Rietveld Refinement Research Articles

Electrosynthesis-Induced Pt Skin Effect in Mesoporous Ni-Rich Ni-Pt Thin Films for Hydrogen Evolution Reaction.

A Pt skin effect, i.e., an enrichment of Pt within the first 1-2 nm from the surface, is observed in as-prepared electrodeposited Ni-rich Ni-Pt thin films. This effect, revealed by Rutherford backscattering (RBS), is present for both dense thin films and mesoporous thin films synthesized by micelle-assisted electrodeposition from a chloride-based electrolyte. Due to the Pt skin effect, the Ni-rich thin films show excellent stability at the hydrogen evolution reaction (HER) in acidic media, during which a gradient in the Pt/Ni ratio is established along the thickness of the thin films, while the activity at the HER remains unaffected by this structural change. Further characterization by elastic recoil detection with He ions analysis shows that hydrogen profiles are similar to those of Pt: a surface hydrogen peak coincides with the Pt skin, and a gradient in hydrogen concentration is established during HER in acidic media, together with a considerable uptake in hydrogen. A comparative study shows that in alkaline media, hydrogen evolution has little to no effect on the structural properties of the thin films, even for much longer times of exposure. The mesoporous thin films, in addition to their higher efficiency at HER compared to dense thin films, also show lower internal stress, as determined by Rietveld refinement of grazing incidence X-ray diffraction patterns. The latter also reveal a fully single-phase and nanocrystalline structure for all thin films with varying Ni contents.

Red mud and bismuth oxide based X-ray shielding tiles for upcoming hospitals: A comprehensive study on phase quantification and physical properties

Red mud (RM) is a solid alumina industry waste generated in millions of tonnes and is stockpiled across the globe. From the environmental perspective, research and innovation strategies are utmost necessary for the minimization and utilization of red mud. In an attempt to develop an environmentally friendly technology, RM was utilized with Bi2O3 for the development of radiation shielding tiles. RM is a source of many metal oxides, which react with Bi2O3 during sintering and form various high-dense phases. The Rietveld refinement of the tiles sintered from 600 to 1100°C confirms the formations and transformations of several high-dense phases like Bi24Ti2O40, BiFeO3, and Na0.5Bi0.5TiO3. The RM-Bi2O3 mixture sintered at 1100°C (RMBi1100) exhibited high density (3.64 ×103 kg m−3), less porosity (10 %), and flexural strength of 24 MPa. The results showed that the developed sample has a half-value layer (HVL) of 1.15 mm at 140 kV. The 15.5 mm, 13.5 mm, and 7 mm thick RMBi1100 tiles can effectively replace 2.3 mm, 2 mm, and 1 mm thick lead sheets respectively, that are used to establish radiation shielding structures in computed tomography, radiography & fluoroscopy, and dental infra oral radiography installations, respectively. It can promote the utilization of red mud and thereby reduce the environmental pollution associated with lead and red mud.

Enhanced ultra-high efficiency in high-energy–density PbHfO3-based antiferroelectric ceramics through synergistic effect design

PbHfO3-based antiferroelectric materials with the giant power density and ultrafast charge–discharge performance have exhibited the potential application in advanced pulsed power microelectronic devices. Nevertheless, the huge challenge of the large driving field of the AFE-FE phase transition (EAFE-FE) accompanied by the poor breakdown electric strength (Eb) still exists up to now and further becomes a key bottleneck restricting the simultaneous realization of high energy storage density and efficiency. Hence, we report the synergistic effect to combine the tailor ABO3 perovskite structure for minimizing the electric hysteresis and increasing bandgap width to obtain the ultrahigh Eb. Rietveld refinements of the XRD patterns and Raman spectra experiments that demonstrate the average electronegativity and a redshift with the elevated Sr content attributable to enhancing bonding energy of cation-O bonds and antipolar ordering in crystalline structure, effectively resulting in stability of the PbHfO3-based antiferroelectric structure. Meanwhile, a ultrahigh Eb of 450 kV/cm is achieved owing to optimizing the average grain size and widening bandgap width. A remarkable energy storage density of 7.29 J/cm3 and record-high energy storage efficiency of 96.40 % are achieved via synergistic effect in (Pb0.93La0.02Sr0.04)(Hf0.475Sn0.475Ti0.05)O3 (PLS4HST) ceramics under respective maximum applied field. In addition, large power density of 173.40 MW/cm3 and excellent discharge energy density of 4.90 J/cm3 as well as fast discharge rate of 166.90 ns and superior frequency stability (1 ∼ 140 Hz), along with outstanding thermal stability (25 ∼ 150°C), have been simultaneously presented in PLS4HST ceramic. These results provide a good paradigm by synergistic effect designing for exploring high-performance dielectrics to meet the demanding requirements of advanced pulsed power electronic devices.

