Fabrication, structural and electrical characterization of lanthanum tungstate films by pulsed laser deposition

Films of lanthanum tungstate, 3 μm in thickness, were fabricated by means of pulsed laser deposition on a Pd foil. The films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and their electrical conductivity was measured at temperatures between 400 and 800 °C in different gas atmospheres. The films' structure and electrical characteristics are close to what is reported in the literature for corresponding polycrystalline material. The films exhibit fairly high proton conductivity at elevated temperatures, which make them interesting for components in hydrogen-related technologies. Changes in microstructure and the crystallographic orientation observed at higher temperatures were accompanied by changes in the conductivity characteristics.     

Chemical solution deposited lanthanum zirconium oxide thin films: Synthesis and chemistry

Pyrochlore lanthanum zirconium oxide (LZO) thin films textured along 〈4 0 0〉 are synthesized using lanthanum acetate hydrate, zirconium propoxide, propionic acid, acetic acid glacial, and methanol as precursors. The materials growth and chemistry are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA). The formation of inkjet printed LZO films on Ni-5%W tape is found to be based on the decomposition of the LZO precursor solution. In the annealing process, Zr metal–oxides bonds are first eliminated between 150 and 250 °C, while carboxylates from precursors remain in LZO after the annealing carried out at 900 °C for an hour. Annealed LZO films have dense and smooth structure that are composed of nanoparticles sizing 10–15 nm and some pinholes sizing 25–35 nm accounted for less than 0.1% of the area are observed.     

Controlled synthesis of CuO nanostructures on Cu foil, rod and grid

CuO nanowires are synthesized by heating Cu foil, rod and grid in ambient without employing a catalyst or gas flow at temperatures ranging from 400 to 800 °C for a duration of 1-12 h. Scanning electron microscopy (SEM) investigation reveals the formation of nanowires. The structure, morphology and phase of the as-synthesized nanowires are analyzed by various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). It is found that these nanowires are composed of CuO phase and the underlying film is of Cu₂O. A systematic study is carried out to find the possibilities for the transformation of one phase to another completely. A possible growth mechanism for the nanowires is also discussed.     

Enhanced conductivity in iodine doped polyaniline thin film formed by thermal evaporation

Thermal evaporation technique was employed to deposit pristine and iodine doped polyaniline (PANI) thin films on glass substrates. PANI was synthesized by the chemical oxidation method. Iodine doping was carried out by evaporation. The polymer synthesized was characterized by Thermo Gravimetric Analysis (TGA), Fourier Transform Infra Red (FTIR) and Ultraviolet-Visible (UV-VIS) spectroscopy. The evaporation temperature was optimized from TGA measurements. The thin film was deposited in vacuum at 1.33 × 10^− 4 Pa by thermal evaporation of PANI. The polymer film was characterized by FTIR and UV-VIS spectroscopy. The surface morphology of the films was studied by field emission scanning electron microscopy. The resistivity was measured by van der Pauw technique. The conductivity of the doped films was seen to increase with the iodine concentration and many fold increase in conductivity was observed in comparison to the pristine films. The increase in conductivity is due to the generation of polaron band in the band gap upon iodine doping.     

Phases in copper-gallium-metal-sulfide films (metal=titanium, iron, or tin)

The incorporation of metal impurities M (M = Ti, Fe, or Sn) into CuGaS₂ films is investigated experimentally as a function of impurity concentration. Films are synthesized by thermal co-evaporation of the elements onto glass/Mo substrates heated to 400 °C-570 °C. The compositions of the resulting films are measured by energy-dispersive X-ray spectroscopy and the structures of the present phases are studied by X-ray diffraction. The formation of Cu-M-S ternary phases is observed in a wide range of conditions. Films of Cu-Ga-Ti-S, synthesized at 500 °C, show the presence of a cubic modification of CuGaS₂ and Cu₄TiS₄. Alloying of CuGaS₂ and tetragonal Cu₂SnS₃ is observed for substrate temperatures of 450 °C. A miscibility gap opens at 500 °C and above with separate Sn-rich and Ga-rich phases. Similarly, alloys of CuFeS₂ and CuGaS₂ are only found in Cu-Ga-Fe-S films synthesized at lower substrate temperature (400 °C), whereas at 500 °C a miscibility gap opens leading to separate Fe-rich and Ga-rich phases.     

