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Phase Transitions

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...

States of Matter and Phase Changes

States of Matter and Phase Changes

The internal energy of a substance—the total kinetic energy of all its molecules and the potential energy of their associated forces—depends on the strength of the intermolecular forces in the condensed phases and the pressure exerted on the substance. The internal energy of a substance is the highest in the gaseous state, the lowest in the solid state, and intermediate in the liquid state. Phase transitions are caused by changes in physical conditions, such as temperature and...

Phase Transitions: Melting and Freezing

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...

Phase Diagram

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).

Phase Changes

Phase Changes

Phase transitions play an important theoretical and practical role in the study of heat flow. In melting or fusion, a solid turns into a liquid; the opposite process is freezing. In evaporation, a liquid turns into a gas; the opposite process is condensation.
A substance melts or freezes at a temperature called its melting point and boils or condenses at its boiling point. These temperatures depend on pressure. High pressure favors the denser form of the substance, so typically, high pressure...

Phase Transitions: Sublimation and Deposition

Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and standard pressure, a piece of dry ice (solid CO2) sublimes, appearing to gradually disappear without ever forming any liquid. Snow and ice sublimate at temperatures below the melting point of water, a slow process that may be accelerated by winds and the reduced atmospheric pressures at high altitudes. When solid iodine is warmed, the solid sublimes...

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Related Experiment Video

Updated: Oct 29, 2025

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Published on: July 17, 2020

High-temperature phase transitions in dense germanium.

Liam C Kelsall¹, Miriam Peña-Alvarez¹, Miguel Martinez-Canales¹

¹SUPA, School of Physics and Astronomy and CSEC, University of Edinburgh, Peter Guthrie Tait Road, Edinburgh EH9 3FD, United Kingdom.

The Journal of Chemical Physics

|July 9, 2021

Summary

Researchers discovered a new high-temperature phase of germanium (Ge-VIII) under extreme pressure and heat. This finding significantly alters our understanding of germanium

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Area of Science:

Materials Science
Solid State Physics
Geochemistry

Background:

Understanding the behavior of germanium (Ge) under extreme conditions is crucial for various scientific fields.
Previous studies have mapped parts of the Ge phase diagram, but high-temperature behavior remains less understood.

Purpose of the Study:

To investigate the pressure-temperature phase diagram of germanium (Ge) at high pressures and temperatures.
To identify and characterize new phases of germanium under extreme conditions.

Main Methods:

High-pressure x-ray diffraction experiments.
In situ laser heating techniques.
Density functional theory (DFT) simulations.

Main Results:

A new high-temperature phase of germanium, denoted as Ge-VIII, was observed in the pressure range of 64-90 GPa and temperatures above 1500 K.
Ge-VIII exhibits a tetragonal crystal structure with space group I4/mmm.
DFT simulations confirmed the instability of the Ge-IV phase at high temperatures and the stability of Ge-VIII.

Conclusions:

The discovery of Ge-VIII significantly expands the known pressure-temperature phase diagram of germanium.
This finding suggests that melting conditions for germanium at high pressures are higher than previously extrapolated.
The existence and properties of Ge-VIII have implications for planetary science and materials science under extreme conditions.