Phytochemical preparation of Zinc Stannate nanoparticles by using lemon and grapefruit peels for removal of cadmium ions

Abstract The synthesis of Zinc Stannate (Zn2SnO4) nanoparticles may be achieved by utilizing lemon and grapefruit peels, as indicated by the results of this study. This analysis outlines a sustainable, cost-effective, and readily available approach. The Zn2SnO4 nanoparticles were generated biologically and were discovered to have a cubic crystalline structure, as established by structural analysis using Rietveld refinement. TEM microstructural examinations revealed that Zn2SnO4 nanoparticles exhibit a homogeneous distribution and possess an average diameter of around 21 nm. The Zn2SnO4 nanoparticles have an optical energy band gap of 3.05 eV and demonstrate a UV region peak, which showed that Zn2SnO4 nanoparticles were being formed. More precisely, the pH of the solution greatly affects the absorption of Cd2+ ions. Kinetic analysis involves the use of two types of models: pseudo-first-order and pseudo-second-order. The previous model yields an R2 value of 0.9031 and a rate constant (k1) of 0.41×10-2 min-1. However, the pseudo-second-order model provides a better match, as seen by its very high R2 value of 0.9932 and rate constant (k2) value of 4.4×10-3 g.(mg.min)−1. In addition, isotherm modeling shows that the experimental data closely match the Freundlich isotherm model.

Investigation on the compressive strength, chloride migration of MK-FA-LS blended cementitious materials with electrochemical techniques

Blended cementitious materials has become an efficient method to reduce the CO2 emission while improving the long-time performance in construction filed, especially for the application of combined supplementary cementitious materials. However, the microstructure and performance evolution of the new materials need further deep investigation. In this study, metakaolin (MK), fly ash (FA) and limestone (LS) was introduced in cementitious materials to form a complicated quaternary system. The compressive strength and chloride migration performance are evaluated, with different MK/FA proportions. Then through the calorimetry test, X-ray Diffraction (XRD)/Rietveld analysis, free water content measurements, and electrochemical impedance spectroscopy (EIS) test, the phase assemblage and microstructure quantification of the blended systems are compared. Finally, to better understand the performance change, the correlation between the compressive strength/chloride migration coefficient and the electrochemical parameters are established. Results showed that the combination of MK, FA and LS is beneficial for the improvement of compressive strength and the chloride resistance in a proper mix design. EIS is a proper nondestructive method to understand the microstructure evolution of blended systems and even predict the chloride resistance of similar systems. This study shields a light for the application of the quaternary system, with a better durability, higher CO2 emission reduction and lower price.

Structural and optical properties of green-synthesised tricobalt tetroxide nanoparticles

In this study, we investigated the structural and optical properties of garlic extract-based green-synthesised tricobalt tetroxide nanoparticles. Transmission electron microscopy revealed a particle size range of 8–22 nm for the prepared powder sample. Powder x-ray diffraction data and Rietveld refinement results confirmed the spinel cubic crystal structure of the tricobalt tetroxide nanoparticles, with an average crystallite size of 11.23 nm. This crystal structure corresponds to the Fd3̅m space group and has an average lattice constant of 0.791 nm. The bond lengths of Co3+–O2− and Co2+–O2− are measured to be 0.188 nm and 0.190 nm, respectively. The FTIR data provided evidence of the presence of various functional bands, which helped qualitatively determine the purity of the sample. The UV–vis spectrum estimated two direct energy band gap values (3.7 eV and 2.2 eV) that may be useful for efficient interaction with a wide range of ray spectra to create more electron–hole pairs for various photo-responsive applications, such as dye degradation, solar cells, and optoelectronic components.

