Artificial ferroelectricity in perovskite superlattices

Tsurumi, Takaaki; Harigai, Takakiyo; Tanaka, Daisuke; Nam, Song−Min; Kakemoto, Hirofumi; Wada, Satoshi; Saito, Keisuke

doi:10.1063/1.1825057

Cited by 83 publications

(43 citation statements)

References 14 publications

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Section: Introductionmentioning

confidence: 99%

“…The deduced value of P CZO =2.3×10 13 e/cm 2 =3.5 μCcm -2 , is in good agreement with the experimentally determined values for a comparable compressively strained 40 uc SrZrO 3 /SrTiO 3 bilayer-heterostructure. 27 In short, the strain induced polarization model can fit well the critical thickness dependence of the sheet carrier density for CZO/STO heteostructures, and can explain largely the metallic conduction at the nonminally-nonpolar perovskite interface between the two band insulators, when the content of oxygen vacancies is negligible. It is noteworthy that the deduced polarization of P CZO =3.5 μCcm -2 in CZO/STO (t≤14 uc) is much lower than that expected at the polar LAO/STO interface, P LAO =e/2a LAO 2 =55.8 μCcm -2 .…”

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confidence: 99%

“…In a similar zirconate system of SrZrO 3 /SrTiO 3 , the compressive strain has been reported to result in ferroelectricity in its superlattices. 27 Theoretical calculations by first principle density functional theory indicate that such 5 strain induced polarization originates from a lattice distortion, which is characterized by a prediction that all the cations move towards the interface with the Zr 4+ exhibiting the largest relative displacement.28 Therefore, we also investigated the lattice distortion of our CZO films in the vicinity of the interface.Remarkably, compared to the CaZrO 3 film that is more than 10 uc away from the interface, we observed unambiguously that both the Ca 2+ and Zr 4+ cations move toward the interface in the first 7 uc CZO layers. As shown in Fig.…”

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Creation of High Mobility Two-Dimensional Electron Gases via Strain Induced Polarization at an Otherwise Nonpolar Complex Oxide Interface

et al. 2015

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ABSTRACT:The discovery of two-dimensional electron gases (2DEGs) in SrTiO 3 -based heterostructures provides new opportunities for nanoelectronics. Herein, we create a new type of oxide 2DEG by the epitaxial-strain-induced polarization at an otherwise nonpolar perovskite-type interface of CaZrO 3 /SrTiO 3 . Remarkably, this heterointerface is atomically sharp, and exhibits a high electron mobility exceeding 60,000 cm 2 V -1 s -1 at low temperatures. The 2DEG carrier density exhibits a critical dependence on the film thickness, in good agreement with the polarization induced 2DEG scheme.* Corresponding Author. Email:yunc@dtu.dk. Phone: +45 4677 5614.2 KEYWORDS: Complex oxide interfaces, oxide electronics, two-dimensional electron gases, strain induced polarization.Atomically engineered complex oxide heterostructures exhibit a variety of exotic interfacial properties because of strong interactions among the spin, charge, and orbital freedoms as well as lattice vibrations.One particular example is the emergence of high mobility two-dimensional electron gases (2DEGs) at the interface between two oxide insulators, 1,2 one of which is SrTiO 3 (STO), the basis material of oxide electronics. These complex oxide 2DEGs consist of strongly coupled electrons and give rise to a rich set of physical phenomena 3-5 , for example, superconductivity 6,7 , magnetism 8,9 , and tunable metal-insulator transitions on nanoscale, 10,11 providing new opportunities for nanoelectronics and mesoscopic physics. Under optimized conditions, the CZO films deposited by pulsed laser deposition (PLD) can be epitaxially grown on the (001) TiO 2 -terminated STO substrates within a layer-by-layer two-dimensional growth mode, as confirmed by the presence of periodic intensity oscillations of the reflection highenergy electron diffraction (RHEED) pattern monitored in-situ during film growth (Supporting information, Fig.S1). Both RHEED intensity oscillations and sharp RHEED patterns can persist up to a film thickness over 50 unit cells (uc), suggesting high quality film growth. A terrace surface of the grown heterostructure is detected by atomic force microscopy (AFM), which shows a regular step height of 0.4 nm (Fig. 1b). High-resolution X-ray diffraction (XRD) further confirms the epitaxial growth of the (001) We further investigated the atomic structure and interface chemistry of our CZO/STO heterostructures by an aberration corrected scanning transmission electron microscopy (STEM) in combination with electron energy-loss spectroscopy (EELS). Figure 2a shows a high-angle annular dark field (HAADF) STEM image of a CZO/STO sample with the CZO layer of approximately 50 uc (~20 nm). The CZO film is found to be coherent with the STO substrate with no obvious defects or dislocations at the interface. The averaged line profiles (Fig. 2b) Fig.1. In a similar zirconate system of SrZrO 3 /SrTiO 3 , the compressive strain has been reported to result in ferroelectricity in its superlattices. 27 Theoretical calculations by first principle density functional ...

