Controlling oxide surface dipole and reactivity with intrinsic nonstoichiometric epitaxial reconstructions

Kim, Seungchul; Sinai, Ofer; Lee, Chan‐Woo; Rappe, Andrew M.

doi:10.1103/physrevb.92.235431

Cited by 16 publications

(22 citation statements)

References 58 publications

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“…When the TiO 2 ‐terminated SrTiO 3 surface without a SiO 2 capping layer is relaxed during the calculations, the three unit cells closest to the surface distort to minimize the surface energy. Consistent with previous studies, we find that in each TiO 2 layer, titanium ions move inwards relative to the oxygen ions, whereas in the SrO atomic layers, Sr ions move outwards relative to oxygen ions (Figure a). This produces layers with opposite polarization and a net dipole moment pr.…”

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confidence: 92%

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Surface Pyroelectricity in Cubic SrTiO₃

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material gives rise to a range of interesting properties such as superconductivity, [1] high electron mobility, [2,3] ferromagnetism [4,5] and 2D electron gases. [6] In the multitude of the properties exhibited by SrTiO 3 , pyroelectricity, ferroelectricity, and piezoelectricity are markedly absent as these properties are symmetry prohibited in centrosymmetric crystal lattices. The polar phase required for exhibiting these properties can, however, be induced artificially by modification of the lattice. Large biaxial strain, [7] light pulses, [8,9] and elemental substitutions [10] can convert SrTiO 3 into a ferroelectric material, whereas strain gradients can induce a polarization via the flexoelectric effect [11,12] or oxygen vacancies migration. [13] Electron diffraction measurements furthermore show that the top TiO 2 surface layer of SrTiO 3 undergoes surface relaxation and oxygen ions move outward from the surface relative to the titanium ions, leading to a polarization of this layer. [14][15][16] This is supported by shell model and density functional theory calculations. However, the calculations also predict that the SrO layers underneath display a polarization opposite to that of the TiO 2 surface layer, [17][18][19] leaving the question of the predicted net polarization and a possible pyroelectricity at the surface wide open.Symmetry-imposed restrictions on the number of available pyroelectric and piezoelectric materials remain a major limitation as 22 out of 32 crystallographic material classes exhibit neither pyroelectricity nor piezoelectricity. Yet, by breaking the lattice symmetry it is possible to circumvent this limitation. Here, using a unique technique for measuring transient currents upon rapid heating, direct experimental evidence is provided that despite the fact that bulk SrTiO 3 is not pyroelectric, the (100) surface of TiO 2 -terminated SrTiO 3 is intrinsically pyroelectric at room temperature. The pyroelectric layer is found to be ≈1 nm thick and, surprisingly, its polarization is comparable with that of strongly polar materials such as BaTiO 3 . The pyroelectric effect can be tuned ON/OFF by the formation or removal of a nanometric SiO 2 layer. Using density functional theory, the pyroelectricity is found to be a result of polar surface relaxation, which can be suppressed by varying the lattice symmetry breaking using a SiO 2 capping layer. The observation of pyroelectricity emerging at the SrTiO 3 surface also implies that it is intrinsically piezoelectric. These findings may pave the way for observing and tailoring piezo-and pyroelectricity in any material through appropriate breaking of symmetry at surfaces and artificial nanostructures such as heterointerfaces and superlattices. PyroelectricitySrTiO 3 has been the object of immense attention for over half a century owing to its multifunctional nature and popularity as a template for epitaxial growth of artificial nanostructures such as heterostructures, superlattices, and vertically aligned nanostructures. It is a classic example whe...

