the electromechanical functionalities, mainly as a function of temperature, where thermal anomalies and phase transitions can be observed. This study investigates the ultrasonic velocity and attenuation and the dielectric, ferroelectric and structural features of Pb0.55Ca0.45TiO3 ceramics from low temperatures (10 or 115 K) up to room temperature as an example of A-site isovalent substitution in PbTiO3. Such a combination of information makes possible the phenomenological deconvolution of the effects of ferroelectric domain wall pinning and structural features on spontaneous electric polarization. The room-temperature symmetry was determined as Pna21. The results show that this model refined by the Rietveld method for synchrotron X-ray diffraction patterns from 115 K to room temperature can explain the polarization extension features of these materials during heating. This study shows a correlation between structural thermal anomalies and low-temperature electric polarization in PbTiO3-based ferroelectric ceramics.

Effects of pore structure and chloride binding capacity on chloride diffusion in limestone cement paste

The limestone powder has been a preferred admixture in cement-based materials due to its abundant availability and potential to reduce carbon emission. The purpose of this study is to clarify the key influencing factors for chloride diffusion in cement paste as limestone is added. The pore structure, chloride binding capacity and chloride diffusivity of cement paste with different limestone addition and fineness were measured. The deconvolution of physically and chemically bound chloride was achieved by combining X-ray diffraction, energy dispersive spectroscopy and the Rietveld method. The results show that the addition of fine limestone increases the number of 50–100 nm pores while the coarse limestone leads to more pores in the size range of 100–1000 nm. As the limestone content increases, less chloride is bound by physical adsorption while more Friedel’s salt is formed. The effective chloride diffusivity is almost unaffected when less than 10 % fine limestone is added because of increased pore tortuosity. The changes of chloride binding capacity and chloride diffusivity are equally important for the chloride diffusion when 20 % fine limestone is added. On the other hand, the reduction of chloride resistance of cement paste containing coarse limestone is mainly due to the increase of the chloride diffusivity.

Synthesis and in-depth structure determination of a novel metastable high-pressure CrTe3 phase

This study reports the synthesis and crystal structure determination of a novel CrTe3 phase using various experimental and theoretical methods. The average stoichiometry and local phase separation of this quenched high-pressure phase were characterized by ex situ synchrotron powder X-ray diffraction and total scattering. Several structural models were obtained using simulated annealing, but all suffered from an imperfect Rietveld refinement, especially at higher diffraction angles. Finally, a novel stoichiometrically correct crystal structure model was proposed on the basis of electron diffraction data and refined against powder diffraction data using the Rietveld method. Scanning electron microscopy–energy-dispersive X-ray spectrometry (EDX) measurements verified the targeted 1:3 (Cr:Te) average stoichiometry for the starting compound and for the quenched high-pressure phase within experimental errors. Scanning transmission electron microscopy (STEM)–EDX was used to examine minute variations of the Cr-to-Te ratio at the nanoscale. Precession electron diffraction (PED) experiments were applied for the nanoscale structure analysis of the quenched high-pressure phase. The proposed monoclinic model from PED experiments provided an improved fit to the X-ray patterns, especially after introducing atomic anisotropic displacement parameters and partial occupancy of Cr atoms. Atomic resolution STEM and simulations were conducted to identify variations in the Cr-atom site-occupancy factor. No significant variations were observed experimentally for several zone axes. The magnetic properties of the novel CrTe3 phase were investigated through temperature- and field-dependent magnetization measurements. In order to understand these properties, auxiliary theoretical investigations have been performed by first-principles electronic structure calculations and Monte Carlo simulations. The obtained results allow the observed magnetization behavior to be interpreted as the consequence of competition between the applied magnetic field and the Cr–Cr exchange interactions, leading to a decrease of the magnetization towards T = 0 K typical for antiferromagnetic systems, as well as a field-induced enhanced magnetization around the critical temperature due to the high magnetic susceptibility in this region.

