Composition Ce Research Articles

Electrochemical Impedance Spectroscopy Study of Ceria- and Zirconia-Based Solid Electrolytes for Application Purposes in Fuel Cells and Gas Sensors

In this study, the structural and electrochemical properties of commercial powders of the nominal compositions Ce0.8Gd0.2O1.9, Sc0.1Ce0.01Zr0.89O1.95, and Sc0.09Yb0.01Zr0.9O1.95 were investigated. The materials are prospective candidates to be used in electrochemical devices, i.e., gas sensors and fuel cells. Based on a comparison of the EIS spectra in different atmospheres (synthetic air, 3000 ppm NH3 in argon, 10% H2 in argon), the reactions on the three-phase boundaries were proposed, as well as the conduction mechanisms of the electrolytes were described. The Ce0.8Gd0.2O1.9 material is a mixed ionic–electronic conductor, which makes it suitable for anode material in fuel cells. Moreover, it exhibits an apparent and reversible response for ammonia, indicating the possibility of usage as an NH3 gas-sensing element. In zirconia-based materials, electrical conduction is realized by oxygen ion carriers. Among them, the most promising from an applicative point of view seems to be Sc0.09Yb0.01Zr0.9O1.95, showing a high, reversible reaction with hydrogen.

Hydrogen-Rich Syngas Production in a Ce0.9Zr0.05Y0.05O2−δ/Ag and Molten Carbonates Membrane Reactor

This study proposes a new dense membrane for selectively separating CO2 and O2 at high temperatures and simultaneously producing syngas. The membrane consists of a cermet-type material infiltrated with a ternary carbonate phase. Initially, the co-doped ceria of composition Ce0.9Zr0.05Y0.05O2−δ (CZY) was synthesized by using the conventional solid-state reaction method. Then, the ceramic was mixed with commercial silver powders using a ball milling process and subsequently uniaxially pressed and sintered to form the disk-shaped cermet. The dense membrane was finally formed via the infiltration of molten salts into the porous cermet supports. At high temperatures (700–850 °C), the membranes exhibit CO2/N2 and O2/N2 permselectivity and a high permeation flux under different CO2 concentrations in the feed and sweeping gas flow rates. The observed permeation properties make its use viable for CO2 valorization via the oxy-CO2 reforming of methane, wherein both CO2 and O2 permeated gases were effectively utilized to produce hydrogen-rich syngas (H2 + CO) through a catalytic membrane reactor arrangement at different temperatures ranging from 700 to 850 °C. The effect of the ceramic filler in the cermet is discussed, and continuous permeation testing, up to 115 h, demonstrated the membrane’s superior chemical and thermal stability by confirming the absence of any chemical interaction between the material and the carbonates as well as the absence of significant sintering concerns with the pure silver.

Low temperature processing and characterization of novel ceria based electrolyte composition Ce0.8−xGd0.1Bi0.1TixO2−δ (x = 0.05,0.1) for intermediate temperature SOFC application

Low temperature processing and characterization of novel ceria based electrolyte composition Ce0.8−xGd0.1Bi0.1TixO2−δ (x = 0.05,0.1) for intermediate temperature SOFC application

Optimizing the composition of (Ce,La)(Co,Fe)5for permanent magnet applications using density functional theory.

In this work, we calculated physical quantities, including the magnetocrystalline anisotropy constant (Ku) and magnetization (Ms), for disordered (Ce,La)(Co,Fe)5systems. Based on the results, we propose CeCo4.7Fe0.3as the optimum composition for high-performance permanent magnets. The calculations employed the full-potential Korringa-Kohn-Rostoker Green's function method, and dealt with the compositional disorder of the systems within the coherent potential approximation. It was found that the La doping reducesKuat 0 K but increases the Curie temperature (TC), which leads to improvement of the magnetic properties at high temperatures. CeCo4.7Fe0.3had the largest magnetic anisotropy ofKu= 15.14 MJ/m3, which is larger than that of CeCo5(Ku= 14.77 MJ/m3).TCof CeCo4.7Fe0.3estimated by the mean-field approximation was 1005 K, which exceeds that of CeCo5(965 K). Further, our calculations showed that while doping of Fe destabilizes the system, CeCo4.7Fe0.3is stable against decomposition into the simple substances. We also show calculated data that are informative for exploring high-performance permanent magnet materials in this paper.

