Ceramic Light Response

Certain ceramic materials will change their shape upon exposure to light. What is the physics here?

Answer

Certain ceramic materials will change their shape upon exposure to light because some molecules in the material have changed their shape upon absorption of particular frequencies of light. If the responses of many molecules are coordinated, the overall effect can be a macroscopic shape change. Called the Photostrictive effect, research began in the 1990s, and some practical devices are beginning to be developed, such as direct conversion of light to mechanical displacement for speakers instead of conversion to an electrical signal first. A telephone speaker could be one of the first products.

These ceramics are examples of a new type of “smart” material. The four most widely used classes of smart materials are piezoelectrics, electro strictors, magneto strictors, and shape memory alloys. The resulting changes in the shapes of these materials are large enough to make them useful as actuators. A sensor receives a stimulus and responds with a signal; an actuator produces a useful motion or action. By definition, smart materials are both sensors and actuators, because they perform both functions.

Photostrictive materials such as PLZT a combination of lead, lanthanum, zirconium, and titanium someday may be used to control robots and machines. Engineers at Pennsylvania State University, for example, are exploring applications for devices that move when light shines on them and have created a two-legged stand that walks very slowly when illuminated.