Which materials/compounds expand in response to cold temperatures?

Which materials or compounds expand in response to cold temperatures?
This material or compound should expand at a slow (but constant rate), from about 0–20 months when in the following temperature range −25 °C to −10 °C. 


Also, the compound should not react with plastic or be toxic to humans or the environment.


Please explain *why* the compound does this as well.




In old time printing using type, the alloy used for the type was designed to have a zero coefficient of thermal expansion over a wide range so that they type did not change shape when cast at a high temperature and then cooled off.


It is very likely that slight modifications of that formula would yield an alloy with either a positive or negative thermal coefficient.


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Perhaps one of the most studied materials to exhibit [negative thermal expansion](http://en.wikipedia.org/wiki/Negative_thermal_expansion) is cubic zirconium tungstate $(\ce{ZrW2O8}).$ 


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It's already been mentioned that certain liquid-solid phase transitions are accompanied by [negative thermal expansion](https://en.wikipedia.org/wiki/Negative_thermal_expansion) (NTE). This also includes elements ($\ce{Si, Ga, Ge, Sb, Bi, Pu}$), alloys (Wood's metal) and numerous materials (zeolites, quartz, tugstates etc.) that obey [virial expansion](https://en.wikipedia.org/wiki/Virial_expansion) due to the way atoms are packed in a crystal lattice:


$$\frac{p}{RT} = \frac{1}{V\_m} + \frac{B\_{2V}(T)}{V\_m^2} + \frac{B\_{3V}(T)}{V\_m^3} + \ldots$$


where $p$ - pressure, $R$ - gas constant, $T$ - temperature, $B\_{iV}(T)$ - $i$-virial coefficient, $V\_m$ - molar volume.




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There is also another physicochemical phenomenon called [Gough–Joule effect](https://en.wikipedia.org/wiki/Gough%E2%80%93Joule_effect). If mechanical stress is applied to the elastomer or rubber string which is subsequently heated, the polymer contracts as a result of the intensive growth of the role of the entropy factor (the maximum entropy in polymers occurs in the coil-like ordering of the molecules). This effect is also utilized in the rubber-band heat engine (Feynman wheel).


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