Zn In Co Research Articles

Studies of structural and dielectric properties in Co0.9Zn0.1Fe2O4 ceramics

Spinel ferrites have been widely studied due to their remarkable properties such as high saturation magnetisation, large magnetic permeability, and high electrical resistivity. Among the oxides-based magneto strictive spinel ferrite, CoFe2O4 (CFO) possess the highest value of absolute magnetostriction coefficient (–110 ppm). But CFO has the disadvantage of large magnetic anisotropy and high coercivity. Therefore, doping of zinc (Zn) at Co-site of CFO is reported to reduce the magnetic coercivity and increases the resistivity (108Ω) keeping the magnetostriction coefficient with a sizable value. Also, substitution of Zn for Co in CFO reduces magnetic anisotropy. So, in view of this we have prepared Zn modified CFO compound: Co0.9Zn0.1Fe2O4 using sol-gel combustion technique. The room temperature (RT) XRD patterns indicate the formation of single-phase material without appearance of any impurity phases within the detection limit of X-ray diffractometer. The Rietveld refinement on the RT XRD pattern of CZFO sample was carried out using cubic crystal structure with space group Fd-3m. A good agreement between the experimental and the fitted data has been observed. The average crystallite size for the composition was calculated from the XRD patterns using Williamson–Hall method. Scanning electron micrographs displays homogeneous distribution of grains throughout the sample microstructure with the presence of minute amount of pores. The dielectric and electrical properties were studied as function of frequencies at different temperatures. Complex impedance spectroscopic technique study on this sample suggests existence of non-Debye type dielectric relaxation behaviour.

Large magnetocaloric effects over a wide temperature range in MnCo1−xZnxGe

The magnetic and structural transitions can be controlled to coincide by partial substitution of Zn for Co in MnCo1−xZnxGe, leading to a large magnetocaloric effects over a wide temperature range. The magnetostructural transition from paramagnetic to ferromagnetic state results in magnetic entropy changes (−ΔSM) of 26 J/kg K at 327 K for ΔH = 5 T in the case of x = 0.045. Interestingly, a structurally driven first-order phase transition between two high magnetization states as observed for x = 0.05 and 0.06 also lead to large values of −ΔSM = 31.4 and 20.6 J/kg K for ΔH = 5 T at 281 and 209 K, respectively. The observed large magnetocaloric effects with tunable phase transition temperatures make these materials promising for near room-temperature magnetic cooling applications.

Zn- and Cu-substituted Co2Y hexagonal ferrites: Sintering behavior and permeability

Y-type polycrystalline hexagonal ferrites Ba2Co2−x−yZnxCuyFe12O22 with 0≤x≤2 and 0≤y≤0.8 were prepared by the mixed-oxide route. Single phase Y-type ferrite powders were obtained after calcinations at 1000°C. Samples sintered at 1200°C show a permeability that increases with the substitution of Zn for Co and display maximum permeability of μ′=35 at 1MHz for x=1.6 and y=0.4. A resonance frequency fr=500MHz is observed for Zn-rich ferrites with y=0 and 0.4. The saturation magnetization increases with substitution of Zn for Co. Addition of Bi2O3 shifts the temperature of maximum shrinkage down to T≤950°C. Moreover, an increase of the Cu-concentration further lowers the sintering temperature to T≤900°C, enabling co-firing of the ferrites with Ag metallization for multilayer technologies. However, low-temperature firing reduces the permeability to μ′=10 and the resonance frequency is shifted to 1GHz. Thus substituted hexagonal Y-type ferrites can be used as soft magnetic materials for multilayer inductors for high frequency applications.

Characterization of (Y 1-xCa x)BaCo 4-yZn yO 7 as cathodes for intermediate temperature solid oxide fuel cells

The effects of Ca and Zn substitution, respectively, for Y and Co in (Y 1-xCa x)BaCo 4-yZn yO 7 (0.25 ≤ x ≤ 0.75 and 1.0 ≤ y ≤ 1.75) on the structure, high-temperature phase stability, thermal expansion coefficient (TEC), and electrochemical performance for intermediate temperature solid oxide fuel cells (IT-SOFC) have been investigated. The (Y 1-xCa x)BaCo 4-yZn yO 7 oxides crystallize in a trigonal P31 c symmetry similar to YBaCo 4O 7. The substitution of Zn for Co improves the long-term phase stability at high temperatures, but at the expense of the electrochemical performance. In contrast, the substitution of Ca for Y is improves electrochemical performances, but deteriorates the long-term phase stability at high temperatures at high Ca contents ( x = 0.75 and 1.0). Among the various chemical compositions investigated in the (Y 1-xCa x)BaCo 4-yZn yO 7 system, the (Y 0.5Ca 0.5)BaCo 2.5Zn 1.5O 7 composition offers a combination of good electrochemical performance and low TEC, while maintaining the phase stability at 600–800 °C for 120 h. The (Y 0.5Ca 0.5)BaCo 2.5Zn 1.5O 7 + GDC (50 : 50 wt. %) composite cathodes exhibit a maximum power density of ∼ 450 mW cm −2 at 700 °C in anode-supported single SOFC.

Electrical conductivity and microcrystalline parameter in Co–Zn ferrites

A series of samples of the system Co1−xZnxFe2O4 (for x = 0·0, 0·2, 0·4, 0·6 and 1·0) were prepared by usual ceramic technique. These prepared samples were examined using X-ray powder pattern, which confirms the presence of a spinel structure. The authors have also carried out line profile analysis of individual Bragg reflections observed in these ferrites, which shows variation in the cell parameter. Further electrical conductivity measurements of these ferrites were carried out as a function of temperature. The observed values of the electrical conductivity have been explained on the basis of Verwey’s hopping mechanism. The activation energy was found to decrease with increasing Zn content. In addition, its variations for varying concentrations of Zn in Co are interpreted in terms of microstructural parameters.

Preparation and magnetic properties of (Co,Zn)-doped γ-Fe/sub 2/O/sub 3/ particles

Oxidation temperatures and times of Fe/sub 3/O/sub 4/ to produce (Co,Zn)-doped /spl gamma/-Fe/sub 2/O/sub 3/ particles were examined in this study to relate these two parameters to void, particle size, saturation magnetization, coercivity, and squareness. The effect of Zn/Co ratio on magnetization and coercivity of the particles was also studied. The partial substitution of Zn for Co in Co-/spl gamma/-Fe/sub 2/O/sub 3/ increased the /spl sigma/ value and environmental stability, but decreased the /sub i/H/sub c/ and the squareness of /spl gamma/-Fe/sub 2/O/sub 3/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>