Incorporation Of Rare Earth Elements Research Articles

Nanomaterials and Rare Earths Used To Evaluate the Photocatalytic Degradation of a Dye, with Potential Use in Decontaminating Water Bodies

In this work, nanomaterials and rare earths were obtained with application in the degradation of dyes since in the developing countries the decontamination of water bodies is essential. We used TiO2 for incorporation of rare earths applied to photocatalytic activity in degradation of methyl blue due to its high chemical stability and corrosion resistance. We obtain nanostructured materials of TiO2, TiO2: Ln3+ (Ln3+ = Sm3+, Gd3+ and Yb3+) by sol gel method, for decontamination of dye such as methylene blue in surface water bodies. Through x-ray diffraction, we found that anatase-rutile phase was achieved in TiO2 and tetragonal anatase phase in TiO2 : Ln3+. Size average in nanometres of 31, 37, 44 y 34 for TiO2, TiO2 : Sm3+, TiO2: Gd3+ and TiO2:Yb3+ respectively determinate by atomic force microscopy and by UV spectroscopy the energy gap (2.94, 2.87, 2.85 and 2.95) eV respectively. As for the degradation of the methylene blue dye, the best catalyst under UV radiation was TiO2 : Gd3+ with 54% degradation compared to TiO2 that presented 52%, 29% for TiO2 : Sm3+ and with 27% to TiO2 : Yb3+ determined by fluorimetry. These materials must be applied in industrial post-treatment processes using photo catalysis for the decontamination of bodies of water.

Garnet trace element geochemistry of Yangla Cu deposit in NW Yunnan, China: Implications for multistage ore-fluid activities in skarn system

Garnet is a common hydrothermal mineral in skarn-type deposits, and is useful for constraining the ore-fluid composition. Based on the mineralogy and geochemical features of different types of garnets from the Yangla Cu deposit, we discuss the factors and mechanism of rare earth elements (REE) incorporation into skarn-type garnet, together with the skarn-forming environment. Garnet from Yangla belongs to the grossular–andradite solid solution series, and can be divided into two types (i.e., zoned and unzoned). Early garnet (Grt I) aggregates (avg. And84.96 Gro9.62 Spe + Pyr + Alm5.42) in the proximal skarn is clearly oscillatory-zoned, whilst most of late garnet (Grt II) (avg. And96.26Gro0.58Spe + Pyr + Alm3.16) in the diopside skarn is unzoned. Grt I is slightly LREE-enriched and HREE-depleted with positive Eu anomalies, whereas Grt II is obviously LREE-enriched and HREE-depleted with positive Eu anomalies. Grt I has higher total REE, Y and HFSE contents than Grt II. We suggest that fluid composition and physicochemical conditions greatly controlled the REE incorporation into garnet. The Grt I oscillatory zoning was likely formed by self-organization under relatively low growth rate, leading to Al/Fe fluctuation in the fluid related to the change of external factors (such as fluid boiling). Based on the differences of microscopic texture and geochemical characteristics between Grt I and Grt II indicate that Grt I was likely formed under a mildly acidic and reducing environment and low W/R ratios, whereas Grt II may have formed in a more acidic and oxidizing environment with higher W/R ratios. The changes in redox, pH and W/R ratios cause the compositional variation from Grt I to II during the ascent of the early hydrothermal fluid. During the process of the crystal formation, the oxygen fugacity increased, and the mildly acidic to acidic ore-forming solution shifted from a low W/R ratios condition to a high W/R ratios condition, causing the precipitation of metal sulfide. The fissures of Grt II are infilled by pyrrhotite, chalcopyrite and pyrite, showing that the garnets form prior to the mineralization of copper and can provide space for the precipitation and enrichment of metals.

