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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Coprecipitation of nickel zinc malonate: A facile and reproducible synthesis route for Ni{sub 1−x}Zn{sub x}O nanoparticles and Ni{sub 1−x}Zn{sub x}O/ZnO nanocomposites via pyrolysis

Nanoparticles of Ni{sub 1−x}Zn{sub x}O and Ni{sub 1−x}Zn{sub x}O/ZnO, which can be good candidates for selective gas sensors, were successfully obtained via a two-step synthetic route, in which the nickel zinc malonate precursor was first synthesized by co-precipitation from an aqueous solution, followed by pyrolysis in air at a relatively low temperature (~500 °C). The precursor was characterized by ICP-AES, FTIR and TG and the results indicate the molecular structure of the precursor to be compatible with Ni{sub 1−x}Zn{sub x}(OOCCH{sub 2}COO)·2H{sub 2}O. The decomposition product, characterized using various techniques (FTIR, XRD, ToF-SIMS, SEM, TEM and XPS), was established to be a doped nickel oxide (Ni{sub 1−x}Zn{sub x}O for 0.01≤x≤0.1) and a composite material (Ni{sub 1−x}Zn{sub x}O/ZnO for 0.2≤x≤0.5). To elucidate the form in which the Zn is present in the NiO structure, three analytical techniques were employed: ToF-SIMS, XRD and XPS. While ToF SIMS provided a direct evidence of the presence of Zn in the NiO crystal structure, XRD showed that Zn actually substitutes Ni in the structure and XPS is a bit more specific by indicating that the Zn is present in the form of Zn{sup 2+} ions. - Highlights: • Coprecipitation synthesis of nickel zinc malonate single bath precursor was achieved. • The as synthesized precursors are an homogeneous mixture of nickel and zinc malonate. • XRD, ToF-SIMS, XPS, SEM and TEM was used to characterized decomposition products. • Ni{sub 1−x}Zn{sub x}O nanoparticles (0.01≤x≤0.1) formed after pyrolysis (~500 °C) of precursor. • Ni{sub 1−x}Zn{sub x}O/ZnO nanocomposite (0.2≤x≤0.5) formed after pyrolysis at 500 °C of precursor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Simple synthetic route to manganese-containing nanowires with the spinel crystal structure

This report describes a new route to synthesize single-crystalline manganese-containing spinel nanowires (NWs) by a two-step hydrothermal and solid-state synthesis. Interestingly, a nanowire or nanorod morphology is maintained during conversion from MnO{sub 2}/MnOOH to CuMn{sub 2}O{sub 4}/Mg{sub 2}MnO{sub 4}, despite the massive structural rearrangement this must involve. Linear sweep voltammetry (LSV) curves of the products give preliminary demonstration that CuMn{sub 2}O{sub 4} NWs are catalytically active towards the oxygen evolution reaction (OER) in alkaline solution, exhibiting five times the magnitude of current density found with pure carbon black. - Highlights: • Synthesis of single-crystalline manganese-containing spinel nanowires. • Binary oxide nanowire converted to ternary oxide wire through solid state reaction. • Approach to structure conversion with shape retention could be generally applicable. • Copper and Manganese display multiple oxidation states with potential for catalysis. • CuMn{sub 2}O{sub 4} nanowires show promise as catalysts for the oxygen evolution reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Aluminum doped nickel oxide thin film with improved electrochromic performance from layered double hydroxides precursor in situ pyrolytic route

Electrochromic materials with unique performance arouse great interest on account of potential application values in smart window, low-power display, automobile anti-glare rearview mirror, and e-papers. In this paper, high-performing Al-doped NiO porous electrochromic film grown on ITO substrate has been prepared via a layered double hydroxides(LDHs) precursor in situ pyrolytic route. The Al{sup 3+} ions distributed homogenously within the NiO matrix can significantly influence the crystallinity of Ni-Al LDH and NiO:Al{sup 3+} films. The electrochromic performance of the films were evaluated by means of UV–vis absorption spectroscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry(CA) measurements. In addition, the ratio of Ni{sup 3+}/Ni{sup 2+} also varies with Al content which can lead to different electrochemical performances. Among the as-prepared films, NiO film prepared from Ni-Al (19:1) LDH show the best electrochromic performance with a high transparency of 96%, large optical modulation range (58.4%), fast switching speed (bleaching/coloration times are 1.8/4.2 s, respectively) and excellent durability (30% decrease after 2000 cycles). The improved performance was owed to the synergy of large NiO film specific surface area and porous morphology, as well as Al doping stifled the formation of Ni{sup 3+} making bleached state more pure. This LDHs precursor pyrolytic method is simple, low-cost and environmental benign and is feasible for the preparation of NiO:Al and other Al-doped oxide thin film. - Graphical abstract: The ratio of Ni{sup 3+}/Ni{sup 2+} varies with Al content which can lead to different electrochemical performances. Among the as-prepared films, NiO film prepared from Ni-Al (19:1) LDH show the best electrochromic performance with a high transparency of 96%, large optical modulation range, fast switching speed and excellent durability. Display Omitted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Structural, optical, and ferromagnetic characterization of Sm-doped LaOCl nanocrystalline synthesized by solvothermal route: Significant effect of hydrogen post treatment

