Flame Pyrolysis Method Research Articles

Iridium Oxide Nanorods Supported on Sb-Doped SnO2 As Highly Active Oxygen Evolution Catalysts for PEM Water Electrolysis

With the increasing installation of renewable energy generation systems such as solar and wind power, efficient energy storage devices are required to overcome the problem of fluctuations in the availability of electric energy. In particular, the splitting of water by electrolysis to produce storable hydrogen and oxygen appears to be one of the most promising approaches for large-scale energy storage. Proton exchange membrane water electrolysis (PEMWE) has received a great deal of attention due to its ability to respond quickly to renewable energy fluctuations and to operate at high current densities. However, a key limitation of PEMWE is the high cost associated with the use of high loadings of noble metal Ir catalysts at the anode electrode, which is necessary due to the slow kinetics of the oxygen evolution reaction (OER). Therefore, reducing the Ir loading at the OER electrode is essential to realize large-scale applications of PEMWE. This requires the development of highly active OER catalysts to accelerate the reaction or reduce the overpotential. Herein, we report a remarkably active OER catalyst of Ir oxide with nanorod-like structure supported on antimony-doped tin oxide (Sb-SnO2), showing an order of magnitude increase in Ir mass-specific activity than a commercial IrOx catalyst at 1.5 V vs. RHE. We also investigated the temperature dependence of the OER activity, as a way to elucidate the mechanism of enhanced catalysis, from both experimental and theoretical perspectives.The Sb-SnO2 support material (Sb dopant content 4 at.%) with fused-aggregate network structure was prepared by flame pyrolysis method.1 The as-prepared support powder was annealed at 700 oC for 2 h in air using a rotary kiln furnace. Sb-SnO2 supported IrOx nanorods (NRs) catalyst was synthesized by a colloidal method.2 The obtained IrOx NRs/Sb-SnO2 powder was heat-treated at 350 °C in N2 atmosphere for 2 h and at 150 °C in 1% H2 (N2 balance) for 2 h. The Ir loading was determined to be 49.3 wt.% by inductively coupled plasma optical emission spectrometry (ICP-OES). The OER activity was evaluated in 0.1 M HClO4 at 25 to 80 oC using the rotating disk electrode (RDE) technique.2,3 From Figure 1a, it can be seen that the Sb-SnO2 support particles present an interconnected network structure, which is considered to be beneficial to enhance the electron conduction and gas diffusion in the electrocatalytic reaction. On the support, the majority of IrOx nanoparticles are shown to have coalesced, forming rodlike structures. Figure 1b shows OER polarization curves (iR-corrected and normalized to the Ir mass) of the IrOx NRs/Sb-SnO2 catalyst compared to commercial IrOx catalyst (TANAKA Precious Metals). It is clear that the IrOx NRs/Sb-SnO2 catalyst significantly outperforms the IrOx reference catalyst over the entire potential range, and the OER onset potential of the IrOx NRs/Sb-SnO2 catalyst is lower. At 1.5 V (Figure 1c), the IrOx NRs/Sb-SnO2 catalyst exhibits a mass activity (MA) of 0.40 A mg-1 Ir, which is about 10 times higher than that of the IrOx reference catalyst. This dramatically enhanced activity makes it possible to significantly reduce the Ir loading on the anode of PEMWE. Experimental observations and density functional theory (DFT) calculations suggest that the nanorod geometry and strong metal-support interactions may play an important role in lowering the energy barrier for the crucial first step of the OER, thereby enhancing the OER activity. Acknowledgement This work was partly supported by the JSPS KAKENHI (23H02059) and by the project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Environmental applications of flame synthesized CuO nanoparticles through removal of Congo Red dye