Nitrates of cerium and samarium deposit on human enamel independently of a salivary pellicle.

The aim of this study was to analyze the precipitation of Cerium(III)nitrate hexahydrate [Ce(NO3)3] or Samarium(III)nitrate hexahydrate [Sm(NO3)3] solutions on human enamel with and without a salivary pellicle. Investigated parameters were At%Ce and At%Sm measured using energy dispersive x-ray spectroscopy (EDX) after test solution (two concentrations) application. Precipitation of Ce(NO3)3 and Sm(NO3)3 solutions was examined on human enamel with and without a salivary pellicle. 6 enamel specimens each were obtained from 12 freshly extracted human third molars. These specimens were ground flat and polished. A salivary pellicle was created on 3 of the 6 specimens per tooth by storing the samples in human saliva. Subsequently, an aqueous solution of Ce(NO3)3 was applied to 2 of the 6 specimens (one with, one without salivary pellicle) for 60 s. The same was carried out with an aqueous solution of Sm(NO3)3 on 2 further specimens. The remaining 2 specimens from each tooth were treated with demineralized water (negative control). Ce(NO3)3 and Sm(NO3)3 solutions were applied at 25 or 50 wt% (aqueous solutions). The test materials and concentrations were distributed using a randomization table. After 60 s exposure and rinsing with demineralized water, the elemental composition (Ce, Sm, Ca, P, O, N, Na, Mg) of the enamel surface was analyzed by EDX. Atomic percentages (At%), differences (ΔAt%) and calcium/phosphorous-ratios (Ca/P-ratios) were calculated and analyzed non-parametrically (α = 0.05). 2.0-2.3 At%Ce (median) was detected on Ce(NO3)3-treated enamel and 0.4-0.7 At% Sm (median) was detected on Sm(NO3)3-treated enamel. Ce was only detected on the surfaces after application of Ce(NO3)3, Sm only after application of Sm(NO3)3. The Ca/P-ratio was significantly lower (1.37-1.59; p = 0.028) after the application of 25% and 50%Ce(NO3)3 as well as 50%Sm(NO3)3 compared to the control treatment (demineralized water; 1.61-1.63). After treatment with Ce(NO3)3, At%Ca and At%Na were significantly lower (p ≤ 0.043) compared to treatment with Sm(NO3)3. No significant differences were found between specimens treated with 25% or 50% lanthanide nitrate solution. Presence of a salivary pellicle had no significant influence on the measured At% with the exception of specimens treated with 50% Sm(NO3)3 with increased At%Sm (p ≤ 0.046). Ce(NO3)3 and Sm(NO3)3 precipitate on human enamel independently of the presence of a salivary pellicle.