Rare-earth (Eu3+) substitution impact on the structural, morphological, magneto-dielectric, and electrochemical properties of Cd0.45Co0.55Fe2−y Eu y O4 spinel nanoferrites

A series of Cd0.45Co0.55Fe2−yEuyO4 (y = 0.0, 0.1, 0.2, 0.3) spinel nanoferrites (SNFs) were synthesized using a self-igniting process and employed as electrode materials for supercapacitor applications. The results demonstrated the formation of a single SNFs phase, as shown by the XRD data. The crystallite size lies between the range of 29.30–51.12 nm. The porosity percentage is within the range of 31.37%–32.99%. Rietveld refinement of XRD and Raman analysis revealed the pure spinel phase and no secondary phase was observed. The saturation magnetization and magnetic anisotropy were also decreased with the addition of Eu3+ in Cd–Co SNFs. The high coercive field was enhanced for Eu3+ doping as compared to pure Cd–Co SNFs. The dielectric constant was improved with the substitution of Eu3+ in Cd–Co SNFs. The dielectric tangent loss was reduced with the doping of Eu3+. The electrochemical performance of the Eu3+ doped Cd–Co SNFs achieved an impressive maximum specific capacitance at a lower scan rate. Based on these findings, the outstanding electrochemical performance of the Eu3+ doped Cd–Co SNFs suggests their potential as promising materials for high-frequency, magnetic ferrofluid, and supercapacitor electrodes.

Effect of calcination temperature on structural, optical, and morphological properties of RAlO3 (R = La, Sm) perovskite oxides

RAlO3 (R = La, Sm) have attracted the research community due to their interesting optoelectronic properties and viable applications. The solution combustion method allows for a faster process and lower calcination temperature than the traditional solid-state method and is an economical alternative to wet chemical synthesis for producing RAlO3. This work explores the thermal, structural, morphological, optical, and electrical properties of RAlO3 (R = La, Sm) synthesised by the solution combustion method using urea as fuel. Thermogravimetric analysis—differential thermal analysis (TGA-DTA) showed the crystallization temperatures of lanthanum aluminate (LaAlO3) and samarium aluminate (SmAlO3) at 864 and 887 °C, respectively. The x-ray diffraction (XRD) and Rietveld analysis revealed the structure of LaAlO3 as rhombohedral (R-3c) and SmAlO3 as orthorhombic (Pbnm). The LaAlO3 and SmAlO3 samples calcinated at 800 °C showed crystallite size (D) of 19.26 nm and 19.06 nm, respectively. The field emission scanning electron microscopy (FE-SEM) images show a highly porous and large sheet-like morphology with voids and cracks. High resolution transmission electron microscopy (HR-TEM) images and the selective area electron diffraction (SAED) pattern show crystalline nature and the indexed planes agreed with the XRD results. The LaAlO3 and SmAlO3 samples had specific surface areas of 16.374 and 12.953 m2 g−1, respectively. The TGA-DTA results were affirmed by Fourier transform infrared spectroscopy (FT-IR) results which showed only the presence of metal-oxide bonds for materials annealed at and above 800 °C. These results were further validated by the electron dispersive x-ray spectroscopy (EDX) and the x-ray photoelectron spectroscopy (XPS) showing no additional peaks. The band gap of 5.08 and 4.82 eV were calculated from ultraviolet-visible spectroscopy (UV–vis) for LaAlO3 and SmAlO3, respectively. The results imply that the solution combustion technique using urea as fuel is a viable route for synthesising RAlO3.

Microstructural analysis and densification of ordinary Portland cement mortars incorporated with minimal nano-TiO2: intermixing and surface coating on both fresh and hardened surfaces

