Room temperature single-crystal diffuse scattering and ab initio lattice dynamics in CaTiSiO5

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Diffuse scattering reveals atomic dynamics in crystals.
• Understanding thermal motion is key to material properties.

Purpose of the Study:

• Investigate the origin of diffuse scattering in synthetic titanite.
• Characterize phonon modes and their relation to material properties.

Main Methods:

• Collected single-crystal diffuse scattering data using neutrons and high-energy X-rays.
• Performed ab initio phonon calculations using density-functional perturbation theory.

Main Results:

• Diffuse scattering is primarily due to atomic thermal motion.
• Calculated phonons accurately reproduce experimental diffuse scattering patterns.
• Observed a band gap and identified modes associated with antiferroelectric Ti-O motion.

Conclusions:

• Diffuse scattering in titanite arises from the phonon spectrum, not static displacements.
• Large LO-TO mode splitting in a Bu mode is linked to Ti-O bond polarizability.
• The phonon model can aid in understanding phase transitions and dispersion curves.