Ying Liu
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Scopus Publications
Qian Zhang, Ranming Niu, Ying Liu, Jiaxi Jiang, Fan Xu, Xuan Zhang, Julie M. Cairney, Xianghai An, Xiaozhou Liao, Huajian Gao,et al.
Springer Science and Business Media LLC
AbstractNanoscale small-volume metallic materials typically exhibit high strengths but often suffer from a lack of tensile ductility due to undesirable premature failure. Here, we report unusual room-temperature uniform elongation up to ~110% at a high flow stress of 0.6–1.0 GPa in single-crystalline <110>-oriented CoCrFeNi high-entropy alloy nanopillars with well-defined geometries. By combining high-resolution microscopy and large-scale atomistic simulations, we reveal that this ultrahigh uniform tensile ductility is attributed to spatial and synergistic coordination of deformation twinning and dislocation slip, which effectively promote deformation delocalization and delay necking failure. These joint and/or sequential activations of the underlying displacive deformation mechanisms originate from chemical compositional heterogeneities at the atomic level and resulting wide variations in generalized stacking fault energy and associated dislocation activities. Our work provides mechanistic insights into superplastic deformations of multiple-principal element alloys at the nanoscale and opens routes for designing nanodevices with high mechanical reliability.
Yongtao Liu, Anna N. Morozovska, Ayana Ghosh, Kyle P. Kelley, Eugene A. Eliseev, Jinyuan Yao, Ying Liu, and Sergei Kalinin
American Chemical Society (ACS)
Nanoscale ferroelectric 2D materials offer the opportunity to investigate curvature and strain effects on materials functionalities. Among these, CuInP2S6 (CIPS) has attracted tremendous research interest in recent years due to combination of room temperature ferroelectricity, scalability to a few layers thickness, and ferrielectric properties due to coexistence of 2 polar sublattices. Here, we explore the local curvature and strain effect on polarization in CIPS via piezoresponse force microscopy and spectroscopy. To explain the observed behaviors and decouple the curvature and strain effects in 2D CIPS, we introduce the finite element Landau-Ginzburg-Devonshire model, revealing strong changes in hysteresis characteristics in regions subjected to tensile and compressive strain. The piezoresponse force microscopy (PFM) results show that bending induces ferrielectric domains in CIPS, and the polarization-voltage hysteresis loops differ in bending and nonbending regions. These studies offer insights into the fabrication of curvature-engineered nanoelectronic devices.
Ying Liu, Ranming Niu, Andrzej Majchrowski, Krystian Roleder, Kumara Cordero-Edwards, Julie M. Cairney, Jordi Arbiol, and Gustau Catalan
American Physical Society (APS)
Ying Liu, Xiangyuan Cui, Ranming Niu, Shujun Zhang, Xiaozhou Liao, Scott D. Moss, Peter Finkel, Magnus Garbrecht, Simon P. Ringer, and Julie M. Cairney
Springer Science and Business Media LLC
AbstractPlastic deformation in ceramic materials is normally only observed in nanometre-sized samples. However, we have observed high levels of plasticity (>50% plastic strain) and excellent elasticity (6% elastic strain) in perovskite oxide Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3, under compression along <100>pc pillars up to 2.1 μm in diameter. The extent of this deformation is much higher than has previously been reported for ceramic materials, and the sample size at which plasticity is observed is almost an order of magnitude larger. Bending tests also revealed over 8% flexural strain. Plastic deformation occurred by slip along {110} <1$$\\bar{1}$$ 1 ¯ 0 > . Calculations indicate that the resulting strain gradients will give rise to giant flexoelectric polarization. First principles models predict that a high concentration of oxygen vacancies weaken the covalent/ionic bonds, giving rise to the unexpected plasticity. Mechanical testing on oxygen vacancies-rich Mn-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 confirmed this prediction. These findings will facilitate the design of plastic ceramic materials and the development of flexoelectric-based nano-electromechanical systems.
