Ab initio piezoelectricity and energy landscape of Y_0.375Al_0.625N

Abstract:

There is high industrial demand for materials with a high piezoelectrical response which are stable at high temperatures. A recent study on ScAlN has explained the microscopic origin of the increased piezoelectric response in the alloy and its effect on the energy landscape. Y is a promising candidate to observe the same phenomena.

The ab initio DFT-GGA calculations for Y_0.375Al_0.625N, using a 128 atom SQS model, show a less pronounced increase of the piezoelectric response. The Y_0.375Al_0.625N energy landscape shows a flattening due to competition between the parent wurtzite phase of AlN and the hexagonal phase of YN. The flattening causes softening of the C₃₃ elastic constant, while the piezoelectric constant e₃₃ is only slightly increased. This slight increase can be explained by the quite stable local tetrahedral environment in Y_0.375Al_0.625N, which is related to the big volume mismatch between the parent YN and AlN. In summary we conclude the importance of the volume matching to obtain high piezoelectric response via phase competition.