Batch Sintering of FeO·OH and Fe2O3 Blends: Chemical and Metallurgical Characterization

A sample of goethite iron ore sinter feed (G_SF) was employed as a raw material in a sintering bed. This sample partially replaced hematite sinter feed (H_SF), which is currently used as raw material in a sintering plant in the state of Minas Gerais, Brazil. This substitution did not adversely affect the chemical and metallurgical proprieties of the sinter mix product, provided that the utilization of G_SF was kept below 30% in weight. Despite the higher proportion of fines in G_SF, the presence of argillaceous minerals in the sample led to an improvement in the granulation index (GI) of the sinter mix product. The GI value increased from 68.4 to 82.7% for the experiments conducted without the presence of goethite ore and with 40% of goethite ore in the sintering mix, respectively. Consequently, the qualities of both the process and the produced sinter product were not compromised. The raw materials and the various sinters produced were characterized through X-ray fluorescence (XRF) and X-ray diffraction (XRD), as well as thermal gravimetric analysis (TGA). The XRD results were used to perform a quantitative assessment of the mineral phase using the Rietveld method (RM). This technique allowed for the determination of goethite content in the studied sample, which was 35.5%. Finally, the incorporation of G_SF in the sintering bed led to a 20% reduction in the cost of raw materials.

Improving the optical and dielectric characteristics of PVA/PVP/PEG/ZnWO4/CdS blends

This work aims to create novel nanocomposite blended polymers by incorporating (1−x)ZnWO4-xCdS into poly (vinyl alcohol) (PVA)/polyvinyl pyrrolidone (PVP)/polyethylene glycol (PEG) blend to employ these nanocomposites in various optoelectronic applications. This study focused on investigating the structural, optical and electrical features of PVA/PVP/PEG/(1−x)ZnMn2O4-xCdS blends. The x-ray diffraction and scanning electron microscope techniques were used to explore the structure and morphology of the formed samples. The structure and percentages of ZnWO4 and CdS in different fillers were performed using Rietveld method. The doped blends exhibited significant absorption of UVA and UVB types. The greatest amounts of absorption were observed when the filler contained 25 % CdS. The direct and indirect optical band gaps of the doped blend became 5.02 and (1.88, 2.37) eV as the amount of CdS became 25 % in the filler sample. The refractive index, optical dielectric constant, optical conductivity, and nonlinear optical parameters are affected by the amount of CdS in the fillers. The fluorescence spectra for the blends affected by the excitation wavelength and amount of CdS in the filler. The maximum energy density of the doped blend was reached when the amount of CdS in the filler reached 25 %. The purities of emitted color in the undoped blend are 83 % and 74 % under excitation wavelengths of 317 nm and 380 nm. The purity of the blend experienced a slight change when loaded with filler samples. As the ZnWO4 doping of the PVA/PVP/PEG blended polymer rose, its electrical dielectric constant and ac conductivity first enhanced and then irregularly declined as the filler's CdS content rose. Incorporating (1−x)ZnWO4-xCdS into the nanocomposite enhanced their optical and electrical properties, making them a potential material for flexible optoelectronic and energy storage uses.

Determine elastic parameters and nanocrystalline size of spinel ferrites MFe2O4 (M = Co, Fe, Mn, Zn) through X-ray diffraction and infrared spectrum: Comparative approach

MFe2O4 (M = Co, Fe, Mn, Zn) nanoparticles were successfully synthesized by coprecipitation. Analyzing the X-ray diffraction by the Rietveld method confirmed the spinel ferrite structure of the samples. Rietveld refinement results show that Co, Mn and Zn occupy both the tetrahedral and octahedral sites. Variation in elastic parameters was determined by Fourier transform infrared spectroscopy, and cation distribution was deduced from X-ray diffraction. X-ray diffraction peak expansion was analyzed by employing a variety of calculating methods such as modified Scherrer, Williamson–Hall, size–strain, and Halder–Wagner to determine the crystallite size and elastic parameters of the cubic-structured MFe2O4 nanoparticles, including intrinsic strain, stress, and energy density. Comparison of the results obtained from these different methods revealed that they are ideally suited to each other. Moreover, the transmission electron microscopy image confirmed that the average size of MFe2O4 (M = Co, Fe, Mn, Zn) nanoparticles ranges from 10 to 14 nm, consistent with the dimensions obtained from the preceding methods.

