Investigation into the vibrational characteristics of monolayered ruddlesden-popper compounds (Sr, Ba)HfO.

The analysis of Raman and Infrared (IR) phonons in monolayered tetragonal (Sr, Ba)HfO compounds, which exhibit D symmetry and belong to the I4/mmm phase of space group 139 with Z = 2, has been conducted using normal coordinates. The SrHfO and BaHfO compounds are the first members of the Ruddlesden-Popper (RP) series denoted as (Sr, Ba)HfO with n = 1. Nine Short-Range Force Constants (SRFC) have been included in theoretical calculations to analyze the optical phonons of SrHfO and BaHfO compounds within the I4/mmm phase. The assignments of optical vibrational modes in (Sr, Ba)HfO compounds have been determined using Wilson's GF-Matrix Method and cross-referenced with data obtained from compounds sharing similar structural characteristics. The analysis also involved studying how the exchange of cation-A (A = Sr, Ba) impacts the lattice dynamics of the isostructural compounds AHfO (A = Sr, Ba) in monolayered tetragonal structures. In this analysis, a comparison has been made between the vibrational modes at the Zone Center, the force constants, and bond lengths to assess the influence of the cation exchange. Furthermore, for each normal mode in the Ruddlesden-Popper phase (Sr, Ba)HfO, the examination of Potential Energy Distribution (PED) sheds light on the significant impact exerted by Short-Range Force Constants on the calculated vibrational modes, providing a deeper understanding of their behavior and interactions.