  Relaxor ferrolectrics are important in technological applications due to a
strong electromechanical response, energy storage capacity, electrocaloric
effect, and pyroelectric energy conversion properties. Current efforts to
discover and design new materials in this class generally rely on
substitutional doping of known ferroelectrics, as slight changes to local
compositional order can significantly affect the Curie temperature,
morphotropic phase boundary, and electromechanical responses. In this work, we
demonstrate that moving to the strong limit of compositional complexity in an
ABO3 perovskite allows stabilization of novel relaxor responses that do not
rely on a single narrow phase transition region. Entropy-assisted synthesis
approaches are used to create single crystal Ba(Ti0.2Sn0.2Zr0.2Hf0.2Nb0.2)O3
[Ba(5B)O] films. The high levels of configurational disorder present in this
system is found to influence dielectric relaxation, phase transitions,
nano-polar domain formation, and Curie temperature. Temperature-dependent
dielectric, Raman spectroscopy and second-harmonic generation measurements
reveal multiple phase transitions, a high Curie temperature of 570 K, and the
relaxor ferroelectric nature of Ba(5B)O films. The first principles theory
calculations are used to predict possible combinations of cations to quantify
the relative feasibility of formation of highly disordered single-phase
perovskite systems. The ability to stabilize single-phase perovskites with such
a large number of different cations on the B-sites offers new possibilities for
designing high-performance materials for piezoelectric, pyroelectric and
tunable dielectric applications.
