Local structures and Raman spectra in the Ca(Zr,Ti)O3 perovskite solid solutions

Local structures and cation distributions in perovskite Ca(Zr,Ti)O-3 solid solutions were analyzed using X-ray absorption fine structure and pair-distribution functions obtained from total neutron scattering. The analyses revealed that the Zr-O and Ti-O bond distances in the solid solutions remain distinct and close to their respective values in the end-compounds, CaZrO3 and CaTiO3. The structural strain in the solid solutions, which results from the ionic size mismatch between Zr and Ti, is accommodated by adjustment of the tilting angles for the different [BO6] octahedra. Additionally, the octahedra are distorted by bending, which affects the O-O distances while preserving a uniform distribution of the B-O distances. Combined experimental and theoretical analyses of Raman spectra demonstrated that high-frequency modes associated with the breathing of oxygen octahedra arise even in the nearly disordered solid solutions. Our results suggest a coexistence of both localized and extended Raman-active breathing vibrations, associated with the octahedra hosting the minority and majority B-cations, respectively. For the dilute solid solutions (< 25 at. %), these modes yield two well-resolved Raman peaks.