Like an ice cube on a warm day, most materials melt — that is, change from a solid to a liquid state — as they get warmer. But a few oddball materials do the reverse: They melt as they get cooler. Now a team of researchers at MIT has found that silicon, the most widely used material for computer chips and solar cells, can exhibit this strange property of “retrograde melting” when it contains high concentrations of certain metals dissolved in it.