The Copper oxide (CuO) transition metal oxide nanoparticles (NPs) synthesized by simple, fast and commercially viable comfortably slight modified flame pyrolysis method. The CuO NPs were synthesized by direct burning of ethanolic copper chloride solution. The prepared CuO NPs were characterized for phase and crystallinity by X–ray Diffraction [XRD] and Fourier Transform Infrared [FT–IR] Spectroscopy, estimation of morphology was done by Field Emission Transmission Electron Microscopy [FE–SEM], average particles size of prepared CuO NPs estimated by High Resolution Transmission Electron Microscopy [HR - TEM] as well purity ensured by Energy Dispersive X–Ray Spectroscopy [EDS]. UV–vis absorption spectroscopy done for adsorption of aqueous Congo Red (CR) dye of flame synthesized CuO NPs. The structural, elemental and morphological characterization emphasised the synthesized CuO NPs are crystalline, pure and exhibited monoclinic structure with spherical morphology. The environmental applications of these flame synthesized CuO NPs were also evaluated by using adsorption of Congo Red (CR) dye and temperature effect on dye adsorption were also verified. HR-TEM revealed the average particles size of around 30 nm with fringe spacing of 2.788 Å and 2.377 Å, which corresponds to (110) and (200) planes of monoclinic phase of CuO NPs. The synthesized CuO NPs exhibited optical bandgap of 2.93 eV. The synthesized NPs showed high dye removal capacity up to 99.90% for the aqueous solution of Congo Red azo dye. These CuO NPs may emerge as the best catalytic adsorption alternative for the removal of industrial dyes, heavy metals and waste water treatment.

Synthesis of cobalt oxide nanoparticles coated with carbon and its catalytic applications in organic reactions

Cobalt oxide nanoparticles coated with carbon were prepared by the modified flame pyrolysis method. The preparation was carried out by simply exposing the cobalt nitrate salt onto a spatula to gas flame, the flame temperature converted the cobalt nitrate into cobalt oxide, which further get coated by carbon produced from the combustion of fuel gas. The obtained product from the flame pyrolysis was characterized using techniques viz. XRD, FTIR and SEM. SEM data show that the short length rod shaped nanoparticles coated with carbon ranging from 0.3 to 1 µm µm formed during the process. XRD and FTIR data also support the formation of cobalt oxide nanoparticles coated with carbon particles. Cobalt oxide NPs were utilized for the catalytic N-formylation reaction of amines at 70–80 °C. The optimization of the catalyst as well as temperature have been done carefully. The product of the reaction were characterized by various techniques viz. FTIR, HRMS and 1H NMR which confirmed the formation of the product.

Cobalt oxide nanoparticles by flame pyrolysis for efficient removal of mixed dyes

The cobalt oxide nanoparticles were prepared by low cost, gram scalable and environment friendly flame pyrolysis method by directly burning ethanolic solution of cobalt chloride. The cobalt oxide formation, functional group identification, morphology and particles size of as-synthesized nanoparticles were carried out using routine techniques viz. XRD, FTIR, FE-SEM, HR-TEM, Raman Spectroscopy and Vibrating Sample Magnetometer (VSM) analysis. The XRD pattern ensured the formation of Cobalt Oxide nanoparticles (CoO NPs). It also emphasized that synthesized CoO NPs are pure, crystalline and single phased. EDS ensured the purity of CoO NPs which contained only cobalt and oxygen. FE-SEM exhibited spherical morphology with particles size of around 30 nm aligned with Debye–Scherrer’s calculated average crystallite size of 20 nm. The optical direct band gap of CoO NPs was estimated using Kubelka - Munk function to be 2.97 eV. The magnetic behavior examined at room temperature by VSM confirmed the formation of CoO NPs with weak ferromagnetic nature. The CoO NPs were utilized successfully for the removal of mixed dye solutions. The CoO NPs showed excellent efficiency for the removal of mixture of hazardous dyes from the aqueous solutions. This makes CoO NPs valuable for removal of industrial dyes and colorants for the waste water treatment processes.

Flame synthesized tetragonal TiO2 nanoparticles for Methylene Blue and Congo Red dye removal applications

Commercially affordable titanium dioxide nanoparticles (TiO2 NPs) catalyst with low toxicity and high efficiency, were prepared by scalable Flame pyrolysis method. For this, titanium iso-propoxide solution was directly burned in air, the product in the form of white soot was collected over water cooled conical flask. The prepared nanoparticles were characterized by various sophisticated techniques viz. UV–Visible, FTIR, XRD, SEM, EDS and TEM. The SEM, TEM and Zeta Potential Analyzer illustrated spherical morphology of the synthesized TiO2 NPs with an average size of about 150 nm. The XRD confirmed formation of prominently dominated anatase phase co-existed with traces of rutile phase. The combination of anatase and rutile phase exhibited increased catalytic activity for removal of dyes. The flame synthesized TiO2 nanoparticles exhibited strong dye removal efficiency of 97.64 % for Methylene Blue and 92.39 % for Congo Red dyes respectively, making it vitally important for the waste water treatment and industrial dyes removal applications. Probable dye degradations mechanism on the surface of TiO2 NPs also proposed based on the LCMS results.

Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni–Co Oxide Catalysts with Amorphous/Crystalline Surfaces

The development of high-performance oxygen evolution reaction (OER) catalysts based on earth-abundant transition metal oxides as alternatives to precious metal oxides is being pursued intensively for the large-scale application of alkaline water electrolysis for hydrogen production. Active OER electrocatalysts can be designed on the basis of fundamental insights into the catalytic phenomena occurring on surfaces. In particular, the temperature dependence of OER activity as a measure of reaction energies/barriers needs to be characterized by taking into account the operating temperature (60–80 °C) of a practical water electrolyzer. In this work, we synthesized Ni–Co oxide solid solution catalysts by the flame pyrolysis method, with particular emphasis on the temperature dependence of the OER catalysis, as a way to elucidate the catalytic reactions, from both experimental and theoretical perspectives. The as-prepared catalysts structured with conductive Ni–Co alloys were heat-treated at different temperatures in the presence of O2 to regulate the crystallinity of the oxide surfaces. The OER activity has been evaluated from 20 to 80 °C in 1 M KOH, and the OER kinetic current density was found to increase with increasing temperature for all catalysts obtained. Interestingly, the Ni–Co/oxide materials with amorphous or poorly crystalline oxide surfaces showed superior activity (3–8 times higher surface-specific activity at 1.55 V vs reversible hydrogen electrode (RHE)) than their crystalline counterparts at all temperatures. The OER activation energy also decreased with decrease of the crystalline oxide phases. It was demonstrated that the catalyst with amorphous Ni–Co oxide surfaces could be readily activated to form active oxyhydroxides under alkaline OER conditions. The amorphous or disordered structure of the surface oxide with low-coordinated sites is proposed to render the surface geometry energetically favorable for the rate-determining step O + OH → OOH, which accelerates the reaction kinetics and thus improves the OER activity, as explained by density functional theory calculations.

Superior energy‐power performance of N‐doped carbon nano‐onions‐based asymmetric and symmetric supercapacitor devices

Highly graphitic nitrogen-doped carbon nano-onions (N-CNO) have attracted much attention in the field of energy storage device applications. Herein, we have synthesized N-CNO by a simple flame pyrolysis method for symmetric and asymmetric (ASC) supercapacitor devices. The nitrogen doping is performed in-situ during the pyrolysis of pyrrole. The synthesized N-CNO has a high surface area of 49 m2 g−1 with 4 at% nitrogen content. The structural properties have confirmed the formation of graphitic N-CNO with highly ordered concentric graphene layers with proper lattice spacing. The fabricated symmetric and asymmetric devices have shown high specific capacitance and excellent energy-power performance. Especially, the ASC device shows a specific capacitance value 205 F g−1 with a high energy density (60 Wh kg−1) and power density (5.5 kW kg−1), leading to an increase in the power density by 260% for a mere 60% decrease in the energy density. In addition, both the novel symmetric and asymmetric devices have shown excellent capacity retention of 96% to 98% over 5000 cycles. The demonstrated results show the superior electrochemical performance of the active material, which indicates that the N-rich-CNOs can be used as a novel anode material in energy storage devices with high energy density and high power performance.

Removal of hexavalent chromium via an adsorption coupled reduction mechanism using olive oil derived carbon nano-onions

