Revealing disorder parameter and deformation electron density using electron diffraction.

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Local atomic-scale disorders significantly impact material properties by altering electron density.
• Experimental determination of electron density is crucial for understanding these disorders.
• Quantitative convergent beam electron diffraction (QCBED) is established for ordered crystals, but its use in disordered systems is uncertain.

Purpose of the Study:

• To investigate the applicability of QCBED for quantifying local disorder parameters in chemically disordered materials.
• To simultaneously determine chemical disorder, deformation electron density (Δρ^EXP), and Debye-Waller factors (DWF).
• To validate QCBED as a robust method for characterizing disordered systems.

Main Methods:

• A multi-beam off-zone axis CBED technique was employed.
• Coherent potential approximation within Bloch wave formalism was utilized.
• Density functional theory (DFT) calculations were performed on supercells with random atomic distributions.

Main Results:

• QCBED successfully determined chemical disorder parameters, Δρ^EXP, and DWF in both ordered L1₀ FePd and disordered γ-phase FePd.
• Chemical disordering was found to significantly increase DWFs.
• The impact of chemical disordering on Δρ^EXP was negligible.

Conclusions:

• QCBED is validated as a robust method for quantifying local disorder in chemically disordered systems.
• This technique bridges a critical gap in the characterization of disordered materials.
• The findings provide insights into the relationship between chemical disorder and lattice dynamics.