Cerium- and samarium-nitrate interaction and accumulation on human dentin

ObjectiveTo investigate the accumulation of cerium-nitrate and samarium-nitrate on dentin without or with smear-layer and to test their antibacterial activity. Design24 dentin-enamel slices were cut from 24 extracted molars. 12 slices underwent smear-layer creation (320 grit, 200 g, 5 s), the other 12 smear-layer removal (20 % EDTA, 300 s). Slices were halved to 48 semilunar-shaped specimens. One specimen per tooth was treated with either Ce(NO3)3 (50 wt% aqueous solution; pH = 1.29; n = 6) or Sm(NO3)3 (50 wt% aqueous solution; pH = 1.88; n = 6). The other specimen served as control (A. demin). After water rinsing, elemental composition (Ce, Sm, Ca, P, O, N, Na, Mg, C) was measured (EDX; EDAX Octane-Elect, APEX v2.5, low-vacuum) in dentin. Atomic percent (At%), Ca/P- and Ca/N-ratios were calculated and analyzed non-parametrically (α = 0.05, error rates method). Additionally, antibacterial activity (2 min exposure) of Ce(NO3)3 and Sm(NO3)3 against Streptococcus mutans, Actinomyces naeslundii, Schaalia odontolytica, and Enterococcus faecalis was determined (colony forming units) after anaerobic incubation at 37 °C for 24 h (control: 0.2 % CHX). ResultsAt% (median) of Ce and Sm were as follows: Ce(NO3)3 3.4 and 0.9 At%Ce with and without smear-layer, respectively; Sm(NO3)3 2.4 and 1.3 At%Sm with and without smear-layer, respectively. Ce(NO3)3 and Sm(NO3)3-application significantly decreased Ca/P-ratios (1.22 – 1.45; p ≤ 0.02) compared to controls (1.47 – 1.63). With smear-layer, significantly higher Ca/N-ratios (5.1 – 29.3) could be detected across all groups (p ≤ 0.004) compared to specimens without smear-layer (0.37 – 0.48). Ce(NO3)3 and Sm(NO3)3 showed reduction rates of up to ≥ 5 log10 steps for S. mutans, A. naeslundii, and S. odontolytica. ConclusionsCerium and samarium nitrate showed accumulation on dentin and certain antibacterial activity and could therefore be identified as potential compounds to treat and prevent dentin and root caries and dentin hypersensitivity.

Enhanced Hydrogen Production in Microwave‐Driven Water‐Splitting Redox Cycles by Engineering Ceria Properties

AbstractSustainable hydrogen, produced from renewable sources such as solar or wind, plays a decisive role in driving industrial decarbonization. Among hydrogen production technologies, steam electrolysis, and solar‐driven thermochemical cycles using reducible solid oxides show promise but face challenges due to high operation temperatures. Microwave‐driven redox chemical looping enables the direct, contactless electrification of the process, reducing the operation temperature and complexity. Previous works showed that microwaves can efficiently drive reduction/water‐splitting cycles using Gd‐doped ceria at low temperatures (<250 °C), but adjustment of material properties is needed. Here, the key properties of materials are explored that affect the redox mechanism by screening a series of doped ceria materials to enhance microwave‐driven hydrogen production. Evaluation of trivalent dopants (La3+, Gd3+, Y3+, Yb3+, Er3+, and Nd3+) reveals that reduction correlates with lattice and electronic properties. The composition Ce0.9La0.1O2‐δ achieves 1.41 mL g−1, the highest hydrogen production among the studied series. Its narrower bandgap allows for reaching higher conductivity upon microwave‐driven reduction at lower temperatures, while a larger ionic lattice size boosts solid‐state oxygen diffusion. Overall, this research remarks on the critical properties of ceria‐based materials that enhance hydrogen production in microwave‐driven water‐splitting cycles, supporting the design of more efficient materials for sustainable chemical production technology.

Ordered Mesoporous Ceria and Cerium Gadolinium Oxide Prepared by Vacuum-Assisted Nanocasting.

Four ceria-based mesoporous oxide materials were prepared using a new vacuum impregnation (VI) templating method developed by the authors, namely, vacuum-assisted nanocasting (VAN). Two hard templates (SBA-15 and KIT-6) were employed, and products with compositions CeO2 and Ce0.9Gd0.1O1.9 (CGO) were made with each. The desired fluorite phase and composition were confirmed by powder XRD and EDS. The product structures were characterised by XRD, TEM, gas physisorption and SAXS. All products contained ordered mesoporous material in high yields. The specific surface areas (SSAs) and pore volumes of the products were determined to be high and the pore size and pore spacings related well to the templates from which the materials were synthesised. The TEM studies confirmed that the samples had a 3D pore structure, with this being the negative of the original template. The target materials were not only produced in high yields, but also displayed a porous single-crystal morphology with non-linear lattice planes. The highest SSA values and pore volumes were reported for materials impregnated using the KIT-6 template and with the CGO composition. The results suggest that VAN is an excellent and reproducible method for producing ordered mesoporous cerias and has considerable potential for wider application. All the mesoporous products showed dramatically increased reducibility in TPR experiments compared with a high-SSA nanoparticulate ceria reference. This is very promising for their potential applications in oxidation catalysts and in fuel cell components.