Carbon nano-onions (CNOs) were obtained in gram-scale by a simple flame pyrolysis method using olive oil. The olive oil carbon nano-onions (OCNOs) obtained had a quasi-spherical chain like onion structure with an average diameter of 46 ± 5.4 nm. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis were employed to determine the existence of surface functional groups (−OH, −COOH) on the OCNOs. The OCNOs were applied as adsorbents for the elimination of Cr(VI) ions from aqueous solutions using batch experiments. The ideal conditions for the sequestration of Cr(VI) ensued at pH = 2, T =25 °C, m =0.05 g, t =720 min, and CO =10 mg/L. The XPS data for Cr after adsorption on the OCNOs revealed that Cr(III) ions were produced in the reaction, consistent with the adsorption coupled reduction mechanism. The sequestration of Cr(VI) proceeded via monolayer surface coverage (Langmuir isotherm), with the kinetic information in line with the pseudo-second-order model. The thermodynamic features showed that the removal progression was viable, exothermic, and involved an associative mechanism. After the adsorbent regeneration, the removal of Cr(VI) ions was improved owing to the −OH ions added by the NaOH (regeneration solution). The CNOs produced by flame pyrolysis gave similar Cr(VI) removal data to that observed using more sophisticated CNO synthesis methods.

The effect of catalyst weight on the photocatalytic performance of ZnO-Ag nanocomposites prepared by flame pyrolysis method

ZnO is the most widely used as a catalyst material for photocatalytic application due to the suitable band gap energy and the chemical stability. It was reported by our previous study that the photocatalytic performance was significantly affected by the Ag content. In this study, ZnO-Ag nanocomposite materials have been successfully fabricated by flame pyrolysis and the effects of catalyst weight ranging from 2 to 10 mg on the photocatalytic performance were also investigated. Zinc acetate and silver nitrate were used as precursors for producing ZnO-Ag nanocomposites. The catalyst products, ZnO-Ag nanocomposite, were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). While, UV Vis spectrometry was used to measure the concentration of methylene blue (MB) before and after irradiations. Photocatalytic performances of nanocomposites were performed by evaluating the degradation of MB under UV and sunlight irradiations. The photocatalytic tests showed that the best performance was attained when the Ag content was 5 wt% and the weight of catalyst was as much as 10 mg after irradiation with sunlight, where the degradation rate of MB was 98% and the rate constant was 0.09/min.

Characterizations of Ag doped ZnO particles via flame pyrolysis method for degradation of methylene blue

Flame pyrolysis is widely used for the fabrication of particles because of great crystallinity and fine size distribution of the products. In this research, ZnO-Ag particle materials have been favourably made by flame pyrolysis. The impacts of Ag loading varying from 0 to 20 wt% on the photocatalytic activity of ZnO-Ag particle under ultraviolet (UV) and sunlight irradiations were studied. ZnO-Ag particles were fabricated based on zinc acetate dihydrate (Zn(CH3COO)2.2H2O) 0.1 M and silver nitrate (AgNO3) as a precursor inside a flame reactor. Crystallinity and morphology of ZnO-Ag particles were identified by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. SEM analysis showed that the particles had irregular sphere-like shapes. The XRD patterns showed that the produced ZnO had a wurtzite structure with different crystallite sizes. XRD analysis also confirmed the existence of Ag particles in ZnO-Ag particles after the addition of Ag greater or equal to 5 wt%. The existence of Ag was indicated by the appearance of the XRD peak at 38.1°. The peak at 38.1° increased with the increase of Ag loading. Finally, the photocatalytic activity was evaluated by estimating the degradation of methylene blue aqueous solution under UV and sunlight irradiations. It noted that the most excellent photocatalytic performance was achieved at 5 wt% Ag loading for both irradiations.

Nitrogen-Doped Carbon Nano-Onions as a Metal-Free Electrocatalyst

Growing environmental and economical concern necessitates novel materials with inherent electrochemical activity in as-prepared. Herein, we report, the electrochemical reactivity of the nitrogen-doped carbon nano-onions (N-CNO) prepared by a simple flame pyrolysis method. The as-obtained N-CNO has high N-content (4 at.%) and a large Brunauer-Emmett-Teller surface area (842.3 m2 g−1). The as-prepared N-CNO were probed as a cathode material for the oxygen reduction reaction (ORR) and as an electrocatalyst for sensitive nitrite ( $$ {\mathrm{NO}}_2^{-} $$ ) determination. The results demonstrate that, compared to N-CNT, as-prepared N-CNO exhibit a significantly enhanced ORR activity in alkaline medium and long-term stability with negligible change in activity. The N-CNO-based electrochemical nitrite sensor exhibits nitrite oxidation with two linear ranges 0.5 to 10 μM (R = 0.996) and 10 to 1000 μM (R = 0.978) with a sensitivity of 811.22 and 400.51 μA mM−1 cm−2, respectively. The detection limit (LOD) was 0.3 μM. The relative standard deviation (RSD) for eight replicate determinations was found to be 2.53%. The values of observed analytical parameters (linear range, sensitivity, and LOD) are comparable or superior to previously reported carbon-based $$ {\mathrm{NO}}_2^{-} $$ sensors.

