Photoluminescent emission of Pr3+ ions in different zirconia crystalline forms

Polycrystalline praseodymium doped-zirconia powders were synthesized by crystallization of a saturated solution and annealed in air at T_a = 950 °C. Monoclinic, tetragonal and cubic crystalline phases of zirconia were obtained. EDS studies showed homogeneous chemical composition over all the powders particles and chemical elemental contents in good agreement with the incorporation of Pr³⁺ ion in Zr⁴⁺ sites. XRD patterns showed stabilization of tetragonal and cubic phases at 1.28 and 2.87 at.% of Pr³⁺ doping concentrations, respectively. Both unit cells expand when Pr³⁺ content increases. All samples showed a crystallite size lower than 27 nm. Diffuse reflectance studies exhibited the presence of the 4f5d absorption band of Pr³⁺, and absorption peaks in 440–610 nm region associated with 4f inter-level electronic transitions in Pr³⁺ ion. Low temperature (20 K) photo-luminescent spectroscopic measurements over excitation of 488 nm for praseodymium doped zirconia, showed multiple emission peaks in the 520–900 nm range of the electromagnetic spectrum, associated with typical 4f inter-level electronic transition in Pr³⁺. Incorporation of Pr³⁺ in more than one zirconia crystalline phase and the incorporation in cubic C₂ sites, were observed. Zirconia powders presented significant differences in its emission spectra as a function of the type of crystalline phase compounds.     

Effects of Zr/Ce molar ratio and water content on thermal stability and structure of ZrO2–CeO2 mixed oxides prepared via sol–gel process

ZrO₂–CeO₂ mixed oxides were synthesized via sol–gel process. Thermal stability, structure and morphology of samples were investigated by powder X-ray diffraction, FT-Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. In this approach, the solvent composition and Zr/Ce molar ratio have great influences on the structure and morphology of final products. With decreasing water content in the mixed solvent, specific surface area of powders increased and the single tetragonal phase was obtained. Only when the volume ratio of water and ethanol and the Zr/Ce molar ratio were 1:1, tetragonal t″-Zr_0.5Ce_0.5O₂ could be stabilized in powders at temperature as high as 1000 °C. Meanwhile, tetragonal (t′) and (t″) phases coexisted in Zr_0.5Ce_0.5O₂ solid solution without peak splitting after calcination at 1100 °C, further transforming into cubic and tetragonal (t′) phases at 1200 °C. The effective activation energy for Zr_0.5Ce_0.5O₂ nanocrystallite growth during annealing is about 5.24 ± 0.15 kJ/mol.     

Sol–gel synthesis and lithium ion conduction properties of garnet-type Li6BaLa2Ta2O12

High lithium ion conductive garnet-type barium lanthanum lithium tantalate, Li₆BaLa₂Ta₂O₁₂ (LLBTO), was prepared by a modified sol–gel Pechini method from the appropriate mixtures of lithium carbonate, lanthanum oxide, barium carbonate and tantalum ethoxide. The thermal decomposition of the precursor powder was investigated by TG/DTA analysis. The LLBTO precursor powders were annealed at various temperatures between 923 and 1123 K for 6 h in air. The transformation process from precursor powder to crystalline garnet-like phase was analyzed by X-ray powder diffraction (XRPD). The morphology of the powders annealed at various temperatures was investigated by scanning electron microscopy (SEM). The resultant pelletized Li₆BaLa₂Ta₂O₁₂, prepared by sol–gel synthesis method, shows a total Li-ion conductivity of 1.69 × 10^?5 S/cm at 298 K and an activation energy is 0.40 eV. The ionic conductivities reported in this study are slightly higher than those reported for LLBTO sample synthesized by conventional solid state synthesis route.     