Partition of Rare Earth Elements Between Sulfate Salts Formed by the Evaporation of Acid Mine Drainage

Acid mine drainage (AMD) contains rare earth element (REE) concentrations several orders of magnitude higher than those of the rest of natural waters and could be a secondary source of REEs. In arid to semiarid climates with a long dry season, the precipitation of efflorescent sulfates constitutes a transient storage of REEs. The REE partition among the Al–Fe–Mg–Ca sulfates formed by the evaporation to dryness of six different AMDs was investigated by statistical methods and by selective dissolution. The chemical composition of the evaporitic salts showed that only three principal components (PCs) could explain more than 80% of the variability in the six samples analyzed. PC1 was associated with Ca and light REEs and interpreted as gypsum, whereas PC2 was associated with Y and heavy REEs, which were not clearly associated with a major sulfate. Finally, PC3 included Mg, Fe and several transition metals (Cu, Ni, Co, Mn and Zn) and was interpreted as Fe(II)-Mg sulfates. Selective dissolution of the salt mixtures with solutions saturated in the major sulfates revealed that the REEs were only retained in gypsum and were practically absent from the rest of the sulfates. The incorporation of REEs into gypsum decreased from Pr-Nd to La and Lu and was strictly ruled by the differences in their atomic radii and that of Ca in eight-fold coordination. However, gypsum concentrated less than 20% of the REE inventory (< 1% for Sc); the rest probably formed one or more unidentified trace minerals. This indicates that gypsum may not be an efficient way to concentrate REEs from AMD.

Ferrihydrite Transformation Impacted by Adsorption and Structural Incorporation of Rare Earth Elements

Understanding the association of rare earth elements (REEs) with iron (oxyhydr)oxides is of great interest in the recovery of REEs from regolith and weathered soils in the world. The objective of this study was to understand the effects of 1 mg L–1 REEs on the ferrihydrite transformation process. Ferrihydrite was synthesized at pH 5 and 7 in the presence of REEs, and the transformation products were characterized using X-ray diffraction, Fe K-edge X-ray absorption spectroscopy, and transmission electron microscopy. During the phase transformation process after 60–120 days, the retention of REEs varied with the REE atomic number. In general, heavy REEs preferably partitioned in aged (≥90 days) ferrihydrite more than light REEs, especially at pH 5. At pH 5, the transformation of ferrihydrite to goethite was retarded by ∼12% when REEs were present. The average structural substitution of REEs was as high as ∼550 mg kg–1, and the substitution of heavy REEs such as Yb and Lu was a critical factor to suppress the ferrihydrite transformation. At pH 7, the formation of hematite was retarded by ∼10%, and the structural incorporation of REEs was more important than adsorbed REEs during the first 30 days. There was no REE-specific retention in aged iron (oxyhydr)oxides at pH 7. The results of this study may explain the association of REEs with iron (oxyhydr)oxides, especially heavy REEs in mildly acidic regolith and weathered soils. This study advanced our understanding of the aqueous geochemical behavior of REEs in iron (oxyhydr)oxide-rich supergene environments.

Selective incorporation of rare earth elements by seaweeds from Cape Mondego, western Portuguese coast

This study examined the mechanism of incorporation of the rare earth elements (REEs), La, Ce, Nd, Eu, Gd, Tb, Yb, into green (Codium tomentosum, Ulva rigida), red (Gracilaria gracilis, Osmundea pinnatifida, Porphyra sp), and brown seaweeds (Saccorhiza polyschides, Undaria pinnatifida) collected from a single site near the coastline of the Cape Mondego, western Portugal. The concentrations of REEs, Mg, Ca, Al, Fe, Zn, and Cu in the biomasses were determined by inductively-coupled plasma mass spectrometry (ICP-MS). The species showed differences in their incorporation and fractionation of REEs from the same environment: the sum of REEs was higher in U. rigida, C. tomentosum, G. gracilis, and O. pinnatifida (0.7–1.7 μg g−1) than in Porphyra sp., S. polyschides, and U. pinnatifida (0.1–0.2 μg g−1). Ratios of Ce/Yb ranged from 13 (in S. polyschides) to 103 (in U. rigida), indicating different proportions of light and heavy REEs among species. Good correlations were found between Al and Fe (R2 = 0.98), and between these elements and La, Ce, Nd, Gd (R2 = 0.88–0.97) and Yb (R2 = 0.66–0.71) for all species except C. tomentosum and G. gracilis. Profiles of REE values normalised to average upper-continental crust composition indicated positive anomalies of Eu and Tb that reinforced the singularity of these elements in the REE group. Correlations between the REEs and Al or Fe suggest that detrital terrigenous particles, adhered to seaweed walls, may be an important mechanism for the incorporation of REEs by seaweeds. Different patterns for C. tomentosum and G. gracilis may also be indicative of the higher influence of cell wall composition on REE incorporation.