Evaluation of the Rietveld method for determining content and chemical composition of inorganic X-ray amorphous materials in soils

Abstract Inorganic X-ray amorphous materials (iXAMs) such as vitreous phases, minerals having an insufficient number of repeating structural units to diffract X-rays, and inorganic solids with exclusively structural short-range order are ubiquitous in soils and relevant for numerous environmental processes, but are notoriously difficult to identify and quantify. To test for the quantification and chemical composition of iXAMs in soil, we prepared four mineral mixtures containing quartz, calcite, feldspars, and clay minerals in different proportions typical of soils and amended them with 10–70 wt% iXAMs in the form of a 1:1 weight mixture of ferrihydrite and opal-A. We quantified these iXAMs in mineral mixtures by analyzing powder X-ray diffraction (PXRD) data using the Rietveld method and compared the results for different sample preparation techniques (conventional and spray drying) based on the internal standard method in Rietveld analysis. The mineral mixtures were also analyzed for their chemical composition by X-ray fluorescence (XRF) spectrometry, and mass balance calculations combining Rietveld and XRF data were carried out to estimate the chemical composition of iXAMs in mineral mixtures. Both sample preparation methods showed no significant difference in determined iXAM contents and yielded accurate results for iXAM contents within ±3 wt% at the 95 % confidence level (2σ). The relative accuracy deteriorated with decreasing iXAM content, but remained below 10 % for iXAM contents > 10 wt% (mean = 3 %). The precision of iXAM content quantification in mineral mixtures prepared by spray drying was slightly better though statistically equivalent to the conventionally prepared mixtures (2σ = 1.49 and 1.61 wt%). The average precision of both sample preparation methods was ±2 wt% at the 95 % confidence level. Levels of detection and quantification of iXAMs in spray-dried mineral mixtures containing 1–10 wt% iXAMs were estimated at 0.8 and 4.0 wt%, respectively. The chemical composition of iXAMs in terms of major oxides was accurately assessed by mass balance calculations with average relative errors for nominal SiO2 and Fe2O3 contents of 9.4 and 4.3 %, respectively (range = 0.02–54.7 %). Even though adsorbed H2O and structural H2O/OH- as quantified by the loss 50 on ignition comprised an important portion of the iXAMs (15.3 wt%), their LOI in mineral mixtures as derived from mass balance calculations could only be quantified with an average relative error of 67.2 % (range = 1.30–371 %). We conclude that iXAMs in soil and related geomaterials present at levels > 4 wt% can be quantified by Rietveld analysis of PXRD data with an accuracy of ±3 wt% at best. Combined results of Rietveld and XRF analyses can yield accurate results for the chemical composition of iXAMs within a relative error of 10 % for major oxides, provided iXAM contents exceed 10 wt% and the content and chemical composition of all crystalline mineral phases is accurately assessed. The results presented in this study lay the foundation to explore iXAM contents and chemical compositions in soils and to examine their impact on soil physicochemical properties and biogeochemical element cycles.

Toward an understanding of the role of structural organization and point defects in the formation of functional pure and Tm3+-doped (Ca3-xSrx)(VO4)2 for diode-pumped and SRS lasers

Whitlockite-type polycrystalline and single-crystal (Ca3−xSrx)(VO4)2 solid solutions were successfully obtained by solid-state synthesis and Czochralski method, respectively. Synchrotron powder X-ray diffraction allowed to reveal actual compositions of polycrystalline (Ca3−xSrx)(VO4)2 solid solutions with х = 0.3, 0.54, 0.9, 1.2, 1.35 refined by Rietveld method, which are slightly different from the initial ones. Synchrotron X-ray single-crystal diffraction analysis of Czochralski-grown undoped (Ca1.8Sr1.2)(VO4)2 (CSVO) revealed its actual composition (Ca2.982(11)Sr0.031)(VО4)2. Difference between initial and refined compositions is analyzed and discussed. In the CSVO structure, Sr2+ ions partially occupy monocapped Ca2 and two-capped Ca3 trigonal prismatic sites and Ca2+ ions are in the Ca5 and Ca5A sites, forming two independent strongly distorted tetrahedral Ca5O4 and octahedral Ca5AO6 oxygen environments. Synchrotron X-ray single-crystal diffraction analysis together with X-ray absorption spectroscopic study of (Сa2.4Sr0.6)(VO4)2 doped with 0.5 and 1.0 wt% Tm2O3 (СSVO:0.5Tm and CSVO:1.0Tm) allowed to establish the absence of cations in the Ca5A site, the localization of Sr2+ ions in the Ca2 and Ca3 sites and additionally in octahedral Ca4 site together with Tm3+ ions, forming an individual eight-coordinated environment, in the refined compositions (Ca2.776(7)Sr0.210(4)Tm3+0.008(1))(VO4)2 and (Ca2.855(7)Sr0.140(7)Tm3+0.009(1)□0.022(7))(VO4)2, respectively, with vacancies (marked by a square,□) in the two-capped Ca1 trigonal prismatic site in the CSVO:1.0Tm structure. Additional interstitial oxygen, participating in the formation of the Tm3+ environment, found in the residual electron density, together with vacancies in the Ca1 site provides electroneutrality to CSVO:0.5Tm and CSVO:1.0Tm crystals. Several structural models of the coordination environment of Tm3+ ions were analyzed and the most correct one was proposed.

