A self-consistent approach to describe unit-cell-parameter and volume variations with pressure and temperature

Area of Science:

• Crystallography
• Materials Science
• Solid State Physics

Background:

• Accurately describing crystal unit-cell parameter variations with external conditions (pressure, temperature) is crucial.
• Existing methods may lack internal consistency, especially for large parameter changes.

Purpose of the Study:

• To present a self-consistent method for modeling large variations in crystal unit-cell parameters.
• To compare different approaches for describing unit-cell angle variations in specific crystal systems.

Main Methods:

• Utilizing linearized equations of state (EoSs) with internal consistency constraints.
• Comparing polynomial functions for unit-cell angles with EoS-derived methods for d-spacings.
• Implementation in the CrysFML Fortran subroutine library and EosFit7c program.

Main Results:

• A self-consistent method for calculating unit-cell parameters, compressibility, and thermal expansion tensors.
• Demonstration of the utility in the EosFit7c program.

Conclusions:

• The developed method provides a self-consistent approach for analyzing crystal behavior under varying pressure and temperature.
• The freeware EosFit7c program offers a practical tool for these calculations.