Fabrication of different rare earth incorporated ZnCo2O4 matrix via chemical-mechanical hybrid mechanism and study their charge carrier dynamics by Motts VRH model

This work reports how microstructural and electrical property varies with different rare-earth (Nd, Sm, Gd, Dy and Y) incorporation in spinel structured ZnCo2O4 nano-cobaltite. These materials have been synthesized using a combination of both chemical and physical methods. Host spinel material was prepared through chemical co-precipitation method and mechanical milling was used to reinforce the rare earth oxides into the spinel structure. Structural, microstructural, elemental and optical characterization has been carried out using XRD, FTIR, FESEM, EDX and UV-Vis spectroscopy. XRD confirms the formation of the nanocrystalline materials. Different microstructural parameters like lattice parameters, microstrain, crystallite size and x-ray density have been estimated from Rietveld analysis, which shows particle size of the doped samples depends on size of the dopant rare earth. Positions of different bonds have been confirmed from FT-IR analysis. FESEM micrographs confirm particle dimensions of the agglomerated spherical grains are in good agreement with Rietveld output. Optical band gap increases with decreasing dopant radii from 3.48 eV to 3.99 eV. Impedance plots show highest conductivity achieved was 1.151 × 10−3 Ω−1cm−1 at 433 K for Yttrium doped ZnCo2O4 nano-composition with lowest activation energy of 0.34 eV. Temperature dependent frequency exponent explains small polaron hopping transaction. Impedance master curves obey time-temperature superposition principle. Motts VRH model applied to electrical properties to get an insight about electrical conduction mechanism of the prepared samples.

Chemical Composition and Genesis Implication of Garnet from the Laoshankou Fe-Cu-Au Deposit, the Northern Margin of East Junggar, NW China

In order to reveal the formation mechanism of different garnets and its implications for the fluid evolution in the Laoshankou Fe-Cu-Au deposit in the northern margin of East Junggar (NW China), three types of garnet have been investigated in detail in this study. (1) Type 1 grossular, formed at Ca-silicate stage (stage I, the pre-mineralization stage), was replaced by Type 2 garnet and magnetite, and displays a compositional range of Grs44–53Adr44–53, which has relatively lower total REE (rare earth elements) contents (8.14–32.8 ppm) and markedly depleted LREE (light rare earth elements) with distinctive positive Eu anomaly (1.36–9.61). (2) Type 2 Al-rich andradite, formed at the early sub-stage of amphibole-epidote-magnetite stage (stage II, the main magnetite mineralization stage), can be divided into two sub-types, i.e., Type 2a and Type 2b. Type 2a garnets exhibit polysynthetic twinning and relatively narrow compositional variations of Adr63–66Grs31–34 with HREE-(heavy rare-earth elements) enrichment and positive Eu anomalies (3.22–3.69). Type 2b garnets own wide compositional variations of Adr55–77Grs21–43 with relatively higher REE contents (49.1–124 ppm), markedly depleted LREE and a distinctive positive Eu anomaly (2.11–4.61). (3) Type 3 andradite (Adr&gt;91) associated with sulfide stage (stage III, the main copper-gold mineralization stage) is different from other types of garnets in Laoshankou, which are characterized by lowest total REE contents (1.66–91.1 ppm), flat HREE patterns, LREE-enrichment and the strongest positive Eu anomalies (3.31–45.48). Incorporation of REE into garnet is largely controlled by external factors, such as fluid chemistry, pH, ƒO2 and water-rock ratios as well as its crystal chemistry. Type 1 and 2 garnets mainly follow the creation of X2+ (e.g., Ca2+) site vacancy, e.g., [X2+]−3VIII[]+1VIII[REE3+]+2VIII. The REE3+ substitution mechanism for Type 3 garnet is the Na+-REE3+ coupled substitutions, e.g., [X2+]−2VIII[X+]+1VIII[REE3+]+1VIII, without the evaluation of the creation of site vacancy. The compositional variations from Type 1 to Type 3 garnet indicate significant differences of fluid compositions and physicochemical conditions, and can be used to trace the fluid–rock interaction and hydrothermal evolution of garnet. Type 1 grossular was formed by magmatic fluid under low water–rock ratios and ƒO2, and neutral pH environment by diffusion metasomatism in a nearly closed system with the preferential incorporation into the grossular of HREE. As the long fluid pore residence and continuing infiltration metasomatism under nearly closed-system conditions, fluids with high water/rock ratios were characterized by increased ƒO2, more active incorporation of Fe3+ and REE, and formed Type 2 Al-rich andradite. In contrast, Type 3 garnet formed by oxidizing magmatic fluid under a mildly acidic environment with highest ƒO2 and water–rock ratios, and was influenced by externally derived high salinity and Ca-rich fluids in an open system. Thus, the geochemical features of different types and generations of garnets in the Laoshankou deposit can provide important information of fluid evolution, revealing a transition from neutral magmatic fluid to oxidizing magmatic fluid with addition of external non-magmatic Ca-rich fluid from the Ca-silicate stage to the sulfide stage. The above proved the fluid evolution process further indicates that the Laoshankou deposit prefers to be an IOCG-like (iron oxide-copper-gold) deposit rather than a typical skarn deposit.

