Public Defense of a Ph.D Research Scholar at Department of Physics

  • 04:00 pm
  • Video Conferencing Hall, UoP

Mr. Muhammad Saleem, a Ph.D. Research Scholar at the Department of Physics, University of Peshawar has  submitted his thesis entitled "Effect of A-Site Defects on the Structure and Microwave Dielectric Properties of Perovskite Ceramics in the [(Ca,Sr)x (La, Nd)2/3-2x/3] TiO3 Model System with 0"  to the University of Peshawar, in partial fulfillment of the requirement for the award of degree of  Doctor of Philosophy (Ph. D) in the discipline of Mathematics.

All those having interest in the said research work, are cordially invited to attend the occasion. The participants would be allowed to raise relevant questions after the presentation by the scholar for further judgment and evaluation of the examiners.

 

Abstract

 Composition dependent structural phase transitions and microwave dielectric properties in the system [(Ca, Sr)x (La, Nd)2/3-2x/3]TiO3 (0 ≤ x ≤ 1) were investigated in the present study. The sample with x = 0 crystallizes in to two phases namely (La, Nd)0.667TiO3 as a major phase and  (La, Nd)4Ti9O24 as a secondary phase. Superlattice reflections were observed for this sample demonstrating the ordering of A-site cations / vacancies. The increase in sintering temperature caused an increase in the observed density of this sample. Calcining the sample in nitrogen atmosphere caused an increase in the quality factor (Qf) nearly by 17% with a negligible effect on the dielectric constant (εr) and temperature coefficient of resonant frequency (τf).

For the samples with 0.1 ≤ x ≤ 0.9, structural phase transition was observed from tetragonal (I4mcm) to orthorhombic (Pbnm) for x ≥ 0.7 as a result of a decrease in the A-site ordering. Secondary phase (La, Nd)4Ti9O24 was observed for the compositions with x = 0.1 and 0.2. Superlattice reflections were observed which disappeared with an increase in x reflecting a decrease in the A-site ordering. εr and Q varied randomly whereas τf was observed to increase with increasing x.

Synchrotron XRD and Raman spectroscopy reveal a structural phase transition from orthorhombic (Pbnm) to tetragonal (I4/mcm) at x = 0.75 in the system Ca(1-x)SrxTiO3. Grains of irregular shape were observed in the SEIs with size ranging from 3 to10 μm. εr increased from 148 to 260 with an increase in x from 0.1 to 0.5 and then decreased to 241 upon further increase in x to 0.9. Q decreased from 7427 GHz to 1487GHz whereas τf increased from +392 to +430 ppm / ºC with an increase in x from 0.1 to 0.9.

For (Ca, Sr)1-xNd2x/3TiO3, a structural phase transition was demonstrated both by synchrotron XRD and Raman spectroscopy results, from orthorhombic (Pbnm) for x = 0.1 and 0.25 to tetragonal (I4/mcm) for x = 0.5 and 0.75, respectively. Increasing Nd content caused an increase in the grain size and a decrease in εr, Qf and τf.