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Nonstoichiometry, Structure, and Properties of BiFeO3 Films
journal contribution
posted on 2016-07-25, 00:00 authored by Liv R. Dedon, Sahar Saremi, Zuhuang Chen, Anoop R. Damodaran, Brent A. Apgar, Ran Gao, Lane W. MartinWe
explore the effect of growth conditions on the cation and anion
chemistry, electrical leakage, conduction mechanisms, and ferroelectric
and dielectric behavior of BiFeO3. Although it is possible
to produce single-phase, coherently strained films in all cases, small
variations in the pulsed-laser deposition growth process, specifically
the laser repetition rate and target composition, result in films
with chemistries ranging from 10% Bi-deficiency to 4% Bi-excess and
films possessing Bi gradients as large a 6% across the film thickness.
Corresponding variations and gradients in the O chemistry are also
observed. As a result of the varying film chemistry, marked differences
in surface and domain morphology are observed wherein Bi-deficiency
stabilizes atomically smooth surfaces and ordered stripe domains.
Subsequent investigation of the current–voltage response reveals
large differences in leakage current density arising from changes
in both the overall stoichiometry and gradients. In turn, the film
stoichiometry drives variations in the dominant conduction mechanism
including examples of Schottky, Poole–Frenkel, and modified
Poole–Frenkel emission depending on the film chemistry. Finally,
slightly Bi-excess films are found to exhibit the best low-frequency
ferroelectric and dielectric response while increasing Bi-deficiency
worsens the low-frequency ferroelectric performance and reduces the
dielectric permittivity.