Intermediate multidomain state in single-crystalline Mn-doped BiFeO3 thin films during ferroelectric polarization switching

Abstract

A intermediate multidomain state and large crystallographic tilting of 1.78° for the (hh0)_pc planes of a (001)_pc-oriented single-domain Mn-doped BiFeO₃ (BFMO) thin film were found when an electric field was applied along the [110]_pc direction. The anomalous crystallographic tilting was caused by ferroelastic domain switching of the 109° domain switching. In addition, ferroelastic domain switching occurred via an intermediate multidomain state. To investigate these switching dynamics under an electric field, we used in situ fluorescent X-ray induced Kossel line pattern measurements with synchrotron radiation. In addition, in situ inverse X-ray fluorescence holography (XFH) experiments revealed that atomic displacement occurred under an applied electric field. We attributed the atomic displacement to crystallographic tilting induced by a converse piezoelectric effect. Our findings provide important insights for the design of piezoelectric and ferroelectric materials and devices.

Figure 1

In situ Kossel line pattern measurements under electric field. (a) Schematic of sample structure and measurement setup. (b) Fe Kα Kossel line pattern under − 20 kV/cm applied electric field after poling by application of − 200 kV/cm electric field. (c) Calculated Kossel pattern by Fe Kα radiation. (d) Schematic of Kossel pattern detection by 2D detector. (e) Orthogonal projection along [001]_pc direction of Fe Kα Kossel line pattern under − 20 kV/cm applied electric field, projected onto Ewald sphere in k-space.

Figure 2

Fe Kα Kossel line patterns under electric field of 0–200 kV/cm. (a–d) Orthographic projection of Fe Kα Kossel line pattern projected onto Ewald sphere in k-space. (e–h) Magnified images of regions indicated by blue-dashed lines in (a–d), respectively. (i–l) Cross-sectional profiles along blue arrows in (e–h), respectively, under (a, e, i) 0 kV/cm, (b, f, j) 50 kV/cm, (c, g, k) 80 kV/cm, and (d, h, l) 200 kV/cm fields. Under 50 and 80 kV/cm fields, the BFMO thin film shows an intermediate multidomain state because of anomalous domain switching.

Figure 3

Fe Kα Kossel line patterns under electric field of 0–200 kV/cm. (a–d) Orthographic projection of Fe Kα Kossel line pattern projected onto Ewald sphere in k-space. (e–h) magnified images of regions indicated by blue-dashed lines in (a–d), respectively. (i–l) Cross-sectional profiles along blue arrows in (e–h), respectively, under (a, e, i) 0 kV/cm, (b, f, j) − 50 kV/cm, (c, g, k) − 100 kV/cm, and (d, h, l) − 200 kV/cm electric fields. Under a − 100 kV/cm field, the BFMO thin film shows an intermediate multidomain state because of anomalous domain switching.

Figure 4

Atomic structure measurements under 0 and 44 kV/cm by in situ inverse XFH. (a) Schematic of sample structure and measurement setup for inverse XFH. (b) Orthographic projection of Fe Kα hologram pattern acquired under 0 kV/cm, projected onto Ewald sphere in k-space after symmetric operations belonging to point group 3 m, (c, d) Two-dimensional atomic images at z = 2 Å plane. (e, f) x–y and (g, h) x–z cross-sectional images around Bi atoms indicated by red circles in (c, d), respectively, under (c, e, g) 0 kV/cm and (d, f, h) 44 kV/cm. The red dots in (e–h) are weight centers of Bi atoms, showing displacement under electric field. For the {x, y, z} coordinate system, the x–y and x–z planes are defined as the [h00]_pc–[0k0]_pc and [h00]_pc–[00 l]_pc planes, respectively, and the origin of (x, y, z) = (0, 0, 0) is set at the position of the Fe atom.

Figure 5

Schematics of ferroelastic 109° domain switching via intermediate multidomain state. (a) schematic of pure 109° domain, (b) Single-domain BFMO thin film and (c) intermediate multidomain structure under electric field. In the 109° domain, the angle between (hh0)_pc planes in the r₁ and r₃ domain is 0.40°. However, in an epitaxially strained single-domain BFMO film, the epitaxially strained layer cannot easily undergo ferroelastic domain switching, resulting in intermediate multidomain state.