High Color-Rendering Index and Stable White Light-Emitting Diodes by Assembling Two Broadband Emissive Self-Trapped Excitons.

White light-emitting diodes (WLEDs) are promising next-generation solid-state light sources. However, the commercialization route for WLED production suffers from challenges in terms of insufficient color-rendering index (CRI), color instability, and incorporation of rare-earth elements. Herein, a new two-component strategy is developed by assembling two broadband emissive materials with self-trapped excitons (STEs) for high CRI and stable WLEDs. The strategy addresses effectively the challenging issues facing current WLEDs. Based on first-principles thermodynamic calculations, copper-based ternary halides composites, CsCu2 I3 @Cs3 Cu2 I5 , are synthesized by a facile one-step solution approach. The composites exhibit an ideal white-light emission with a cold/warm white-light tuning and a robust stability against heat, ultraviolet light, and environmental oxygen/moisture. A series of cold/warm tunable WLEDs is demonstrated with a maximum luminance of 145cd m-2 and an external quantum efficiency of 0.15%, and a record high CRI of 91.6 is achieved, which is the highest value for lead-free WLEDs. Importantly, the fabricated device demonstrates an excellent operation stability in a continuous current mode, exhibiting a long half-lifetime of 238.5min. The results promise the use of the hybrids of STEs-derived broadband emissive materials for high-performance WLEDs.

Hydrothermal calcite-fluid REE partitioning experiments at 200 °C and saturated water vapor pressure

