The effects of grain size on electrical properties and domain structure of BiFeO3 thin films by sol–gel method

Abstract

BiFeO 3 (short for BFO) thin films with different grain sizes were fabricated via sol-gel spin-coating method. The effects of grain size on leakage behavior, dielectric, ferroelectric, piezoelectric properties and domain structure of BFO thin films have been investigated systematically. The X-ray diffraction results show that BFO thin films are rhombohedral distortion perovskite structure. Compared with the films annealed at 550°C, the grain size of BFO thin films annealed at 600°C is larger and the roughness is less, and the crystallinity and purity are higher. The leakage current density of BFO thin films with larger grain size is much lower than that of the films with smaller grain size. It is found that the conduction behavior of BFO thin films with smaller grain size transforms from Ohmic to space-charge-limited current and Fowler-Nordheim tunneling conduction as electric field increases. But there is the only transition from Ohmic conduction to space-charge-limited conduction for the thin films with larger grain size as electric field increase. The room temperature dielectric constant and remnant polarization of BFO thin films with larger grain size are higher than that of the films with smaller grain size. The ferroelectric domain size increases with the increase of grain size so that the ferroelectric polarization in BFO thin films with larger grain size enhances. Moreover, it is found that there are negatively charged ''tail to tail'' domain wall in BFO thin films with smaller grain size and positively charged ''head to head'' domain wall in the sample with larger grain size. The majority carriers including positively charged hole or oxygen vacancy assemble on negatively charged ''tail to tail'' domain wall in p-type BFO thin films with smaller grain size and result in relative higher leakage current. The piezoelectric coefficient of the films with larger grain size is much higher than that of the sample with smaller grain size.

Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa0.5Sr0.5CoO3-(1−x)BiFeO3

“…One of them is the diminution of piezoelectric effect when the grain size is reduced. It has been observed by Lei et al 43 in the nanostructured and polycrystalline BFO films. The piezoelectric coefficient is reduced ten times when the grain size is reduced from 150 to 85 nm.…”

(001)‐oriented BiFeO3 films integrated on Si with enhanced electrical performances

“…Because when the measuring frequency increases from 1 to 2 and 5 kHz, the space‐charge polarization with longer polarization time cannot keep up with the change in applied alternating electric field. This reduces the total polarization switching achieved at the same maximum applied field 19,48 . However, the reduced extent of 2 P r of the thick sample with the increase in frequency is less than that of thin sample, which further indicates that the concentration of oxygen vacancies in thick BFO films is lower than that in thin ones.…”

“…It may be mainly attributed to the effect of grain size (the inset in Figure 1 shows that the grain size of our BFO films is increased with the film thickness). It is well known that the dielectric constant of the grain is higher than that of the grain boundary (GB) in ferroelectric films, 19 so that the dielectric constant of the BFO films with larger grain size (the less GB) is higher. It is worth noting that, in the frequency region that we tested, the loss tangent value of all our BFO films is less than 0.06 (tan δ < 0.05), which is much lower than those reported sputtered BFO films, especially in the high‐frequency region 10 .…”

“…At present, many attempts have been made to improve the electrical properties (especially ferroelectric performance) of BFO films. For example, the improvement in the fabrication technology/method, 9,10 tailoring of film thickness, 11–15 fine control of microstructures (crystallographic orientation, domain, phase, and defects), 16–19 and optimization of substrate and/or buffer layer 9,20–23 . Among these attempts, many of them improve the electrical properties by using perovskite single‐crystal substrate (such as SrTiO 3 , LaAlO 3 , and YAlO 3 ) to grow high‐quality BFO films, 15,16,20 which is mainly due to the good lattice matching between these substrates and BFO.…”

Effect of sintering temperature on magnetoelectric properties of PbTiO3/NiFe2O4 composite ceramics

“…The change of leakage current may be related to the conduction mechanism at different sintering temperatures [39]. There are two conductive mechanisms in dielectric materials, one is electrode-limited and the other is bulk-limited.…”