Composition Zn0 Research Articles

Effect of doping with nickel ions on the structural state of a zinc oxide crystal

The fine structure of a hexagonal zinc oxide crystal doped with nickel ions of the composition Zn1 − xNixO has been studied using neutron diffraction and magnetic measurements. It is established that even at very low doping levels (x = 0.0004), the crystal undergoes local distortions in basal planes of the initial hexagonal lattice. The local distortions are assumed to be sources of the formation of ferromagnetism in compounds of this class.

Effect of Al and Sb doping on the magnetic properties of ZnMnO and ZnCoO

The bulk polycrystalline samples with nominal compositions Zn0.98−y(Mn∕Co)0.02(Al∕Sb)yO (y=0, 0.01, and 0.03) have been synthesized via solid state reaction route. The x-ray diffraction results reveal the presence of mainly wurtzite structure of pure ZnO in all the Al∕Sb codoped ZnMnO and ZnCoO samples. EDAX results confirm the presence of all elements in the samples in the stoichiometric ratio. While the Zn(Mn∕Co)O samples show paramagnetic behavior at room temperature, the Al∕Sb codoped ZnMnO samples exhibit room temperature ferromagnetism (RTFM) with saturation magnetization (Ms). The M-H curves of Al∕Sb codoped ZnCoO samples show almost linear variation with a small kink at the origin, indicating the presence of weak ferromagnetism in the Al∕Sb codoped ZnCoO samples. Possible mechanisms of the observed RTFM in Al∕Sb codoped Zn(Mn∕Co)O samples are discussed in this paper.

Low‐Temperature Sintering and Microwave Dielectric Properties of V2O5‐Added Zn2SiO4 Ceramics

V2O5 was added to ceramics of nominal composition Zn1.8SiO3.8 (ZS) in order to decrease their sintering temperature for application to low‐temperature cofired ceramic devices. For the specimens sintered at 875°C, a dense microstructure was developed when the V2O5 content exceeded 9.0 mol% due to the presence of the liquid phase containing SiO2 and V2O5. The microwave dielectric properties of the ZS ceramics were influenced by the V2O5 content. Good microwave dielectric properties of Q×f=17 500 GHz, ɛr=7.3, and τf=−28 ppm/°C were obtained from the specimen containing 12.0 mol% V2O5 sintered at 875°C for 2 h.

Low‐Temperature Sintering and Microwave Dielectric Properties of the Zn2SiO4 Ceramics

B2O3 was added to nominal composition Zn1.8SiO3.8 (ZS) ceramics to decrease their sintering temperature for application to low‐temperature cofired ceramic (LTCC) devices. B2O3 reacted with SiO2 to form a liquid phase containing SiO2 and B2O3. The composition and melting temperature of the liquid phase depended on the sintering temperature and the B2O3 content. The specimen containing 20.0 mol% of B2O3 sintered at 900°C exhibited high microwave dielectric properties of Q×f=53 000 GHz, ɛr=5.7, and τf=−16 ppm/°C, confirming the promising potential of the B2O3‐added ZS ceramics as candidate materials for the LTCC devices.

Effect of Zn/Si Ratio on the Microstructural and Microwave Dielectric Properties of Zn2SiO4 Ceramics

Zn2SiO4 ceramics synthesized by the conventional solid‐state method exhibited a low Q×f value, possibly due to the formation of a ZnO second phase. However, with a small ZnO reduction from the Zn2SiO4 ceramics, the ZnO second phase disappeared and grain growth occurred due to the formation of a Si‐rich liquid phase. Specimens with a large grain size exhibited an improved Q×f value. In particular, the ceramics with nominal composition Zn1.8SiO3.8 sintered at 1300°C exhibited improved microwave dielectric properties of ɛr=6.6, Q×f=147 000 GHz, and τf=−22 ppm/°C.

Magnetism in Mn and Co doped ZnO bulk samples

Bulk samples with nominal composition Zn0.95Co0.05O and Zn0.92Co0.05Mn0.03O were fabricated by a solid-state reaction method at 600°C. X-ray diffraction experiment showed that the peaks of secondary phase Co3O4 with a cubic structure were visible in both samples, besides the main peaks of wurtzite structure as ZnO. Magnetization measurement indicated that doping Co alone can induce ferromagnetism in ZnO itself, while the introduction of Mn significantly enhances ferromagnetism. However, both samples showed different magnetic behavior at temperatures below 50 K. It was also noted that ferromagnetic coupling interaction was weakened due to the presence of antiferromagnetic Co3O4.

