M. Ashraf Chaudhry

Electrical properties of Cd-substituted copper ferrites

Abstract Room temperature resistivity measurements were carried out for Cu1−xCdxFe2O4 ferrite samples for 0.0≤x≤1.0 prepared by ceramic method. At lower Cd concentration, the increase in DC resistivity is attributed to the hindering of the hopping mechanism between Fe2+ and Fe3+. This may be due to the stable bond formation of Cu3++Fe2+ at octahedral sites. The decrease in resistivity at higher Cd content is attributed to the lower concentration of the stable bond of Cu3++Fe2+. Two distinct regions have been noted for temperature dependent resistivity, namely paramagnetic and ferrimagnetic regions. Activation energy in paramagnetic region is greater than in the ferrimagnetic region which shows hopping conduction at higher temperatures. Seebeck coefficient (α) was measured for all the samples which shows that all the CuCd ferrite samples are degenerate-type semiconductors.

Temperature dependent electrical resistivity of Co–Zn–Fe–O system

Abstract Cobalt zinc ferrites with composition Co 0.2 Zn 0.73 Fe 2 O 4 , Co 0.30 Zn 0.60 Fe 2 O 4 , Co 0.37 Zn 0.51 Fe 2 O 4 and Co 0.5 Zn 0.34 Fe 2 O 4 , were prepared by solid state reaction technique in a single phase form. The electrical resistivity, X-ray density, bulk density and porosity of each sample have been measured. A change of slope has been observed in the Arrhenius plots indicating the presence of two regions of activation energy.

Optical absorption studies of sodium cadmium phosphate glasses

Abstract A photoabsorption method was used to study the fundamental absorption edges in sodium cadmium phosphate glasses. The measurements were performed in the UV-visible region of the spectrum. The optical band gap energies lie in the range 2.82 to 3.48 eV and are found to decrease with increasing amount of sodium oxide. The extent of band tailing was worked out from the Urbach plots which show an exponential dependence of absorption coefficients on energies of the photons used.

Optical characteristics of some binary and ternary phosphate glasses

The optical absorption spectra of some binary and ternary phosphate glasses are studied in the UV-visible region by using a spectrophotometer. The observed absorbance versus wavelength curves do not show any sharp edges in these glasses. The optical band gap energies are found to depend significantly on glass composition. The optical band gap energy is found to increase with increasing ZnO content in binary and ternary glass systems.

Concentration-dependent electrical conductivity of phosphate glasses containing zinc oxide

Abstract A range of glass samples of x % ZnO-(100- x )% P 2 O 5 with 20 ⩽ x ⩽ 40 and x % ZnO-(50- x )% CdO-50% P 2 O 5 with 30 ⩽ x ⩽ 45 were prepared by the melt quench technique. The measured values of electrical conductivity of these samples as a function of ZnO concentration for two fixed bias voltages are reported here. The electrical conductivity shows a linear decrease with ZnO concentration. This decrease is explained in terms of the partial opening of the 3-d network structure which increases the number of non-bridging oxygen atoms and the energy gap with the addition of ZnO in these samples.

EFFECT OF ZINC OXIDE ON THE BAND GAP OF CADMIUM–ZINC–PHOSPHATE GLASSES

The fundamental absorption edges of cadmium–zinc–phosphate glass samples were measured in the UV visible wavelength region of the spectrum by photoabsorption method. It is found that the optical band gaps of these glasses are composition-dependent and occur at a photon energy in the range 2.85–3.33 eV. The value of the optical band gaps enhances with ZnO content. The absorption coefficient depicts an exponential dependence on photon energy for the glass samples reported in this communication.

A study of optical absorption in 9,10-anthraquinone crystals

Single crystals of 9,10-anthraquinone having dimensions 5 mm × 5 mm × 1.5 mm were grown from the melt using the Bridgeman technique. The starting material was purified by sublimation and zone-refining techniques in specially, designed crystal-growth tubes. The crystals were transparent and yellow in colour, and could be cleaved easily along ab-, bc-planes and poorly along the ac-planes of the crystal. Thin layer chromatography of the final crystals was performed, and no impurity was detected in these crystals by this technique. The cleaved crystals were found to have a surface photocurrent of ∼ 10−11 A, which increased non-linearly with the increasing voltage at room temperature. This is attributed to the formation of triplets in the bulk of the crystal which migrate and dissociate at the surface of the crystal. The optical absorption spectrum in benzene and ether solutions were found to exhibit similar behaviour in the visible range, i.e. 320–450 nm. From the optical absorbance data, the optical band gap was found to be ∼ 3.4 eV.

LOW FIELD AC MAGNETIC SUSCEPTIBILITY MEASUREMENTS OF MANGANESE ALUMINOSILICATE GLASSES

The magnetic susceptibility of MnO.Al2O3.SiO2 spin glasses has been measured over a temperature range of 1.5–150 K using a low-field ac mutual inductance technique. The measuring frequency was 250 Hz with a field of 417 mOe (peak). The Mn concentration varied from 6 to 19 atomic percent (at %). At temperatures above 70 K, the susceptibilities follow a Curie-Wiess behavior with a negative Curie temperature and a Bohr magneton number corresponding nearly to the free ion value of Mn. However, below 70 K all glass samples show strong deviation from the Curie-Wiess behavior (a decrease in 1/χ), culminating in spin glass susceptibility maxima at liquid helium temperature for Mn concentration above 9 at %. These results suggest the formation of antiferromagnetic cluster which grows in size with decreasing temperature and becomes infinitely large as the spin glass freezing temperature is approached.

PHOTOCONDUCTIVE RESPONSE IN 9,10-ANTHRAQUINONE SINGLE CRYSTALS

The photoconductive response of ‘home-grown’ 9,10-anthraquinone single crystals has been studied using two types of cells — sandwich and surface types. The existence of true bulk conductivity as well as surface conductivity has been established in such crystals. The photocarrier mobility on the surface is much higher than in the bulk of the crystal specimens. The photocurrent dependence on wavelength in the range 380–550 nm and applied bias field up to 9 kV/cm has been examined in these crystals. The field dependence of photocurrent at constant wavelength shows a nonohmic behavior. The effect of making front-illuminated electrode positive or negative with respect to the back electrode is also examined and the photocurrent is found to be electronic in nature.

AN INVESTIGATION INTO THE OBSERVATION OF WATER ADSORPTION INTO BARBITONE POWDER

The adsorption of water in a sample of barbitone has been studied by the dielectric technique over a frequency span between 10 Hz and 100 kHz. It has been found that the adsorbed water only contributes a small component to the dielectric response although the indications are that a large amount of water has been adsorbed. This means that the adsorbed water is in a bound form.