Structural changes induced by lattice-electron interactions: SiO2 stishovite and FeTiO3 ilmenite

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Synchrotron radiation is advantageous for single-crystal structure analysis under non-ambient conditions.
• Lattice-electron interactions under high pressure induce significant structural changes.
• Understanding electron density distribution is crucial for elucidating chemical bonding.

Purpose of the Study:

• To investigate pressure-induced changes in electron density distributions in FeTiO3 ilmenite and gamma-SiO2 stishovite.
• To elucidate the behavior of bonding electrons under high pressure.
• To determine the effective charge of cations and analyze thermal displacement parameters.

Main Methods:

• Single-crystal diffraction studies using synchrotron radiation.
• High-pressure experiments utilizing a diamond anvil pressure cell.
• Deformation electron density analysis and the maximum entropy method.

Main Results:

• Valence electrons become more localized around cations with increasing pressure for both FeTiO3 and gamma-SiO2.
• Bonding electron density decreases with increasing pressure, consistent with molecular orbital calculations.
• Thermal displacement parameters for both samples are reduced under high pressure.

Conclusions:

• High pressure leads to increased electron localization around cations in FeTiO3 and gamma-SiO2.
• The observed changes in electron density distribution provide insights into chemical bonding under pressure.
• Reduced thermal displacement parameters indicate a more rigid crystal structure at high pressures.