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Take, for example, a wire made from a combination of nickel and titanium—two elements that form a shape memory alloy. By wrapping the wire around a finger and subsequently applying heat, it can be seen that the wire straightens out when heated, returning to its "remembered" shape.
This intriguing transition reveals that while the wire is cold, its atoms are arranged diagonally, forming a monoclinic structure known as martensite. Upon heating, the atoms reconfigure into a cubic arrangement, termed austenite, which allows the wire to assume a straight form.