Calcite is a common vein mineral associated to ore deposits and alteration zones geothermal systems. The concentration of rare earth elements (REE) in calcite can potentially be used to fingerprint the changing physicochemical conditions during mineralization from hydrothermal fluids. Previous calcite-fluid partitioning experiments have been carried out at ambient temperature but models aiming at predicting the behavior of REE at elevated temperature have not yet been developed. This study aims at determining the controls on REE incorporation into calcite mineralized from hydrothermal aqueous fluids above 100 °C. Here, we present a series of hydrothermal batch-type REE partitioning experiments at 200 °C and saturated water vapor pressure (15.5 bar). The experiments were designed to synthesize REE-doped calcite from fluid mixing with varying initial REE concentrations (250 ppb to 1000 ppb) and permit in situ sampling of the aqueous fluids. Calcite-fluid partition coefficients (KD) were observed to depend on the ionic radius of the REE and vary as a function of initial REE concentrations: logKD of 0.86–1.67 at 250 ppb REE; logKD of 1.05–1.70 at 500 ppb REE; logKD of 0.47–1.07 at 1000 ppb REE. These data fit a parabola according to the lattice strain model from which calculated Young’s modulus (ES) values range between 21.6 and 63.2 GPa. The fits indicate that the partitioning of the light REE is controlled by the strain-induced Ca2+ substitution in the calcite structure, whereas the heavy REE deviate from these trends. The development of a binary REE(OH)3 - CaCO3 solid solution model based on the dual-thermodynamic (DualTh) approach suggests that the REE partitioning is controlled by the following possible coupled substitutions at pH of 6:Eu3++3OH-⇔Ca2++CO32-Eu3++O2-+OH-⇔Ca2++CO32-The lattice strain fits are useful to interpret deviations of the experimental data from the solid solution model and possible non-ideal mixing behavior. Application of this model to natural systems yields some limitations because of the variability of experimental mineral-fluid KD values with REE concentrations in the aqueous fluids. The DualTh approach considers the aqueous speciation and activity-concentration relationships of the aqueous fluids, and therefore, provides an efficient method to evaluate the partitioning of REE between mineral and aqueous fluids. This research is a first step in building an experimental database of calcite-fluid partitioning data at hydrothermal conditions and aims at developing more accurate models for predicting the behavior of the REE in natural mineral-fluid systems.

Development of a water erosion tracer using industrial residue as a source of rare earth elements

This study was aimed at developing a water erosion tracer from montmorillonite (MMT) chemically modified with rare earth elements (REE) as chemical signatures to understand the landscape sediment mobilization dynamics. A new route of development involving the use of an industrial residue from the REE extraction process was evaluated for its REE incorporation efficiency in the clay mineral to enable further tracer applications on a field scale. This industrial residue-modified MMT tracer was compared with a reference tracer based on the chemical modification of MMT with a commercial REE precursor. These REE-modified MMT tracers were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray fluorescence spectroscopies, inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffractometry, scanning electron microscopy (SEM), and N2 physisorption measurements were performed to verify whether the MMT tracer modified with the industrial residue had the same chemical signature (REE) content and chemical stability as those of the commercial REE precursor-based tracer. Chemical stability tests under different pH conditions were carried out to evaluate possible REE content variations in the tracers, mainly over the targeted soil pH range (pH = 4.0–7.7). The clay modified with the industrial residue was further submitted to laboratory horizontal mobility tests using a soil flume. The chemical modification method was effective in producing a chemically stable MMT-based tracer that also displayed multi-chemical signature due to the use of the ClLa40-INB solution, which will potentially enhance the tracer detection in sediments. The mobility tests confirmed the suitability of the modified clay as a tracer.

In situ major and trace elements of garnet and scheelite in the Nuri Cu–W–Mo deposit, South Gangdese, Tibet: Implications for mineral genesis and ore-forming fluid records

Garnet and scheelite are common hydrothermal silicate mineral and metal mineral in skarn or porphyry–skarn deposits, and can aid in constraining the composition of ore-forming fluid. Based on in situ major and trace element analyses of garnet and scheelite from the Nuri Cu–W–Mo deposit, we discuss the factors and mechanisms controlling the incorporation of rare earth elements (REEs) into the garnet and scheelite, and investigate the associated hydrothermal fluid characteristics. The garnets from the Nuri deposit belong to the grossular–andradite (grandite) solid solution series and range in composition from Adr64Grs34 to Adr91Grs8. The REE patterns of garnet are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs). The REEs characteristics indicates that the incorporation of REEs into the Nuri garnet was controlled by the surface adsorption and element substitution in the mineral structure. Based on the cathodoluminescence (CL) images of scheelite, two growth stages (early and late stages) are identified. These two stages of scheelite belong to the scheelite-powellite series, and are enriched in LREEs and depleted in HREEs. However, the early scheelite exhibits negative or no Eu anomalies (0.34–0.95), whereas the late scheelite presents positive Eu anomalies (1.25–2.89). The Mo content in the early scheelite is positively correlated with the δEu value, while the Mo content in the late scheelite is negatively correlated with δEu. These characteristics indicate that the redox state of the ore-forming fluid gradually changed from the oxidized state to the reduced state. The preferred REE3+ substitution for Ca2+ in the Nuri scheelite is 3Ca2+ = 2REE3+ + [ ]Ca (where [ ]Ca is a Ca site vacancy). The REE features of the scheelite are mainly controlled by the REE nature of the ore-forming fluid. According to the characteristics of trace elements in garnet and scheelite, we suggest that the ore-forming fluid of the Nuri deposit is a magmatic fluid mixed with a slightly acidic external fluid. Chloride complexes may be the main transport ligand of the REEs, and the oxygen fugacity of the ore-forming fluid gradually decreased.

