C. Vishnuvardhan Reddy

High temperature lattice parameters and thermal expansion of Y1−xCexAl2 (x = 0,0.15, 1) intermetallics

Abstract Precise determination of the lattice parameters of the quasi-binary compounds Y 1− x Ce x Al 2 was made from room temperature to about 800 K using a Unicam (diameter, 19 cm) high temperature powder camera and Cu Kα radiation. The coefficients of thermal expansion at different temperatures were evaluated by an analytical method. It was observed that the lattice parameter increased non-linearly with increasing temperature, whereas the coefficient of thermal expansion decreased with increasing temperature in these compounds. This result is similar to that observed in many of the isotypic RAl 2 intermetallics.

Synthesis and Characterization of Co-Doped Ceria Ceramics by Sol-Gel Method

Doped and co-doped ceria electrolyte materials are very useful in solid oxide fuel cells. The Ce0.9Sm1−xSrxO2 (x = 0–0.09) compositions were synthesized through the sol-gel method. Dense Ce0.9Sm1−xSrxO2 ceramics were obtained through sintering the pellets at 1300°C for 8 h. XRD measurements indicate that all synthesized materials crystallized in cubic fluorite-type structure. Average crystallite size of the samples was in the range 21–27 nm. The relative density of Ce0.9Sm1−xSrxO2 samples was over 94% of the theoretical density. The lattice parameter increased linearly with increasing Sr concentration in Ce0.9Sm1−xSrxO2 following Vegards rule. Surface morphology was analyzed using SEM. It was observed that the thermal expansion increased linearly with increasing temperature. The two-probe a.c. impedance spectroscopy was used to study the grain, grain boundary and total ionic conductivity of doped and co-doped ceria in the temperature range 250°–500°C. The Ce0.9Sm0.07Sr0.03O2 composition showed higher grain ionic conductivity and minimum activation energy at 500°C.

Characterization and thermal expansion of Sr2FexMo2−xO6 double perovskites

Double perovskite oxides Sr2 FexMo2−xO6 (x = 0.8, 1.0, 1.2, 1.3 and 1.4) (SFMO) of different compositions were prepared by sol–gel growth followed by annealing under reducing atmosphere conditions of H2/Ar flow. X-ray powder diffraction studies revealed that the crystal structure of the samples changes from tetragonal to cubic at around x = 1.2. Lattice parameters and unit cell volume of these samples found to decrease with the increase in Fe content. The characteristics absorption bands observed in the range 400–1000 cm−1 of Fourier transform infrared spectra indicate the presence of FeO6 and MoO6 octahedra and confirm the formation of double perovskite phase. The value of g ∼ 2.00 obtained from electron spin resonance studies indicates that Fe is in 3+ ionic state in the SFMO samples. Dilatometric studies of these samples reveal that the average value of coefficient of thermal expansion (α¯

Unusual thermal expansion behaviour of scandium vanadate at elevated temperatures

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Preparation and characterization of Ce1–xDyx–ySryO2–δ system

) increases with the increase in temperature or Fe content in SFMO samples. The low value of coefficient of thermal expansion 1.31 × 10−6∘C−1 obtained for Sr2Fe0.8Mo1.2O6 in the present study in the temperature range of 40–100∘C makes it useful as anode material in fuel cells. The coefficient of thermal expansion (α¯

X-ray study of the thermal expansion anisotropy in neodymium vanadate

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Investigation of magnetic transitions through ultrasonic measurements in double-layered CMR manganite La1.2Sr1.8Mn2O7

) and the unit cell volume (V) of SFMO samples vary inversely with composition in agreement with Grüneisen relation.

Characterization of SDC-Al2O3 solid electrolyte

The thermal expansivity of zircon-type scandium vanadate (ScVO4) was determined by the X-ray powder diffraction method in the temperature range 300-634 K. The thermal expansion is anisotropic at room temperature as it has a larger coefficient of expansion along the a direction than along the perpendicular direction ( alpha a> alpha c). At about 400 K, alpha c becomes equal to alpha a and, above 400 K and up to 634 K, alpha c is greater than alpha a. The mean values of alpha a and alpha c, evaluated in the temperature range 300-634 K, are found to be 9.16*10-6 K-1 and 11.27*10-6 K-1, respectively.

Crystal structure, electrical conductivity and thermal expansion of Nd1–xCaxCoO3–δ (0≤x≤0·5)

Abstract The effect of dysprosium and strontium on the total ionic conductivity of ceria in the system Ce 1– x Dy x – y Sr y O 2–δ was studied. In this system, few compositions were prepared with x =0.15, y =0.015, 0.03 and 0.045 by modified sol–gel process using maltose and pectin as organic precursors. Rietveld refinement of XRD patterns confirms the cubic structure with space group. SEM images show relatively uniform grains with clean and distinct grain boundaries. Four probe AC impedance measurements were carried out to evaluate the total ionic conductivity in the temperature range of 150–500 °C and frequency range of 40 Hz–1 MHz. The composition Ce 0.85 Dy 0.12 Sr 0.03 O 2–δ shows higher electrical conductivity than single-doped ceria samples.

Anisotropic thermal expansivity of some zircon-type rare earth arsenates

Abstract The thermal expansivity of zircon-type neodymium vanadate (NdVO4) was studied using the X-ray powder diffraction method in the temperature range 301–691 K. The thermal expansion is anisotropic, having a larger expansion coefficient along the c-axis than along the a-axis (αc > αa). The mean values of αa and αc, evaluated in the temperature range 301–691 K are found to be 3.74 × 10−6 K−1 and 10.57 × 10−6 K−1, respectively. The temperature variation of αc is unusual, for it decreases with increasing temperature.