Revisiting Bond Breaking and Making in EuCo₂ P₂ : Where are the Electrons?

Area of Science:

• Materials Science
• Solid-State Physics
• Quantum Chemistry

Background:

• EuCo2P2 exhibits a pressure-induced structural collapse.
• Understanding electronic structure changes during phase transitions is crucial for materials science.
• Traditional electron counting models may not fully describe complex metallic systems.

Purpose of the Study:

• To investigate the electronic structure modifications in EuCo2P2 under pressure.
• To elucidate the mechanism of pressure-induced structural collapse.
• To evaluate the applicability of the Zintl-Klemm concept in metallic systems undergoing phase transitions.

Main Methods:

• X-ray absorption spectroscopy (XAS) at Eu L3-edge and Co, P K-edges.
• Quantum-chemical calculations.
• Analysis of spectral changes and electron density redistribution.

Main Results:

• XAS revealed significant electron density redistribution at Eu, Co, and P sites.
• Observed changes contradict formal charges predicted by the Zintl-Klemm concept.
• Quantum-chemical calculations indicated electron transfer from Eu 4f to hybridized 5d and 6s states, strengthening Eu-P and P-P bonds.
• Increased electron density on P atoms was confirmed by P K-edge XAS.

Conclusions:

• Formal electron counting schemes are inadequate for describing phase transitions in metallic systems with significant electronic state mixing.
• The study highlights the importance of considering electronic orbital hybridization in understanding pressure-induced phase transitions.
• XAS and quantum-chemical calculations provide a comprehensive picture of electronic structure evolution in EuCo2P2.