Temperature-Driven Magnetic Ordering, Spin-Glass State, and Structural Transitions in Pyrochlore Pb_2.8Nb₂O_7.8

This study explores the vibrational, structural, and magnetic properties of Pb2.8Nb2O7.8. First-principles calculations based on density functional perturbation theory were employed to investigate its vibrational characteristics. The crystal structure was refined using the Rietveld method applied to powder X-ray diffraction data, revealing an orthorhombic phase belonging to space group Cmc21. Group theory analysis predicted Raman and infrared-active vibrational modes, which were experimentally validated through Raman spectroscopy. Temperature-dependent Raman spectra unveiled phase transformations associated with structural changes and phase transitions, evidenced by the emergence and shift of vibrational modes associated with structural transformations. Additionally, alternating current susceptibility measurements indicated a spin-glass-like state, suggesting frustrated magnetic interactions. These findings provide valuable insights into the fundamental vibrational and magnetic behavior of Pb2.8Nb2O7.8, enhancing our understanding of complex oxides with potential functional applications.