Ying Liu, Ran-Ming Niu, Scott D. Moss, Peter Finkel, Xiao-Zhou Liao, and Julie M. Cairney
AIP Publishing
The core structures of dislocations are crucial for understanding the plastic deformation mechanisms and the functional properties of materials. Here, we use the scanning transmission electron microscopy imaging techniques of high-resolution high angle annular dark field and integrated differential phase contrast to investigate the atomic structure of a pair of climb-dissociated 1 2 a [ 01 1 ¯ ] dislocations in a bending-deformed relaxor ferroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb1/3)O3–PbTiO3 single crystal. Cations at one dislocation core are found to arrange in the same way as the climb-dissociated 1 2 a [ 01 1 ¯ ] dislocation core in SrTiO3, while the other one is different. Oxygen depletion was observed at both dislocation cores. Geometric phase analysis of the lattice rotation shows opposite signs at both sides of the dislocations, demonstrating the strain gradient, which is known to give rise to flexoelectric polarization. Using the peak finding method, the polarization (a combination of ferroelectric and flexoelectric) around dislocations was mapped at the unit-cell scale. The polarization direction obtained is consistent with that predicted based on the flexoelectric effect in a perovskite oxide with [011] geometry. Head-to-head positively charged and tail-to-tail negatively charged domain walls were revealed based on the polarization map, suggesting a new way to stabilize charged domain walls via dislocations. A distinct dislocation core configuration has been observed, and a unit-cell scale polarization map helps understand the flexoelectric effects (coupling between strain gradient and polarization) around dislocations in a relaxor ferroelectric.
Fan Ji, Pankaj Sharma, Tongzheng Xin, Dawei Zhang, Ying Liu, Ranming Niu, Julie M. Cairney, and Jan Seidel
Wiley
2D electron gas at LaAlO3/SrTiO3 (LAO/STO) interfaces has emerged as an attractive platform for novel nanoelectronic devices. Control over the active functional interface by electrical or mechanical means in this regard is of special interest. A new means of electric‐field control by lateral gating of the interface and modification of its electronic properties in cross‐sectional samples that allows direct access to depth‐resolved physical‐property measurements is investigated. Local scanning probe measurements in conjunction with electrical characterization allow it to be established that field‐driven reversible migration of oxygen vacancies is the origin of enhancement and suppression of electronic conductivity in LAO/STO. These results point to new possibilities of device property control in complex oxide heterostructures and thin films that contain highly conductive engineered interfaces.
Blake Regan, Alireza Aghajamali, Johannes Froech, Toan Trong Tran, John Scott, James Bishop, Irene Suarez‐Martinez, Ying Liu, Julie M. Cairney, Nigel A Marks,et al.
Wiley
Diamond is known to possess a range of extraordinary properties that include exceptional mechanical stability. In this work, it is demonstrated that nanoscale diamond pillars can undergo not only elastic deformation (and brittle fracture), but also a new form of plastic deformation that depends critically on the nanopillar dimensions and crystallographic orientation of the diamond. The plastic deformation can be explained by the emergence of an ordered allotrope of carbon that is termed O8‐carbon. The new phase is predicted by simulations of the deformation dynamics, which show how the sp3 bonds of (001)‐oriented diamond restructure into O8‐carbon in localized regions of deforming diamond nanopillars. The results demonstrate unprecedented mechanical behavior of diamond, and provide important insights into deformation dynamics of nanostructured materials.
Ning Mo, I. McCarroll, Qiyang Tan, A. Ceguerra, Y. Liu, J. Cairney, H. Dieringa, Yuanding Huang, B. Jiang, F. Pan,et al.
Ying Liu, Junhai Xia, Peter Finkel, Scott D. Moss, Xiaozhou Liao, and Julie M. Cairney
Elsevier BV
Yunlong Tang, Yinlian Zhu, Xiuliang Ma, Zijian Hong, Yujia Wang, Wenyuan Wang, Yaobin Xu, Ying Liu, Bo Wu, Lang Chen,et al.
Wiley
[111]‐Oriented perovskite oxide films exhibit unique interfacial and symmetry breaking effects, which are promising for novel quantum materials as topological insulators and polar metals. However, due to strong polar mismatch and complex structural reconstructions on (111) surfaces/interfaces, it is still challenging to grow high quality [111] perovskite heterostructures, let alone explore the as‐resultant physical properties. Here, the fabrication of ultrathin PbTiO3 films grown on a SrTiO3(111) substrate with atomically defined surfaces, by pulsed laser deposition, is reported. High‐resolution scanning transmission electron microscopy and X‐ray diffraction reveal that the as‐grown [111]PbTiO3 films are coherent with the substrate and compressively strained along all in‐plane directions. In contrast, the out‐of‐plane lattices are almost unchanged compared with that of bulk PbTiO3, resulting in a 4% contraction in unit cell volume and a nearly zero Poisson's ratio. Ferroelectric displacement mapping reveals a monoclinic distortion within the compressed [111]PbTiO3, with a polarization larger than 50 µC cm−2. The present findings, as further corroborated by phase field simulations and first principle calculations, differ significantly from the common [001]‐oriented films. Fabricating oxide films through [111] epitaxy may facilitate the formation of new phase components and exploration of novel physical properties for future electronic nanodevices.
