Dielectric Properties of Nanostructured PZTSynthesised by Chemical Methods

In this study, the dielectric behaviour of smart material, lead zirconate tiatanate (PZT), whichis important for wide industrial applications, has been explored. Two samples of nanostructuredPb(Zr0.52Ti0.48)O3 ceramic powders were prepared by hydroxide co-precipitation and aqueoussolution method (water bath technique). The XRD pattern of the  powder exhibited the presenceof major tetragonal and minor rhombohedral crystalline phases indicating the mixed-phasecomposition, which is close to the morphotropic phase boundary (MPB). SEM analysis revealedgood homogeneity of the materials. The plot of real part versus imaginary part of the compleximpedance was observed nearly a semicircle, indicating that the samples are good dielectricmaterials, whose resistance decreases considerably with the increase of temperature. Similar tothe normal ferroelectric materials, the dielectric constant () of PZT has been found to be increasinggradually with temperature and attains a maxima (max). The detailed analysis for the shift in peaktemperature and dielectric constant were carried out

Structural Characterization of Metal Hydrides for Energy Applications

Hydrogen can be an unlimited source of clean energy for future because of its very high energy density compared to the conventional fuels like gasoline. An efficient and safer way of storing hydrogen is in metals and alloys as hydrides. Light metal hydrides, alanates and borohydrides have very good hydrogen storage capacity, but high operation temperatures hinder their application. Improvement of thermodynamic properties of these hydrides is important for their commercial use as a source of energy. Application of pressure on materials can have influence on their properties favoring hydrogen storage. Hydrogen desorption in many complex hydrides occurs above the transition temperature. Therefore, it is important to study the physical properties of the hydride compounds at ambient and high pressure and/or high temperature conditions, which can assist in the design of suitable storage materials with desired thermodynamic properties. The high pressure-temperature phase diagram, thermal expansion and compressibility have only been evaluated for a limited number of hydrides so far. This situation serves as a main motivation for studying such properties of a number of technologically important hydrides. Focus of this dissertation was on X-ray diffraction and Raman spectroscopy studies of Mg2FeH6, Ca(BH4) 2, Mg(BH4)2, NaBH4, NaAlH4, LiAlH4, LiNH2BH3 and mixture of MgH 2 with AlH3 or Si, at different conditions of pressure and temperature, to obtain their bulk modulus and thermal expansion coefficient. These data are potential source of information regarding inter-atomic forces and also serve as a basis for developing theoretical models. Some high pressure phases were identified for the complex hydrides in this study which may have better hydrogen storage properties than the ambient phase. The results showed that the highly compressible B-H or Al-H bonds and the associated bond disordering under pressure is responsible for phase transitions observed in brorohydrides or alanates. Complex hydrides exhibited very high compressibility suggesting possibility to destabilize them with pressure. With high capacity and favorable thermodynamics, complex hydrides are suitable for reversible storage. Further studies are required to overcome the kinetic barriers in complex hydrides by catalytic addition. A comparative study of the hydride properties with that of the constituting metal, and their inter relationships were carried out with many interesting features