The origin of the anomalous, 400% increase of the piezoelectric coefficient in Sc$_x$Al$_{ 1-x}$N alloys is revealed. Quantum mechanical calculations show that the effect is intrinsic. It comes from a strong change in the response of the internal atomic coordinates to strain and pronounced softening of C$_{ 33}$ elastic constant. The underlying mechanism is the flattening of the energy landscape due to a competition between the parent wurtzite and the so far experimentally unknown hexagonal phases of the alloy. Our observation provides a route for the design of materials with high piezoelectric response.
Categories: cond-mat.mtrl-sci cond-mat.dis-nn