S. Li, Y.J. Wang, Y.L. Zhu, Y.L. Tang, Y. Liu, J.Y. Ma, M.J. Han, Bo Wu, and X.L. Ma
Elsevier BV
M.J. Han, Y.J. Wang, D.S. Ma, Y.L. Zhu, Y.L. Tang, Y. Liu, N.B. Zhang, J.Y. Ma, and X.L. Ma
Elsevier BV
Ying Liu, Yu-Jia Wang, Yin-Lian Zhu, Chi-Hou Lei, Yun-Long Tang, Shuang Li, Si-Rui Zhang, Jiangyu Li, and Xiu-Liang Ma
American Chemical Society (ACS)
Ferroelectric flux-closures are very promising in high-density storage and other nanoscale electronic devices. To make the data bits addressable, the nanoscale flux-closures are required to be periodic via a controlled growth. Although flux-closure quadrant arrays with 180° domain walls perpendicular to the interfaces (V-closure) have been observed in strained ferroelectric PbTiO3 films, the flux-closure quadrants therein are rather asymmetric. In this work, we report not only a periodic array of the symmetric flux-closure quadrants with 180° domain walls parallel to the interfaces (H-closure) but also a large scale alternative stacking of the V- and H-closure arrays in PbTiO3/SrTiO3 multilayers. On the basis of a combination of aberration-corrected scanning transmission electron microscopic imaging and phase field modeling, we establish the phase diagram in the layer-by-layer two-dimensional arrays versus the thickness ratio of adjacent PbTiO3 films, in which energy competitions play dominant roles. The manipulation of these flux-closures may stimulate the design and development of novel nanoscale ferroelectric devices with exotic properties.
Sirui Zhang, Yinlian Zhu, Yunlong Tang, Ying Liu, Shuang Li, Mengjiao Han, Jinyuan Ma, Bo Wu, Zuhuang Chen, Sahar Saremi,et al.
Wiley
Ferroelectricity is generally deteriorated or even vanishes when the ferroelectric films are downsized to unit cell scale. To maintain and enhance the polarization in nanoscale ferroelectrics are of scientific and technological importance. Here, giant polarization sustainability is reported in a series of ultrathin PbTiO3 films scaled down to three unit cells grown on NdGaO3(110) substrates with La0.7Sr0.3MnO3 as bottom electrodes. Atomic mappings via aberration‐corrected scanning transmission electron microscopy demonstrate the robust ferroelectricity for the sub‐10 nm thick film. For the 1.2 nm thick film, the polarization reaches ≈50 µC cm−2. The 2 nm thick film possesses a polarization as high as the bulk value. The films ranging from 10 to 35 nm display a giant elongation of out‐of‐plane lattice parameter, which corresponds to a polarization of 100 µC cm−2, 20% larger than that of the bulk PbTiO3. The giant enhancement of polarization in the present films is proposed to result from the charge transfer at the La0.7Sr0.3MnO3/PbTiO3 interface, as supported by the anomalous decrease of Mn valence measured from X‐ray photoelectron spectroscopy. These results reveal the significant role of charge transfer at interfaces in improving large polarizations in ultrathin ferroelectrics and are meaningful for the development of future electronic devices.
