High Pressure Studies on Piezoelectrics

Mondal, Anshuman (2019) High Pressure Studies on Piezoelectrics. Masters thesis, Indian Institute of Science Education & Research Kolkata.

PDF (MS dissertation of Anshuman Mondal (14MS044)) 14MS044.pdf - Submitted Version Restricted to Repository staff only Download (16MB)

Abstract

The concern over the hazardous effect of Pb in conventional piezoelectrics leads to huge interest in finding new lead-free Piezoelectric samples. BaTiO₃ based alloy system 0.5Ba(Ti₀.₈Zr₀.₂)O₃ - 0.5(Ba₀.₇Ca0.3)TiO₃ has attracted great attention recently with its very large piezo-response. The primary goal of this thesis is to study this system at high pressures by X-ray diffraction, Raman Spectroscopy and AC dielectric constant measurements and understand the changes in its piezoelectric properties. The instantaneous changes in the high-pressure Raman spectra have indicated two structural transitions, which are then verified by indexing and Rietveld refinement of high-pressure XRD data. Our data show the evidence of two structural phase transitions, one around 4.7 GPa, which is ferroelectric tetragonal to paraelectric cubic transition and another one has been indexed to an isostructural transition near 10.36 GPa. The strong Raman spectra in the cubic phase indicate the displacement in the positioning of Ti atoms from the actual body-centered position, that leads to a disordered cubic structure allowing Raman activity. The high-pressure dielectric measurements show a huge drop in the dielectric constant value near 4.7 GPa verifying the tetra-cubic transition. The second transition is due to the breakage of one of the Ti-O bonds, which gets highly distorted with pressure leading to this re-ordering.

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