Pure and Sm-doped lanthanum oxychloride (LaOCl) nanomaterials were synthesized by solvothermal route followed by a subsequent heat treatment process. The objective of the present work is to study and develop conditions required to create stable room-temperature ferromagnetic (RT-FM) properties in LaOCl. To achieve that aim, magnetic samarium Sm{sup 3+} ions were used as dopant sources for stable FM properties. Systematic structural, optical, and magnetic properties of undoped and Sm-doped LaOCl samples were investigated as function of post-annealing conditions (temperature and atmosphere). The optical absorption properties were studied by diffuse reflection spectroscopy (DRS). The magnetic measurements reveal that Sm-doped LaOCl nanopowders have partial RT-FM properties due to the doped ions. The variations of magnetic properties with pre-annealing temperature were investigated. Furthermore, the electronic medium of host LaOCl crystalline lattice, which carries the spin-spin (S.S) exchange interaction between localised dopant Sm{sup 3+}(4f{sup 5}) spins, was developed by annealing in hydrogen gas (hydrogenation). It was established that annealing in hydrogen atmosphere boosts the RT-FM properties so that the saturation magnetisation could be increased by more than 100%. Physical explanations and discussions were given in this paper. Thus, it was proved that the magnetic properties could be tailored to diamagnetic LaOCl compound by Sm-doping and post treatment under H{sub 2} atmosphere. Therefore, LaOCl nanocrystals could be used as a potential candidate for optical phosphor applications with magnetic properties. - Graphical abstract: M-H dependence of Sm-doped LaOCl powders. Study the effect of hydrogenation. - Highlights: • Synthesis of Sm-doped LaOCl nanoparticles. • DM LaOCl transforms to FM with dilute concentration of Sm doping. • Annealing under H{sub 2} atmosphere induces drastic boost in the FM properties. • Saturation magnetization attained 29 memu/g with little doping and hydrogenation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

A low-temperature synthetic route to ternary iron-manganese metal fluorides nanoparticles

Ternary metal fluoride Fe{sub x}Mn{sub 1−x}F{sub 2} (x = 0.00, 0.25, 0.50, 0.75, and 1.00), which is a potential cathode material for next-generation Li-ion batteries, were synthesized via a convenient, low-temperature, bottom-up solution-phase method. The lattice dimensions deduced from X-ray diffraction suggested formation of homogeneous solid solutions. With increasing Fe content, the morphology of the solid changed from cubic particles to dendritic, with an average particle size of 20–40 nm. The results suggested that this synthetic method constitutes a translatable route to large-scale production of ternary metal fluoride nanoparticles. - Graphical abstract: Homogeneous random solid solutions of ternary metal fluoride Fe{sub x}Mn{sub 1−x}F{sub 2} can be prepared by room temperature coprecipitation of precursors followed by drying and calcination at 350 °C. Display Omitted - Highlights: • Homogeneous ternary mixed metal iron-manganese fluoride Fe{sub x}Mn{sub 1−x}F{sub 2} nanoparticles prepared by room temperature coprecipitation and calcination. • Fe{sub x}Mn{sub 1−x}F{sub 2} nanoparticles form different morphology aggregates depending on the composition. • Lattice dimensions from X-ray diffraction suggested formation of homogeneous solid solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