Magnetization study of Fe-doped ZnO co-doped with Cu: Synthesized by wet chemical method

Fe- and Cu-doped ZnO of nominal compositions Zn0.95Fe0.05O and Zn0.94Fe0.05Cu0.01O were synthesized by a wet chemical route. X-ray diffraction analysis of the samples annealed at 575 K showed that they are single phase without any secondary phases. DC magnetization measurements of Cu co-doped samples (Zn0.94Fe0.05Cu0.01O) as a function of field at room temperature showed ferromagnetic signature while the samples without Cu co-doping (Zn0.95Fe0.05O) are paramagnetic in nature. On increasing the temperature of annealing from 575 K to 1,075 K an impurity phase emerges in both the samples, which has been identified as a variant of ZnFe2O4. Both the samples heated at and above 1,075 K are found to be paramagnetic at room temperature. These observations, the absence of room temperature ferromagnetism in Zn0.95Fe0.05O and the disappearance of ferromagnetism in Zn0.94Fe0.05Cu0.01O on raising the temperature of annealing clearly rules out the likelihood of room temperature ferromagnetism arising from the impurity phases like γ-Fe2O3 and/or ZnFe2O4 that might have been formed during the synthesis. Our results strongly suggest that room temperature ferromagnetism in Zn0.94Fe0.05Cu0.01O can be attributed to the formation of a secondary phase of Cu-doped ZnFe2O4.

The structural and magnetization studies of Co-doped ZnO co-doped with Cu: Synthesized by co-precipitation method

Co- and Cu-doped ZnO of nominal composition Zn0.95Co0.05O and Zn0.94Co0.05Cu0.01O were synthesized by a co-precipitation method in organic media. Rietveld refinement of X-ray diffraction data of the samples annealed at 725 K showed that they are single phase without any secondary phases. DC magnetization measurements of samples with Cu co-doping (Zn0.94Co0.05Cu0.01O) as a function of field at room temperature showed a ferromagnetic signature while the samples without Cu co-doping (Zn0.95Co0.05O) are paramagnetic in nature. Both the samples heated at 1075 K are found to be paramagnetic at room temperature. Resistivity measurements above room temperature clearly showed a semiconducting behavior with a decreased resistivity value for Zn0.94Co0.05Cu0.01O compared to Zn0.95Co0.05O and ZnO, confirming additional carriers in Zn0.94Co0.05Cu0.01O due to Cu co-doping. Our results are in agreement with a recent computational study that doping additional carriers are necessary for realizing room temperature ferromagnetism in Co-doped ZnO.

Preparation and Characterization of Mn-Zn Ferrite for High Frequency Power Applications

Manganese-zinc-ferrous ferrites of estimated structural compositions Zn0.216Mn0.706Fe0.078Fe204 and Zn0.197Mn0.683 Fe0.120Fe2O4 were ferritized at 1120° and 1090°C using air atmosphere during heating and soaking periods and argon atmosphere during cooling. This ferritized powder after grinding to ≅ 5 μm was pressed into toroid and cylindrical pellets. Sintering of shapes was done in air at temperatures of 1220° and 1250°C and for a soaking periods of 6 hours, while the heating and cooling were done in air and argon respectively. Lattice parameters were determined by the X-ray method; the values ranged between 4.487 and 4.497 A for materials ferritized under different conditions. Real and imaginary parts of complex permeability, μ' and μ″ and quality factor Q were determined in the frequency range 100–2000 kHz using impedance bridge on toroidal samples. The values varied in the range 370–648 (for μ'), 30–54 (for μ″) and 7–16 (for Q) at 100 kHz. The permeability at 100 kHz range was 373–651 against the expected value of 1500 for such applications. The d.c. resistivity was determined using complex impedance analysis and values ranged between 276 and 5762 ohm-cm as compared to values of ≅ 700 ohm-cm reported in the literature. The values of saturation magnetization (σs) ranged between 96 and 108 emu/gm and Curie temperatures for compositions 1 and 2 were found to be 245° and 281°C respectively.

The catalytic activity and defect structure of zinc chromate

Computer simulation techniques are used to develop defect models for the non-stoichiometric spinel with composition Zn1+xCr2−xO4 system. The results are used to provide an interpretation of the variation with composition of the catalytic activity of the monophasic material. We suggest that the increase in the catalytic activity with the Zn/Cr ratio is associated with an increased concentration of oxygen vacancies.

Structural realization of oxygen nonstoichiometry in nickel-zinc ferrite

We have carried out a study of nickel-zinc ferrite of composition Zn0.218Ni0.752Fe2.03O4+y, with varying oxygen nonstoichiometry y. The method used was to measure the intensity of three groups of X-ray reflections on single crystal specimens with subsequent division of the amounts of mean-square dynamic and static displacement of the ions on the sublattices. From the amount of static displacement compared to two calculated models, one of which was based on an ionic approximation while the other was based on approximation of an elastically isotropic continuum, the character and distribution of point defects in the spine structure was determined. It was established that in nickel-zinc ferrite with y 0 vacancies appear in the octahedral cation sublattice.