Preparation of PVA Fluorescent Gel and Luminescence of Europium Sensitized by Terbium (III).

Polyvinyl alcohol (PVA) gel has a very wide range of applications in agriculture, military, industry, and other fields. As a widely used water-soluble polymer, PVA has good mechanical properties, excellent spinnability, good hydrophilicity, remarkable physical and chemical stability, good film formation, is non-polluting, and exhibits good natural degradation and biocompatibility. It is an ideal gel preparation material. Incorporation of rare-earth elements into PVA polymers can be used to prepare rare-earth luminescent gel materials. Results show that the luminescent efficiency of complexes is mainly related to their structure, ligand substituents, synergists, and the electronic configuration of doped rare-earth ions. Fluorescent gel films were prepared by adding europium, terbium, and europium/terbium co-doped into PVA, and their fluorescence properties were compared and analyzed. It was found that, in addition to the above factors, the sensitization of terbium to europium, and the fluorescence-quenching effect of hydroxyl groups, will influence the fluorescence properties. This has opened a new route for the application of rare-earth materials and may have value in the field of new materials.

Incorporation of Rare Earths and Yttrium in Calcite: A Critical Re-evaluation

The reported partition coefficients of REE with calcite are reviewed and critically discussed. In some of the reported experimental sets, REE concentrations are found to be supersaturated with respect to individual REE2(CO3)3 but never to REE(OH)3. Although the solutions are unsaturated with respect to individual REY carbonates, REY including Y are incorporated in calcite surfaces, where they are overgrown by calcite. Charge balances may be obtained by building {REY–Na-(CO3)2}n or by exchange of 2Ca2+ against REY3+ + blank space calcite lattice. These surface compounds may either be homogeneously distributed or clustered. Both the size and frequency of clusters increase with [REY]/[Ca] or [ΣREY3+]/[Ca2+] in solution. If these surface precipitates are removed into solutions saturated with respect to ΣREE2(CO3)3, they start growing in the aqueous phase. In this case, the apparent DREY and kREY values decrease with increasing REY concentrations in solution. In previous studies, only the individual distribution coefficients are reported not considering that the entirety of REY determines their behavior in partitioning. Given enough time, these surface clusters equilibrate with the aqueous phase before being overgrown by calcite. In the double logarithmic plots of {REY}/{Ca} versus [REY]/[Ca] or [REY3+]/[Ca2+], two relationships evolve characterizing the REY distribution in marine calcite and experimental calcites grown in Mg2+-free solutions. The double logarithmic plots of partition coefficients of REYi3+ in calcite grown from seawater show a slope exceeding unity, whereas those from fluids without Mg2+ depict slopes less than unity being both in contrast to the Henderson–Kracek rule.

Electrochemical leaching of rare-earth elements from spent NdFeB magnets

Spent NdFeB magnets are highly appealing secondary resources for rare earth elements (REEs), especially for Nd. The goal of this study was to investigate electrochemical leaching of Fe and rare earths from NdFeB magnets with sulfuric and oxalic acids at different acid concentrations and current densities and reveal the mechanism of the leaching in varying conditions. The metals were leached from polished magnet surface and from crushed magnets using a 3D-printed Ti basket. Electron and atomic force microscopic analysis showed a highly heterogeneous structure of the magnets containing on average 60 wt-% of Fe and 25 wt-% of Nd. According to Kelvin probe force microscopy, the Volta potential difference between the matrix and the REE-rich grains was over 500 mV. Addition of oxalic acid (H2C2O4) in the sulfuric acid leach solution allows leaching at lower cell voltage and separation of the REE-oxalate precipitates. Some incorporation of rare-earth element oxalates in the cathodic sediment was also observed. Finally, the leaching mechanism is discussed.