Structure-dielectric properties relationships in copper-substituted magnesium ferrites

Nanocrystalline powders of copper-substituted magnesium ferrites with general formula Mg_1−xCu_xFe₂O₄ (x = 0.00, 0.17, 0.34, 0.50, 0.67, 0.84, 1.00) were prepared for the first time by sol–gel auto-combustion method, using glycine as fuel agent. Solid phase chemical reactions and the occurrence of spinel structure were monitored by using infrared spectroscopy. X-ray diffraction analysis confirmed the spinel single-phase formation. A shift from cubic structure to tetragonal structure starting with x = 0.84 was also observed. Microstructure of the samples was analyzed by scanning electron microscopy and particle size was estimated from the micrographs.Analysis of dielectric properties revealed very low values of dielectric loss at frequencies over 10 MHz.     

PAN–PEO solid polymer electrolytes with high ionic conductivity

The transparent and flexible solid polymer electrolytes (SPEs) are fabricated from polyacrylonitrile–polyethylene oxide (PAN–PEO) copolymer. The formation of the copolymer is confirmed by Fourier-transform infrared spectroscopy (FTIR) and Gel permeation chromatography (GPC) measurements. The effects of acrylonitrile (AN) wt% content and M_n(PEO) on ionic conductivity are investigated by alternating current (ac) impedance spectroscopy. By controlling and adjusting the AN wt% content and doping PEO with high molecular weight, the ionic conductivity of SPEs is optimized. The ionic conductivity of PAN–PEO solid polymer electrolytes is found to be high 6.79 × 10⁻⁴ S cm⁻¹ at 25 °C with an [EO]/[Li] ratio of about 10, and are electrochemically stable up to about 4.8 V versus Li/Li⁺. The conductivity and interfacial resistance remain almost constant even at 80 °C.     

Electrical conductivity of Ca1−xSrxTi0.65Fe0.35O3−δ, x = 0, 0.5 and 1, polycrystalline compounds in the 300–500 K range

Bulk and grain boundary electrical conductivity of oxygen deficient Ca_xSr_1?xTi_0.65Fe_0.35O_3?δ, x = 0, 0.5 and 1.0, polycrystalline specimens were evaluated by impedance spectroscopy measurements in the 5 Hz–13 MHz frequency range from 300 to 500 K. The ceramic powders were synthesized by solid state reaction and by a chemical route, the polymeric precursor technique. The X-ray diffraction of the samples at room temperature shows the following perovskite crystalline structures: cubic for x = 0 and orthorhombic for x = 0.5 and 1.0. The impedance plots are composed of two semicircles ascribed to grains (bulk) and interfaces (grain boundaries) contributions. The impedance data show that sintered pellets using powders prepared by solid state synthesis present higher intergranular and intragranular resistivity values than pellets prepared by the chemical route. Observations of scanning probe microscopy topographic images of the surfaces of the sintered pellets show evident differences between the grain morphology of the pellets prepared with powders synthesized by the two routes.     

Synthesis and electrochemical properties of nanosized LiFeO2 particles with a layered rocksalt structure for lithium batteries

Layered rocksalt-type LiFeO₂ particles (O3-LiFeO₂) with average particle sizes of ca. 40 and 400 nm were synthesized by an ion exchange reaction from α-NaFeO₂ precursors. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images confirmed the formation of nanosized O3-LiFeO₂. 40-nm LiFeO₂ exhibited a higher discharge capacity (115 mAh g^?1) than 400-nm LiFeO₂ (80 mAh g^?1), and also had better rate characteristics. The downsizing effect and cation disorder between the lithium and iron layers may have improved the electrochemical activity of the LiFeO₂ particles. Transmission electron microscopy (TEM) observation indicated a phase transition from O3-LiFeO₂ to a cubic lattice system during the electrochemical process. The cubic lithium iron oxide exhibited stable electrochemical reactions based on the Fe²⁺/Fe³⁺ and Fe²⁺/Fe⁰ redox couples at voltages between 4.5 and 1.0 V. The discharge capacities of 40-nm LiFeO₂ were ca. 115, 210, and 390 mAh g^?1 under cutoff voltages of 4.5–2.0 V, 4.5–1.5 V, and 4.5–1.0 V, respectively.     

