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New type of material that heat can't bloat

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12:01pm, October 28, 2003
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Most substances expand when warmed. That can be bad, especially in devices such as precision telescopes, whose components must maintain their shapes across a wide temperature range. Now, scientists have discovered a metallic compound that nixes thermal expansion by what appears to be an unprecedented mechanism.

Mercouri G. Kanatzidis and his colleagues at Michigan State University in East Lansing created the compound by heating a mixture of equal parts of ytterbium, gallium, and germanium to 850C and then cooling the melt to room temperature.

The resulting silvery metal neither enlarges nor shrinks over the broad range of about –200C to room temperature, the scientists report in the Oct. 16 Nature.

That stability may result from internal electron rearrangements, the researchers propose. With heating, the material's crystal lattice swells normally. However, some thermally excited ytterbium ions expel an electron and therefore shrink just enough to compensate for the lattice expansion.

Because many other elements should be capable of ytterbium's shrinking trick, the new approach could amount to a versatile strategy for making zero-expansion materials, says Kanatzidis.

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