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Creation of High Mobility Two-Dimensional Electron Gases via Strain Induced Polarization at an Otherwise Nonpolar Complex Oxide Interface

et al. 2015

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“…22,23 These studies highlighted the fact that three main factors govern the physics of multilayers: epitaxial strain, electrical boundary conditions, and interfacial effects.…”

Section: Introductionmentioning

confidence: 99%

First-principles study of competing ferroelectric and antiferroelectric instabilities inBaTiO3/BaOsuperlattices

2010

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We report a first-principles study of ͑BaTiO 3 ͒ m / ͑BaO͒ n superlattices for a wide range of periodicities m / n. We show that such a system develops a polar zone-center instability for sufficiently large m / n ratio, which can be understood, at least qualitatively, from a simple electrostatic model and should lead to a ferroelectric ground state. However, the analysis of the phonon-dispersion curves also points out the appearance of stronger antiferroelectric instabilities at the zone boundaries around m = 4, before the critical ratio for ferroelectricity is reached and which still dominate beyond it. The dominant character of the antiferroelectric instability is explained from the depolarizing field which hardens the ferroelectric mode. This analysis allows us to predict that, ͑BaTiO 3 ͒ m / ͑BaO͒ n superlattices should present an antiferroelectric ground state for m larger than 4, which should smoothly evolve to a multidomain structure for increasing m values and only become ferroelectric for large m.

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“…On the other hand, the artificial super lattice of BT/SrTiO 3 hetero-epitaxial thin films had an extremely high dielectric constant due to local lattice strain at the interfaces between BT and ST films. 8) Both results indicated that the local lattice strain was quite important for enhancing the dielectric properties. Figures 11(a) and 11(b) show cross-sectional TEMs of Pt/BT NC 3D-assemblies/Pt capacitors applied for a practical measurement and the schematic image, respectively.…”

Section: Origin Of the High Dielectric Properties Of Bt Nc 3d-assembliesmentioning

confidence: 60%

Processing of dielectric nanocube 3D-assemblies and their high electrical properties for next-generation devices

Mimura

2016

J. Ceram. Soc. Japan

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Nanocrystals have great potential to achieve extremely high electrical properties induced by their shapes, size, and facet surfaces. BaTiO 3 nanocube (BT NC) 3D-assemblies with numerous interfaces and closely packed nanostructure are attracting as materials for next-generation dielectric devices due to their advantages for enhancing dielectric properties such as high packing density, high orientation, and interaction of the interfaces between the nanocubes. In this paper, we review our studies on the solutionbased processing of BT NC 3D-assemblies and their high dielectric properties. BT NCs 15 nm in size have already been synthesized by the hydrothermal method with aqueous compounds and surfactants. As NCs were well-dispersed in non-polar organic solvent, BT NC 3D-assemblies were fabricated by a dip-coating process while controlling the up-stroke rate of the substrate and evaporation rate of the solvent. The capillary force generated through the dip-coating assisted in ordering the NCs. We also successfully fabricated micro-patterning of BT NC assemblies using polymeric micro-molds and removing them by a chemical wet process. This soft process has the great advantages of avoiding both etching damage occurring in the dry process and the clamping effect of substrate. The ordering and cubic shape of the BT NC 3D-assemblies were maintained under heattreatment up to 900°C. The local strain at the BT NC interfaces was induced by epitaxial attachment with small angle tilting between neighboring NCs. The dielectric constant of the BT NC assembly heat-treated at 850°C achieved above 4000 with relatively low loss tangent below 7%. The local strain at the interfaces seemed to enhance the dielectric properties without the nanosize effect and thickness effect of dielectric materials.

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Artificial ferroelectricity in perovskite superlattices

Abstract: Evidence of short-range antiferroelectric local states in lanthanum-and titanium-modified Sr 0.3 Ba 0.7 Nb 2 O 6 ferroelectric ceramics

Cited by 83 publications

References 14 publications

Creation of High Mobility Two-Dimensional Electron Gases via Strain Induced Polarization at an Otherwise Nonpolar Complex Oxide Interface

Creation of High Mobility Two-Dimensional Electron Gases via Strain Induced Polarization at an Otherwise Nonpolar Complex Oxide Interface

First-principles study of competing ferroelectric and antiferroelectric instabilities inBaTiO3/BaOsuperlattices

Processing of dielectric nanocube 3D-assemblies and their high electrical properties for next-generation devices

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