Effect of different catalyst preparation methods on the synthesis of carbon nanotubes with the flame pyrolysis method

The Flame pyrolysis method used to synthesize carbon nanotubes was studied in this work. In order to improve the quality of synthesized carbon nanotubes, it is important to change the corresponding natures of the catalyst. Two catalyst preparation methods, namely, the sol-gel method and the impregnation method, were compared in this experiment. The properties of the catalyst are analyzed in depth by energy dispersive spectrometer (EDS), x-ray diffraction (XRD), temperature program reduction (TPR). The generation of carbon nanotubes was systematically analysed through scanning electron microscope (SEM), molecule dynamics (MD), raman spectroscopy and transmission electron microscope (TEM). The results show that the catalysts prepared by the impregnation method are stickier, dispersed and easier to dip onto the probe or substrate, which is beneficial for the large-scale production of carbon tubes. The specific surface area of alumina is larger and the iron and molybdenum oxide are more evenly dispersed on the surface of alumina. The carbon nanotubes produced by the catalysts prepared by impregnation method are flatter and have less impurities. The ratio of ID/IG+ is 29.7% lower than that of the sol-gel method in the Raman spectra. The TEM statistics show that the average diameter of the carbon tubes decreases by 23.3%. Therefore, the impregnation method can improve the quality of carbon nanotubes in the case of a similar degree of difficulty in the preparation of the catalyst.

Toxicity of 11 Metal Oxide Nanoparticles to Three Mammalian Cell Types In Vitro.

The knowledge on potential harmful effects of metallic nanomaterials lags behind their increased use in consumer products and therefore, the safety data on various nanomaterials applicable for risk assessment are urgently needed. In this study, 11 metal oxide nanoparticles (MeOx NPs) prepared using flame pyrolysis method were analyzed for their toxicity against human alveolar epithelial cells A549, human epithelial colorectal cells Caco2 and murine fibroblast cell line Balb/c 3T3. The cell lines were exposed for 24 h to suspensions of 3-100 μg/mL MeOx NPs and cellular viability was evaluated using. Neutral Red Uptake (NRU) assay. In parallel to NPs, toxicity of soluble salts of respective metals was analyzed, to reveal the possible cellular effects of metal ions shedding from the NPs. The potency of MeOx to produce reactive oxygen species was evaluated in the cell-free assay. The used three cell lines showed comparable toxicity responses to NPs and their metal ion counterparts in the current test setting. Six MeOx NPs (Al2O3, Fe3O4, MgO, SiO2, TiO2, WO3) did not show toxic effects below 100 µg/mL. For five MeOx NPs, the averaged 24 h IC50 values for the three mammalian cell lines were 16.4 µg/mL for CuO, 22.4 µg/mL for ZnO, 57.3 µg/mL for Sb2O3, 132.3 µg/mL for Mn3O4 and 129 µg/mL for Co3O4. Comparison of the dissolution level of MeOx and the toxicity of soluble salts allowed to conclude that the toxicity of CuO, ZnO and Sb2O3 NPs was driven by release of metal ions. The toxic effects of Mn3O4 and Co3O4 could be attributed to the ROS-inducing ability of these NPs. All the NPs were internalized by the cells according to light microscopy studies but also proven by TEM, and internalization of Co3O4 NPs seemed to be most prominent in this aspect. In conclusion, this work provides valuable toxicological data for a library of 11 MeOx NPs. Combining the knowledge on toxic or non-toxic nature of nanomaterials may be used for safe-by-design approach.

Experimental Comparative Study of Carbon Nanotubes Synthesized from CO and CH<sub>4</sub> by Flame Pyrolysis Method

In this paper, carbon nanotubes (CNTs) were synthesized by catalytic pyrolysis of CO and CH4 using flame pyrolysis method. The effects of using the two different carbon sources to the preparation of CNTs with all other conditions being equal were comparatively studied. The results showed that: the morphology of CNTs synthesized from different carbon source gases had certain difference. Higher yield of carbon nanotubes could be synthesized using CH4 as carbon source than using CO. At the same time, the former had less number of tube walls and the vascular bundles arranged more neatly. Synthetizing CNTs via catalytic decomposition of CH4 had more advantages than using CO by flame pyrolysis method.