Strong correlation of electrical transport and magnetic properties to ionic states, structure, and morphology of Al-substituted Ni–Co ferrite systems: A comprehensive study

This paper presents the structure, morphology, magnetic, ionic states, and electrical transport characteristics of spinel Ni0.5Co0.5AlxFe2-xO4 (x = 0.0, 0.5, and 1.0) nanocrystalline ferrites, synthesized by using the sol-gel auto-combustion method. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to analyze the structural characteristics. The synthesized ferrites were found to have a crystallite size of less than 40 nm when the Rietveld method was applied to refine XRD patterns in single-phase cubic spinel-related structures that belong to the Fd-3m space group. Furthermore, since the ionic states are visible in X-ray photoelectron spectroscopy (XPS), variations in Al3+ ion concentration have been found to affect the locations, occupancy, and Wyckoff's cationic position of the ions as well as the lattice constant (a), the crystallite size (D), and the micro-strain of the composites. Thermogravimetric analysis was used to examine the temperature-dependent spinel phase formation and % weight loss of the sample. The x = 1.0 composition is said to be the best dielectric material out of the three samples since it has the highest polarization permittivity, the lowest dissipation factors, and exceptional temperature stability. These nanoparticles have relatively high impermanent magnetization values and are ferrimagnetic, according to the vibrating sample magnetometer (VSM) investigation. Additionally, it was found that the presence of Al3+ decreases the magnetization values of the spinel Ni0.5Co0.5AlxFe2-xO4 (x = 0.0, 0.5, and 1.0) system because the Al3+ exclusively occupies the Fe-sites, which reduces the super-exchange interaction between the Fe2+/Fe3+, Co2+/Co3+, and the Ni2+/Ni3+ ions. The unique magnetic characteristic of these compositions below 40 nm is predicted to make them appealing for storage applications.

Phase equilibria of the Nb–Si-Gd ternary system at 1273 K

The phase equilibria of the Nb–Si-Gd ternary system at 1273 K in all the composition ranges were investigated by X-ray diffraction (XRD), electron probe microanalysis (EPMA), and Scanning electron microscopy (SEM) equipped with Energy dispersive spectroscopy (EDS). The isothermal section comprises 12 single-phase regions, 22 two-phase regions, and 11 three-phase regions. The existing of Nb3Si phase was confirmed at 1273 K by couple diffusion. A new ternary compound Gd2Nb3Si4 was discovered and its crystal structure was analyzed by the Rietveld method with Rwp = 2.11%, Rp = 1.54%, Rexp = 0.75%. It belongs to the space group P41212 (No.92) with the lattice parameter a = b = 6.99048 Å, c = 12.94393 Å, α = β = γ = 90°.

