Zhong Fang’s research while affiliated with Chinese Academy of Sciences and other places

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Publications (4)


The schematic diagrams of DW chirality and step structures. (a) A schematic diagram of the Ising, Néel, and Bloch type polarization components for a 180° DW model, where the yellow surface represents a typical 180° DW. (b) A neutral step model with polarization parallel to the step plane and no charge accumulation. (c) A tail-to-tail charged step model with negative bound charges. (d) A head-to-head charged step model with positive bound charges.
Atomic models of four types of steps. (a) and (b) are neutral step models with polarization parallel to the step planes of PbO and TiO2, respectively. (c) and (d) are charged step models with step planes of PbO and TiO2, respectively. The polarization directions of the domains are marked by the black orientation symbols, and the black and blue solid lines represent the DWs and step planes, respectively. The pink boxes represent periodic supercells. To reveal the step models more clearly, three periods are shown in the direction parallel to the domain walls.
Various polarization component distributions of a neutral step. (a) The three-dimensional polarization vector distribution of the model. (b) and (c) correspond to the distributions of Ising and Bloch components, respectively. (d) shows the step planes fitted by Ising and Bloch components. To reveal the schematic step planes more clearly, a 1.5 period is shown in the direction perpendicular to the domain walls.
Different polarization component distributions of a charged step. (a) A three-dimensional polarization vector distribution. (b)–(d) correspond to the Ising, Bloch, and Néel component distributions, respectively. (e) A projection of the polarization vectors onto the (0 1 0) plane.
(a) and (b) are the schematic diagrams of the motion process of the neutral and charged steps obtained by the NEB methods, respectively. The black solid lines represent the PbO DWs and blue solid lines represent the approximate crystallographic planes of the reassigned steps. The marks of ① and ② are the initial and final states, respectively. The pink dashed lines represent the saddle points. The red arrows indicate the motion directions of the steps. (c) represents the energy profiles along the migration path corresponding to charged and neutral steps, respectively.

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Huge mobility difference between the neutral and charged steps on 180° domain walls of PbTiO3 by first-principles calculations
  • Article
  • Full-text available

January 2024

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48 Reads

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1 Citation

Zhong Fang

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Yu-Jia Wang

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Xiu-Liang Ma

The microscopic mechanism of ferroelectric switching is the motion of domain walls, which is actually accomplished by the movement of tiny steps on the domain walls. Using first-principles calculations, the detailed polarization structures and the motion barriers of neutral and charged steps on 180° domain walls of prototypical ferroelectrics PbTiO3 are elaborately revealed in this study. While the Bloch components get weakened near all neutral steps, they become weakened/strengthened near the head-to-head/tail-to-tail charged steps. The neutral step possesses a lower formation energy but a higher migration barrier, indicating that the charged step could move faster. Based on these results, the possible motion picture of steps on one 180° domain wall of tetragonal ferroelectrics is proposed, which provides a better understanding of the mechanism of domain wall motion and may shed light on the future development of domain wall–based functional devices.

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Creating charged domain walls in PbTi O 3 / LaCo O 2.5 superlattices by oxygen vacancy engineering

January 2024

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84 Reads

Charged domain walls in ferroelectric materials exhibit nontrivial electronic and transport properties, which have promising application in many electronic devices, such as high-density nonvolatile memories. Taking advantage of oxygen vacancy engineering, charged domain walls are introduced into the PbTiO3/LaCoO2.5 superlattice system, and the quasi-two-dimensional electron gas is formed near the domain walls, featuring an intrinsic n-type conductive characteristic. The charged domain walls can be erased by eliminating oxygen vacancies in the LaCoO2.5, resulting in an insulating state. The proposed scheme of writing and erasing of charged domain walls may facilitate the development of domain wall based devices.


Anisotropic strain-modulated monoclinic phases with giant piezoelectricity in high-index-oriented PbTiO3 films

August 2023

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218 Reads

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1 Citation

By combining phase-field simulations and first-principles calculations, we proposed to modulate the monoclinic phases of high-index-oriented PbTiO3 films through epitaxial anisotropic strain to obtain superior piezoelectric performance. It was found that the piezoelectric coefficients e22 were remarkably enhanced (up to 2400%) in both (111)- and (110)-oriented PbTiO3 films. The excellent piezoelectric property is mainly attributed to the polarization rotation due to the flatter energy landscapes in the monoclinic phases, while the variation of polarization magnitude contributes little to piezoelectricity. Our research suggests modulating material properties through anisotropic strain, which might bring some insight to other functional materials.