UC Berkeley

Ab initio methods provide a powerful tool in the search for novel polar materials. In particular, there have been efforts to identify lead-free piezoelectric material systems to re- place PbZr0.52Ti0.48O3. This work first utilizes the Materials Project database of piezoelectric tensors to develop a design rule for disorder-tolerant piezoelectric materials based on the presence of multiple stable optical phonon modes which contribute to the polar response. This criteria is used to produce novel materials with large computationally predicted response. A methodology for exploring alloy systems utilizing a Vegard’s law-like linear interpolation of properties is then developed to capitalize on these identified disorder-tolerant materials. A parent ferroelectric Sr2Nb2O7 compound is chosen as a parent material for which all reasonable isovalent cation substitutions are considered and explored. Based on our approximations, thermodynamic analysis and density-functional theory (DFT) validation of the large scale system, Sr2Nb2−2xV2xO7 arises as a promising polar system. Sr2Nb2−2xV2xO7 is synthesized as single-crystalline thin-film heterostructures using pulsed-laser deposition and an enhanced dielectric response is observed at x = 0.05 and x = 0.1. This alloy and methodology are presented to aid the search for additional lead-free piezoelectric systems to replace PbZr0.52Ti0.48O3 (PZT). Finally we present a software package, Automated X-Ray Diffraction to Structure (AXS), to aid in the materials discovery bottleneck of characterization. The algorithm is based solely on symmetry considerations, and an efficient structure generation algorithm coupled with DFT. AXS is benchmarked against a diverse dataset of structures for which is solves 92% of cases and is also demonstrated to provide ground state structures for showcased experimental systems.