Structural and ionic conduction study of Sm–Pr co-doped ceria electrolyte materials for LT-SOFC applications

Samarium praseodymium (Sm–Pr) co-doped ceria was synthesized by the co-precipitation technique as an electrolyte for low-temperature solid oxide fuel cell (LT-SOFC) applications. The structural, morphological, compositional, and electrical characterization of the synthesized samples were evaluated via x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX) and impedance spectroscopy. The generation of a single-phase fluorite structure of co-doped ceria without any secondary phases has been verified by XRD analysis, exhibiting the successful incorporation of Sm and Pr ions into the ceria lattice. Vegard's law is utilized for Pr redox behavior explaining the variation in lattice constant values. SEM pictures show that the co-doped ceria powder has a homogeneous and well-dispersed microstructure, and has enhanced particle size. The impedance spectroscopy results indicate that Sm–Pr co-doped ceria has much higher ionic conductivity than single-doped ceria. The highest amount of ionic conductivity (σionic) for the composition Ce0.80Sm0.10Pr0.10O2−δ recorded as 2.12×10−2S/cm at 500°C, and 6.19×10−2S/cm at 750°C with the lowest activation energy Ea=0.48eV, which has been not reported earlier. Sm and Pr are chosen as dopants because of their capacity to generate oxygen vacancies and improve ceria's ionic conductivity. This study contributes to the enhancement in the ionic conductivity of co-doped ceria by co-precipitation technique and the temperature-dependent frequency exponent factor "s" is also explored to comprehend the conduction mechanism of the prepared samples.

Phase Relationship and Ni Solubility in Nanoparticles of Ce0.9Zr0.1O2

AbstractThe phase relationship, defect formation, and incorporation of Ni in Ce0.9Zr0.1O2 have been investigated in samples of nominal composition (Ce0.9Zr0.1)1‐xNixO2‐δ with x=0.03, 0.05 and 0.1, synthesized by a cation complexation route and heat treated at 600, 800 and 1000 °C. Several structural (XRD, XAS, HRTEM) and spectroscopic (XPS, Raman) techniques have been used. Our data show the lattice parameters determined from XRD do not significantly vary with the Ni content or annealing temperature. The increasing defect concentration with increasing Ni content revealed by Raman spectra was associated to the formation of oxygen vacancies in the bulk due to coexistence of NiO and Ce0.9Zr0.1O2. On the other hand, no variation in the oxygen vacancies concentration was detected at the surface with increasing the Ni content by XPS data. In those samples with the lowest Ni concentrations (3 and 5 %) and heat treated at 600 °C, the analysis of the EXAFS zone of the K‐edge of Ni indicates that local order around Ni cations is not long‐range, suggesting the presence of a noncrystalline phase. When the Ni content is higher (10 %) and/or the temperature of the thermal treatment is increased, the crystallization of NiO is clearly detected by XRD, EXAFS and HRTEM.

S-doping Fe–Ce composites derived from PBA to accelerate Fe(iii)/Fe(ii) cycle in the Fenton-like process

S doping promoted the conversion of Fe(iii) to Fe(ii), which greatly improved the performance of the Fenton-like reaction.

