Precursor Solution Method Research Articles

Hydrogen Affinity of Silica-based Nanocomposite for High Temperature Hydrogen Separation Membranes

AbstractHydrogen Affinity of Silica-based Nanocomposite for High Temperature Hydrogen Separation Membranes Japan Fine Ceramics Center, 2-4-1, Mutsuno, Nagoya, 456-8587, Japan Yumi H. Ikuhara, Tomohiro Saito, Koji Hataya, Yuji Iwamoto and Seiji Takahashi Because of concerns about global warming, increasing attention is being directed to find an alternative to fossil hydrocarbon fuels and hydrogen is rapidly becoming one of the leading candidates. For hydrogen production, high temperature membrane reactor is applicable by simplify the process of producing hydrogen from natural gas and purifying it by combining these process into single step. Among the materials, ceramic membranes with molecular sieve-like properties have been expected for application in membrane reactors for conversion enhancement in dehydrogenation and methane reforming reactions. Amorphous silica (Si-O) membranes prepared by sol-gel method have been intensively studied as molecular sieve membranes for gas separation at high temperature. To enhance the hydrogen permselectivity, we have developed Ni nanoparticle-dispersed amorphous Si-O based composite membrane through the precursor solution method and achieved higher hydrogen permeance compared to helium and nitrogen at 573K to 773K. In order to understand the phenomenon of the high hydrogen permeance of the novel nanocomposite membrane, it is important to clarify the expected high temperature hydrogen affinity, i.e., hydrogen adsorption properties. Here, the relationship between microstructure and hydrogen affinity of the nanocomposite was intensively studied from the view point of concentration of Ni nanoparticle in the amorphous Si-O matrix and reversible hydrogen adsorption property. Ni nanoparticles with about 3 to 5 nm in size were homogeneously dispersed in the amorphous Si-O matrix, and the Ni nanoparticles reached to saturate in the Si-O matrix with Ni/(Si+Ni) ratio of 0.2. The reversibly adsorbed hydrogen was hardly detected on the amorphous Si-O and Ni at 573 K, while Ni nanoparticle-dispersed amorphous silica apparently exhibited reversible hydrogen adsorption property. There was appreciable pressure dependence of the reversible hydrogen adsorption on the composite. Further study of the relationship between the increase amount of the reversibly adsorbed hydrogen (Vr) and Ni content on the composite powders revealed that the Vr gradually increased with increasing the Ni content and the highest Vr was ascertained for the composite with the Ni/(Si+Ni) ratio of 0.2. Combining the results of the unique hydrogen permeance through the composite membrane and the hydrogen affinity in the composite powder, we conclude that the existence of reversibly adsorbed hydrogen due to the extensive dispersion of Ni nanoparticles in the Si-O-based membrane involve the enlargement of the number of solubility site for hydrogen, which resulted in the selective enhancement in the hydrogen permeance of the nanocomposite membrane. Contact persons: Y

Photoluminescence properties of nanocrystalline Tb3+ doped Y2O3 phosphor prepared through a novel synthetic route

Green emitting cubic Y2O3:Tb3+ nanocrystalline phosphor having particle size of 22nm was synthesized by TEA (triethanolamine) based precursor solution method. We have characterized our nanocrystalline sample by XRD, HRTEM and Raman spectroscopic measurement. We compared the photoluminescence properties of our nanocrystalline sample with the bulk one. Due to the presence of defect states and lower phonon density of nanomaterials, cross relaxation process seems to be less effective in nanosized sample reflecting higher blue/green ratio in nanosized sample. Relative intensity of 5D4–7F5 transition with respect to 5D4–7F6 transition is reduced in nanosized sample due to greater transition probability of the latter transition in the distorted nanostructured material. Our analysis suggests that change of local environments takes place with decreasing the particle size and it is reflected in the photoluminescence spectra.

Phase transition in Sr modified Pb(SnTi)O 3 system

The effect of Sr substitution on the structural and ferroelectric properties of Pb(SnTi)O 3 system has been studied. The nanosized ceramic powders were synthesized by precursor solution method. Relative density >85% was obtained after sintering by covering it with lead zirconate powders in order to prevent lead loss. XRD shows that single-phase compound has been formed at 550 °C. The crystallite size varied from 55 to 80 nm. The increase in concentration of Sr content has lead to the increase in lattice parameters due to the reason that the ionic radius of Sr is more than that of substituting ion Pb. The structure of the phase formed is the same irrespective of the concentration of Sr. Detailed studies of the dielectric properties of the compounds show non-relaxor type ferroelectric transition. The diffusivity ( γ) ranged from 1 to 1.2 revealing diffuse phase transition.

