Understanding microscopic properties of materials using Raman spectroscopy

Abstract

This thesis investigates the structural, vibrational, and electronic properties of strontium titanate, a prototypical perovskite, utilizing advanced Raman spectroscopy to elucidate its phase transitions and potential Fano effects, with significant implications for optoelectronic and energy applications. Polarized Raman spectroscopy reveals a cubic-to-tetragonal phase transition at approximately 105 K, characterized by the emergence of first-order B2g modes at 144 cm⁻¹ and 445 cm⁻¹ at low temperatures (93 K and 88 K), with polarization-dependent intensity variations confirming tetragonal domain alignment and anisotropic vibrational properties, underscoring SrTiO3’s quantum paraelectric behaviour, though local strains indicate areas for further exploration. Additionally, the study explores potential Fano resonance in STO’s low-frequency TO2-TA mode, which exhibits asymmetric line shapes suggestive of quantum interference, drawing comparisons with established Fano effects in heavily doped silicon (520 cm⁻¹ peak) and vanadium pentoxide (995 cm⁻¹ Ag mode), where temperature-dependent asymmetries and photoexcitation amplify nonlinear behaviours. While anharmonic phonon interactions in SrTiO3 hinder definitive Fano confirmation, a framework leveraging silicon and vanadium pentoxide’s nonlinear properties is proposed to investigate Fano effects in complex oxides, enhancing understanding of sample’s lowtemperature dynamics and its potential in oxide electronics. The developed temperature-dependent and polarized Raman methodologies provide a robust approach for studying perovskites, offering valuable insights for optimizing materials in solar cells, microelectronics, and catalysis.