Electrochemical deposition and characterization of elongated CdO nanostructures

CdO nanostructures were synthesized by electrodeposition on the indium doped tin oxide conducting glass substrate at low temperatures (70, 80 and 90 °C) from aqueous solution. Scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to characterize the CdO nanostructures. The results demonstrated that the CdO nanostructures synthesized by electrodeposition grew preferably along the [1 1 1] and have face-centered cubic CdO structures and possessed good crystallinity. XPS measurements showed that the nanostructures had Cd and O elements present in the oxide state and no traces of metallic Cd were observed. The nanostructures were highly transparent in the visible region of spectrum and their energy gap was about 2.45 eV.     

Annealing study of titanium oxide nanotube arrays

Titanium dioxide nanotube arrays fabricated by anodization of titanium foil and annealed at different temperatures were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and positron annihilation spectroscopy (PAS). The crystallization process and morphological changes of the nanotubes have been discussed. It was found that anatase (1 0 1) only appeared on the walls of the nanotubes. The atomic concentration of fluoride and the ratio of Ti/O decreased when the annealing temperature increased. Vacancy type defects were found to diffuse toward the surface when the samples were annealed at 200 °C and 400 °C and healing of vacancies occurred at 600 °C. In addition, fluoride may form some complexes with vacancies on the surface hence lowering the value of S parameter.     

Synthesis and conductivity of cerium oxide nanoparticles

Cerium oxide (CeO₂) nanoparticles have been synthesized through composite-hydroxide-mediated approach. The X-ray powder diffraction (XRD) measurement proved that the pure cubic CeO₂ could be obtained at a low temperature region (170-220 °C). The particle size, micrograph morphology and microstructure were investigated by transmission electron microscope (TEM) and environmental scanning electron microscope (ESEM). The conductivity of as-synthesized CeO₂ was measured by a standard four-probe method. The conductivity of CeO₂ increases slightly with the increase of temperature. And the conductivity increases rapidly to 0.02418 s cm^− 1 at 830 °C. The product is a potential material for intermediate temperature solid oxide fuel cells (ITSOFC).     

Fabrication of highly oriented (002) ZnO film on glass by sol-gel method

In this study high quality (002) ZnO films were deposited on glass substrate by a sol-gel spin coating process. The as-coated films were post-annealed at different temperatures in air to investigate the effect of annealing temperature in particular. The chemical composition of the precursor sol and the intermediates produced in the films heating process were analyzed by thermo gravimetric analysis/differential thermal analysis (TGA/DTA). The microstructure and its optical properties of ZnO films were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), ultraviolet-visible spectroscopy (UV-Vis) and photoluminescence. TGA/DTA showed that a significant weight loss occurred at around 200-300 °C and the weight stabilized at 300 °C. An extremely sharp (002) diffracted peak in XRD patterns indicated the high preference in crystallinity of these films. FESEM micrographs revealed that the films were filled with particulates with size ranging from 10 to 25 nm as post annealing temperature increased from 400 to 500 °C and turned into porous films at 600 °C. UV-Vis has shown that the films were highly transparent under visible light and had a sharp absorption edge in the ultraviolet region at 380 nm. The measured optical band gap values of the ZnO thin films were around 3.24-3.26 eV. Photoluminescence spectra revealed a strong UV emission centered at about 390 nm corresponding to the near-band-edge emission with a weak defect-related emission at about 520 nm. The intensity of UV emission increased with the annealing temperature. This may be attributed to a higher quality ZnO film while annealed at higher temperature.     

A novel method to low temperature synthesis of nanocrystalline forsterite

Nanocrystalline forsterite (Mg₂SiO₄) powder was synthesized using sucrose as a chelating agent and template material from an aqueous solution of magnesium nitrate and colloidal silica. The synthesized powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermal analysis (STA), and scanning electron microscopy (SEM). The synthesized nano-powder had particle size smaller than 200 nm and average crystallite size of powders calcined at 800 °C for 3 h was in the range of 10-30 nm. Also the effect of addition 2 and 4 wt.% forsterite seed on nucleation temperature and crystallite size of forsterite was investigated. The presence of small amounts of Mg₂SiO₄ as seed obviously accelerated the crystallization of forsterite. According to DTA results the inceptive formation temperature of Mg₂SiO₄ without any seed was 760 °C, while this temperature for the specimen containing 4 wt.% seed was 700 °C.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel via sucrose process

Nanocrystalline MgAl₂O₄ spinel powder was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600 and 700 °C. The calcined powder at 800 °C for 2 h has faced shaped morphology and its crystallite size is in the range of 8-12 nm. Further studies also showed that the amount of polymeric matrix to metal ions has significant influence on the crystallite size of synthesized magnesium aluminate spinel powder.     