A simple route to synthesize manganese germanate nanorods

Manganese germanate nanorods have been synthesized by a simple route using germanium dioxide and manganese acetate as the source materials. X-ray diffraction observation shows that the nanorods are composed of orthorhombic and monoclinic manganese germanate phases. Scanning electron microscopy and transmission electron microscopy observations display that the manganese germanate nanorods have flat tips with the length of longer than 10 micrometers and diameter of 60-350 nm, respectively. The role of the growth conditions on the formation of the manganese germanate nanorods shows that the proper selection and combination of the growth conditions are the key factor for controlling the formation of the manganese germanate nanorods. The photoluminescence spectrum of the manganese germanate nanorods exhibits four fluorescence emission peaks centered at 422 nm, 472 nm, 487 nm and 530 nm showing the application potential for the optical devices. - Research Highlights: {yields} Manganese germanate nanorods have been synthesized by simple hydrothermal process. {yields} The formation of manganese germanate nanorods can be controlled by growth conditions. {yields} Manganese germanate nanorods exhibit good PL emission ability for optical device.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Relationship between crystallographic structure of the Ti{sub 2}O{sub 3}/MnS complex inclusion and microstructure in the heat-affected zone (HAZ) in steel processed by oxide metallurgy route and impact toughness

A new method based on electron back scattered diffraction (EBSD) is proposed to determine the structure of titanium oxide/MnS complex inclusion which induced the formation of intragranular acicular ferrite (IAF) in heat-affected zone (HAZ) in steel processed by oxide metallurgy route. It was found that the complex inclusion was Ti{sub 2}O{sub 3}/MnS, the orientation relationship between Ti{sub 2}O{sub 3} and MnS was also examined, and the crystallographic orientation relationship among IAF, Ti{sub 2}O{sub 3}/MnS complex inclusion, austenite, bainite formed at lower temperature is researched systematically. It was observed that MnS precipitated on Ti{sub 2}O{sub 3} at specific habit plane and direction and MnS had a specific orientation relationship ((0001) Ti{sub 2}O{sub 3}//(111) MnS), <10–10> Ti{sub 2}O{sub 3}//<110> MnS) with respect to Ti{sub 2}O{sub 3}. Intragranular acicular ferrite (IAF) nucleated on MnS part of the Ti{sub 2}O{sub 3}/MnS complex inclusion had no specific orientation relationship with MnS. IAF and the surrounding bainite had different Bain groups, so that there was an increase in high angle boundaries, which was beneficial for the toughness of HAZ. - Highlights: • The inclusion of TiO{sub x}/MnS that induced IAF formation is identified to be Ti{sub 2}O{sub 3}/MnS. • The inclusion is identified based on electron back scattered diffraction (EBSD). • MnS and Ti{sub 2}O{sub 3} had specific orientation relationship of Ti{sub 2}O{sub 3}/MnS complex inclusion. • The IAFs formed on the same inclusion tend to be in one Bain group. • IAF and the surrounding bainite tend to be in different Bain groups.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Influence of powder metallurgy route on precipitation processes in MgTbNd alloy

Solution treated MgTb3Nd2 alloy (nominal composition in wt.%) (ST) and the alloy prepared by hot extrusion of isostatically pressed powder (PM) were isochronally heat treated and studied by electrical resistivity and hardness measurements and by differential scanning calorimetry. Microstructure development was investigated in transmission electron microscopy. Successive precipitation of transient phases in the sequence β″ (D0{sub 19} plates) → β′(cbco) → β{sub 1} (Mg{sub 3}Gd type, fcc) → β (Mg{sub 5}Gd type, fcc) known from the ST alloy was identified also in the PM alloy. The early precipitation stage (D0{sub 19} clusters) revealed in the ST alloy as well as precipitation of equilibrium β{sub e} phase Mg{sub 41}(Tb,Nd){sub 5} manifest themselves only slightly in the PM alloy. Powder metallurgy route does not change the values of activation energies but shifts the temperature ranges of these processes. Vickers hardness of the as prepared state is higher in the PM alloy and is very resistant against the heat treatment up to 510 °C. Contrary to the ST alloy precipitation due to isochronal annealing does not lead to pronounced hardness changes in the PM alloy. - Highlights: • Powder metallurgy (PM) does not change precipitation sequence in MgTbNd alloy. • Temperature ranges of transient phase precipitations are shifted in PM alloy. • Hardness is resistant against isochronal heat treatment up to 510 °C in the PM alloy. • PM procedure does not change activation energies of precipitation.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Rapid microwave synthesis of indium filled skutterudites: An energy efficient route to high performance thermoelectric materials

