M. Suleman Malik

Different effects of nickel and cobalt additions on the electronic conduction of copper tellurite glasses

Measurements of the d.c. electrical conductivity were made on 65TeO2-(35-x)CuO-x(MO) (mol %) glasses wherex=0, 0.5, 1, 2, 3, 4 and M represents nickel or cobalt. A variation in the conductivity and activation energy of the glasses is observed as CuO is replaced by NiO and by CoO. It is found that withx=0.5 to 3 mol % of NiO, the conductivity increases and the activation energy decreases due to the decrease in effective electron hopping distance between the transition metal (TM) ions. The conductivity is found to decrease with the substitution of 4 mol % of NiO and 0.5 to 4 mol % of CoO and this is attributed to the decrease in relative concentration of hopping centres because of the decrease in the hopping transitions between ions of the same element (e.g. Cu+ and Cu2+ ions) and between the ions of different TM elements (e.g. Cu+ and Ni2+, Cu+ and Co2+). This decrease in conductivity has also been described due to the formation of Ni-O-Ni, Cu-O-Ni and Co-O-Co, Cu-O-Co bridge bonds in NiO-and CoO-doped glasses respectively. The CoO-doped glasses have been found to be of a more insulating nature.

Control of electrical conductivity with the admixture of chlorine in copper tellurite glasses

Copper tellurite glasses containing. CuCI2 with composition 65TeO2-(35−x)CuO-xCuCl2 (mol%) with x=0, 1, 2, 3, 4, 5 were prepared by quenching the melt. An increase in density with the addition of CuCl2 and with a corresponding decrease in molar volume, has been observed. The d.c. conductivity of copper tellurite glasses is found to be very sensitive to the reduced valency rationC=[Cu+]/[Cutotal] and depends on the relative concentrations of Cu+ (reduced valency state) and Cu2+ (higher valency state) ions. It is found that by adding cupric chloride to the melt when the glass is formed, the chlorine in the salt which acts as an oxidizing agent alters the ratio of the concentrations of Cu+ and Cu2+ ions in the glass and hence the conductivity. It is found that more than 2 mol% of cupric chloride reduces the conductivity very sharply due to the formation of chlorine clusters in the form of local TeCl2+ whereas less than 2 mol% of CuCl2 leads to an increase in conductivity due to the Cu+→Cu2+ transition which is negligibly affected by the chlorine due to the formation of TeCl2 which is amorphous in nature. The increase and decrease of electrical conductivity of glasses containing less or more than 2 mol% CuCl2 is also interpreted in terms of the electronic transitions between the orbitals of tellurium 3d electrons, their binding energies and peak widths on the basis of XPS (X-ray Photoelectron Spectroscopy) study, and it was found that the increase in bandwidth supports the idea of clustering of chlorine above 2 mol% CuCl2 and causing a decrease in the conductivity. Overall the conductivity is found to be somewhat uncontrollable in these glasses because it is not simply dependent on the concentration of Cu2+ ions.

The effect of chloride ions on the optical properties of TeO2-CuO-CuCl2 glasses

The glasses with composition 65TeO2-(35−x)CuO-xCuCl2 (x=0, 1, 2, 3, 4, 5 mol%) were prepared by a melt quenching technique and thin films of different thicknesses were made by blowing. The optical energy gap was studied and its variation with composition is discussed in terms of the effective role played by chloride ions which reduce the non-bridging oxygen ions and modify the structure of the network. The infrared spectra of all these glass samples at room temperature, recorded between 200 and 2400 cm−1, are discussed in terms of anti-symmetric vibrations of the heteronuclear atoms.

Chemical approach to the conduction mechanism in copper tellurite glasses containing lutetium oxide

Measurements of d.c. electrical conductivity were made on 65TeO2-(35 -x)CuO-xLu2O3 (mol%) glasses with x=0, 1, 2, 3, 4. The experimental results show that whenx is changed from 1 to 2 mol%, the conductivity increases due to the additional electrons obtained by the oxidation of TeO2 as well as due to the Cu+ → Cu2+ transition under the effect of interelectronic repulsion in the 4f shell of the lutetium present in the glass. Whenx is increased to greater than 2 mol%, the conductivity decreases because hopping is inhibited due to the formation of oxygen bridge associates or because of the strong ligand repulsive field of lutetium indicating its non-reactivity in the glassy network. The conductivity has a distinct maximum atx=2.

