The friction imaging of newlycleaved surface domains of single crystal BaTiO3 energy storage materials under both positive and negative voltage bias is investigated by scanning force microscope. When the bias was applied and reversed, three regions with different brightness and contrast in friction image indicated different response to the biases: the friction image of domain A displayed a great change in brightness while domains B and C displayed only a very small change. Possible mechanisms of the interesting phenomena originating from different static force between different charged tip and the periodical array of surface charges inside the inplane domains were proposed. These results provide a new method for the determination of the polarization direction for the domain parallel to the surface and may be useful in the investigation of ferroelectric energy storage materials, especially the relationship between the polarization direction of domain and the bias.
Ferroelectric barium titanate ceramic (BaTiO3) is a promising advanced material with the outstanding performance in dielectric properties for energy storage applications. With the high permittivity and volumetric efficiency [
It is worth mentioning that the performance of the BaTiO3-based MLCCs was significantly affected by microstructures such as domain orientation, domain walls, and point defects [
Many previous works have reported the applications of friction imaging on characterizing the ferroelectric domain structure, which provided a clear picture for domain structures due to variant friction coefficients of different domains [
In this report we investigate the friction imaging of newly cleaved surface of single crystal BaTiO3 under different voltage biases. It was found that different domains showed different dependence on voltage. Under different voltage biases, the friction imaging of a fraction of domains displayed a great change in brightness while that of the other domains displayed only a very small change. Possible mechanisms of the interesting phenomena originating from different static force between different charged tip and the periodical array of surface charges inside the inplane domains were proposed.
The multidomain single crystal BaTiO3 was prepared by the Institute of Physics, Chinese Academy of Sciences. First, the specimen was broken into two parts, one of which was about 1 millimeter thick. The newly formed cross section with the dimensions of 4 mm × 1 mm was regarded as the newly cleaved surface. The newly cleaved surface was preferred because it was almost not affected by the pollutants and the free charges in air. The relative humidity was controlled to be <40%, and the experiments were carried out in about one hour.
Friction imaging was obtained through a commercial scanning force microscope SPA-300HV (Seiko, Japan). The scanning direction was perpendicular to the long beam of the cantilever Sil-AF01A. The cantilever with a resonant frequency of 12 kHz, a spring constant
The friction imaging was obtained on a same region of the newly cleaved surface under three different experimental conditions: without voltage bias, +12 voltage, and −12 voltage. The imaging region is about 20
Figure
The morphologic image (a) and the friction images on a same region of the newly cleaved surface of single crystal multidomain BaTiO3 under three different experimental conditions: without voltage bias (b), +12 voltage (c), and −12 voltage (d). The specimen stage is grounded.
For single crystal materials, the regions with different brightness in friction image were sometimes considered as ferroelectric domains with different polarization directions [
Correia et al. [
It was well known that BaTiO3 was tetragonal at room temperature, where Ti4+ was at the off-center position of the tetrahedral symmetry [
The alignment of the permanent electrical dipoles in the domain of BaTiO3 with the polarization direction parallel to the surface.
Different charged tip corresponds to different inhomogeneous energetic barrier distribution on the domain parallel to the surface, which is sketched as in Figure
The friction force between the voltage-biased tip and the domain of BaTiO3 with the polarization direction parallel to the surface for the voltage bias is positive (left) and negative (right). It is assumed that the tip is scanned from left to right in the friction imaging. The Coulomb interaction between the charged tip and the inhomogeneous charge distribution of the domain leads to a zigzag energetic barrier distribution, which results in different friction force.
Based on the above discussions and our experimental results, the brightness of the image for the domain A charged a lot: the friction force was much larger for the positive charged tip than that for the negative charged tip. It was thought that region A corresponded to the domain with polarization direction parallel to the surface and is almost the same as the scanning direction of the tip. As to the regions B and C, the contrasts of them were not affected by the biases, and their boundaries well agreed with the morphologic image. So due to the titling of the domains, the polarization directions of domains B and C could not be judged only based on the friction force imaging and morphologic image and further investigations were necessary.
The newly cleaved surface of a single crystal multidomain BaTiO3 was investigated through the friction imaging with atomic force microscope. It was found that the brightness of some regions changed when the tip was differently voltage biased. It was proposed that the inhomogeneous charge distribution in the domain with polarization direction parallel to surface resulted in this change. The experimental results may provide a new method for the determination of the polarization direction for the domain parallel to the surface, which may be useful in the investigation of ferroelectric energy storage materials.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This investigation was supported by National Natural Science Foundation of China (NSFC) (Grant nos. 10974259, 11274391, and 11104357), Science and Technology Planning Project of Guangdong Province, China (Grant no. 2012B060100003), Fundamental Research Funds for the Central Universities (Grant nos. 121gpy36 and 09lgpy29), National Key Technology R&D Program of the Ministry of Science and Technology (2011BAK15B04), and Science and Technology Planning Project of General Administration of Quality Supervision, Inspection and Quarantine of China (2011QK315).