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With the aim of understanding the structural, electronic, and magnetic properties of nanocrystalline Co doped SnO2 diluted magnetic semiconductors, prepared by the tartaric acid gel route, a systematic investigation as a function of annealing temperature has been carried out. The precursor was characterized by TG-DTA to determine thermal decomposition and crystallization temperature. The XRD, TEM, FT-IR, and laser Raman studies revealed that all the samples have a tetragonal rutile structure with single phase. The average particle sizes obtained from TEM are in the range of 18−50 nm. The changes in Raman spectra were analyzed with varying crystallite size. The optical absorbance measurements revealed that the nanometric size of the materials influences the energy band gap values. From the XPS studies, the oxidation state of cobalt is found to be +2, and particle size induced implications in the core level XPS peaks of Co 2p and O 1s have been analyzed. The presence of room temperature ferromagnetism has been confirmed by the magnetization studies. Finally, it has been concluded that the ferromagnetic properties depend not only on the surface diffusion of Co ions and the distribution of defects such as oxygen vacancies or vacancy clusters but also on nanometric size of the materials and their surface conditions.

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The optical and electrical properties of the lead bearing glasses in the PbO-TiO2, PbO-TeO2, and PbO-CdO systems have been investigated. The density, refractive index, optical band-gap, and Urbach energies of these glasses are reported. It is shown that the additive nature of oxide ion polarizabilities reported for the simple oxides can be extended to glass systems as well. A modified linear relationship between (Eopt)1/2 and 1−(Rm/Vm) holds good for glasses. The oxide ion polarizabilities deduced from two different experimental quantities viz., refractive index and optical band-gap energy agree well. The dc electrical conductivities have been measured in the temperature range 350–700 K. The activation energies are close to 1 eV. The low melting 70PbO-30TeO2 glass shows higher isothermal conductivity compared to other glasses of similar composition. In PbO-TiO2 glass the PbO content contributes significantly to conductivity and composition dependence of pre-exponential factor (σ0) supports tunneling mechanism.

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