Solution combustion synthesis of CeO2–CeAlO3 nano-composites by mixture-of-fuels approach

Nano-composites of CeO2–CeAlO3 are synthesised by solution combustion method employing (a) urea and (b) a mixture of urea and glycine as fuels with corresponding metal nitrates. The as-prepared powders are all nano-sized (5–30 nm) and the same is confirmed by broadening of the X-ray diffraction peaks and transmission electron microscopy. A starting composition of Ce:Al in the atomic ratio 4:6 gives rise to different phases depending on the fuel being used for combustion. When urea alone is used as fuel, nano-crystalline CeO2 phase is formed with Al2O3 being in the amorphous state. When the mixture of fuels is used, a mixture of nano-sized CeO2 and CeAlO3 phases is obtained. However, upon sintering at 1400 � C in air, the stable phases CeO2 and a-Al2O3 are formed in both the cases. Combustion synthesis using mixture-of-fuels is proposed to be a route to stabilise low oxidation compounds such as CeAlO3

High-temperature dilatometric studies on the (RE)BaCuO system (RE = Y,Nd)

Thermal expansion measurements have been carried out using dilatometry on the (RE)BaCuO system in the temperature range 300–1100 K. The peak in the thermal expansion coefficient (α) at 890 K presages the high-temperature orthorhombic-to-tetragonal phase transition in $YBa_2Cu_3O_{7-\delta}$. The thermal expansion behaviours of $YBa_2Cu_3O_{7-\delta}$, $Y_2BaCuO_5$, $NdBa_2Cu_3O{7-\delta}$ and $Nd_4Ba_2Cu_2O_{10}$, which are the constituent phases of melt-processed high-$J_c$ superconducting ceramics, are compared. The relevance of dilatometric studies at high temperature to such multiphase ceramic bodies is discussed

Synthesis of nanocrystalline CeAlO3 by solution-combustion route

CeAlO3 was synthesised by a modified solution-combustion route using a mixture of urea and glycine as fuel. A trivalent oxidation state of cerium was stabilised and high-quality single phase polycrystalline CeAlO3 was obtained by optimising the ratio of fuels. The transmission electron micrography and powder X-ray diffraction investigations showed that the particles were nanocrystalline in nature. Rietveld refinement confirmed the space group of the structure to be I4/mcm with lattice parameters a = 5.3278(1) Å, c = 7.5717(3) Å. Magnetisation measurements indicated that the sample was paramagnetic up to 2K. The susceptibility data fitted the Curie–Weiss model in the temperature range 100–300K with �p = −40 K. The value of �eff = 2.2�B was close to that expected for a Ce3+ ion. The magnetic properties were comparable to that reported for single crystals indicating the high quality of CeAlO3 prepared in the present work. The semiconducting band gap as estimated from UV–visible spectroscopy was 3.26 eV

Search for a novel zero thermal expansion material: dilatometry of the AgI-CuI system

AgI is a well-known superionic conductor possessing a negative thermal expansion (NTE) coefficient while CuI is a p-type semiconductor possessing a positive thermal expansion coefficient. Pellets of X-Ray Diffraction (XRD) characterized compositions in the AgI-CuI system namely, beta AgI, gamma AgI, Ag0.5Cu0.5I, Ag0.25Cu0.75I, Ag0.10Cu0.90I, Ag0.05Cu0.95I and gamma CuI have been examined by quartz pushrod dilatometry measurements in order to look for a zero thermal expansion material. It is found that the systematic displacement of Ag by Cu gradually reduces the NTE anomaly in AgI. The composition Ag0.25Cu0.75I apparently exhibits near-zero thermal expansion. The results are discussed qualitatively in terms of relevant models

Effect of synthesis route on the structure of Nd_3-x}Ba_{3+x}Cu_6O_{14-2}_\delta (x=0, 1) system: a neutron diffraction study

Structural studies on Nd_{3-x}Ba_{3+x}Cu_6O_{14-2}_\delta with 0≤x≤1 were carried out by Rietveld refinement procedure using neutron diffraction data. The composition x=1 was prepared both by the solid-state method and the nitrate-decomposition method. Quantitative multiphase analysis coupled with variation in the method of synthesis has shown conclusively that Nd did substitute for Ba even in a stoichiometric composition $NdBa_2Cu_3O_{7 - \delta }$ , irrespective of the method of synthesis. The fractional atomic substitution of Nd at the Ba site has been determined to be about 15%. The composition x=0, synthesised by the nitrate-decomposition method, has been found to be tetragonal with the space group P4/mmm. Nd has been found to substitute for Ba according to $Nd(Ba_{0.75}Nd_{0.25})_2Cu_3O_{7 - \delta}$ and no random distribution of cations has been found along the c-direction. The observed tetragonality has been attributed to the additional oxygen taken into the basal (001) plane due to the substitution of trivalent Nd at the divalent Ba site