Graphical abstract: Filled skutterudites are promising thermoelectric materials. We report the microwave assisted synthesis of CoSb{sub 3} and In{sub 0.2}Co{sub 4}Sb{sub 12}. This method reduces the calcination time for skutterudite phase formation from 2 days to 2 min, thereby significantly reducing the time and energy needed to produce materials suitable for property and device testing. Highlights: Black-Right-Pointing-Pointer The microwave assisted solid state synthesis of CoSb{sub 3} and In{sub 0.2}Co{sub 4}Sb{sub 12} is reported. Black-Right-Pointing-Pointer This method allows the calcination time to be reduced from 2 days to 2 min. Black-Right-Pointing-Pointer Physical properties of microwave samples match those prepared conventionally. -- Abstract: Filled skutterudites are promising thermoelectric materials due to reduced thermal conductivity upon inserting a guest atom or 'rattler' into the CoSb{sub 3} structure. By using an indium rattler dimensionless Figure of Merit (ZT) values >1 at 650 K have been reported. The conventional synthesis of these compounds typically takes several days ({approx}3 days) to obtain the final well-sintered material for property measurements. We report here a microwave-assisted synthesis method that reduces the initial calcination time from 2 days to 2 min. This route significantly reduces the time needed to produce materials suitable for property and device testing.

36 MATERIALS SCIENCE↗
DOE OSTI2012

A new route for the synthesis of titanium silicalite-1

Graphical abstract: Well-prepared TS-1 was synthesized by an innovative procedure using inexpensive reagents such as fumed silica and TPABr as structure-directing agent. This is the first time when highly crystalline TS-1 is obtained in basic medium, using sodium hydroxide as HO{sup -} ion source required for the crystallization process. Hydrolysis of titanium source has been prevented by titanium complexation with acetylacetone before structuring gel. Highlights: Black-Right-Pointing-Pointer TS-1 was obtained using cheap reagents as fumed silica and tetrapropylammonium bromide. Black-Right-Pointing-Pointer First time NaOH was used as source of OH{sup -} ions required for crystallization process. Black-Right-Pointing-Pointer The hydrolysis Ti alkoxides was controlled by Ti complexation with 2,4-pentanedione. -- Abstract: A new and efficient route using inexpensive reagents such as fumed silica and tetrapropylammonium bromide is proposed for the synthesis of titanium silicalite-1. High crystalline titanium silicalite-1 was obtained in alkaline medium, using sodium hydroxide as HO{sup -} ion source required for the crystallization process. Hydrolysis of titanium source with formation of insoluble oxide species was prevented by titanium complexation with before structuring gel. The final solids were fully characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared, ultraviolet-visible diffuse reflectance, Raman and atomic absorption spectroscopies, as well as nitrogen sorption analysis. It was found that a molar ratio Ti:Si of about 0.04 in the initial reaction mixture is the upper limit to which well formed titanium silicalite-1 with channels free of crystalline or amorphous material can be obtained. Above this value, solids with MFI type structure containing both Ti isomorphously substituted in the network and extralattice anatase nanoparticles inside of channels is formed.

36 MATERIALS SCIENCE↗
DOE OSTI2012

The reactivity of lattice carbon and nitrogen species in molybdenum (oxy)carbonitrides prepared by single-source routes

Highlights: Black-Right-Pointing-Pointer Molybdenum (oxy)carbonitrides have been prepared from single source routes. Black-Right-Pointing-Pointer Nitrogen species are more reactive than carbon species within the carbonitrides. Black-Right-Pointing-Pointer The reactivity of nitrogen species is a function of carbonitride composition. -- Abstract: Molybdenum (oxy)carbonitrides of different compositions have been prepared from hexamethylenetetramine molybdate and ethylenediamine molybdate precursors and the reactivity of the lattice carbon and nitrogen species within them has been determined by temperature programmed reduction and thermal volatilisation studies. Nitrogen is found to be much more reactive than carbon and the nature of its reactivity is influenced by composition with the presence of carbon enhancing the reactivity of nitrogen. The difference in reactivity observed indicates that molybdenum carbonitrides are not suitable candidates as reagents for which the simultaneous loss of nitrogen and carbon from the lattice would be desirable.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Simple route for the synthesis of supercapacitive Co-Ni mixed hydroxide thin films

