Figure 1. Thermal Expansion Properties of LaFe10.5Co1.0Si1.5 (Image by HUANG Rongjin)
Negative thermal expansion (NTE) materials contract instead of expanding when heated. When mixed with more common metals that expand under heat, they can form a composite that neither expands nor contracts upon heating. This is valuable in technologies such as reflective grating devices, optical mirrors, and machinery parts. However, finding materials that do this in practice is relatively rare, due to the narrow temperature window under which they show NTE effects. In addition, most of the known NTE materials have small thermal expansion effects, so have limited value.
Now Laifeng Li and co-workers at the Technical Institute of Physics and Chemistry, CAS have found a way to expand this NTE behavior window (DOI: 10.1021/ja405161z). The compound La(Fe,Si)13 undergoes a phase change where there is a coinciding change in both magnetism and volume. It also exhibits NTE behavior, but only over a narrow temperature range. The researchers replaced the Fe with Co, and the transition temperature widely broadened and even includes room temperature. The effect was also large enough to counter thermal expansion in metallic composites. This discovery may be valuable for volume sensitive devices in the future, leading to machines that run better and optical devices that stay in tune.
(pubs.acs.org)
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