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The Mean Inner Potential of Hematite α-Fe2O3 Across the Morin Transition
Avi Auslender1,2, Adham Basha1, Daniel A Grave3,4
1Department of Materials Science and Engineering, The Iby and Aladar Fleischman Faculty of Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel.
Summary
The mean inner potential (MIP) of hematite (α-Fe2O3) was measured across its magnetic transition. A significant MIP reduction below the Morin transition indicates increased ionic bonding, validating MIP as a chemical bonding parameter.
Area of Science:
- Materials Science
- Solid-State Physics
- Crystallography
Background:
- The mean inner potential (MIP) is sensitive to valence electron distribution and chemical bonding in solids.
- Hematite (α-Fe2O3) exhibits a Morin magnetic phase transition, offering a unique opportunity to study bonding changes without structural alterations.
- Previous studies reported changes in hybridized Fe-3d and O-2p states across the Morin transition, suggesting an impact on ionic bonding.
Purpose of the Study:
- To measure the temperature dependence of the MIP in hematite (α-Fe2O3).
- To investigate the sensitivity of the MIP as a chemical bonding parameter by correlating it with the Morin magnetic phase transition.
- To confirm the minor temperature dependence of MIP in a non-magnetic analogue, α-Al2O3.
Main Methods:
- Electron holography and transmission electron microscopy were employed to measure the MIP.
- Temperature-dependent MIP measurements were conducted on hematite (α-Fe2O3) and sapphire (α-Al2O3) across a range of temperatures (95 K to 295 K).
- The Morin transition temperature in hematite was utilized as a critical point for observing bonding-induced MIP changes.
Main Results:
- The MIP of α-Al2O3 remained constant at approximately 16.8 V between 95 K and 295 K, confirming minimal temperature-induced changes in non-magnetic materials.
- Above the Morin transition, the MIP of α-Fe2O3 was measured to be around 17.85–17.93 V at 295 K and 230 K.
- Below the Morin transition, at 95 K, a significant reduction in MIP to 16.56 V was observed, a decrease of approximately 1.3 V.
Conclusions:
- The observed significant reduction in MIP below the Morin transition in hematite is attributed to charge redistribution, leading to enhanced ionic bonding.
- The mean inner potential (MIP) demonstrates sensitivity to changes in chemical bonding, validating its potential as a quantitative bonding parameter for crystalline materials.
- Electron holography provides a powerful tool for probing subtle changes in electronic structure and chemical bonding through MIP measurements.
Keywords:
Morin transition temperaturehematite (α-Fe2O3)mean inner potential (MIP)off-axis electron holographysapphire (α-Al2O3)More Related Videos
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