Enhanced electric conductivity at ferroelectric vortex cores in BiFeO3

Abstract

Topological defects in ferroic materials are attracting much attention both as a playground of unique physical phenomena and for potential applications in reconfigurable electronic devices. Here, we explore electronic transport at artificially created ferroelectric vortices in BiFeO 3 thin films. The creation of one-dimensional conductive channels activated at voltages as low as 1 V is demonstrated. We study the electronic as well as the static and dynamic polarization structure of several topological defects using a combination of first-principles and phase-field modelling. The modelling predicts that the core structure can undergo a reversible transformation into a metastable twist structure, extending charged domain walls segments through the film thickness. The vortex core is therefore a dynamic conductor controlled by the coupled response of polarization and electron-mobile-vacancy subsystems with external bias. This controlled creation of conductive one-dimensional channels suggests a pathway for the design and implementation of integrated oxide electronic devices based on domain patterning.

Super switching and control of in-plane ferroelectric nanodomains in strained thin films

“…Orthorhombic (110)-DyScO 3 substrates do not have a totally squared in-plane lattice, however, the difference between the two in-plane parameters is small: the two in-plane lattice directions are [1][2][3][4][5][6][7][8][9][10] 31,32 . This is consistent with a transition to an in-plane ferroelectric phase predicted under increasing tensile strain (blue area in Fig.…”

“…2a). These variants define micron-size 'superdomains' with a resultant inplane component of polarization along the [110] and [1][2][3][4][5][6][7][8][9][10] directions (see wide blue arrows). Similar patterns have been observed in single crystals of BaTiO 3 (lamellae and dots) 12,14,15 , dots of PZT 17 and lamellae of PZN-PT 18 , as well as in relatively thick PZT and PbTiO 3 films 38,39 , which included a fraction of domains with out-of-plane polarization and partial strain relaxation by dislocations.…”

“…Increasing miniaturization in ferroelectric materials allows creating complex domain structures, offering novel functionalities [1][2][3][4] that could be particularly useful for the development of nanoelectronic devices. Most studies in thin films focus on domain patterns with up/down polarization for ferroelectric memories, while domain structures with purely inplane polarization have not been much investigated.…”

Domain-wall nanoelectronics in ferroelectric memory

“…Fundamentally, the physical origin of the domainwall conduction in ferroelectric/multiferroic oxides are still obscure in that ferroelectric domain walls are natural defects with the discontinuity of ferroelectric polarization or crystal orientation, which indeed involves complicated physical and chemical structures in such a reduced dimension. Several main possibilities were already proposed in different domain-wall systems such as charge accumulation in head-to-head polarization, center of closure domains [8] and chemical-induced charge defects (Fe 3+ / Fe 4+ ) [9]. Can people also succeeded in creating conduc-tion in domain walls without crystal/chemical defects [10]?…”

Sequential piezoresponse force microscopy and the ‘small-data’ problem

“…8 As far as Scanning Probe Microscopy (SPM) is concerned, the recent developments in functional imaging-modes have been paralleled with a growing interest in studying various local phenomena. A few examples of such phenomena include electrical conduction at ferroelectric/ferroelastic domain walls, [9][10][11][12] polarization dynamics in ferroelectrics, [13][14][15][16][17][18] temperature/time/ voltage dependent study of ergodicity (time dependence) of polarization in relaxor-ferroelectrics, 14,19 and local magnetoelectricity. [20][21][22][23][24][25][26][27][28] Probing such local phenomena essentially requires measuring a response I ij (x i , P j ) on an X × Y grid, as a function of a spectral parameter P j (j = 1,…,M); where x i is the spatial coordinate index (i = 1,…,N; N = X × Y).…”