Effect of CNT filler and temperature on fracture toughness of epoxy composites reinforced with carbon fabric

AbstractIn present research the fracture behavior of carbon fabric‐epoxy composites (CE composites) was evaluated with the addition of 0.1, 0.2, 0.5, and 0.75 weight percentages of carbon nano tubes (CNTs) at different temperatures. The CE composites with different wt.% of CNT were fabricated using land layup method and cured by hot pressing. The fracture toughness of fabricated composites was evaluated in mode–I condition at different temperature. From the results it was shown that the highest fracture toughness was observed at 0.75 wt.% of reinforcement of CNT functional fillers. The fracture toughness of 0.75 wt.% CNT filled CE composites was increased by 19.73% compared to unfilled CE composites. The fracture toughness of CNT filled CE composites diminishes with increase in temperature and the composite filled with 0.75 wt.% CNT exhibits better fracture toughness than the unfilled CE composite at all the temperatures. The fracture toughness was improved by 57.76% and 71.65% at 40 and 60°C, respectively, at 0.75 wt.% reinforcement of CNT fillers. The fractured surfaces of composites were analyzed using Scanning Electron Microscope (SEM) to study the filler contribution to enhance the fracture toughness and failure mechanism of composites.

MgF2-doped MgO-YAG:Ce composite ceramics prepared by pressureless vacuum sintering for laser-driven lighting

Laser-driven solid-state lighting has attracted much attention in recent years. However, the super-high luminous flux under high-power-density laser irradiation is accompanied by an enormous amount of heat. Here, to enhance the thermal robustness of phosphor converter materials, we prepared composite ceramics of YAG:Ce combined with high-thermal-conductivity MgO via simply vacuum sintering. 1.0 mol% MgF2 was employed as the liquid-phase sintering additive to accelerate the densification process. The optimum temperature proves to be 1400 °C, at which MgO-YAG:Ce composites exhibit highly dense composite structure, without obvious reaction between MgO and YAG phases. Additionally, low sinterability of commercial YAG:Ce particles dragged down the densification process, which limits the YAG:Ce content of the composites. As a result, MgF2-doped MgO-10 vol% YAG:Ce composite ceramic (MYF10) sintered at 1400 °C exhibits the highest relative density of 99.33 % and thermal conductivity of 42.05 W/(m·K). Under 34.06 W/mm2 blue laser excitation in a reflection mode, a stable laser-driven white light is obtained with the luminous flux of 2834 lm and luminous efficiency of 166 lm/W, respectively.

Ce0.9(Mg,Ni)0.1O2: Composite or Solid Solution

Samples of the composition Ce0.9(Mg1 – xNix)0.1O2 (0 ≤ x ≤ 1, step x = 0.1) have been obtained by gel combustion followed by hydrothermal treatment. X-ray powder diffraction data have showed that after gel combustion and annealing at 1100°C, composite CeO2 (fluorite structure)/solid solution Mg1 – xNixO (halite structure) is formed, and additional hydrothermal treatment followed by annealing promotes the formation of limited solid solution Ce0.9(Mg1 – xNix)0.1O2. According to the results of IR spectroscopy, the CeO2/Mg1 – xNixO composite does not adsorb CO2 even in the presence of water vapor, which is also confirmed by diffuse reflectance spectra in the UV-visible region. On the contrary, the Ce0.9(Mg1 – xNix)0.1O2 solid solution absorbs CO2, as evidenced by the results of IR spectroscopy and thermogravimetric analysis.

The Ga-admixed GSAG:Ce single crystal scintillator: Composition tuning

The scintillation, luminescence and optical properties of the multicomponent Gd3Sc2Ga(2+x)Al(1-x)O12:Ce (x = 0, 0.25, 0.5, 0.75, 1), Gd2.957Sc1.905Ga(2.138+x)Al(1-x)O12:Ce (x = 0, 1) and the (200, 1000, 5000 ppm) Mg2+ co-doped Gd3Sc2Ga2.75Al0.25O12:Ce single crystals grown by the μ-PD method were characterized. Scintillation decay kinetics and light yield were correlated with the sum of the content of Ga and Sc in the host. While the Ga-admixed GSAG:Ce composition exhibited higher scintillation efficiency compared to pure GSAG:Ce, it also showed very high afterglow, due to an intense delayed electron-hole recombination at Ce3+ centres. This was supported by the calculated activation energy obtained from the temperature dependence of photoluminescence decay times. Codoping with Mg2+ significantly improved afterglow compared to pure GSAG:Ce, however, at the expense of light yield.