Comparative study on the physical properties of rare-earth-substituted nano-sized CoFe2O4

Nanotechnology manufacturing is rapidly developing and promises that the essential changes will have significant commercial and scientific impacts be applicable in an extensive range of areas. In this area, cobalt ferrite nanoparticles have been considered as one of the competitive candidates. The present study is based on the investigation of the effect of rare-earth (RE) incorporation on the physical properties of CoFe2O4. Rare-earth ions doped cobalt ferrites with composition CoRE0.025Fe1.975O4 where RE are Ce, Er and Sm have been synthesized by citrate auto combustion technique. Characterization is achieved using X-Ray diffraction (XRD) technique for structural analysis. The obtained data show that the samples exhibit a single-phase spinel structure. RE is successfully substituted into the spinel lattice without any distortion and it acts as inhibiting agent for grain growth. Room temperature M–H curves exhibit ferrimagnetism behavior with a decrease in saturation magnetization and coercivity indicating these materials can be applicable for magnetic data storage and magneto-recording devices. The electrical conductivity is studied as a function of frequency in the temperature range of 300–700 K. The conduction mechanism is attributed to the hopping mechanism. The Seebeck coefficient S is found to be positive for Ce indicating that Co/Ce ferrite behaves as a p-type semiconductor. While it is fluctuated between positive and negative for Er/Sm-doped samples throughout the studied temperature range. The cobalt doped with Er3+ and Sm3+ exhibits degenerated semiconductor trends at higher temperatures. Such data offer a new opportunity for optimizing and improving the performance of cobalt ferrite where the physical properties are decisive.

Direct detection of rare earth ion distributions in gallium nitride and its influence on growth morphology

The dopant distribution and surface and structural properties of Er- and Eu-doped GaN samples were investigated using atom probe tomography (APT) and atomic force microscopy (AFM). Erbium accumulation within host GaN threading dislocations was directly detected by APT allowing for the dislocations to be imaged in three dimensions. In addition, photoluminescence spectroscopy with high lateral resolution, by means of scanning near-field optical microscopy, was performed on Eu-doped GaN samples. By combining these results with AFM mappings of the same area, it was concluded that Eu3+ ions also accumulate at threading dislocations. Moreover, high-resolution surface profiles of both samples show that even dilute doping (&amp;lt;0.2%) of Eu and Er has a significant influence on the growth morphology of the GaN host material and the nature of the threading dislocations within it. Transmission electron microscopy techniques were used to show the influence of rare-earth incorporation on the growth of GaN lattice and the propagation of threading dislocations.

Rare earth element geochemistry and fluid characteristics of scheelite in the Hutti gold deposit, Hutti-Maski schist belt, Raichur district, Karnataka, India

Scheelite occurs as thin smears, isolated grains and veinlets in auriferous quartz reefs and sulfidized and auriferous biotite-chlorite schist in the Hutti deposit. Major host rocks at Hutti are mafic and sill-like felsic volcanic rocks and quartz reefs located at the shear contact of these rocks. Laser-Raman and fluid inclusion studies on scheelite show that H2O + CH4 ± CO2 + NaCl fluids, similar to gold mineralizing fluid are responsible for scheelite mineralization at Hutti. Rare Earth Element (REE) geochemistry of scheelite shows two types of chondrite normalized REE patterns which are classified as Type I (hump-shaped pattern), characteristic of REE incorporation by coupled substitution involving Na or K, and Type II (flat pattern) involving REE substitution with creation of a vacancy. The type I pattern is seen in scheelite within biotite schists whereas Type II pattern is associated with scheelite in felsic volcanic rocks and quartz mylonites. The Type II pattern is subdivided into Type IIa and Type IIb pattern based on Eu/Eu* values with Type IIa showing larger Eu/Eu* values than Type IIb. The lower ratio in Type IIb scheelite which occurs in altered felsic volcanic rocks is attributed to the overall enhancement of MREE, due to some degree of coupled substitution involving Na relative to Type IIa. The slope of the REE distribution pattern of scheelite is distinctly different from that of felsic volcanic rocks but similar to that of mafic volcanic rocks. It is inferred that REE fractionation between mineralizing fluids and greenschist–facies metamorphosed mafic rocks of the schist belt is not significant.

