Synthesis, Crystal Structural and Electrical Conductivity Properties of Fe-Doped Zinc Oxide Powders at High Temperatures

The synthesis, crystal structure and electrical conductivity properties of Fe-doped ZnO powders (in the range of 0.25-15 mol%) were reported in this paper. I-phase samples, which were indexed as single phase with a hexagonal (wurtzite) structure in the Fe-doped ZnO binary system, were determined by X-ray diffraction (XRD). The solubility limit of Fe in the ZnO lattice is 3 mol% at 950 degrees C. The above mixed phase was observed. And the impurity phase was determined as the cubic-ZnFe2O4 phase when compared with standard XRD data using the PDF program. This study focused on single I-phase ZnO samples which were synthesized at 950 degrees C because the limit of the solubility range is the widest at this temperature. The lattice parameters a and c of the I-phase decreased with Fe-doping concentration. The morphology of the I-phase samples was analyzed with a scanning electron microscope. The grain size of the I-phase samples increased with heat treatment and doping concentration. The electrical conductivity of the pure ZnO and single I-phase samples was investigated using the four-probe dc method at 100-950 degrees C in air atmosphere. The electrical conductivity values of pure ZnO, 0.25 and 3 mol% Fe-doped ZnO samples at 100 degrees C were 2x10(-6), 1.7x10(-3) and 6.3x10(-4) S.cm(-1), and at 950 degrees C they were 3.4, 8.5 and 4 S.cm(-1), respectively

Spectrophotometric determination of samarium(III) with chrome azurol S in the presence of cetylpyridinium chloride

A sensitive, simple method for the determination of trace amounts of samarium by spectrophotometry is described based on the formation of the samarium-chrome azurol S (CAS) complex in micellar medium. The molar absorptivities of the complexes at pH 7.5 at 505 nm were 3.6 x 10(4) and 1.4 x 10(5) 1 mol(-1) cm(-1) for water media and cetylpyridinium chloride (CPC), respectively. Beer's law is obeyed from 0.05-2 mg 1(-1) of samarium at 505 nm as Sm-CAS-CPC complex. Optimal conditions such as reagent amounts, and pH for the samarium determination were reported. The effects of foreign ions were also investigated. The proposed method was successfully applied to the determination of samarium contents in synthetic samples. (C) 2000 Elsevier Science B.V. All rights reserved

Trace metal accumulation caused by traffic in an agricultural soil near a motorway in Kayseri, Turkey

The metal pollution accumulation caused by the traffic in Kalkancik village near the Kayseri-Ankara motorway was investigated. For this purpose, soil samples were collected from various stations in Kalkancik village. Samples were digested with aqua regia and metal concentrations were determined by flame atomic absorption spectrometry (FAAS). Seasonal fluctuations of heavy metal contents in the soil samples were investigated. Iron and manganese levels in the soil samples were independent of the distance from the Kayseri-Ankara motorway while the lead, nickel, zinc, copper and cadmium contents were dependent on it. The cobalt levels in all samples were less than 3 mu g/g. Significant correlation data were found to exist between the metal concentrations of the soil samples from Kalkancik village

Effect of Doping and High-Temperature Annealing on the Structural and Electrical Properties of Zn1-XNiXO(0 <= X <= 0.15) Powders

This paper reported the synthesis, crystal structure and electrical conductivity properties of Ni-doped ZnO powders (i.e. Zn1-XNiXO binary system, X=0, 0.0025, 0.005, 0.0075 and in the range 0.01 <= X <= 0.15). I-phase samples, which were indexed as single phase with a hexagonal (wurtzite) structure in the Zn1-XNiXO binary system, were determined by X-ray diffraction (XRD). The widest range of the I-phase was determined as 0 <= X <= 0.03 at 1200 degrees C; above this range the mixed phase was observed. The impurity phase was determined as NiO when compared with standard XRD data, using the PDF program. We focused on single I-phase ZnO samples which were synthesized at 1200 degrees C because of the widest range of solubility limit at this temperature. It was observed that the lattice parameters a and c of the I-phase decreased with Ni doping concentration. The morphology of the I-phase samples was analyzed with a scanning electron microscope. The electrical conductivity of the pure ZnO and single I-phase samples were studied by using the four-probe dc method at temperatures between 100 and 950 degrees C in air atmosphere. The electrical conductivity values of pure ZnO and 3 mol% Ni-doped ZnO samples at 100 degrees C were 2x10(-6) and 4.8x10(-6) Omega(-1).cm(-1), and at 950 degrees C they were 1.8 and 3.6 Omega(-1).cm(-1), respectively. In other words, electrical conductivity increased with Ni doping concentration

Determination of electron temperature and energy relaxation of 2DEG in AlGaAs/GaAs HEMT channel

We have investigated the electron energy relaxation of two-dimensional electron gas (2DEG) in AlGaAs/GaAs high electron mobility transistor (HEMT) channel at lattice temperature of T-L = 1.7 K under zero magnetic field. The electron temperature of 2DEG has been determined by using the absolute power dissipation in HEMT channel in the temperature range of 1.7-60 K. The experimental results are compared with theoretical results which include both acoustic phonon via deformation coupling and polar optic phonon scattering mechanisms. A good agreement is obtained between experimental and theoretical results for all electron temperatures. A transition between acoustic phonon and polar optic phonon regime has been seen at the electron temperature T-e = 40 K. The results are consistent with other studies where different techniques but similar sample structures have been used. The results also provide useful information about the relative magnitude of acoustic phonon via deformation potential coupling and polar optic phonon contributions to power loss of 2DEG. (C) 2003 Elsevier B.V. All rights reserved