Emergent electric field control of phase transformation in oxide superlattices

Di Yi¹, Yujia Wang², Olaf M J van ʼt Erve³, Liubin Xu⁴, Hongtao Yuan⁵, Michael J Veit^{6

7}, Purnima P Balakrishnan^{6

8}, Yongseong Choi⁹, Alpha T N'Diaye¹⁰, Padraic Shafer¹⁰, Elke Arenholz^{10

11}, Alexander Grutter¹², Haixuan Xu¹³, Pu Yu^{14

15

16}, Berend T Jonker³, Yuri Suzuki^{6

7}

Affiliations

¹ Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA. diyi.mse@gmail.com.
² State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, China.
³ Materials Science and Technology Division, US Naval Research Laboratory, Washington, DC, 20375, USA.
⁴ Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
⁵ National Laboratory of Solid-State Microstructures, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, 210093, Nanjing, China.
⁶ Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA.
⁷ Department of Applied Physics, Stanford University, Stanford, CA, 94305, USA.
⁸ Department of Physics, Stanford University, Stanford, CA, 94305, USA.
⁹ Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA.
¹⁰ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
¹¹ Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY, 14853, USA.
¹² NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899-6102, USA.
¹³ Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA. hxu8@utk.edu.
¹⁴ State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, China. yupu@mail.tsinghua.edu.cn.
¹⁵ Frontier Science Center for Quantum Information, Beijing, 100084, China. yupu@mail.tsinghua.edu.cn.
¹⁶ RIKEN Center for Emergent Matter Science (CEMS), Saitama, 351-0198, Japan. yupu@mail.tsinghua.edu.cn.

PMID: 32060300
PMCID: PMC7021769
DOI: 10.1038/s41467-020-14631-3

Emergent electric field control of phase transformation in oxide superlattices

Di Yi et al. Nat Commun. 2020.

. 2020 Feb 14;11(1):902.

doi: 10.1038/s41467-020-14631-3.

Authors

Affiliations

¹ Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA. diyi.mse@gmail.com.
² State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, China.
³ Materials Science and Technology Division, US Naval Research Laboratory, Washington, DC, 20375, USA.
⁴ Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
⁵ National Laboratory of Solid-State Microstructures, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, 210093, Nanjing, China.
⁶ Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA.
⁷ Department of Applied Physics, Stanford University, Stanford, CA, 94305, USA.
⁸ Department of Physics, Stanford University, Stanford, CA, 94305, USA.
⁹ Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA.
¹⁰ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
¹¹ Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY, 14853, USA.
¹² NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899-6102, USA.
¹³ Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA. hxu8@utk.edu.
¹⁴ State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, China. yupu@mail.tsinghua.edu.cn.
¹⁵ Frontier Science Center for Quantum Information, Beijing, 100084, China. yupu@mail.tsinghua.edu.cn.
¹⁶ RIKEN Center for Emergent Matter Science (CEMS), Saitama, 351-0198, Japan. yupu@mail.tsinghua.edu.cn.

PMID: 32060300
PMCID: PMC7021769
DOI: 10.1038/s41467-020-14631-3

Abstract

Electric fields can transform materials with respect to their structure and properties, enabling various applications ranging from batteries to spintronics. Recently electrolytic gating, which can generate large electric fields and voltage-driven ion transfer, has been identified as a powerful means to achieve electric-field-controlled phase transformations. The class of transition metal oxides provide many potential candidates that present a strong response under electrolytic gating. However, very few show a reversible structural transformation at room-temperature. Here, we report the realization of a digitally synthesized transition metal oxide that shows a reversible, electric-field-controlled transformation between distinct crystalline phases at room-temperature. In superlattices comprised of alternating one-unit-cell of SrIrO₃ and La_0.2Sr_0.8MnO₃, we find a reversible phase transformation with a 7% lattice change and dramatic modulation in chemical, electronic, magnetic and optical properties, mediated by the reversible transfer of oxygen and hydrogen ions. Strikingly, this phase transformation is absent in the constituent oxides, solid solutions and larger period superlattices. Our findings open up this class of materials for voltage-controlled functionality.

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Conflict of interest statement

The authors declare no competing interests.