Ying Liu, Yin-Lian Zhu, Yun-Long Tang, Yu-Jia Wang, Shuang Li, Si-Rui Zhang, Meng-Jiao Han, Jin-Yuan Ma, Jagadeesh Suriyaprakash, and Xiu-Liang Ma
American Chemical Society (ACS)
Functional oxide interfaces have received a great deal of attention owing to their intriguing physical properties induced by the interplay of lattice, orbital, charge, and spin degrees of freedom. Atomic-scale precision growth of the oxide interface opens new corridors to manipulate the correlated features in nanoelectronics devices. Here, we demonstrate that both head-to-head positively charged and tail-to-tail negatively charged BiFeO3/PbTiO3 (BFO/PTO) heterointerfaces were successfully fabricated by designing the BFO/PTO film system deliberately. Aberration-corrected scanning transmission electron microscopic mapping reveals a head-to-head polarization configuration present at the BFO/PTO interface, when the film was deposited directly on a SrTiO3 (001) substrate. The interfacial atomic structure is reconstructed, and the interfacial width is determined to be 5-6 unit cells. The polarization on both sides of the interface is remarkably enhanced. Atomic-scale structural and chemical element analyses exhibit that the reconstructed interface is rich in oxygen, which effectively compensates for the positive bound charges at the head-to-head polarized BFO/PTO interface. In contrast to the head-to-head polarization configuration, the tail-to-tail BFO/PTO interface exhibits a perfect coherency, when SrRuO3 was introduced as a buffer layer on the substrates prior to the film growth. The width of this tail-to-tail interface is estimated to be 3-4 unit cells, and oxygen vacancies are supposed to screen the negative polarization bound charge. The formation mechanism of these distinct interfaces was discussed from the perspective of charge redistribution.
S. Li, Y. L. Zhu, Y. J. Wang, Y. L. Tang, Y. Liu, S. R. Zhang, J. Y. Ma, and X. L. Ma
AIP Publishing
Flux-closure domain structures in ferroelectric thin films are considered to have potential applications in electronic devices. It is usually believed that these structures are stabilized by the depolarization field and the contact with electrodes tends to screen the depolarization field and may limit their formation. In this work, the influence of oxide electrodes (SrRuO3 and La0.7Sr0.3MnO3) on the formation of flux-closure domains in PbTiO3 thin films deposited on (110)-oriented GdScO3 substrates by pulsed laser deposition was investigated by Cs-corrected transmission electron microscopy. It is found that periodic flux-closure domain arrays can be stabilized in PbTiO3 films when the top and bottom electrodes are symmetric, while a/c domains appear when asymmetric electrodes are applied. The influence of asymmetric electrodes on the domain configuration is proposed to have a connection with their different work functions and conductivity types. These results are expected to shed light on understanding th...
Y. L. Tang, Y. L. Zhu, Y. Liu, Y. J. Wang, and X. L. Ma
Springer Science and Business Media LLC
Yuehan Liu, Yinlian Zhu, Yunlong Tang, Yujia Wang, Yixiao Jiang, Yaobin Xu, Bin Zhang and Xiuliang Ma
Ferroelectrics hold promise for sensors, transducers, and telecommunications. With the demand of electronic devices scaling down, they take the form of nanoscale films. However, the polarizations in ultrathin ferroelectric films are usually reduced dramatically due to the depolarization field caused by incomplete charge screening at interfaces, hampering the integrations of ferroelectrics into electric devices. Here, we design and fabricate a ferroelectric/multiferroic PbTiO3/BiFeO3 system, which exhibits discontinuities in both chemical valence and ferroelectric polarization across the interface. Aberration-corrected scanning transmission electron microscopic study reveals an 8% elongation of out-of-plane lattice spacing associated with 104%, 107%, and 39% increments of δTi, δO1, and δO2 in the PbTiO3 layer near the head-to-tail polarized interface, suggesting an over ∼70% enhancement of polarization compared with that of bulk PbTiO3. Besides that in PbTiO3, polarization in the BiFeO3 is also remarkably enhanced. Electron energy loss spectrum and X-ray photoelectron spectroscopy investigations demonstrate the oxygen vacancy accumulation as well as the transfer of Fe3+ to Fe2+ at the interface. On the basis of the polar catastrophe model, FeO2/PbO interface is determined. First-principles calculation manifests that the oxygen vacancy at the interface plays a predominate role in inducing the local polarization enhancement. We propose a charge transfer mechanism that leads to the remarkable polarization increment at the PbTiO3/BiFeO3 interface. This study may facilitate the development of nanoscale ferroelectric devices by tailing the coupling of charge and lattice in oxide heteroepitaxy.