Flame pyrolysis synthesis of self-oriented carbon nanotubes

In this paper, the flame pyrolysis method to synthesize self-oriented carbon nanotubes (CNTs) with Fe/Mo/Al2O3 as catalyst is studied. The outcome arrays are well aligned and relatively good in morphology. Furthermore, after electric field being applied to flame pyrolysis synthesis, the arrays become straighter and longer significantly, with higher yield.

Redox properties of Co- and Cu-based catalysts for the steam reforming of ethanol

Co- and Cu-based catalysts prepared by means of a flame pyrolysis (FP) technique are proposed as possible substitutes for Ni-based catalysts, very active for the Ethanol Steam Reforming reaction, but showing poor stability towards coke formation when operating at relatively low temperature.The FP method allowed to achieve a partial incorporation of the active phase into the support, leading to high dispersion and lower reducibility, at least in the case of Co. Cu was much more reducible than both Co and Ni, but it was almost completely inactive for the reforming reaction, mainly leading to ethanol dehydrogenation to acetaldehyde. The two different supports chosen, characterized by semiconducting behaviour and different reducibility (SiO2 and TiO2), were able to differently interact with the active phase. The best results, especially at 625 and 750 °C, were achieved with 10 wt% Co/SiO2, which led to higher activity, good C balance and low CO/CO2 ratio. This was ascribed to the high initial dispersion of Co into the silica matrix, which led to available Co particles well dispersed and stable on the catalyst surface.

Flame synthesis of 26-faceted maghemite polyhedrons grown via 14-faceted polyhedrons and their carbon composites for Li-ion battery application

26-faceted truncated cuboctahedrons of maghemite (γ-Fe2O3) nanocrystals are grown via 14-faceted truncated octahedrons through simple and effective flame pyrolysis method by direct burning of ferrocene in different solvents in an alcohol lamp. Systematic investigations showed that the solvent plays an important role in the formation and development of the polyhedral maghemite nanocrystals. The maghemite polyhedral structures are characterized by XRD, TEM and HR-SEM analysis in detail and on the basis of these, the crystal growth mechanism is discussed. Some solvents generated maghemite–carbon composites by encapsulation of maghemite polyhedron by graphene-like layered carbon surrounded by amorphous carbon shell. The as-prepared maghemite–carbon composite showed superior storage performance when tested for Li-ion battery applications. Compared to pure maghemite, the carbon composite exhibited a stable discharge capacity of ∼400 mA h g−1 even after 50 cycles, while the discharge capacities of bare maghemite dropped to ∼100 mA h g−1 after 20 cycles.

Optical Characterization of Eu-Doped and Undoped Gd2O3 Nanoparticles Synthesized by the Hydrogen Flame Pyrolysis Method

Rare-earth-doped nanoparticles are promising materials for fluorescent labeling, as they are characterized by a high Stokes shift, narrow emission spectra, long lifetimes, minimized photobleaching, and low toxicity. We examined the structural and optical properties of europium-doped gadolinium oxide nanoparticles synthesized by the flame pyrolysis method, with specific emphasis on full spectral characterization and fluorescence kinetics. The emission-excitation characterization revealed the presence of predominantly monoclinic but also highly luminescent cubic phases with a prominent oxygen-to-europium charge-transfer band in the 230-260 nm range. A broad emission band in the visible region, corresponding to a similar band in undoped Gd(2)O(3), related to the matrix surface defects, was observed in time-gated spectroscopy of doped nanopowders. All of the examined nanopowders showed very short decay components, on the order of 2 ns, and much longer millisecond decay times characteristic of lanthanide ions. At intermediate times, on the order of 20-100 ns, a complex behavior of the decay was observed, indicative of progressive energy transfer to the lanthanide ion, which varied with different intrashell transitions. Structural characterization data by means of XRD measurements allowed for unambiguous determination of the Eu:Gd(2)O(3) crystallographic structure and cell dimensions to be consistent with a predominantly monoclinic phase.