Temperature sensing by means of a near-infrared luminescent Ca8NaBi(PO4)6F2:Nd3+ fluorapatite phosphor

Microrods of calcium sodium bismuth fluorapatite doped with neodymium, denoted as Ca8NaBi1-xNdx(PO4)6F2 (with x ranging from 0 to 0.5), were synthetized using a modified Pechini sol–gel method. The crystalline structure of these phosphors was refined using the Rietveld method and exhibited hexagonal symmetry with space group P63/m—C26h, where the lattice parameters were a = 9.3855(5) Å and c = 6.8998(6) Å for x = 0.2. The particles morphology was analyzed through SEM, revealing an average length of approximately 1.5 µm. When excited at 808 nm, the Ca8NaBi(PO4)6F2:0.2Nd3+ microrods emitted strongly at 872, 957 and 1055 nm, falling within the near-infrared region. These emissions correspond to the 4F3/2 → 4I9/2 (P2), 4F5/2 → 4I11/2(P3), 4F3/2 → 4I11/2(P1) transitions of Nd3+ ions, respectively, and are situated within the first and second biological windows. The luminescence lifetime of the 4F3/2 state of Nd3+ was measured to be 294.4 µs for the sample with the lowest Nd3+ concentration of x = 0.05. In addition, the luminescence intensity ratios P2/P1 and P3/P1 were found to be temperature dependent, potentially making it suitable for luminescent ratiometric thermal sensing. These findings suggest that the synthesized Ca8NaBi(PO4)6F2:Nd3+ microrod thermometers exhibit favorable characteristics in terms of relative sensitivity, temperature uncertainty, and repeatability within the temperature range of 303–403 K.

Realization of new n = 3 and n = 4 Dion-Jacobson layered perovskite series with interlayer K+ ions and perovskite blocks stabilized by Pr3+ ions

The structural flexibility of the perovskite blocks in the Dion-Jacobson family of layered perovskite oxides has successfully resulted in the generation of KPrNan-2NbnO3n+1 and KPrCan-2Nb2Tin-2O3n+1 (n = 3, 4). The stabilization of K+ ions preferring a six coordination in the interlayer region is significant compared to the facile formation of layered perovskite oxides possessing bigger Rb+ or Cs+ ions with an eight coordination in the interlayer. The structure of the n = 3 members, KPrNaNb3O10 (S. G. Cmcm; a = 3.8858(1) Å, b = 29.6553(9) Å, c = 7.7635(3) Å) and KPrCaNb2TiO10 (S. G. Cmcm; a = 3.8634(2) Å, b = 29.4808(2) Å, c = 7.6945(5) Å) were confirmed respectively using the Rietveld and Le Bail methods utilizing the powder X-ray diffraction data. The n = 4 members, KPrNa2Nb4O13 and KPrCa2Nb2Ti2O13 are synthesized through high-temperature ceramic methods. The compounds are phase pure as confirmed from the X-ray diffraction data and were characterized by UV–visible diffuse reflectance measurements. These two-dimensional oxides also undergo facile topochemical ion-exchange and intercalation reactions and opens up several interesting possibilities. We have replaced the K+ ions in the interlayer by H+, Li+, Na+ ions and [CuCl]+ groups through low temperature reactions. The usefulness of various Dion-Jacobson layered perovskite oxides for potential photocatalytic applications has been explored by determining the optical band gaps, the valence band, and the conduction band energy levels based on the UV–visible diffuse reflectance measurements.

SYNTHESIS AND CHARACTERIZATION OF CaO PREPARED FROM LIMESTONE USING SOL-GEL METHOD

The sol-gel method has been successfully applied to the synthesis and characterization of calcium oxide (CaO) derived from calcite-based natural limestone from Pamekasan, Madura, East Java Indonesia. Controlled dissolution, titration, gel formation, and subsequent calcination at temperatures 650°C and 900°C were the steps involved in the synthesis. X-ray diffraction was used for characterization to identify the phase that had formed. Supporting software, MATCH! used to analyze the phases and structures and Rietica for refinement using the Rietveld method. The Ca(OH)2 phase formed was 59.65 ± 2.45 %wt before the calcination process, according to the XRD results. 23.71 ± 0.61 %wt CaO was produced by the calcination process at 650°C, and 64.52 ± 1.85 %wt was produced at 900°C. Meanwhile, after calcination at 900°C, crystal size analysis using MAUD software produced CaO with a size of 534 ± 74 nm. K CaO powder synthesized using the sol-gel method is calcined at 900°C to get a higher percentage than at 600°C. The CaO powder can be used for CO2 capture applications because it comes from natural resources and is environmentally friendly.