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confidence: 92%

“…This is supported by shell model and density functional theory calculations. However, the calculations also predict that the SrO layers underneath display a polarization opposite to that of the TiO 2 surface layer, leaving the question of the predicted net polarization and a possible pyroelectricity at the surface wide open.…”

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confidence: 75%

Surface Pyroelectricity in Cubic SrTiO₃

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“…If E FG >E FS , electrons will be transferred to the semiconductor from graphene during the formation of the heterojunction until the system reaches the equilibrium Fermi energy, E F [76]. This electron transfer at the heterointerface will give rise to the formation of a surface dipole [77][78][79] as shown in Fig. 6(a).…”

Section: E Photocatalytic Mechanismmentioning

confidence: 99%

Enhanced photocatalytic dye degradation and hydrogen production ability of Bi25FeO40-rGO nanocomposite and mechanism insight

Basith

Ahsan

Zarin

et al. 2018

Sci Rep

101

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A comprehensive comparison between BiFeO3-reduced graphene oxide (rGO) nanocomposite and Bi25FeO40-rGO nanocomposite has been performed to investigate their photocatalytic abilities in degradation of Rhodamine B dye and generation of hydrogen by water-splitting. The hydrothermal technique adapted for synthesis of the nanocomposites provides a versatile temperature-controlled phase selection between perovskite BiFeO3 and sillenite Bi25FeO40. Both perovskite and sillenite structured nanocomposites are stable and exhibit considerably higher photocatalytic ability over pure BiFeO3 nanoparticles and commercially available Degussa P25 titania. Notably, Bi25FeO40-rGO nanocomposite has demonstrated superior photocatalytic ability and stability under visible light irradiation than that of BiFeO3-rGO nanocomposite. The possible mechanism behind the superior photocatalytic performance of Bi25FeO40-rGO nanocomposite has been critically discussed.

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“…The presence of hydroxyl groups (OH – ), probably bonded to Ti 4+ ions, and O L -H + adsorbates could affect the polarization in different coexisting ways. First in dark conditions, they provide charges contributing to reduce the depolarizing field and pinning a fraction of ferroelectric domains, thus reducing the switchable polarization . This effect can be hardly observed in our films by comparing the loops in Figure a,b measured in dark conditions because P r value change after the steam treatment is very small.…”

Section: Results and Discussionmentioning

confidence: 78%

Control of the Polarization of Ferroelectric Capacitors by the Concurrent Action of Light and Adsorbates

Liu

Fina

Sauthier

et al. 2018

ACS Appl. Mater. Interfaces

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Ferroelectric perovskites hold promise of enhanced photovoltaic efficiency and photocatalytic activity. Consequently, the photoresponse of oxide ferroelectric thin films is an active field of research. In electrode/ferroelectric/electrode devices, internal charge in the ferroelectric, free charge in the electrodes, and buried adsorbates at interfaces combine to screen the ferroelectric polarization and to stabilize the polar state. Under illumination, photoinduced carriers and photodissociated adsorbates may disrupt the screening equilibrium, modifying the switchable polarization and altering its expected benefits. Here, we explore the photoresponse of BaTiO thin films in a capacitor geometry, focusing on the effects of visible illumination on the remanent polarization. By combining ferroelectric and X-ray photoelectron spectroscopy, we discover that photoreaction of charge-screening HO-derived adsorbates at the buried metal-ferroelectric Pt/BaTiO interface plays an unexpected pivotal role, enabling a substantial modulation (up to 75%) of the switchable remanent polarization by light. These findings illustrate that the synergy between photochemistry and photovoltaic activity at the surface of a ferroelectric material can be exploited to tune photoferroelectric activity.

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Controlling oxide surface dipole and reactivity with intrinsic nonstoichiometric epitaxial reconstructions

Cited by 16 publications

References 58 publications

Surface Pyroelectricity in Cubic SrTiO₃

Surface Pyroelectricity in Cubic SrTiO₃

Enhanced photocatalytic dye degradation and hydrogen production ability of Bi25FeO40-rGO nanocomposite and mechanism insight

Control of the Polarization of Ferroelectric Capacitors by the Concurrent Action of Light and Adsorbates

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Controlling oxide surface dipole and reactivity with intrinsic nonstoichiometric epitaxial reconstructions

Cited by 16 publications

References 58 publications

Surface Pyroelectricity in Cubic SrTiO3

Surface Pyroelectricity in Cubic SrTiO3

Enhanced photocatalytic dye degradation and hydrogen production ability of Bi25FeO40-rGO nanocomposite and mechanism insight

Control of the Polarization of Ferroelectric Capacitors by the Concurrent Action of Light and Adsorbates

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Surface Pyroelectricity in Cubic SrTiO₃

Surface Pyroelectricity in Cubic SrTiO₃