Solution combustion synthesis of LiMn2O4 fine powders for lithium ion batteries

In this work, fine powders of spinel-type LiMn₂O₄ as cathode materials for lithium ion batteries (LIBs) were produced by a facile solution combustion synthesis using glycine as fuel and metal nitrates as oxidizers. Single phase of LiMn₂O₄ products were successfully prepared by SCS with a subsequent calcination treatment at 600–1000 °C. The structure and morphology of the powders were studied in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrochemical properties were characterized by galvanostatic charge–discharge cycling and cyclic voltammetry. The crystallinity, morphology, and size of the products were greatly influenced by the calcination temperature. The sample calcined at 900 °C had good crystallinity and particle sizes between 500 and 1000 nm. It showed the best performance with an initial discharge capacity of 115.6 mAh g⁻¹ and a capacity retention of 93% after 50 cycles at a 1 C rate. In comparison, the LiMn₂O₄ sample prepared by the solid-state reaction showed a lower capacity of around 80 mAh g⁻¹.     

Polymer–inorganic nano-composite thin film upconversion light emitters prepared by double-beam matrix assisted pulsed laser evaporation (DB-MAPLE) method

The work was to investigate the possibility of making polymer–inorganic nano-composite films with upconversion fluorescence properties using the double beam matrix-assisted pulsed laser evaporation (DB-MAPLE) method. The existing pulsed laser deposition vacuum chamber was modified to accommodate two laser beams of different wavelengths for simultaneous ablation of two separate targets: a polymer host and a rare earth containing rare earth ion enriched upconversion fluoride dopant. The polymer target was prepared in chlorobenzene and kept frozen during the ablation with circulating liquid nitrogen in accordance with the MAPLE procedure. It was ablated with 1064 nm beam from a pulsed Nd:YAG laser. The pellets made of the synthesized powders of inorganic phosphors of NaYF₄:Yb³⁺, Er³⁺ and NaYF₄:Yb³⁺, Ho³⁺were ablated with 532-nm beam from the same laser. The plumes from both targets were kept overlapping on the substrate during the deposition. X-ray diffraction analysis revealed that the most favorable for upconversion emission of the inorganic target materials was the hexagonal, beta phase of the NaYF₄ matrix existing at a baking temperature between 400 and 600 °C. The fabricated nano-composite films were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and optical fluorescence spectroscopy. The polymer nano-composite films generally retained the crystalline structure and the upconversion fluorescence properties of the initial rare earth compounds due to better control of the deposition process of the materials with substantially different properties. The proposed method can be potentially used for making a wide variety of nano-composite films.     

Low-temperature synthesis of Li7La3Zr2O12 with cubic garnet-type structure

In this paper, we report the direct synthesis of Li₇La₃Zr₂O₁₂ with the cubic garnet-type structure at low temperature with a lattice constant of 13.0035 Å. The synthesis condition is optimized to be at 750 °C for 8 h with 30 wt% excess lithium salt. No intermediate grinding was involved in this straightforward route. Without the adventitious of Al³⁺, the cubic Li₇La₃Zr₂O₁₂ is unstable above 800 °C and has an ionic conductivity of the order of 10^?6 S cm^?1.     

Layered iron orthovanadate microrods as cathode for lithium ion batteries with enhanced cycle performance

Iron orthovanadate microrods with layered structure have been synthesized by a simple hydrothermal method. The composition and structure of the microrods were investigated by X-ray powder diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Electrochemical measurements indicated that the microrods maintained high capacity when used as lithium ion battery cathode. As-obtained iron orthovanadate microrods electrode exhibits a stable and reversible capacity of over 250 mAh g⁻¹ at 16 mA g⁻¹ between 1.6 V and 4.7 V after 15 cycles. Detailed investigations reveal that the layered structure may reduce the lithium ion diffusion path and be helpful for stable capacity.     

