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Related Concept Videos

Phase Transitions02:31

Phase Transitions

Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to occupy...
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Phase Transitions

A phase transition is the process in which a substance changes from one state of matter to another, like from a solid to a liquid, liquid to gas, or vice versa, at a specific temperature and under given pressure conditions. This change is spontaneous and is affected by alterations in temperature and pressure. These parameters impact the strength of the forces between molecules (intermolecular forces) in the substance.During a phase transition, both the initial and final phases of the substance...
Ferromagnetism01:31

Ferromagnetism

Materials like iron, nickel, and cobalt consist of magnetic domains, within which the magnetic dipoles are arranged parallel to each other. The magnetic dipoles are rigidly aligned in the same direction within a domain by quantum mechanical coupling among the atoms. This coupling is so strong that even thermal agitation at room temperature cannot break it. The result is that each domain has a net dipole moment. However, some materials have weaker coupling, and are ferromagnetic at lower...
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Microbial activity plays a pivotal role in the biogeochemical cycling of iron and manganese, especially at the redox gradients characteristic of stratified aquatic environments. These cycles are driven by microbial transformations between oxidized and reduced forms of the metals, allowing organisms to exploit them for metabolic energy and structural purposes.Iron Cycling Across Redox GradientsIn neutral, oxygen-rich surface waters, iron is predominantly found in its oxidized, insoluble ferric...
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Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
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Phase Diagram

The phase of a given substance depends on the pressure and temperature. Thus, plots of pressure versus temperature showing the phase in each region provide considerable insights into the thermal properties of substances. Such plots are known as phase diagrams. For instance, in the phase diagram for water (Figure 1), the solid curve boundaries between the phases indicate phase transitions (i.e., temperatures and pressures at which the phases coexist).

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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
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Oscillatory phase transition induced structural extension during iron oxide reduction.

Haoyang Fu1,2, Qingze Chen3, Benzhi Min2

  • 1State Key Laboratory for Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.

Fundamental Research
|June 11, 2026
PubMed
Summary

Investigating iron oxide reduction reveals unexpected oscillatory phase transitions at the nanoscale. This challenges traditional views and offers insights into catalyst behavior.

Keywords:
CatalysisEpitaxial nanoislandsIn-situ TEMNonclassical reductionOxide reduction

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Area of Science:

  • Materials Science
  • Surface Chemistry
  • Nanotechnology

Background:

  • Understanding oxide redox mechanisms is crucial for catalysis and materials development.
  • Conventional models of oxide reduction do not fully capture complex behaviors.
  • Probing subsurface transformations in single-crystalline iron oxide (α-Fe2O3) is challenging.

Purpose of the Study:

  • To investigate the molecular-level redox behavior and mechanism of single-crystalline α-Fe2O3.
  • To provide an in-situ view of oxide reduction beyond conventional wisdom.
  • To understand the dynamic processes governing oxide reduction and phase transitions.

Main Methods:

  • In-situ transmission electron microscopy (TEM) was employed to observe reduction processes.
  • Single-crystalline α-Fe2O3 samples were studied under reducing conditions.
  • Analysis focused on subsurface structural and phase changes during reduction.

Main Results:

  • Observed epitaxial nanoisland formation with oscillatory phase transitions (α-Fe2O3 → defective γ-Fe2O3 → α-Fe2O3) at the subsurface.
  • Identified dynamic equilibrium of lattice oxygen and limited oxygen replenishment as drivers for subsurface transformation.
  • Demonstrated spontaneous polymorphic transition (defective γ-Fe2O3 → α-Fe2O3) under heating, accompanied by stress release and nanoisland extension.

Conclusions:

  • The reduction of α-Fe2O3 exhibits complex oscillatory phase transitions, differing from conventional understanding.
  • Subsurface processes, including oxygen dynamics and stress evolution, play a critical role in oxide reduction.
  • Findings contribute to understanding oxide catalyst site evolution in working conditions.