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How Negative Thermal Expansion Works
Bill Kendrick writes "Scientists at the University of California, Santa Cruz, are discovering why compounds like zirconium tungstate 'are acting like they are from Bizarro world': contracting, rather than expanding, when heated.
They believe it's a combination of geometrical frustration (which sounds a lot like what it is), and a 'twisting' motion of the atoms."
RTFL. They said the theoretical right mix of expanding and contracting elements which would produce zero change is what the ultimatly are wanting to develop. This is the first material that contracts over large temperature ranges, so it may be perfect for such a mix. Obviously they are still working on it.
Bronze expands as it cools, and in a mold it will therefore fill all the little details. This is why you have statues made of bronze.
Plaster of Paris expands slightly as it sets, and then contracts again. This is also why people use plaster to cast things.
Fascism trolls keeping me up every night. When I starts a preachin', he HITS ME WITH HIS REICH!
Clockmakers have used such a material for a long time; it's a complex alloy called invar. The linked article gives the composition of one type of invar, which has an expansion coefficient of 1.6 ppm. This means that a bar of invar ten kilometres long that heats up by one kelvin will get longer by 1.6cm. That's pretty good. The equivalent steel bar would expand by 11cm.
And yeah, the above figures were very nearly copied verbatim from the article; read it if you're interested.