The present study investigated the microstructural properties of ordinary Portland cement (OPC)-modified with minimum dosage of nano TiO2 on fresh and hardened cement mortar surfaces and intermixed samples. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were used to analyze the morphology and hydration products of the OPC specimens doped with nanotitanium (NT).Additionally, XRD coupled with Rietveld refinement was employed to quantify the crystal phases and refine the crystal structure model through the comparison of the calculated diffraction pattern to the measured pattern. Subsequently, crystallographic analysis was conducted to evaluate the crystallographic structure and to confirm the existence of specific atoms and bonds within the crystal structure altered with NT. The findings revealed that the addition of minimal NT resulted in a more compact and denser microstructure, characterized by increased formation of calcium silicate hydrate (CSH) gel and a reduction in calcium hydroxide (CH) crystals.This led to a reduction in the porosity of the hardened coating surface, with similar improvements observed for the fresh coating and intermixed samples compared to those of the control mortar. A decrease in the lattice parameters, accompanied by an increase in the number of atoms, bonds and polyhedra in the crystal structure, led to alterations in the interatomic spacing and contributed to the densification of the cementitious matrix.The findings also showed that NT integration led to a more compact structure with shorter bond distances and smaller polyhedral volumes for the Ti samples than for the control sample. Moreover, compared with the freshly cast and hardened coating samples, the NT-intermixed samples exhibited the shortest Ti–O bond distances and the smallest polyhedral volume. Overall, the analysis presented in this study significantly contributes to the development of novel and environmentally friendly photocatalytic cementitious materials at minimal dosages.

Type-II superconductivity at 9K in Pb–Bi alloy

In the present work, we report the synthesis of Pb–Bi alloy with enhanced Tc of up to 9K, which is higher than that of Pb. The alloy is synthesized via a solid-state reaction route in the vacuum-encapsulated quartz tube at 700°C in an automated furnace. The synthesized sample is characterized by X-ray Diffraction(XRD) and Energy dispersive X-ray analysis(EDAX) for its phase purity and elemental composition. Rietveld refinement of XRD reveals that the end product is a majority hexagonal Pb7Bi3, with minor rhombohedral Bi. The electronic transport measurement shows metallic behavior with the Debye temperature of 108K and a superconductivity transition temperature (Tc) below 9K, which is the maximum to date for any reported Pb–Bi alloy, Pb or Bi at ambient pressure. Partial substitution of Bi at the Pb site may modify the free density of electronic states within the BCS model to attain the optimum Tc, which is higher by around 2K from the reported Tc of Pb. The superconductor phase diagram derived from magneto-transport measurements reveals that the synthesized alloy is a conventional superconductor with an upper critical field (Hc2) of 3.9 T, which lies well within the Pauli paramagnetic limit. The magnetization measurements carried out following ZFC(Zero Field Cool) protocols infer that the synthesized alloy is a bulk superconductor below 9K. The isothermal M-H(Magnetization vs. Field) measurements performed below Tc establish it as a type-II superconductor. The specific heat capacity measurements show that the Pb–Bi alloy is a strongly coupled bulk superconductor below around 9K with possibly two superconducting gaps.

Luminescence and Dosimetry Investigations of Eu(III) Doped Ca2CeVO6 Novel Double Perovskite

A novel composition of vanadate double perovskite Ca2CeVO6 doped with Eu3+ was successfully synthesized using combustion synthesis, wherein the doping levels of Eu3+ ranged from 1 to 6 mol%. The Rietveld refinement of the powder X-ray diffraction (XRD) data confirmed the orthorhombic structure of the phosphors. Scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX) were employed to investigate the surface morphology and elemental distribution in the phosphor, respectively. Under the excitation at 280 nm and 467 nm, the phosphor exhibited strong down-conversion red photoluminescence (PL) emission, attributed to Eu3+ transitions (5D0-7FJ, where J=0-3) originating from its 4f states. The intensity of PL emission shows increasing trend with increasing doping concentration. However, exceeding the threshold doping concentrations led reduction in PL intensity due to multipolar interaction effects. Additionally, the Eu3+ doped Ca2CeVO6 phosphors were subjected to irradiation with a radioactive 90Sr/90Y beta source to explore their thermoluminescence (TL) properties. Post-irradiation, the phosphors displayed prominent TL glow curves, with the most intense peak at around 94°C, followed by peaks at 160°C and 288°C. The TL intensity of these peaks exhibited a linear dose response within the dose range of 1 Gy to 50 Gy. Besides, the TL fading and reproducibility tests showed satisfactory results. Furthermore, Tmax-Tstop experiments revealed the presence of three trap centres within the trap depth range of 0.7-2.1 eV in the Ca2CeVO6:Eu3+ phosphor. Additionally, the glow curve deconvolution (GCD) was employed to determine trapping parameters, providing valuable insights into the TL behaviour of the phosphor. Overall, the results suggest that the novel phosphor under study holds promise for its applications in lighting devices and TL dosimetry (TLD).