Synthesis of nanocrystalline forsterite (Mg2SiO4) powder by combined mechanical activation and thermal treatment

This study investigates the synthesis of single-phase nanocrystalline forsterite powder by mechanical activation with subsequent annealing. To produce forsterite powder, a mixture of talc and magnesium oxide powders was first milled by a planetary ball mill, and then annealed at 1000 and 1200 °C for 1 h. The synthesized powder was characterized by X-ray diffraction (XRD), simultaneous thermal analysis (STA), scanning electron microscopy (SEM), and atomic absorption spectrometry (AAS). The initial temperature of forsterite crystallization was reduced to about 825 °C after 20 h of mechanical activation. The forsterite powder synthesized by 5 h of mechanical activation with subsequent annealing at 1000 °C for 1 h had crystallites 40 nm in size. The particle size of this sample was less than 500 nm.     

Green hydrothermal synthesis and optical absorption properties of ZnO2 nanocrystals and ZnO nanorods

A green hydrothermal method was proposed for the controllable synthesis of ZnO₂ nanocrystals and ZnO nanorods, using the common and cost-effective 2ZnCO₃·3Zn(OH)₂ powder and 30 mass% H₂O₂ aqueous solution as the raw materials. The characterization results from X-ray diffraction, high resolution transmission electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy indicated that the products synthesized at 100-120 °C for 6 h or at 170 °C for 0 h were cubic phase ZnO₂ nanocrystals; while those synthesized at 170 °C for 3-6 h were hexagonal phase ZnO nanorods. The UV-vis absorption spectra showed that the as-synthesized ZnO₂ nanocrystals and ZnO nanorods had optical band gaps of about 4.1 and 3.3 eV, respectively.     

Synthesis and characterization of NiO-YSZ for SOFCs

Nickel oxide and yttria-stabilized zirconia ceramic materials were prepared by three methods: physical mixture, a modified Pechini route, and impregnation with Ni(NO₃)₂·6H₂O. Temperature-programmed reduction (TPR) analysis showed the presence of different reduction peaks for each sample and that the reduction temperature was influenced by the employed preparation procedure. Nickel oxide species are completely reduced at temperatures up to 1000 °C and their temperature-programmed reduction profiles indicated that a higher temperature reduction corresponds to a higher calcination temperature. Furthermore, the composites synthesized through impregnation presented nickel oxide species more easily reducible than those prepared by the two other methods. Scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) evidenced a larger nickel oxide coating on yttria-stabilized zirconia for the composite synthesized through the impregnation method. The electrical conductivity of impregnation sample was 117 S cm⁻¹ at 850 °C, a value three times higher than that of the physical mixture.     

ZnFe2O4 thin films from a single source precursor by aerosol assisted chemical vapour deposition

A single source heterobimetallic complex [Fe₂(acac)₄(dmaeH)₂][ZnCl₄] (1) (acac = 2,4-pentanedionate, dmaeH = N,N-dimethylaminoethanol), was synthesized in high yield. The complex was analyzed by melting point, Fourier transfer infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The structure of the cation was established by single crystal X-ray analysis on a derivative, [Fe₂(acac)₄(dmaeH)₂][ZnCl₃(THF)]₂·THF (1a) (THF = tetrahydrofuran). TGA analysis showed that complex (1) undergoes facile thermal decomposition at 450 °C to give ZnFe₂O₄ residue. In-house designed aerosol assisted chemical vapour deposition equipment was used to deposit thin films of ZnFe₂O₄ on fluorine doped SnO₂ coated conducting glass substrate at 450 °C. X-ray diffraction analysis proved the formation of crystalline ZnFe₂O₄ phase and scanning electron microscopy revealed the film morphology with well defined crystalline particles evenly distributed in the range 150-200 nm. The indirect and direct bandgap energies of the thin films were estimated to be 1.76 and 2.10 eV, respectively.     