Fabrication of color-graded feldspathic dental prosthetics for aesthetic and restorative dentistry.

Feasibility investigation of natural teeth shades replication on dental prosthetics fabricated via functionally graded additive manufacturing (FGAM) using combination of feldspathic porcelain (FP) and yttrium aluminum garnet cerium (Y3Al5O12:Ce, YAG:Ce) as a promising esthetic restoration option. Color-graded feldspathic crown fabrication parameter through FGAM method was comprehensively examined from the slurry rheology, cure depth, debinding to sintering temperature. Effect of light absorbent also checked towards overcuring reaction during UV exposure by the shape comparison. Lastly, the flexural bending strength measured following ISO 6872:2015 to assure the applicability. Applying the studied parameter, natural teeth shades then imitated and investigated by alteration of FP and FP +0.1wt% YAG:Ce (Y-FP). Generated color across the structure captured through mobile camera, interpreted through the CIELAB coordinate and the gradation confirmed by the color differences (ΔE00) calculated using CIEDE2000 formula. Parameter study indicated that 70wt% of FP slurry with 3wt% dispersant and 0.2wt% light absorbent is favored. It produces excellent flowability in our FGAM system with less overcuring justified by edge margin reduction from 95.65° to 90.00° after UV exposure on rectangle shapes masking. The obtain structure also offers adequate flexural bending strength of 106.26MPa (FP) and 101.36MPa (Y-FP) after sintering at 780°C. This validated the materials as class 2 dental prosthetics citing ISO 6872:2015. Color gradation was verified by the yellow b*value reduction (14.8 to -3.33) as it shifted from cervical to incisal area while ΔE00 further affirmed the differences from each segment in comparison with the FP and Y-FP. Color gradation was successfully replicated by FP and YAG:Ce composition shift via FGAM technique. This result highlights the potential of FGAM as an alternative for fabricating dental prosthetics with high efficiency and improved esthetic appeal.

Magnetic properties, crystalline and magnetic microstructures of dual-main-phase (Nd, Ce)-Fe-B sintered magnets

The (Nd, Ce)-Fe-B sintered magnets were prepared by a dual-main-phase (DMP) process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and (Nd, Ce)-Fe-B strips. The crystalline and magnetic microstructures of DMP (Nd, Ce)-Fe-B magnets with the remanence of 11.92–12.68 kGs, the intrinsic coercivity of 3.97–5.31 kOe, and the maximum energy product of 23.08–32.99 MGOe have been investigated. Magnetic force microscope (MFM) investigations reveal that the DMP (Nd, Ce)-Fe-B magnets show maze-like patterns, which are like that of standard anisotropy Nd-Fe-B sintered magnets by and large. However, much finer domain structures mixing with coarse ones can be observed obviously in DMP (Nd, Ce)-Fe-B sintered magnets. The size distribution of the domain width of the DMP (Nd, Ce)-Fe-B magnet is not uniform obviously. The average domain width is W = 0.912 μm, and the fine domain width has only 0.216 μm. The smaller domain width and more branch domain patterns exist in poorer coercivity DMP magnets. This is caused by the non-uniform Ce composition of poorer property DMP magnets and the grain boundary microstructure that is not conducive to improving the coercivity. Furthermore, it is found that some domains of rare-earth-rich grain boundary phases exhibit the characteristics of plate-like patterns rather than no-contrast by using MFM, indicating their ferromagnetism. Obvious correlations between the crystalline microstructure, chemical composition of phases, and magnetic structure were demonstrated for the DMP magnets.

Construction of Super-Hydrophobic Lignocellulosic Nanofibrils Aerogels as Speedy Oil Absorbents.