Structural,thermal and vibrational characterization of mechanical alloyed In50Te50

Structural, chemical, thermal and vibrational studies of InTe produced by mechanical alloying were carried out using X-ray diffraction, energy dispersive spectroscopy, transmission electron microscopy, differential scanning calorimetry and Raman spectroscopy. The main crystalline phases formed after 2 h of milling were the tetragonal (TlSe-type) and high-pressure cubic (NaCl-type) InTe phases. Minority cubic In₂O₃ phase was also nucleated. Mean crystallite size and phase fraction variations with the increase of the milling time were obtained from Rietveld analyses. The distribution of the particle size (centered at about 39 nm) was obtained by images of transmission electron microscopy. Differential scanning calorimetry measurements showed no evidence of nonreacted materials and Raman measurements showed peaks that can be associated with the InTe (TlSe-type) phase and/or the existence of molecular structures of Te (chains/rings). The structural stability of the nanocrystaline phases of the In₅₀Te₅₀ sample milled for 15 h was attested by systematical X-ray diffraction measurements performed up to one year after its production.     

Facile synthesis,characterization and photocatalytic activity of niobium carbide

Niobium carbide (NbC) powders were prepared via a novel route at 550 °C and 8 h, using metallic magnesium powders, niobium pentoxide (Nb₂O₅), and potassium acetate (CH₃COOK) as starting materials. The structure and morphology of the product were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that as-prepared product was crystallized in pure cubic NbC phase and the size of the sample was estimated to be around 120 nm. The Rietveld refinement of the XRD data gives the cell constant a = 4.4718 Å. According to the Scherrer formula, the real grain size was about 70 nm. The BET surface area of the sample was ca.29.3 m²/g. The grain size distribution of the sample was about 467 nm, which was characterized by N4 PLUS submicron Particle Size Analyzer. The cubic NbC powders exhibited photocatalytic activity in degradation of Rhodamine-B (RhB) under 300 W mercury lamp light irradiation.     

Nb2O5 hollow nanospheres as anode material for enhanced performance in lithium ion batteries

Nb₂O₅ hollow nanospheres of average diameter ca. ～29 nm and hollow cavity size ca. 17 nm were synthesized using polymeric micelles with core–shell–corona architecture under mild conditions. The hollow particles were thoroughly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermal (TG/DTA) and nitrogen adsorption analyses. Thus obtained Nb₂O₅ hollow nanospheres were investigated as anode materials for lithium ion rechargeable batteries for the first time. The nanostructured electrode delivers high capacity of 172 mAh g^?1 after 250 cycles of charge/discharge at a rate of 0.5 C. More importantly, the hollow particles based electrodes maintains the structural integrity and excellent cycling stability even after exposing to high current density 6.25 A g^?1. The enhanced electrochemical behavior is ascribed to hollow cavity coupled with nanosized Nb₂O₅ shell domain that facilitates fast lithium intercalation/deintercalation kinetics.     

Synthesis and spectroscopy of transparent colloidal solution of Gd2O3: Er3+, Yb3+ spherical nanocrystals by pulsed laser ablation

The synthesis and the spectroscopy of upconverting nanocolloidal solutions have recently generated considerable interest due to their potential application as biolevels and in biological assays. This paper reports the synthesis of lanthanides doped transparent colloidal solution via pulsed laser ablation (PLA) which is highly fluorescing. Er³⁺, Yb³⁺ co-doped Gd₂O₃ phosphor has been laser ablated to synthesize the colloidal solution in triply distilled water. Spherical shaped nanoparticles of the average diameter in the range of 8–26 nm have been synthesized and characterized. Efficient multicolor upconversion (UC) emission has been observed and possible UC mechanism has been suggested. This approach will provide a method to synthesize highly UC efficient, non-agglomerated, pure transparent nanocolloidal solution for biological applications from already reported efficient phosphors.     

