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  • Author or Editor: A. Tawfik x
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A series of samples in the system Co1−xZnxFe2O4 (x=0.3, 0.4, 0.6, 0.8 and 1) were prepared by the usual ceramic technique. The D. C. electrical resistivity and thermoelectric power were measured in the temperature range from room temperature up to about 600 K. Transition from the ferrimagnetic region to the paramagnetic region is accompanied by an increase in the activation energy by an amountΔE, which varies in the range 0.052–0.090 eV. The large values ofΔE obtained may be due to the fairly strong B-B exchange interaction in Co-Zn ferrites.

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Polycrystalline PbTe thin film is prepared on glass substrate at 200 °C. PbTe thin film isN-type and the carriers are electrons. The incident energy of photons, 3.4 eV, generates more electron carriers as the distance decreases which give rise to photoelectric current. The density of donorsN d was determined to be 1.1×1020 cm−3 which is consistent with theN-type conduction of PbTe. The activation energies ofN-type PbTe thin films are 0.139, 0.139 and 0.126 eV below 60 °C which change toP-type above 60 °C. This may be due to generation of Pb vacancies in the lattice. The piezoresistivity is measured, the increase of conductivity may be due to displacements of lattice defects under applied stress.

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A series of samples in the system Ni0.65Zn0.35CuxFe2−xO4 (x=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by the usual ceramic technique. X-ray analysis showed that they were cubic spinel (single phase). Young's modulus, the dielectric loss and the change in capacitance under mechanical stress were measured for the samples. Young's modulus decreased with increasing Cu content. This is due to the fact that Cu2+ ions entered the lattice substitutionally for Fe3+ ions at the octahedral sites, creating lattice vacancies gave rise to lattice strain.

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The I–V characteristics of an illuminated thin film of HgTe and of a dark sample were recorded. The high values of the photoelectric current of the illuminated sample as the distance decreased may be due to the impurity conductivity, that can be higher than the band conduction predominating at higher incident energy. In the dark, the impurity conductivity is always low compared to the band conductivity occurring at the higher incident energy of mercury light. The low mobility and the increase of the activation energy with increasing temperature suggest that more than one conduction mechanism is involved. The high density of acceptor centres in the thin layer of HgTe may affect the conduction current in certain temperature ranges.

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The crystalline structure, electrical conductivity and pyroelecricity of freshly prepared Hg0.7Cd0.3Te thin film have been investigated in detail.

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