Highlights: Black-Right-Pointing-Pointer Novel method for deposition of Co-Ni mixed hydroxide. Black-Right-Pointing-Pointer Nanoparticle network of Co-Ni hydroxide. Black-Right-Pointing-Pointer High specific capacitance of 672 F g{sup -1}. Black-Right-Pointing-Pointer High discharge/charge rates. -- Abstract: Facile synthesis of Co-Ni mixed hydroxides films with interconnected nanoparticles networks through two step route is successfully established. These films have been characterized by X-ray diffraction (XRD), Fourier transform infrared technique (FTIR), scanning electron microscopy (SEM) and wettability test. Co-Ni film formation is confirmed from XRD and FTIR study. SEM shows that the surface of Co-Ni films is composed of interconnected nanoparticles. Contact angle measurement revealed the hydrophilic nature of films which is feasible for the supercapacitor. The electrochemical performance of the film is evaluated by cyclic voltammetry, and constant-current charge/discharge cycling techniques. Specific capacitance of the Co-Ni mixed hydroxide electrode achieved 672 F g{sup -1}. Impedance analysis shows that Co-Ni mixed hydroxide electrode provides less resistance for the intercalation and de-intercalation of ions. The Co-Ni mixed electrode exhibited good charge/discharge rate at different current densities. The results demonstrated that Co-Ni mixed hydroxide composite is very promising for the next generation high performance electrochemical supercapacitors.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Cd–cysteine precursor nanowire templated microwave-assisted transformation route to CdS nanotubes

Graphical abstract: Cadmium sulfide polycrystalline nanotubes have been successfully synthesized by microwave-assisted transformation method using Cd–cysteine precursor nanowires as the source material and template in ethylene glycol at 160 °C or ethanol at 60 °C. Display Omitted Highlights: ► Cd–cysteine precursor nanowires were successfully synthesized in alkaline solution. ► CdS nanotubes were prepared by templated microwave-assisted transformation method. ► CdS nanotubes can well duplicate the size and morphology of precursor nanowires. ► This method has the advantages of the simplicity and low cost. -- Abstract: We report the Cd–cysteine precursor nanowire templated microwave-assisted transformation route to CdS nanotubes. In this method, the Cd–cysteine precursor nanowires are synthesized using CdCl{sub 2}·2.5H{sub 2}O, L-cysteine and ethanolamine in water at room temperature. The Cd–cysteine precursor nanowires are used as the source material and template for the subsequent preparation of CdS nanotubes by a microwave-assisted transformation method using ethylene glycol or ethanol as the solvent. This method has the advantages of the simplicity and low cost, and may be extended to the synthesis of nanotubes of other compounds. The products are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

36 MATERIALS SCIENCE↗
DOE OSTI2013

A facile route to synthesis of CoPt magnetic nanoparticles

Graphical abstract: CoPt NPs are successfully synthesized by sol–gel method. Different distinct particle sizes with narrow particle size distribution of CoPt nanoparticles are obtained. The maximum coercivity of 254,720.3 A/m is obtained for 800 °C heat-treated sample. Display Omitted Highlights: ► L1{sub 0}-CoPt NPs with FCT structure are successfully synthesized by sol–gel method. ► The maximum value of 254,720.3 A/m is obtained for the samples heated at 800 °C. ► The synthetic route proposed in this study is less toxic and easy-to-handle. -- Abstract: The face-centered tetragonal (FCT) ordered L1{sub 0} CoPt nanoparticles (NPs) are prepared by the sol–gel method. Their structure and magnetic properties are characterized by the X-ray diffraction (XRD), the transmission electron microscope (TEM) and the vibrating sample magnetometer (VSM). The results indicate that the CoPt NPs heated at 400 °C are the disordered face-centered cubic (FCC) structure, whereas the samples annealed at the temperature above 600 °C exhibit an ordered FCT structure. TEM images show the increase of the particle size as the annealing temperature increases. SAED images show the appearance of the L1{sub 0} phase at 800 °C, and the maximum coercivity is 254,720.3 A/m.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