Lithium selective adsorption on 1-D MnO2 nanostructure ion-sieve

β-MnO₂, spinel-type Li₄Mn₅O₁₂ and pure cubic phase MnO₂ nanorod, with the size about 20–140 nm in diameter and 0.8–4 μm in length, were synthesized via a combination of hydrothermal synthesis and low temperature solid-phase reaction, more favorable to control the nanocrystalline structure with well-defined pore size distribution and high surface area than the traditional high temperature calcination process. Further, the MnO₂ ion-sieves with lithium selective adsorption property were prepared by the acid treatment process to completely extract lithium from the spinel Li₄Mn₅O₁₂ precursor with little change to the Mn–O lattice structure and the 1-D nanorod morphology. The effects of hydrothermal and solid-phase reaction process on the nanostructure, chemical stability and ion-exchange property of the ion-sieve material were examined with powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), N₂ adsorption–desorption at 77 K, and Li⁺ selective adsorption measurements. The lithium selective adsorption capacity was improved remarkably to 6.62 mmol g^?1 at equilibrium and about 5 mmol g^?1 at the initial lithium concentration of only 5.0 mmol l^?1, which is significant for lithium extraction from aqueous solutions with very low lithium content.     

Synthesis and characterization of thermally evaporated Cu2SnSe3 ternary semiconductor

Copper Tin Selenide (CuSnSe) powder was mechanically alloyed by high energy planetary ball milling, starting from elemental powders. Synthesis time and velocity have been optimized to produce Cu₂SnSe₃ materials. Thin films were prepared by thermal evaporation on Corning glass substrate at T_s = 300 °C. The structural, compositional, morphological and optical properties of the synthesized semiconductor have been analyzed by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM) and transmission electron microscopy. The analyzed powder exhibited a cubic crystal structure, with the presence of Cu₂Se as a secondary phase. On the other hand, the deposited films showed a cubic Cu₂SnSe₃ ternary phase and extra peaks belonging to some binary compounds. Furthermore, optical measurements showed that the deposited layers have a relatively high absorption coefficient of 10⁵ cm⁻¹ and present a band gap of 0.94 eV.     

Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite

A zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO₂ nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous–nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous–nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m² · g^? 1) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.     

High surface area nanocrystalline hausmannite synthesized by a solvent-free route

Nanocrystalline high surface area Mn₃O₄ powder was obtained at low temperature by a solvent-free route. The precursor was a mixture of manganese (II) acetate, 3,6,9-trioxadecanoic acid (TODA) and ammonium acetate that were intimately mixed by grounding in an agate mortar. Nanocrystalline Mn₃O₄ was obtained by thermal treatment at 120 °C. Powder X-ray diffraction, selected area electron diffraction, high resolution transmission electron microscopy, and Fourier transformed infrared characterization confirmed the formation of the hausmannite phase. The as-prepared mesoporous material has high specific surface area (120 m² g^?1). The performances of tape casted Mn₃O₄ nanopowder electrodes were investigated as anode material for lithium ion batteries. High capacity values were achieved at diverse C rates. Capacity fading was found to be dependent on the upper cut off voltage, the presence of a plateau at 2.25 V vs. Li⁺/Li being detrimental for long term cyclability.     

Cation distribution in the Bi4 − xRExTi3O12 (RE = La,Nd) solid solution and Curie temperature dependence

Bi_4 ? xRE_xTi₃O₁₂ (RE = La, Nd) ferroelectric powders were prepared by a co-precipitation route. Raman spectroscopy and X-ray diffraction were employed to determine the crystal site of La³⁺ and Nd³⁺ as well as the effect of their addition on the crystal structure. It was found that La atoms were not only placed preferentially in pseudo-perovskite A sites for concentrations x ≤ 1.2 but also substituted for Bi³⁺ in (Bi₂O₂)^2 + layers for greater concentrations. A similar behavior was observed with the limit value x = 0.8 in case of Nd³⁺. In solid solution La or Nd³⁺ ions diminish the distortions in the octahedron formed by oxygen atoms, so there is a tendency to undergo a transition in crystal symmetry from orthorhombic to tetragonal. Finally differential scanning calorimetry (DSC) shows a linear dependence of the Curie temperature (T_c) when the amount of La³⁺ or Nd³⁺ was increased.