CaLi2PN3 - A Quaternary Chain-Type Nitridophosphate by Medium-Pressure Synthesis.

Nitridophosphates are in the focus of current research interest due to their structural versatility and properties, such as ion conductivity, ultra-incompressibility and luminescent properties when doped with suitable activator ions. Multinary representatives often require thorough investigation due to the competition with the thermodynamically more stable binary and ternary compounds. Another point of concern is the synthetic control of structural details, which is usually limited by conventional bottom-up syntheses. In this study, we report on the synthesis and characterization of the quaternary nitridophosphate CaLi2PN3. Various synthesis protocols were used for the preparation of CaLi2PN3, including the novel nitridophosphate double salt approach. The crystal structure was solved and refined from single-crystal X-ray diffraction data and confirmed by Rietveld refinement, solid-state NMR spectroscopy, EDX measurements and low-cost crystallographic calculations. The experimental results were corroborated by DFT calculations, which revealed the electronic band structure. Formation energy calculations allowed conclusions to be drawn about the stability in comparison to the initial ternary nitridophosphates. The synthesis of CaLi2PN3 exemplifies the enormous potential of medium-pressure syntheses in the field of nitridophosphate research. Furthermore, the presented new synthesis route allows a certain degree of structural control, which is a promising addition to previous synthesis strategies in nitridophosphate chemistry.

Exploring the effect of Hf (IV) doping in spinel ferrite CoHfxFe2-xO4 on magnetic properties, electrochemical impedance, and photocatalytic activity: In-depth structural study

In this study, CoHfxFe(2−x)O4 nanoparticles (x = 0.0, 0.04, 0.08, and 0.12) were synthesized using the co-precipitation method. X-ray diffraction (XRD) analysis confirmed a pure spinel phase for the x = 0.04 sample, validated by Rietveld refinement, with crystallite sizes between 39 and 59 nm. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed the formation of the spinel structure and the proper valence states of the elements. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) verified the morphology and homogeneity of the samples. Magnetic property analysis revealed reduced saturation magnetization with increased Hf content. Impedance spectroscopy showed enhanced electrical resistivity with Hf incorporation. Photocatalytic tests demonstrated that doping improves the degradation efficiency of Orange G dye under UV-Vis irradiation, achieving yields between 9 % and 35 % after 60 min.

On the structure of Tl2Pb(SO4)2 and crystal chemistry of thallium‐containing sulfates

Single crystal of a thallium‐containing sulfate Tl2Pb(SO4)2 was prepared through hydrothermal crystallization starting from Tl2CO3, Pb(NO3)2 and H2SO4. The crystal structure was solved from single‐crystal X‐ray diffraction data: Tl2Pb(SO4)2 crystallizes in space group R[[EQUATION]]m with lattice parameters of a = 5.5955(2) Å, c = 22.1001(9) Å, and Z = 3, which is also corroborated by Rietveld refinement on X‐ray powder data. The crystal structure can be regarded as [Pb(SO4)2]2‐ sheets intercalated by double layers of Tl+ along the c‐axis. From a mineralogical perspective, Tl2Pb(SO4)2 belongs to the palmierite family and can further be classified within palmierite‐supergroup. Validation of the structure models was carried out utilizing various concepts including Bond Valence (BV), Charge Distribution (CD) and Madelung Part of Lattice Energy (MAPLE). Notably, a contrast in stereochemical activity of 6s2 lone electron pair (LEP) between Tl+ and Pb2+ is interpreted in terms of bonding behaviours as well as Wang‐Liebau Eccentricity (WLE) parameters. Moreover, an extensive investigation into the crystal chemistry of thallium‐containing sulfates was conducted for the first time, focusing on the coordination environment and bonding behaviour of Tl+ and corresponding WLE parameters. A comparative analysis of these structurally related compounds including Tl2Pb(SO4)2, Tl3H(SO4)2, TlBi(SO4)2, TlIn(SO4)2, TlRh(SO4)2, and TlAl(SO4)2 was delineated.