Dielectric relaxation in Sr modified PST ceramics

Nanocrystalline powders of strontium modified PbSn0.15Ti0.85O3 (PST) having the formula Pb0.94Sr0.06Sn0.15 have been synthesized by a precursor solution method. The electrical behavior of Pb0.94Sr0.06Sn0.15Ti0.85O3 sintered pellets has been studied by complex impedance spectroscopy analysis. The plot of the real and imaginary parts of the impedance shows that the semicircle exhibits a depression degree with a distribution of relaxation time. The modulus curve indicates the possibility of non-exponential type conductivity. The values of the activation energy calculated from both plots of Z” and M”, are 1.06 and 1.09 eV, which reveals that the species responsible for conduction are same. It also confirms that oxygen vacancies play an important role in conduction. The non-overlapping of the peaks in the plot of M”/M”max and Z”/Z”max as a function of logarithmic frequency measured at 350 °C indicates short-range conduction. The compounds exhibit a negative temperature coefficient of resistance with an α value of -5×10-2 °C at 375 °C. The frequency (ω) dependence of conductivity satisfies the ωn power law. The variation of n with temperature suggests that ac conduction is due to small polaron tunneling.

Structural and electrical properties of Ca 2+-modified PZT electroceramics

A perovskite ceramic oxide having the general formula Pb 0.97Ca 0.03Zr 0.05Ti 0.95O 3 (PCZT) was prepared using precursor solution method. The compound belongs to the tetragonal system. TEM micrographs show that the particles are more or less spherical in shape. Complex impedance analysis indicates the presence of grains separated by grain boundaries, which are also evident from the SEM micrographs. The sample impedance behavior has been explained in terms of the bricklayer model. The relaxation process taking place is short range. The conductivity variation shows a typical Arrhenius-type behavior having linear dependence on logarithm of conductivity.

Effect of Ca-additions on structural and electrical properties of Pb(SnTi)O 3 nano-ceramics

Polycrystalline samples of Ca-modified Pb(SnTi)O 3 (i.e., Pb 1− x Ca x Sn 0.15Ti 0.85O 3, x = 0, 0.03, 0.06 and 0.09) were prepared by the precursor solution method. X-ray diffraction (XRD) of the compounds suggests that they exhibit single phase with tetragonal crystal structure. SEM micrograph of the materials shows uniform grain distribution on the surface of the samples. TEM micrographs of the above compounds reveal that their particle size is less than 30 nm. Detailed dielectric studies of the compounds at different temperature suggest that with increasing Ca concentration in the compound, the value of the dielectric constant first increases for ( x = 0, 0.03 and 0.06) and then decreases for ( x = 0.09). The compounds do not exhibit any ferroelectric relaxor behavior, i.e., they exhibit diffuse phase transition and frequency dependent high permittivity. Some impedance and electrical properties of the materials were studied using an impedance spectroscopic technique (CIS) in a wide range of temperature (30–500 °C). The Nyquist plot clearly shows the presence of both bulk and grain boundary effects in all the compounds.

Impedance spectroscopy study of the nanocrystalline ferroelectric (PbMg)(ZrTi)O3 system

Nanosized ceramic powder having a general formula Pb1-xMgxZr0.05Ti0.95O3 (PMZT) with x=0, 0.03, 0.06 and 0.09 has been synthesized by a metal ion complex precursor solution method. Preliminary structural analysis of PMZT compounds using the X-ray diffraction technique suggests that they exhibit a single phase with tetragonal crystal structure. Complex impedance spectroscopy analysis has been carried out to investigate the electrical properties. The physical structure of the samples has been visualized most prominently near 400 °C from the Nyquist plot as consisting of grains separated by grain boundaries. The presence of a single arc in the complex modulus spectrum at different temperatures confirms the single-phase character of the PMZT compounds.

Synthesis and Characterization of Nanosized Ba1 − x Mg x Sn0.15Ti0.85O3 Ceramics

Nanosized Ba1− x Mg x Sn 0.15 Ti 0.85 O 3 (x = 0, 0.03, 0.06 and 0.09) powder was prepared by the thermal decomposition of metal complex based aqueous precursor solution method. Preliminary structural study of the compounds with XRD data shows the formation of single phase exhibiting orthorhombic structure when Mg was doped. TEM studies have provided information about the uniform distribution of nanosized spherical grains having particle size ranging from 14–20 nm. Detailed dielectric study of sintered pellets as a function of temperature at three different frequencies (10, 50 and 100 kHz) shows that with increase in concentration of Mg the Curie temperature shift to higher temperature side and the value of the dielectric constant decreases. The plot of diffusivity graph shows that the diffuseness of the peak increases with increase in doping concentration. The plot of M″ with frequency shows the presence of single peak indicating dielectric relaxation process.

Impedance spectroscopy of Ba1–xSrxSn0·15Ti0·85O3ceramics

The electrical properties of Ba1–xSrxSn0·15Ti0·85O3 (BSST) (x=0, 0·03, 0·06, 0·09) ceramics synthesised by the precursor solution method were investigated by impedance spectroscopy in the temperature range from room temperature to 500°C. SEM micrographs show the grain distribution. Nyquist plots reveal the presence of a bulk effect for x=0 and of bulk and grain boundary effects for x=0·03, 0·06 and 0·09. Variation in bulk ac conductivity as a function of frequency demonstrates that the compounds exhibit Arrhenius type electrical conductivity. The ac activation energy increases with increasing Sr concentration.

