Transition-metal oxides offer an exciting platform for electronics owing to the allure of phenomena they offer, including ferroic functionality, correlated-electron behavior, and coexisting contraindicated properties. Owing to the sensitivity of their properties on (local and crystal) structure and composition, picoscale structure-property relationships are necessary to design function. Here, I briefly provide an overview of our progress in identifying these relationships and finding new phases through quantum-mechanical approaches combined with multiple materials-theory methods. Then, I describe two examples of how external perturbations to picometer scale distortions of bond lengths and angles produce unanticipated phenomena in thin films and bulk oxides of the form An+1BnO3n+1 (n = 1-∞), originally discovered by Ruddlesden and Popper (RP) in the 1950s. First, although large epitaxial strains are believed to induce ferroelectricity, I show that biaxial strain induces an unforeseen polar-to-nonpolar (P-NP) transition in (001) thin films of Ca3Ti2O7 (n = 2) at experimentally accessible biaxial compressive and tensile strains owing to strain-tunable BO6 octahedral rotation modes. Second, I describe how to use local electrostatic interactions among atomic metal-monoxide planes (AO and A'O) to induce differential bond distortions. These changes in local structure produce massive and gap changes of up to ∼2 eV without modifying chemical composition and even drive a metal-insulator transitions in the band insulator LaSrAlO4. I conclude by emphasizing that older complex oxides, which are now understood to exhibit nontrivial lattice mode anharmonicities, offer a plentiful playground for realizing new functionalities with both static and dynamic fields in thin film and bulk form.
An interview with Dr. Rondinelli about his work and this talk is available here.