Lignocellulosic nanofibrils (LCNF) aerogels have a three-dimensional structure, with large specific surface area, low density, which is promising to be developed into a new type of adsorbent with high absorption capacity. However, LCNF aerogels have the problem of simultaneous oil and water adsorption. This high hydrophilicity directly leads to low adsorption efficiency in oil-water systems. This paper suggests a facile and economical method for the synthesis of biocompatible CE-LCNF aerogels using LCNF and Castor oil triglycidyl ether (CE) was successfully established. The use of LCNF enabled aerogels to possess remarkably uniform pore size and structural integrity, while the introduction of hydrophobic silica produced stable superhydrophobicity for more than 50 days at room temperature. These aerogels presented desirable hydrophobicity (131.6°), excellent oil adsorption capacity (62.5 g/g) and excellent selective sorption property, making them ideal absorbents for oil spill cleaning. The effects of ratios of LCNF to CE composition, temperatures and oil viscosity on the oil adsorption performance of aerogels were estimated. The results displayed that the aerogels had the maximum adsorption capacity at 25 °C. The pseudo-secondary model had higher validity in oil adsorption kinetic theories compared to the pseudo-first-order model. The CE-LCNF aerogels were excellent super-absorbents for oil removal. Moreover, the LCNF was renewable and nontoxic, which has the potential to promote environmental applications.

Geochemical signature of the bed sediments at the outlet of the Ibrahim River (Lebanon): temporal variation

Bed sediments were collected monthly at the outlet of the Ibrahim River between May 2016 and July 2017. Their physical and chemical characteristics were studied to highlight the impact of seasonal variations and discharge on the sediments' geochemical signatures. Granulometric analysis showed that samples collected after rain events contained abundant sand fractions (> 80%), while the clay fraction was more present at the beginning of the dry season, at low monthly average flows (1 m3/s). Ten major elements, 14 rare earth elements (REE), and 30 trace elements (TE) were analyzed. An excess of CaO reflected the contribution of the carbonate rocks of the Ibrahim karstic springs (30.35 ± 3.91%) but CaO concentration decreased during periods of high water. On another hand, no REE enrichment was detected, both in high and low flows. Most sediments collected at low flow had a pronounced REE depletion that occurred particularly for LREE composition (Nd, Pr, Ce, and La). A negative Ce anomaly (0.992) and a positive Eu anomaly (1.313) were revealed with an average La/Yb ratio of 0.570, reflecting a slight enrichment in HREE. Most studied TE were less concentrated than the averages mentioned in PAAS, UCC, and WSA references. However, a Ze enrichment was mainly due to the regional geochemical background, an As enrichment was associated with anthropogenic contribution, and a Zr enrichment was linked to discharges from pharmaceutical industries located at the river outlet. This study still needs to be complemented binding both spatial and temporal criteria for further fluvial sediments' monitoring of the entire catchment area.

Order and disorder in cerium-rich ceria-zirconia solid solutions revealed from reverse Monte Carlo analysis of neutron and x-ray total scattering

A reverse Monte Carlo analysis of neutron and x-ray total scattering data from two ceria-zirconia samples of composition Ce0.75Zr0.25O2 is performed to analyze the distribution of cations and to examine the possibility of oxide-ion disorder. For the first material, heated in air under moderate conditions (800 °C), the structure is a single-phase solid-solution with the statistical distribution of cations, but a local tetragonal symmetry is found, consistent with the different coordination preferences of Ce and Zr. For the second material, heated under H2 at 1050 °C followed by reoxidation at 400 °C, the structure shows a considerable disorder, with evidence for oxygen interstitials (Frenkel-ion defects) and a non-statistical distribution of cations with significantly higher concentrations of like–like cation nearest neighbors, highlighting the existence of cation-rich nano-domains. The results highlight the dynamic nature of this solid-solution, with structural evolution upon thermal treatment, which is of relevance to understanding its stability under redox catalytic conditions in practical applications.