Robotics/Components/Actuation Devices/Shape Memory Alloys
Here is a good introduction about what Shape Memory Alloys (SMA) are.
The main use of SMA in robotics is to imitate human muscles. One of the better known SMAs is Nitinol wire. It contracts about 5 to 7% of its length and consumes a lot of power.
One of the most popular nitinol driven robots is Stiquito.