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Thermal Expansion

Thermal Expansion

The expansion of alcohol in a thermometer is one of many commonly encountered examples of thermal expansion, which is the change in size or volume of a given system as its temperature changes. The most visible example is the expansion of hot air. When air is heated, it expands and becomes less dense than the surrounding air, which then exerts an upward force on the hot air to, for example, make steam and smoke rise, and hot air balloons float. The same behavior happens in all liquids and gases,...

Thermal Strain

Thermal Strain

Thermal strain is a concept that arises when we consider how temperature changes affect structures. Unlike the conventional assumption that structures remain constant under load, real-world scenarios often involve temperature fluctuations that can significantly impact these structures. Consider a homogeneous rod with a uniform cross-section resting freely on a flat horizontal surface. If the rod's temperature increases, the rod elongates. This elongation is proportional to the temperature...

Thermal Stress

Thermal Stress

If the temperature of an object is changed while it is prevented from expanding or contracting, the object is subjected to stress. The stress is compressive if the object expands in the absence of constraint and tensile if it contracts. This stress resulting from temperature change is known as thermal stress. It can be quite large and can cause damage. To avoid this stress, engineers may design components so they can expand and contract freely. For instance, on highways, gaps are deliberately...

Thermal expansion and Thermal stress: Problem Solving

Thermal expansion and Thermal stress: Problem Solving

San Francisco's Golden Gate Bridge is exposed to temperatures ranging from -15 °C to 40 °C. At its coldest, the main span of the bridge is 1275 m long. Assuming that the bridge is made entirely of steel, what is the change in its length between these temperatures?
To solve the problem, first, identify the known and unknown quantities. The initial length (L) of the bridge is 1275 m, the coefficient of linear expansion (α) for steel is 12 x 10-6/°C, and the change in temperature (ΔT) is 55 °C.

Imperfections in Crystal Structure: Point, Line and Plane Defects

Imperfections in Crystal Structure: Point, Line and Plane Defects

A perfect crystal, in theory, has a uniform structure with the same unit cell and lattice points throughout. However, any deviation from this periodic arrangement is known as an imperfection or defect. These defects can be categorized into three types: point, line, and plane defects.Point defects occur when there is a deviation from the ideal due to missing atoms, displaced atoms, or additional atoms. These imperfections might occur due to imperfect packing during crystallization or because of...

Imperfections in Crystal Structure: Non-Stoichiometric Defects

Imperfections in Crystal Structure: Non-Stoichiometric Defects

Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...

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Related Experiment Video

Updated: May 23, 2026

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Published on: June 7, 2018

Negative thermal expansion in isotropic crystals.

Tong Li¹, Martin T Dove^1,2,3

¹Department of Mechanical Engineering, Guizhou University of Engineering Science, Bijie, 695013, China.

Materials Horizons

|May 22, 2026

Summary

Negative thermal expansion (NTE) in crystals is explained by four key principles: network structure, low-frequency vibrations, vibration distribution, and dynamic disorder. Understanding these principles aids in predicting and designing new NTE materials.

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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Published on: May 15, 2017

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Last Updated: May 23, 2026

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Published on: June 7, 2018

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Published on: May 15, 2017

Area of Science:

Materials Science
Solid-State Physics
Crystallography

Background:

Negative thermal expansion (NTE) is counterintuitive, as most materials expand when heated.
Understanding NTE in isotropic crystals has been challenging despite experimental and theoretical advancements.

Purpose of the Study:

To demystify the phenomenon of negative thermal expansion (NTE) in isotropic crystals.
To rationalize the existence of NTE and predict its occurrence in new materials.

Main Methods:

Review of experimental and theoretical investigations on NTE.
Identification and explanation of four core principles governing NTE in cubic crystals.
Application of principles to specific examples, including NaZr2(PO4)3.

Main Results:

NTE in cubic crystals is rationalized by four principles: network structure, low-frequency vibrations, vibration distribution in reciprocal space, and dynamic disorder.
These principles also apply to anisotropic crystals, with additional factors influencing NTE.
NTE arises from a balance between mechanisms promoting expansion and contraction.

Conclusions:

A unified understanding of NTE is achieved through the interplay of four principles and chemical effects.
The study provides a practical framework for understanding NTE, moving beyond single-mechanism explanations.
Research on NTE materials has significantly advanced the general understanding of thermal expansion phenomena.