Novel Magnetite (Fe3O4)-Methylcellulose Nanocomposites Synthesized Using the Reverse Co-Precipitation Approach

A simple approach was used to create Fe3O4-methylcellulose (MC) nanocomposites, which were then analyzed using XRD, FTIR, and FE-SEM to determine their structure. The effective factors for enhancing the ratio of magnetite NPs in the samples were investigated using RTFM and optical absorbance. Fe3O4 was synthesized utilizing the reverse co-precipitation technique and magnetic characteristics. Fe3O4/MC nanocomposites with magnetite/MC weight ratios of 0, 0.07, 0.15, and 0.25 have been developed. The diffraction pattern of magnetite is well indexed in accordance with the spinal reference pattern of Fe3O4 (space group: R¯3m), as confirmed by the Rietveld analysis of XRD data of magnetite NPs with an average crystallite size of 50 nm. Magnetite’s insertion into the MC network causes a red shift in the band gap energy (Eg) as the weight percentage of magnetite nanoparticles in the samples rises. The MC, MC-7, MC-15, and MC-25 samples have Eg values of 5.51, 5.05, 2.84, and 2.20 eV, respectively.

Role of Fe supplantation in tailoring structural, electrical conductivity, and magnetic properties in La2Ni1-xFexMnO6 double perovskites

Double perovskite system La2Ni1-xFexMnO6 (x = 0, 0.2, 0.5, 0.8 & 1.0) were developed using sol-gel method. Rietveld refinement revealed monoclinic structure (ordered) along with occurrence of rhombohedral and orthorhombic structures suggesting antisite cationic disorder. Crystallite size and average grain size of samples varied between 454 and 1058 Å and 0.774–1.429 μm respectively. XPS revealed the dual oxidation states of Ni, Fe, and Mn ions. La2NiMnO6 attained the highest DC conductivity among all compositions. The increase in DC conductivity with temperature suggested the semiconducting behavior of the samples, that explained by Thermal Activation (TA) and Variable Range Hopping (VRH) conduction mechanisms. Obtained activation energy(Edc) showed increasing trend with temperature. M-H loops exhibit a ferromagnetic nature accompanied by antiferromagnetic interactions as suggested by exchange bias and partially saturated loops. La2NiMnO6 attained the highest saturation magnetization (29.81emu/g) and decreased with Fe supplantation. The possible mechanism of tuning conductivity and magnetic properties of La2Ni1-xFexMnO6 has been discussed in detail.

The B-site ordering in RFe0.5Cr0.5O3 ceramics and its effect on magnetic properties

Abstract To insight into the B-site ordering in RFe0.5Cr0.5O3 ceramics, a series of RFe0.5Cr0.5O3 ceramics (R = La, Y, Lu) were synthesized by the sol-gel method, and the structural and magnetic properties were systemically investigated. By using the Rietveld refinement of all samples, it is found that the structural distortion is increased as the R ionic radius decreases, leading to the weakened interactions between Fe/Cr ions. Besides, the Fe and Cr are arranged in disorder in LaFe0.5Cr0.5O3, but partially ordered in YFe0.5Cr0.5O3 and LuFe0.5Cr0.5O3, showing an increasing trend of the proportion of ordered domains with the decrease of R ionic radius. Through fitting the temperature-dependent magnetizations, it is identified that the magnetization reversal (MR) in disorder LaFe0.5Cr0.5O3 is resulted from the competition between the moments of Cr and Fe sublattices. In the partially ordered YFe0.5Cr0.5O3 and LuFe0.5Cr0.5O3 ceramics, because of the presence of Fe-O-Cr networks in the ordered domains whose moment is antiparallel to that of Fe-O-Fe and Cr-O-Cr in the disordered domains, the compensation temperature Tcomp of MR is increased by nearly 50 K. These results suggest that the changing of R-site ions could be used very effectively to modify the Fe-O-Cr ordering, apart from the structural distortion, which has a direct effect on the magnetic exchange interactions in RFe0.5Cr0.5O3 ceramics. Then at values of composition where ordered domains are expected to be larger in number as compared to disordered domains and with a weaker structural distortion, one can expect a higher transition temperature Tcomp, providing a different view for adjustment of the magnetic properties of RFe0.5Cr0.5O3 ceramics for practical applications.