New synthetic route to Mg–Al–CO{sub 3} layered double hydroxide using magnesite

Highlights: ► The use of magnesite to prepare Mg–Al–CO{sub 3} LDH is novel. ► The result sample is systematically studied. ► Furthermore, the cost of preparing Mg–Al–CO{sub 3} LDH may be reduced through this synthetic route. ► In the synthesis process, there is no CO{sub 2} released. That is significant to environmental protection. - Abstract: A novel synthesis of Mg–Al–CO{sub 3} layered double hydroxide (LDH) through chemical precipitation and hydrothermal methods has been investigated in this paper. The advantages of this method are using magnesite as magnesium source and no CO{sub 2} released in the process of preparation. Mg–Al–CO{sub 3} LDH (ZY) prepared under the optimized condition (the molar ratio of magnesite and Al(NO{sub 3}){sub 3}·9H{sub 2}O was 2.5:1; the aging time and temperature were 16 h and 100 °C, respectively) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric and differential thermal analyser (TG–DTA) and scanning electron microscope (SEM). The crystal morphology of the prepared LDH displays platelet-like structure with a hexagonal shape, which is agreed with the LDH produced by industrial chemicals. Through elemental analysis and inductively coupled plasma-atomic emission spectrometry (ICP-AES), the chemical formula of ZY is determined as Mg{sub 0.70}Al{sub 0.30}(OH){sub 2}(CO{sub 3}){sub 0.15}·0.6H{sub 2}O.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Pumping-route-dependent concentration quenching and temperature effect of green up- and down-conversion luminescence in Er{sup 3+}/Yb{sup 3+} co-doped Gd{sub 2}(WO{sub 4}){sub 3} phosphors

Graphical abstract: A comparative study on the concentration quenching behaviors of green down- and up-conversion emissions was carried out for the first time, and the different concentration quenching mechanisms were analyzed. Secondly, the thermal effect induced by 980 nm LD irradiation was investigated, it was observed that the equilibrium temperature of Gd{sub 2}(WO{sub 4}){sub 3}:Er{sup 3+}/Yb{sup 3+} sample was decided by both the excitation power and Er{sup 3+} doping concentration. Highlights: ► Gd{sub 2}(WO{sub 4}){sub 3}:Er/Yb phosphors were prepared via a co-precipitation reaction. ► Morphology and structure of the phosphors were characterized by XRD and SEM. ► Concentration quenching mechanisms for down and up emissions were studied. ► Thermal effect induced by laser irradiation was studied via temperature sensing tech. - Abstract: Gd{sub 2}(WO{sub 4}){sub 3} phosphors with various Er{sup 3+} concentrations and fixed Yb{sup 3+} concentration were synthesized via a co-precipitation method, and their crystal structure and morphology were characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The concentration quenching behaviors of green up- and down-conversion emissions of Er{sup 3+} were analyzed, and it was confirmed that the difference between quenching concentration for up- and down-conversion emissions resulted from the different population routes. The temperature sensing properties of the Gd{sub 2}(WO{sub 4}){sub 3}:Er{sup 3+}/Yb{sup 3+} phosphors were studied, and it was found that the Er{sup 3+} doping concentration slightly affected the sensitivity, and Gd{sub 2}(WO{sub 4}){sub 3}:Er{sup 3+}/Yb{sup 3+} phosphors could be used in a broad temperature region for detecting temperature. Finally, the thermal effect induced by 980 nm LD irradiation was investigated, it was observed that the equilibrium temperature of Gd{sub 2}(WO{sub 4}){sub 3}:Er{sup 3+}/Yb{sup 3+} sample was decided by both the excitation power and Er{sup 3+} doping concentration.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Nanocrystalline spinel ferrite (MFe{sub 2}O{sub 4}, M = Ni, Co, Mn, Mg, Zn) powders prepared by a simple aloe vera plant-extracted solution hydrothermal route

