Materials which undergo NTE have a range of potential engineering, photonic, electronic, and structural applications.
In 2011, Liu et al.[1] showed that the NTE phenomenon originates from the existence of high pressure, small volume configurations with higher entropy, with their configurations present in the stable phase matrix through thermal fluctuations.
[2] Alternatively, large negative and positive thermal expansion may result from the design of internal microstructure.
[3] Negative thermal expansion is usually observed in non-close-packed systems with directional interactions (e.g. ice, graphene, etc.)
However, in a paper,[4] it was shown that negative thermal expansion (NTE) is also realized in single-component close-packed lattices with pair central force interactions.
Perhaps one of the most studied materials to exhibit negative thermal expansion is zirconium tungstate (ZrW2O8).
[6] Other materials that exhibit NTE behaviour include other members of the AM2O8 family of materials (where A = Zr or Hf, M = Mo or W) and HfV2O7 and ZrV2O7, though HfV2O7 and ZrV2O7 only in their high temperature phase starting at 350 to 400 K.[7] A2(MO4)3 also is an example of controllable negative thermal expansion.
[8] Ordinary ice shows NTE in its hexagonal and cubic phases at very low temperatures (below –200 °C).
[9] In its liquid form, pure water also displays negative thermal expansivity below 3.984 °C.
This commercially available material is used in the optics, aerospace, and cryogenics industries in the form of optical spacers that prevent thermal defocus, ultra-stable struts, and washers for thermally-stable bolted joints.
[13][14] Fairly pure silicon (Si) has a negative coefficient of thermal expansion for temperatures between about 18 K and 120 K.[15] Cubic Scandium trifluoride has this property which is explained by the quartic oscillation of the fluoride ions.
[16] ScF3 exhibits this property from 10 to 1100 K above which it shows the normal positive thermal expansion.
[17] Shape memory alloys such as NiTi are a nascent class of materials that exhibit zero and negative thermal expansion.
Negative and positive thermal expansion hereby compensate each other to a certain amount if the temperature is changed.
[8][20] Especially in engineering there is a need for having materials with a CTE close to zero i.e. with constant performance over a large temperature range e.g. for application in precision instruments.
In general, due to its brittleness temperature gradients in glass might cause cracks.
The expansion of the different phases compensate each other so that there is not much change in volume of the glass-ceramic with temperature and crack formation is avoided.
An everyday life example for the need for materials with tailored thermal expansion are dental fillings.