S. Li, Yinlian Zhu, Yunlong Tang, Y. Liu, Siyang Zhang, Yuzheng Wang and Xueli Ma
Yaogan Liu, Y. Zhu, Yunlong Tang and Xueli Ma
Effects of crystal tilt on the determination of the relative positions of different ion columns in compounds such as ferroelectric PbTiO 3 are of critical importance, because the displacements of Ti and O relative to Pb correlate directly to the spontaneous polarization and ferroelectric properties. Here a study about the effects of small-angle crystal tilt on the relative image spots positions of different ions in PbTiO 3 was carried out under high angle angular dark-field (HAADF) and bright-field imaging for aberration corrected Scanning Transmission Electron Microscope. The results indicate that crystal tilt affects the relative positions of Pb, Ti, and O greatly, and the effects are proved to depend highly on crystal tilt angle and PTO thickness. HAADF image simulations on PbTiO 3 , SrTiO 3 , and SrRuO 3 indicate that the difference in atomic number is a main contributor to the relative image spot position change of different ion columns when crystal tilts.
Yunlong Tang, Yinlian Zhu, Z. Hong, E. Eliseev, A. Morozovska, Yi Wang, Ying Liu, Y. B. Xu, B. Wu, Long-qing Chen,et al.
Although the strong coupling of polarization to spontaneous strain in ferroelectrics would impart a flux-closure with severe disclination strains, recent studies have successfully stabilized such a domain via a nano-scaled multi-layer growth. Nonetheless, the detailed distributions of polarizations in three-dimensions (3D) and how the strains inside a flux closure affect the structures of domain walls are still less understood. Here we report a 3D polarization texture of a 4-fold flux closure domain identified in tensile strained ferroelectric PbTiO 3 /SrTiO 3 multilayer films. Ferroelectric displacement analysis based on aberration-corrected scanning transmission electron microscopic imaging reveals highly inhomogeneous strains with strain gradient above 10 7 /m. These giant disclination strains significantly broaden the 90° domain walls, while the flexoelectric coupling at 180° domain wall is less affected. The present observations are helpful for understanding the basics of topological dipole textures and indicate novel applications of ferroelectrics through engineering strains.
W. Wang, Yinlian Zhu, Yunlong Tang, Yaobin Xu, Y. Liu, Shuiming Li, Sirui Zhang, Yuzheng Wang and Xiuliang Ma
Exotic domain states, like vortex, offer the promise of superior properties and the potential disclination strain is a key factor for their formation in ferroelectrics. Here we show that large scale arrays of four-state vortex domains can be obtained in rhombohedral BiFeO3 thin films grown on PrScO3 substrates by pulsed laser deposition. Cs-corrected scanning transmission electron microscopy demonstrates that each vortex domain is comprised of four ferroelectric variants with two 180° domain walls and two 109° domain walls. Atomic mappings of the lattice distortions unit cell by unit cell reveal that the cores of the vortex might be charged. The strains are mainly concentrated on domain walls. The formation mechanism of such large scale vortex-like states was discussed.
Y. B. Xu, Y. Tang, Y. L. Zhu, Y. Liu, S. Li, S. Zhang and X. Ma
Ying Liu, Yun-Long Tang, Yin-Lian Zhu, Wen-Yuan Wang, and Xiu-Liang Ma
Wiley
walls and crystallographic defects in PbTiO3 films is directly visualized via aberration-corrected scanning transmission election microscopy (STEM) by Xiu-Liang Ma and co-workers in article 1600342. This is a schematic illustration based on atomic-scale STEM mapping showing the atomic configurations of the formation of positively charged 90 ̊ domain wall as a result of spatial coupling between domain walls and dislocations. Ferroelectric Films
Ying Liu, Yun-Long Tang, Yin-Lian Zhu, Wen-Yuan Wang, and Xiu-Liang Ma
Wiley
Revealing interactions between defects and domain walls is important for understanding the ferroelectric and piezoelectric behaviors of a ferroelectric film, especially when considering the trend of device downscaling. By means of aberration‐corrected transmission electron microscopy, domain patterns resulting from the interactions between 90°/180° ferroelectric domain walls and dislocations in the PbTiO3 thin films grown on SrTiO3 are systematically studied. It is found that the coupling of 90° and 180° domain walls with dislocations may induce the formation of 90° charged domain walls and some other novel metastable domain configurations. Such domain patterns are observed to relax with 180° domain walls annihilation and the reversal of polarization directions of a‐ and c‐domain. The configurations of both dislocations and stacking faults may lead to a dramatic change of the domain patterns. Unusual dislocation strain field is identified for a dislocation with the burgers vector 45° apart from a 90° domain wall. These results provide new insights into the defect and domain wall interactions which are of critical importance for the development of nanoscale devices.