A. Basumallick

Effect of alkaline earth metal doping on thermal, optical, magnetic and dielectric properties of BiFeO3 nanoparticles

Substrate-free pure-phase BiFeO3 (BFO) nanoparticles doped with alkaline earth metals (Ba, Sr and Ca) have been synthesized by a sol–gel route and their thermal, optical, dielectric and magnetic properties are discussed. The characteristic structural phase transitions of BFO nanoparticles are found to occur at much lower temperatures. A reduction of the Neel temperature has been observed in the doped samples in comparison with the pristine one, whereas the band gap shows a reverse trend. Iron was found to be only in the Fe3+ valence state in all the doped samples. Magnetoelectric coupling is seen in our samples. Weak ferromagnetism is observed at room temperature in all of the doped and undoped BFO nanoparticles with the largest value of coercive field ~1.78 kOe and saturation magnetization ~2.38 emu g−1 for Ba and Ca doped BFO nanoparticles, respectively.

Effect of microstructure and residual stresses on nano-tribological and tensile properties of Al2O3- and SiC-reinforced 6061-Al metal matrix composites

In this investigation, wear and tensile properties of 6061-Al/Al2O3 and 6061-Al/SiC metal matrix composites were studied with respect to their microstructural features and residual stresses. Variation in the residual stress values in the composites differed from each other due to their particulate size and thermal expansion coefficient. Tribological behavior of the composites studied with the aid of nanoscratch tester showed higher amount of debris in 6061-Al/SiC composite than that in 6061-Al/Al2O3 composite due to the presence of higher residual stresses and shorter interparticle distance in the former. Variation of wear volume, coefficient of friction and wear rate at different load were analyzed and correlated with the variation of microstructure along the scratch tracks. It is seen that wear resistance of 6061-Al/Al2O3 is better than that of 6061-Al/SiC composite, where as tensile property revealed that ultimate tensile stress and yield stress is higher in case of 6061-Al/SiC composite compared to 6061-Al/Al2O3. Fractographic studies shows bimodal fracture failure where cleavage type brittle fracture failure is dominant in 6061-Al/Al2O3 whilst ductile failure is dominant in 6061-Al/SiC composite.

Microstructure-Property Correlations of Multifunctional Si-Fe Nanocomposite

Multifunctional Si-Fe nanocomposites with varying atom percent of Fe were prepared by the high energy ball milling technique. Presence of pristine Fe and Si as separate entities in the nanocomposites was confirmed through the analyses of their Mössbauer spectrum and, x-ray diffraction patterns. The average grain size of Si has been found to be 40nm and the superparamagnetic Fe particles in the nanocomposite systems has been found to increase with increase in milling time. Transmission electron microscopic images revealed discontinuous distribution of Fe in the Si matrix. The Si-Fe nanocomposites exhibit both magnetic and photoluminescence properties at room temperature. The photoluminescence intensity was found to decrease with increase in Fe content in the nanocomposite samples, however, saturation magnetization and retentivity increases. Thus it is imperative that by adjusting the composition of Si-Fe nanocomposites their properties can be tailored to suit the desired requirements for applications in electronic devices.