A study of electron spin resonance phenomena in TeO2-CuO-CuCl2 glasses

We present the results of ESR powder spectra taken on unannealed glass samples having the composition 65TeO 2 -(35-x)CuO-xCuCl 2 with x varying from 1 to 5 in mol%. ESR studies were carried out tube at room temperature and at X-band frequency

Comparative study of the effect of the incorporation of cobalt and nickel oxides on the density and optical properties of copper tellurite glasses

Two series of ternary semiconducting glasses with composition 65 TeO2-(35−x)CuO-xMO in mole percent (x=0, 0.5, 1, 2, 3, 4 and M stands for Co or Ni) were prepared by a melt quenching technique. The densities of annealed and unannealed disc-shaped samples and the optical energy gap of thin blown films of both series of glasses were measured, and the comparative effect of each transition metal (TM) oxide was estimated. It was found that forx=0.5 to 1 mol% andx=2 to 4mol%, the optical energy gap (Eopt) was somewhat greater in TeO2-CuO-NiO than in TeO2-CuO-CoO glasses. This increase inEopt is interpreted in terms of the decreasing number of non-bridging oxygen ions with the increase of each TM oxide. NiO was found to be more effective in increasing the density than CoO in annealed copper tellurite glasses.

Effect of cobalt oxide on the a.c. conduction mechanism of copper tellurite glasses

Electrical measurements on binary and ternary glasses of compositions 65TeO2-35CuO and 65TeO2-34CuO-1CoO (mol%) are reported at temperatures between 293–458 K in the frequency range up to 10−6 Hz. The measured conductivity shows a frequency dependence obeying the equation σ(ω) =Aωs withs <1 but taking different values at different temperatures. The capacitance of the glasses shows an increase in value with increase in temperature at low frequencies. The tangent of the loss angle (tan δ) and dielectric loss factor ɛr″were found to increase with the increase in temperature and decrease in frequency but the usual Debye loss peaks were absent even at high temperatures. The relative dielectric constant ɛr was unexpectedly high, approximately 103, and was found to decrease very slightly with increasing frequency. Overall the effect of a small amount of CoO (ã 1 mol%) is found to have a dominant effect on the dielectric properties of copper tellurite glasses.

A relaxation trend in the electron spin resonance phenomena in copper tellurite glasses containing NiO, CoO and Lu2O3

Copper tellurite glasses containing NiO, CoO and Lu2O3 were prepared by the melt-quenching technique. The composition used was 65TeO2-(35-x)CuO-xTMO (mol%), where TMO indicates NiO, CoO, Lu2O3, and for NiO- and CoO-doped glasses,x has the values 0, 0.5, 1 to 4, and for Lu2O3 doped glasses x=0 to 4. Electron spin resonance (ESR) spectra of all glasses were recorded at room temperature. The results on glasses doped with NiO, CoO and Lu2O3 are discussed in terms of oxidation-reduction, cross-relaxation and interelectronic repulsion processes, respectively. Cobalt oxide is found to be more effective in relaxing the ESR spectrum than nickel and lutetium oxides when substituted in copper tellurite glasses.

Some effects of substituted cobalt and nickel oxides on the infrared spectra of copper tellurite glasses

Infrared absorption bands due to resonant vibrations of ions in glasses may reveal information about the structure of the glasses. The position and shape of the peak of the absorption band can be found by examining the radiation transmitted through the material as a function of frequency. Glasses have a complicated and random structure so infrared spectroscopy is of limited use but may be complementary to other methods of investigating glass structure, such as X-ray diffraction. The infrared spectra of tellurite glasses have been measured by many previous workers [1, 2 and 7-9]. In this letter we present and compare our experimental results on infrared spectroscopy of unannealed copper tellurite glasses containing CoO and NiO, at room temperature. The glass compositions covered the mol % range 65TEO2-(35 -- x)CuO-xMO where x = 0, 0.5, 1, 2, 3, 4 and M stands for Co or Ni. The glasses were prepared by melt quenching then cast into disc shapes. The discs were ground into fine powder in a clean mortar, then a small amount of glass powder was mixed and again ground with KBr in the ratio 1:20 depending upon the composition of the glass. The glass pellets, transparent to infrared radiation, were formed by pressing the mixture at 15 tons for 3 to 5 min under vacuum. The infrared spectra of the glasses were recorded at room temperature using an infrared spectrophotometer (Unicam SP 2000) operating in the double-beam mode in the range 200 to 2400 cm- 1. The results for the infrared transmission are recorded in Figs 1 and 2. Tables I and II summarize the characteristic infrared absorption band positions for TeO2-CuO-CoO and TeO2-CuO-NiO glasses, binary TeOz-CuO and the respective crystalline spectra of TeO2, CoO and NiO. The bands at 345,660 to 670 and 775cm -j of TeO2 are very close to the previously reported values [4, 5 and 7-9]. The bands