About this Research Topic
Most materials expand on heating, known as positive thermal expansion. Thermal expansion is critical in many technological applications, like precise instruments, glazes and coating materials, optical and electronic devices, high-temperature materials design. As a matter of fact, different materials in contact with each other can have different thermal expansion, giving rise to thermal shock breakage. For these reasons, controlling thermal expansion represents a challenge for material design.
Negative thermal expansion (NTE), that is material contraction on heating over a certain temperature range, is relatively rare but has important technological applications. Since the discovery in 1996 that zirconium tungstate exhibits large isotropic NTE over a wide temperature range, the interest in NTE has rapidly grown to become the most promising route to achieve the control of thermal expansion. In principle, this is because NTE can be used to control thermal expansion by compensating the positive thermal expansion. Since then, many NTE materials have been discovered, such as cyanides, metal-organic frameworks, metal fluorides and so on.
NTE phenomenon is known to arise from a range of different physical mechanisms, such as ferroelectricity and magnetic transitions, valence transitions in the case of intermetallic and fulleride materials, low-energy vibrational modes for open-framework solids. In particular, it is well accepted that the mechanism driving NTE in the framework materials (i.e., open structures of corner-sharing polyhedral units) involves transverse vibrational displacement of the central linking atom. However, this does not lead to straightforward control of thermal expansion. Moreover, composites of negative and positive thermal expansion materials may fail after repeated cycling, so direct control of thermal expansion within a single homogenous phase is desirable and yet difficult to achieve.
The present Research Topic will include a collection of original research and review (mini review) articles dedicated to the physical-chemical phenomena connected to NTE and to the state-of-the-art for control thermal expansion, including chemical intercalation, chemical substitution, nano-size effects.
Keywords: Tailoring Thermal Expansion, Negative Thermal Expansion, Thermal Stress
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