Ferroelectric and Dielectric Properties of Lanthanum-Modified Bismuth Titanate Thin Films Obtained by the Polymeric Precursor Method

Lanthanum-modified bismuth titanate, Bi4 − xLaxTi3O12 (BLT), thin films with a La concentration of 0.75 was grown on Pt/Ti/SiO2/Si substrates by using the polymeric precursor solution and spin-coating method. The scanning electron microscopy (SEM) showed rounded grains, which is not typical for these system. The BLT films showed well-saturated polarization-electric field curve which 2Pr = 41.4 μC/cm2 and Vc = 0.99 V. The capacitance dependence on the voltage is strongly nonlinear, confirming the ferroelectric properties of the film resulting from the domains switching. These properties make BLT a promising material for FERAM applications.

Characterization of lanthanum-doped bismuth titanate thin films prepared by polymeric precursor method

Lanthanum-modified bismuth titanate, Bi 4− x La x Ti 3O 12 (BLT), with x ranging from 0 to 0.75 was grown on Pt/Ti/SiO 2/Si substrates using a polymeric precursor solution and spin-coating method. The dielectric constant of highly doped bismuth titanate was equal to 148 while dielectric losses remained low (tan δ=0.0018), and the films showed well-saturated polarization-electric field curves (2 P r=40.6 μC/cm 2 and V c=0.99 V). The leakage current densities improve for the lanthanum-doped system. For five-layered BLT films with x=0.75, a charge storage density of 35 fC/μm 2 and a thickness of 320 nm were found.

Electrical Characterization of Lanthanum-Modified Bismuth Titanate Thin Films Obtained by the Polymeric Precursor Method

Lanthanum-modified bismuth titanate, Bi− x LaxTi3O12 (BLT), thin films with a La concentration ranging from 0 to 0.75 were grown on Pt/Ti/SiO2/Si substrates using a polymeric precursor solution and spin-coating method. The scanning electron microscopy shows a change of morphology with increasing the lanthanum concentration. The BLT films show well-saturated polarization-electric field curves whit remnant polarizations of 14.7, 20.5, 21.5, and 20.4 μ C/cm2 for × = 0, 0.25, 0.50 and 0.75, respectively. The dielectric constant of BLT (x = 0.75 mol% La) is equal to 158 while dielectric loss remain low (tanδ = 0.0018).

Chemical synthesis of nanocrystals of tantalum ion-doped tetragonal zirconia

A polymer matrix-based precursor solution method is explored for the preparation of tantalum ion-doped tetragonal (t) zirconia polycrystals. The matrix is composed of sucrose and polyvinyl alcohol (PVA), which are the dispersing agents for the metal cations and finally act as a template for the nanoparticle through the formation of a mesoporous structure. The t-phase is formed in powders of zirconia with 5, 10, 15 and 20 at.% tantalum ion, and the phase is stable up to the calcining temperature of 1100 °C. The particle size distribution is narrow with the size range 20–40 nm for the sample containing 5 at.% tantalum ions calcined at 700 °C. The stabilization of the metastable tetragonal form is probably due to the strong TaO bonds, which hinder the reorientation of atoms during phase transformation.

Chemical synthesis of nanocrystalline zirconia by a novel polymer matrix-based precursor solution method using triethanolamine

Nanocrystalline cubic ZrO 2–Y 2O 3 powders were synthesized by a novel polymer matrix-based method, using triethanolamine. Solid solutions of ZrO 2 containing various mole percent of Y 2O 3 with cubic structure were produced at low temperature (approximately bed-temperature 250°C). The produced powder was characterized using differential thermal analysis (DTA), differential thermogravimetry (DTG), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average crystalline size of the powder calcined at 650°C ranges from 7.0 to 13.0 nm and the particle size ranges from 20.0 to 40.0 nm.

Synthesis of YBa 2Cu 4O y powder by the EDTA solution method and oxine coprecipitation under ambient pressure

The YBa 2Cu 4O y superconducting powder were synthesized by the ethylene-diamine-tetra-acetic (EDTA) precursor solution method and 8-hydroxyquinoline-triethylamine coprecipitation. Pure 124 phase can be obtained through repeated heat treatment at 800°C in flowing oxygen. The effects of heat treatment temperature and sintering time were investigated.

Preparation of single high-T c phase BiPbSrCaCuO superconductor by the EDTA precursor solution method

High fraction of 110 K phase Bi-based superconductor was prepared by the EDTA precursor solution method. The process is based on the formation of EDTA complexes to form a submicron-size fine powder of the correct stoichiometry without segregation. Using this simple technique more than 90% fraction of high- T c phase can be obtained with 100 hours sintering at 858°C.