Experimental study of trivalent rare-earth element incorporation in CaTiO3 perovskite: evidence for a new substitution mechanism

Samples of calcium titanate perovskite (CaTiO3) substituted with variable amounts of trivalent La, Pr, Nd or Sm were synthesized by solid-state reaction. The synthesized compounds were characterized by means of electron microprobe (EMPA), powder X-ray diffraction and µ-Raman spectroscopy. The incorporation of the studied lanthanides in the CaTiO3 perovskite leads to the formation of complex (Ca1-2xLn2x)(Ti1-xCax)O3 perovskites with a Pbnm disordered structure. This mechanism was revealed by the Ca/Ti ratio analyses of the samples, the study of the lattice parameter evolution and the Raman A1g octahedral breathing mode frequency comparison for all systems.

Influence of annealing on luminescence and energy transfer in ZnO multilayer structure co-doped with Tb and Eu

The influence of rapid thermal annealing (RTA) on structural and optical properties of ZnO multilayer structures co-doped with Tb and Eu ions has been investigated by X-ray diffraction, Time-of-Fligth Secondary Ion Mass Spectrometry, Specular Infrared reflection, micro-Raman and photoluminescence (PL) methods. It is shown that incorporation of rare earth (RE) ions in ZnO host is accompanied by the formation of intrinsic defects in oxygen and zinc sub-lattices of ZnO. The appearance of intense Raman mode at 275 cm−1 is ascribed mainly to Eu ion incorporation on Zn site in ZnO matrix. The PL of RE ions localized in ZnO and other crystal phases is revealed. The effect of energy transfer from Tb3+ to Eu3+ ions in ZnO is identified. It is shown that the RTA improves crystal structure of ZnO host, i.e. stimulates the increase of coherent domain sizes and strain relaxation, as well as promotes the redistribution of RE ions across the structure. The effect of RTA on RE ion PL depends strongly on the annealing temperature. It is found that RTA at 500 °C promotes Eu incorporation into ZnO and the enhancement of Eu3+ PL due to energy transfer from Tb3+ to Eu3+, while RTA at 800 °C stimulates segregation of RE ions and the decrease of their PL.

Development of rare-earth oxides based hybrid AMCs reinforced with SiC/Al2O3: mechanical & metallurgical characterization

The paper presents the study on the mechanical and microstructural behaviour of aluminium matrix hybrid composites of Al-6061 alloy with Al2O3, SiC and CeO2 as reinforcement particles processed through stir casting route. For the experimental investigations, hybrid composites were fabricated by varying weight percentages of 5,10 and 15wt.-% of (SiC+Al2O3) mixture and weight percentage of 0.5, 1.5 and 2.5wt.-% of CeO2 keeping total wt.-% of reinforcement less than 30wt.-%. Mechanical properties like ultimate tensile strength, micro and macro hardness and percentage elongation were examined on the aluminium matrix hybrid composites at room temperature. The microstructure analysis was done using SEM, XRD and EDS techniques. Micro hardness value of the base alloy was increased by 17.02% on addition of 2.5wt.-% of CeO2 as rare earth element along with (Al2O3+SiC) mixture. In comparison to non-rare earth element (Alloy+15wt.-% (Al2O3+SiC) mixture), the hardness increased by only 13.70%. Rockwell hardness of the base alloy increased by 33.80% on successful incorporation of rare earth element. The SEM microstructure analysis shows a very significant refinement of the composites after addition of rare earth particles. XRD and EDS analysis shows very good results in terms of fabrication of hybrid composite particles.