Dielectric, thermal, and mechanical properties of the semiorganic nonlinear optical crystal sodium p-nitrophenolate dihydrate

Physical properties such as dielectric, specific heat, thermal expansion, and mechanical hardness have been measured for sodium p-nitrophenolate dihydrate single crystals. The dielectric measurements were made both as a function of frequency (in the range 15 kHz-10 MHz) and temperature (in the range 30-80 degreesC). For the range of frequencies measured the values were found to vary between 4.03 and 3.69 for epsilon (11), 8.11 and 7.05 for epsilon (22), and 5.71 and 5.36 for epsilon (33) at room temperature, and piezoelectric resonances were observed at certain frequencies. The dielectric measurements made as a function of temperature did not exhibit any anomaly in the temperature range measured. The specific heat studies carried out for this compound showed approximate to 30% increase in C-p with the temperature in the measured range. The thermal expansion measured as a function of temperature in the range 30-80 degreesC exhibited linear behavior and the average thermal expansion coefficients were found to be alpha (1)=7.48x10(-5) K-1, alpha (2)=4.30x10(-6) K-1, and alpha (3)=1.99x10(-5) K-1. The polar plots drawn for these coefficients were correlated with crystallographic features of the structure. The Vickers hardness measurements, carried out along the three crystallographic axes, also exhibited anisotropy

Synthesis and thermal expansion hysteresis of Ca1-xSrxZr4P6O24

The low thermal expansion ceramic system, Ca1-xSrxZr4P6O24, for the compositions with x = 0, 0.25, 0.50, 0.75 and 1 was synthesized by solid-state reaction. The sintering characteristics were ascertained by bulk density measurements. The fracture surface microstructure examined by scanning electron microscopy showed the average grain size of 2.47 mum for all the compositions. The thermal expansion data for these ceramic systems over the temperature range 25-800degreesC is reported. The sinterability of various solid solutions and the hysteresis in dilatometric behaviour are shown to be related to the crystallographic thermal expansion anisotropy. A steady increase in the amount of porosity and critical grain size with increase in x is suggested to explain the observed decrease in the hysteresis

50 MeV Li3+Li^{3+} irradiation effects on the thermal expansion of Ca1−xSrxZr4P6O24Ca_{1-x}Sr{_x}Zr{_4}P{_6}O_{24}

The influence of 50 MeV Li3+ ion irradiation on the thermal expansion of the low thermal expansion ceramic Ca1-xSrxZr4P6O24 (x = 0.00, 0.25, 0.50, 0.75 and 1.00) belonging to the sodium zirconium phosphate (NZP) family of ceramics was studied in the temperature range 300-1100 K. The observed changes in XRD, microstructure and thermal expansion are reported. These changes are strongly dependent upon the strontium substitution at calcium sites in the basic structure, The XRD and scanning electron microscope (SEM) studies indicate that the ion irradiation causes amorphization, especially at the grain boundaries. The thermal expansion hysteresis reduces due to Sr substitution and is further reduced upon irradiation. It is suggested that the amorphization due to irradiation helped release of thermal stress and thereby lead to the reduction in the hysteresis in thermal expansion. The composition with x = 0.50 having low coefficient of thermal expansion (CTE), low hysteresis and the least thermal expansion anisotropy is least affected by the Li3+ irradiation and hence may qualify as the radiation resistant material. (C) 2002 Elsevier Science B.V. All rights reserved

50 MeV Li3+ irradiation effects on the thermal expansion of Ca1âxSrxZr4P6O24

The influence of 50 MeV Li3+ ion irradiation on the thermal expansion of the low thermal expansion ceramic Ca1-xSrxZr4P6O24 (x = 0.00, 0.25,0.50, 0.75 and 1.00) belonging to the sodium zirconium phosphate (NZP) family of ceramics was studied in the temperature range 300-1100 K. The observed changes in XRD, microstructure and thermal expansion are reported. These changes are strongly ependent upon the strontium substitution at calcium sites in the basic structure, The XRD and scanning electron microscope (SEM) studies indicate that the ion irradiation causes morphization, especially at the grain boundaries. The hermal expansion hysteresis reduces due to Sr substitution and is further reduced upon irradiation. It is suggested that the amorphization due to irradiation helped release of thermal stress and thereby lead to the reduction in the hysteresis in thermal expansion. The composition with x = 0.50 having low coefficient of thermal expansion (CTE), low hysteresis and the least thermal expansion anisotropy is least affected by the Li3+ irradiation and hence may qualify as the radiation resistant material