Figures

**Fig. 1. Electric-field control of structural transition.**
a Schematic of ionic liquid gating (ILG) that induces the ion transfer between oxides and ionic liquid. Four types of oxides were studied, i.e. manganate (La_1-xSr_xMnO₃) and iridate (SrIrO₃) films, solid solution (Sr(Mn_0.5Ir_0.5)O₃) films and superlattices ([(La_0.2Sr_0.8MnO₃)_m(SrIrO₃)_m]_n) on SrTiO₃ substrates. b Modulation of out-of-plane lattice constant (∆c/c) during voltage cycling (with incremental positive voltages to +2.5 V and −3.0 V) for different samples (SS refers to Sr(Mn_0.5Ir_0.5)O₃ and SL refers to [(La_0.2Sr_0.8MnO₃)₁(SrIrO₃)₁]₂₀). The lattice constant was extracted from in situ measurements of the (002) peak position. The end of the curves for all samples except the superlattice corresponds to phase decomposition above certain voltages. c In situ X-ray diffraction results of the superlattices around the (002) peak during ILG in repeated voltage cycling (sequence of +2.5 V, −3.0 V, +2.5 V, −3.0 V), showing a reversible electric-field-controlled transformation between two phases of the superlattices. d Full-range X-ray diffraction of a superlattice in as-grown pristine state, positively gated state and reversibly gated state. e Schematic of the reversible phase transformation mediated by dual-ion (both H⁺ and O²⁻) transfer.

**Fig. 2. Chemical characterization.**
a Depth profiles of H and Ti signals in the two phases of the superlattices, measured by using secondary-ion mass spectrometry. The H signal was obtained in phase A and B of the superlattices stabilized by ILG. The Ti signal from the substrate indicates the position of the interface between substrate and superlattice. b Depth profiles of ¹⁸O and Ti signals in the two phases of the superlattices after thermal annealing in ¹⁸O₂. To measure ¹⁸O signal, the superlattices were first stabilized in phase A and B under ILG, and then thermally annealed in ¹⁸O₂ gas.

**Fig. 3. Valence characterization.**
X-ray absorption (XA) spectra of a Mn L-edge, b Ir L₃-edge, and c oxygen K-edge of the two phases. Figure 3a inset shows the valence changes of the superlattices and La_0.2Sr_0.8MnO₃ films under ILG. The shifts of absorption peaks at the Mn L-edge (a) and Ir L₃-edge (b) reveal a significant decrease of valence for both Mn and Ir cations in phase B. The oxygen K-edge results (c) show a full suppression of hybridization between oxygen 2p orbitals and Mn/Ir d orbitals, and the appearance of features associated with hydroxyl bonds in phase B.

**Fig. 4. Electric-field control of resistivity and electrochromic effect.**
a Schematic of the device for in situ measurement of the transport properties under ILG. b Reversible modulation of resistivity between the two phases during repeated voltage cycling at room temperature. c Temperature dependence of resistivity of the superlattice during voltage cycling (incremental positive voltages to +2.5 V and −3 V). d Optical transmittance spectra of a superlattice during voltage cycling. Inset shows the photographs of a double-side polished SrTiO₃ substrate and superlattices that are stabilized in the two phases by ILG.

**Fig. 5. Electric-field control of magnetic properties.**
a Magnetic hysteresis loops of a superlattice under ILG, probed with in situ magneto-optic Kerr effect (MOKE). An offset is applied for illustration. b Magnetic hysteresis loops and c temperature dependence of magnetization of the superlattice during voltage cycling, probed with ex situ SQUID magnetometry. All measurements were performed along the out-of-plane direction, which is the magnetic easy axis due to interface perpendicular magnetic anisotropy. A field of 0.2 T was applied to obtain results in (c).

**Fig. 6. DFT calculations.**
a Top view of the superlattice without ionic defects. The IrO₆ and MnO₆ octahedra of the superlattice show different magnitudes of rotation. The calculated rotation angle (θ) along the c axis ([001]) is about 14.5° and 2.9° for IrO₆ and MnO₆ octahedra, respectively. b Side view of the superlattice with the three kinds of oxygen vacancy sites. Due to the atomically layered structure, three distinct oxygen sites were considered, labelled as O1 (in the SrO layer), O2 (in the IrO₂ layer) and O3 (in the MnO₂ layer). Further results on hydrogen interstitial are included in the Supplementary Note 13.

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Emergent electric field control of phase transformation in oxide superlattices

Affiliations

Emergent electric field control of phase transformation in oxide superlattices

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

References

Grants and funding

LinkOut - more resources

Full Text Sources

Research Materials