orbital ordering patterns in KBF (B = Sc, Ti, Fe, Co) perovskites

Area of Science:

• Solid State Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Transition metal perovskites exhibit complex orbital ordering (OO) due to partially occupied d-orbitals.
• The coupling between B-site transition metals in KBF perovskites leads to numerous possible OO patterns.

Purpose of the Study:

• Investigate the quantum mechanical behavior of orbital ordering in KBF perovskites (B = Sc, Ti, Fe, Co).
• Characterize the energy landscape and structural implications of various OO patterns.
• Develop a predictive model for orbital ordering in larger supercells.

Main Methods:

• Quantum mechanical calculations using a Gaussian type basis set and B3LYP hybrid functional.
• Supercell approach with 40 atoms to model KBF perovskites.
• Classification of numerous OO patterns into 162 equivalent configuration classes.

Main Results:

• All four KBF perovskite compounds displayed similar energy and volume dependencies on the OO pattern.
• The energy spanned by different OO configurations was small (1-2 mE per formula unit).
• A linear model based on relative orbital order in adjacent sites accurately reproduced the energy order.

Conclusions:

• Most orbital ordering configurations in these KBF perovskites are likely occupied at room and low temperatures.
• The developed linear model shows promise for studying orbital ordering in larger and more complex supercells.
• The findings provide insights into the electronic and structural properties of transition metal perovskites.