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Nonstoichiometry, Structure, and Properties in Ba1-xTiOy Thin Films

Abstract

The effect of growth conditions on the chemistry, structure, electrical leakage, dielectric response, and ferroelectric behavior of Ba1-xTiOy thin films is 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 effect of these defects 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 defects states, which grow in concentration with increasing barium and oxygen deficiency, at ~0.4 eV and ~1.2 eV above the valence band edge which are attributed to VBa''-VO.. defect-dipole complexes and VBa'' 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 function in these complex materials.

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Publication details

The article was received on 04 Jun 2018, accepted on 07 Sep 2018 and first published on 10 Sep 2018


Article type: Paper
DOI: 10.1039/C8TC02725K
Citation: J. Mater. Chem. C, 2018, Accepted Manuscript
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    Nonstoichiometry, Structure, and Properties in Ba1-xTiOy Thin Films

    A. Dasgupta, S. Saremi, X. Ruijuan, L. R. Dedon, S. Pandya, A. R. Damodaran and L. Martin, J. Mater. Chem. C, 2018, Accepted Manuscript , DOI: 10.1039/C8TC02725K

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