• E C Subbarao

      Articles written in Bulletin of Materials Science

    • Analytical methods for RE-Co alloys

      T A Padmavathy Sankar H O Gupta E C Subbarao K P Gupta N R Bonda D K Goel S N Kaul A K Majumdar R C Mittal G Sarkar M V Satyanarayana K Shankara Prasad J Subramanyam E M T Velu

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      Total RE, Co and Fe in mischmetal and its cobalt alloys are determined by visual complexometric methods and instrumental x-ray fluorescence techniques. As Fe causes interference in the determinations of RE and Co and its own determination is affected by the presence of Co, it is removed by precipitation. The iron is determined from the precipitate and RE and Co from the filtrate. Accuracy of the method is checked by analysing synthetic mixtures of RE, Co and Fe. The individual REs in mischmetal are determined by x-ray fluorescence method. The analysis technique is based on comparison of the oxides of the test samples with standards (both in pressed pellet form) in the appropriate composition range. The total RE content of mischmetal determined through complexometric analysis is compared with the total RE determined through x-ray fluorescence.

    • Oxide dielectrics

      E C Subbarao

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      Three aspects of oxide dielectrics are covered (i) structure engineering: making use of crystal structure and crystal chemistry, the dielectric behaviour can be finely tuned, as illustrated in the systems (Ba, Pb) (Ti, Zr)O3 and (Ba, Pb) (Ti, Nb)O3 studied by Biswas. (ii) Defect structure: control of defect structure of Mn-doped BaTiO3 inhibits the reduction of BaTiO3 in reducing atmospheres at high temperatures thus making the use of base metal electrodes possible in manufacturing ceramic capacitors. (iii) Composites: Diphasic composites of oxide dielectrics with other materials may be utilized for producing voltage stable capacitors and dense or flexible piezoelectrics with outstanding properties.

    • Synthesis and properties of manganese-doped barium titanate

      L M Arunachalam D Chakravorty E C Subbarao

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      An oxalate route for the production of BaTiO3 has been modified to incorporate Mn (upto 2%) as a dopant and the reaction sequence has been studied. The resulting Mn-doped BaTiO3 exhibits a dielectric constant with an increasing insensitivity to temperature and applied a.c. field as the Mn content is increased. These samples possess a high electrical resistivity even after treatment in hydrogen at 1100°C and are therefore suitable as dielectric for multilayer capacitors with base metal electrodes.

    • A second ceramic age—A new materials frontier

      E C Subbarao

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      A second ceramic age started in the mid-twentieth century as a new, exciting materials frontier. Electroceramics with phenomenally wide range of electrical resistivity (spread over 30 orders of magnitude) span insulators, semiconductors, metal-like conductors, ionic conductors, and, recently, superconductors. They also include ferroelectrics, piezoelectrics, pyroelectrics and electro-optics beside ferrites. Advances in electroceramics have been fascinating and rapid, leading to unprecedented rates of industrial growth. Age-old limitations of poor mechanical strength and brittleness of ceramics are being overcome by outstanding toughness and strength achieved in zirconiabased ceramics exploiting the martensitic transformation at the tetragonal-monoclinic phase change. The dimensional changes at this transition which prevented the use of zirconia earlier has now been turned into a mechanism for toughening ceramics to significant levels. Ceramics with near-zero overall thermal expansion coefficient offer new opportunities to science and industry.

    • Microdeformations in ferroelectrics

      E C Subbarao

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      Ferroelectrics undergo one or more crystallographic phase transitions, which involve lattice distortions. The direction of spontaneous polarization in ferroelectrics can be reoriented by an applied electric field (or mechanical stress). There is a spontaneous strain accompanying spontaneous polarization. Phase transitions and domain reorientations thus result in microdeformations. Many devices such as actuators and transducers are based on this behaviour. The origin of microdeformations in ferroelectrics and their consequences are discussed here.

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