Preparation and characterisation of La10−xGe5.5Al0.5O26±δ apatites by freeze-drying precursor method

Nanocrystalline powders of La_10−xGe_5.5Al_0.5O_26±δ (x = 0-0.5) with an average crystallite size of 50 nm were prepared by a freeze-drying precursor method. These powders were used to obtain dense ceramic materials at rather low temperature as 1100-1200 °C for 1 h and to study the transport properties by impedance spectroscopy. The composition with the highest La-content (x = 0) exhibits a second-order phase transition from triclinic () to hexagonal (P6₃/m) space groups around 750 °C, whereas for x ≥ 0.2 the materials presents hexagonal structure in the whole temperature range studied. The thermal properties of these materials were investigated by high temperature X-ray diffraction (XRD), thermal analysis (TG/DTA) and impedance spectroscopy. These results confirmed the incorporation of water in the germanate-apatite structure. However, the conductivity resulted to be independent on the gas atmosphere used, which seems to indicate that the proton contribution to the overall conductivity is negligible in these materials.     

Effect of annealing on the optical properties of Nd:YAG transparent ceramics

The Nd:YAG transparent ceramics were fabricated by vacuum sintering at 1750 °C for 20 h, where the raw nanopowders were synthesized by a modified co-precipitation method. Subsequently the Nd:YAG ceramic specimens were annealed or even re-annealed in air or vacuum at 1250-1500 °C for 20 h. The Nd:YAG ceramic specimens were investigated by X-ray diffraction, ultraviolet spectroscopy, inductively coupled plasma atomic emission spectroscopy, electron paramagnetic resonance spectroscopy and scanning electron microscopy. The results showed that post-annealing could improve the optical properties and microstructure of Nd:YAG transparent ceramics. By air annealing, the in-line transmittances of the specimens increased, mainly due to the decrease of oxygen vacancies concentration in specimens. The air annealing at 1450 °C for 20 h was optimum for preparation of Nd:YAG transparent ceramics. Furthermore, the red shift of UV absorption edge after air annealing could be attributed to the absorption by Fe³⁺ charge transfer bands.     

Order-disorder phase transitions and high-temperature oxide ion conductivity of Er2+xTi2−xO7−δ (x = 0, 0.096)

The Er_2+xTi_2−xO_7−δ (x = 0.096; 35.5 mol% Er₂O₃) solid solution and the stoichiometric pyrochlore-structured compound Er₂Ti₂O₇ (x = 0; 33.3 mol% Er₂O₃) are characterized by X-ray diffraction (phase analysis and Rietveld method), thermal analysis and optical spectroscopy. Both oxides were synthesized by thermal sintering of co-precipitated powders. The synthesis study was performed in the temperature range 650-1690 °C. The amorphous phase exists below 700 °C. The crystallization of the ordered pyrochlore phase (P) in the range 800-1000 °C is accompanied by oxygen release. The ordered pyrochlore phase (P) exists in the range 1000−1200 °C. Heat-treatment at T ≥ 1600 °C leads to the formation of an oxide ion-conducting phase with a distorted pyrochlore structure (P2) and an ionic conductivity of about 10⁻³ S/cm at 740 °C. Complex impedance spectra are used to separately assess the bulk and grain-boundary conductivity of the samples. At 700 °C and oxygen pressures above 10⁻¹⁰ Pa, the Er_2+xTi_2−xO_7−δ (x = 0, 0.096) samples are purely ionic conductors.     

One simple synthesis route to whisker-like nanocrystalline boron nitride by the reaction of NaBH4 and NaN3

Nanocrystalline boron nitride (BN) was synthesized via a simple route by the reaction of sodium borohydride with sodium azide in an autoclave at 600 °C. X-ray powder diffraction pattern indicated that the product was hexagonal BN, and the cell constant was a = 2.495 Å, c = 6.687 Å. Transmission electron microscopy image showed that it consisted of whisker-like particles with an average size of 200 nm × 20 nm. The product was also studied by FT-IR, XPS and TGA. It has good thermal stability and oxidation resistance in high temperature.     

One simple synthesis route to nanocrystalline tantalum carbide via the reaction of tantalum pentachloride and sodium carbonate with metallic magnesium

Nanocrystalline tantalum carbide (TaC) was synthesized via a simple route by the reaction of metallic magnesium with sodium carbonate and tantalum pentachloride in an autoclave at 600 °C. X-ray powder diffraction pattern indicated that the product was cubic TaC, and the cell constant was a = 4.451 Å. Field emission scanning electron microscopy image showed that it consisted of particles with an average size of 40 nm. The product was also studied by TGA in the flowing air. It had good thermal stability and oxidation resistance below 450 °C in air. The mechanism of the formation of TaC was also discussed in this paper.