The effects of growth conditions on the chemistry, structure, electrical leakage, dielectric response, and ferroelectric behavior of Ba1−xTiOy thin films are explored. Although single-phase, coherently-strained films are produced in all cases, small variations in the laser fluence during pulsed-laser deposition growth result in films with chemistries ranging from BaTiO3 to Ba0.93TiO2.87. As the laser fluence increases, the films become more barium deficient and the out-of-plane lattice parameter expands (as much as 5.4% beyond the expected value for Ba0.93TiO2.87 films). Stoichiometric BaTiO3 films are found to be three orders of magnitude more conducting than Ba0.93TiO2.87 films and the barium-deficient films exhibit smaller low-field permittivity, lower loss tangents, and higher dielectric maximum temperatures. Although large polarization is observed in all cases, large built-in potentials (shifted loops) and hysteresis-loop pinching are present in barium-deficient films-suggesting the presence of defect dipoles. The effects of these defect dipoles on ferroelectric hysteresis are studied using first-order reversal curves. Temperature-dependent current-voltage and deep-level transient spectroscopy studies reveal at least two defect states, which grow in concentration with increasing deficiency of both barium and oxygen, at ∼0.4 eV and ∼1.2 eV above the valence band edge, which are attributed to defect-dipole complexes and defect states, respectively. The defect states can also be removed via ex post facto processing. Such work to understand and control defects in this important material could provide a pathway to enable better control over its properties and highlight new avenues to manipulate functions in these complex materials.
Bibliographical noteFunding Information:
A. D. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and the Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 (Materials Project program KC23MP) for the study of ferroic complex oxides. S. S. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award Number DE-SC-0012375 for the development of the ferroelectric thin films. R. X. acknowledges support from the National Science Foundation under Grant DMR-1708615. L. R. D. acknowledges support from the National Science Foundation under Grant OISE-1545907. S. P. acknowledges support from the Army Research Office under Grant W911NF-14-1-0104. A. R. D. acknowledges support from the Gordon and Betty Moore Foundation’s EPiQS Initiative, under Grant GBMF5307. L. W. M. acknowledges support from the National Science Foundation under Grant DMR-1608938.