Chemical-Pressure Tuning of Lattice Dynamics: Temperature-Dependent Raman Scattering and X-Ray Diffraction of La₂SmNi₂O₇ and La₂PrNi₂O₇

Recent studies of La₃Ni₂O₇ superconductivity onset near 80 K under high pressure; subsequent single-crystal work on La₂SmNi₂O₇ pushes the onset toward ~92 K, motivating an investigation into how elemental substitution modulates the lattice dynamics. In this work, we synthesize polycrystalline Samarium (Sm)/Praseodymium (Pr)-substituted bulk samples via solid-state sintering (isovalent A-site chemical pressure) and perform temperature-dependent Raman scattering and variable-temperature X-ray diffraction (XRD) at ambient pressure to search for charge-density-wave (CDW)-consistent anomalies and to establish a baseline across the La→Sm/Pr series. This framework constrains how A-site chemical pressure tunes lattice dynamics and density-wave propensity, establishing a spectroscopic basis for future correlation with transport and ultrafast dynamics measurements.