Stacking Structure of Vaterite Revealed by Atomic Imaging and Diffraction Analysis.

Area of Science:

• Crystallography
• Materials Science
• Biomineralization

Background:

• Anhydrous calcium carbonate exists as three polymorphs: calcite, aragonite, and vaterite.
• Vaterite is a metastable phase, rarely found geologically but common in biominerals.
• Understanding vaterite's structure is crucial for comprehending biomineralization.

Purpose of the Study:

• To elucidate the long-standing question of vaterite's crystal structure.
• To determine the stacking sequence and atomic arrangement in vaterite.
• To provide insights into vaterite's thermodynamic stability and biomineralization role.

Main Methods:

• Combined atomic imaging and diffraction analysis.
• Simulations of disordered stacking sequences.
• Analysis of electron and X-ray diffraction patterns.

Main Results:

• Proposed the actual crystal structure of vaterite.
• Identified vaterite's layered structure of calcium and carbonate sheets.
• Determined a predominant four-layer stacking sequence with specific rotations.
• Replicated diffraction pattern intensity distributions through stacking characteristics.

Conclusions:

• The crystal structure and stacking sequence of vaterite have been largely elucidated.
• Findings offer insights into vaterite's thermodynamic stability.
• Comprehension of biomineralization processes and calcium carbonate growth dynamics is enhanced.