Investigation of physicochemical characteristics of Dy3+ modified ZnO nanoparticles

In this report, pristine and Dy3+ modified ZnO nanoparticles [Zn(1-x)DyxO NPs, where x = 0, 0.05, and 0.10] were synthesized using the sol–gel route, and their physicochemical characteristics were investigated. x-ray diffractograms of all the compositions possess P63mc space group depicting hexagonal crystallinity with wurtzite-type crystal structure with no signature of impurities as confirmed using the Rietveld refinement technique. The granular microstructure displayed grain growth with Dy3+ incorporation in the ZnO crystal framework and an increment in average grain size was found to be 22.83 nm for x = 0 to 36.34 nm. The optical energy band gap also increased from 3.35 eV to 3.88 eV with Dy3+ doping in the host ZnO. Dy3+ substitution inhibits the conduction in ZnO and improves the resistivity (36 Ωcm–79 Ωcm) as carrier concentration diminishes from 7.36 × 1016 cm−3 to 4.23 × 1016 cm−3. Similarly, the mean free path length for ZnO and Dy3+ doped ZnO NPs declines from 0.0301 nm to 0.0198 nm. Dielectric properties of all the compositions were investigated using an LCR impedance analyzer and it was observed that Dy3+ substitution enhances the value of the dielectric constant from 32 to 91 with a low tangent loss at 50 Hz.

Synthesis, characterization and structure-property relations in mullite-type Pb2(Pb1−x Sn x )O4 solid solution

Abstract The crystal structures of both Pb2PbO4 (Pb3O4) and Pb2SnO4 at room temperature can be described using mullite-type setting in the space groups P42/mbc and Pbam, respectively. At what chemical extend the crystal structure prefers either of the space groups would be an excellent playground in the Pb2(Pb1−x Sn x )O4 solid solution. Members of the solid solutions have been prepared by solid-state reactions carried out in sealed quartz tubes. Each sample has been found to be phase pure confirmed by X-ray powder diffraction data Rietveld refinement. Samples with higher tin content require higher synthesis temperatures, and controlled decomposition of Pb3O4 serves as the source for both Pb2+ and Pb4+ cations. Since the Pb4+ cation is larger than Sn4+, the MO6 polyhedral volume decreases with increasing Sn-content. As such, each metric parameter shows a linear trend following Vegard’s rule. The concomitant contraction of the MO6 octahedra and the high stereo-chemical activity of the 6s 2 lone electron pairs of lead in the Pb2+O4 distorted pyramid results in symmetry reduction. DFT suggests dynamical instability of the tetragonal Pb3O4 while Pb2SnO4 keeps orthorhombic symmetry at low temperatures, which agrees well with the experimental findings. The global blue shift of the vibrational mode frequencies is explained by the quasi-harmonic approach. The indirect band-gap linearly increases from 2.1(1) eV (x = 0) to a maximum value of 2.5(1) eV for x = 0.8 followed by a sharp drop towards Pb2SnO4. Thermogravimetric analysis demonstrates higher thermal stability with increasing Sn-content, which is explained in terms of higher bond strength of Sn–O than that of Pb–O in the MO6 octahedra.

Thermal Behavior of Clinoptilolite

Understanding the thermal properties of zeolites is crucial for their industrial applications. This study explores the thermal stability and dehydration process of clinoptilolite using high-temperature X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Clinoptilolite’s thermal decomposition was monitored from 25 °C to 1200 °C, with results analyzed based on its crystal structure. Principal components analysis (PCA) of the DRIFT spectra indicated progressive water removal and dehydration upon heating, leading to the formation of hydrogen bonds. Thermogravimetric analysis (TGA) revealed a two-step endothermic weight loss: initially, physically adsorbed water was lost up to 100 °C, followed by the removal of tightly bound water and hydroxyl groups until 800 °C. Clinoptilolite remained the dominant phase up to 800 °C, after which albite and cristobalite took over. Rietveld refinement showed that the sample initially contained 70% clinoptilolite, 24% albite, and 6% cristobalite. Above 800 °C, clinoptilolite disappeared, leaving 93% albite and 7% cristobalite. FT-IR spectra changes due to water loss were evident: drying of adsorbed water occurred up to 75 °C and minimal changes were observed from 75 °C to 135 °C, followed by further dehydration until 240 °C. Complete dehydration was confirmed by the disappearance of OH stretching vibration bands by 395 °C, consistent with TGA findings.