Graphical abstract: This figure shows the specific magnetization curves of the as-prepared MFe{sub 2}O{sub 4} (M = Ni, Co, Mn, Mg, Zn) powders obtained from room temperature VSM measurement. These curves are typical for a soft magnetic material and indicate hysteresis ferromagnetism in the field ranges of ±500 Oe, ±1000 Oe, and ±2000 Oe for the CoFe{sub 2}O{sub 4}, MgFe{sub 2}O{sub 4} and MnFe{sub 2}O{sub 4} respectively, whereas the samples of NiFe{sub 2}O{sub 4} and ZnFe{sub 2}O{sub 4} show a superparamagnetic behavior. Highlights: ► Nanocrystalline MFe{sub 2}O{sub 4} powders were synthesized by a novel hydrothermal method. ► Metal acetylacetonates and aloe vera plant-extracted solution are used. ► This biosynthetic route is very simple and provides high-yield oxide nanomaterials. ► XRD and TEM results indicate that the prepared samples have only spinel structure. ► The maximum M{sub s} of 68.9 emu/g at 10 kOe were observed for the samples of MnFe{sub 2}O{sub 4}. - Abstract: Nanocrystalline spinel ferrite MFe{sub 2}O{sub 4} (M = Ni, Co, Mn, Mg, Zn) powders were synthesized by a novel hydrothermal method using Fe(acac){sub 3}, M(acac){sub 3} (M = Ni, Co, Mn, Mg, Zn) and aloe vera plant extracted solution. The X-ray diffraction and selected-area electron diffraction results indicate that the synthesized nanocrystalline have only spinel structure without the presence of other phase impurities. The crystal structure and morphology of the spinel ferrite powders, as revealed by TEM, show that the NiFe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} samples contain nanoparticles, whereas the MnFe{sub 2}O{sub 4} and MgFe{sub 2}O{sub 4} samples consist of many nanoplatelets and nanoparticles. Interestingly, the ZnFe{sub 2}O{sub 4} sample contains plate-like structure of networked nanocrystalline particles. Room temperature magnetization results show a ferromagnetic behavior of the CoFe{sub 2}O{sub 4}, MnFe{sub 2}O{sub 4} and MgFe{sub 2}O{sub 4} samples, whereas the samples of NiFe{sub 2}O{sub 4} and ZnFe{sub 2}O{sub 4} exhibit a superparamagnetic behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Magnetic properties of nanocrystalline ε-Fe{sub 3}N and Co{sub 4}N phases synthesized by newer precursor route

Graphical abstract: Nanocrystalline ε-Fe{sub 3}N and Co{sub 4}N nitride phases are synthesized first time by newer chemical routes. The ε-Fe{sub 3}N phase crystallizes in hexagonal structure with unit cell parameters, a = 4.76 Å and c = 4.41 Å. The Co{sub 4}N phase crystallizes in face centred cubic (fcc) structure with unit cell parameters, a = 3.55 Å. The estimated crystallite size for ε-Fe{sub 3}N and Co{sub 4}N phases are 29 nm and 22 nm, respectively. The values of saturation magnetization for ε-Fe{sub 3}N and Co{sub 4}N phases are found to be 28.1 emu/g and 123.6 emu/g respectively. The reduction of magnetic moments in ultrafine materials compared to bulk materials has been explained by fine particle size and surface effects. We have synthesized the high moment ε-Fe{sub 3}N and Co{sub 4}N nitride with reduced coercivity which may find applications as soft magnetic materials. - Highlights: • Nanocrystalline ε-Fe{sub 3}N and Co{sub 4}N nitride phases are synthesized. • The ε-Fe{sub 3}N and Co{sub 4}N crystallizes in hexagonal and fcc structure respectively. • The observed magnetic parameters indicate soft magnetic properties. • The magnetic properties have been explained on the basis of fine particle magnetism. - Abstract: Nanocrystalline ε-Fe{sub 3}N and Co{sub 4}N nitride phases are synthesized first time by using tris(1,2-diaminoethane)iron(II) chloride and tris(1,2-diaminoethane)cobalt(III) chloride precursors, respectively. To prepare ε-Fe{sub 3}N and Co{sub 4}N nitride phases, the synthesized precursors were mixed with urea in 1:12 ratio and heat treated at various temperatures in the range of 450–900 °C under the ultrapure nitrogen gas atmosphere. The precursors are confirmed by FT-IR study. The ε-Fe{sub 3}N phase crystallizes in hexagonal structure with unit cell parameters, a = 4.76 Å and c = 4.41 Å. The Co{sub 4}N phase crystallizes in face centred cubic (fcc) structure with unit cell parameters, a = 3.55 Å. The estimated crystallite size for ε-Fe{sub 3}N and Co{sub 4}N phases are 29 nm and 22 nm, respectively. The scanning electron microscopy (SEM) studies confirm the nanocrystalline nature of the materials. The values of saturation magnetization for ε-Fe{sub 3}N and Co{sub 4}N phases are found to be 28.1 emu/g and 123.6 emu/g, respectively. The reduction of magnetic moments in ultrafine materials compared to bulk materials have been explained by spin pairing effect, lattice expansion, superparamagnetic behaviour and canted spin structures at the surface of the particles.

36 MATERIALS SCIENCE↗