Control of Oxygen Vacancy Ordering in Brownmillerite Thin Films via Ionic Liquid Gating

Abstract

Oxygen defects and their atomic arrangements play a significant role in the physical properties of many transition metal oxides. The exemplary perovskite SrCoO 3-δ ( P- SCO) is metallic and ferromagnetic. However, its daughter phase, the brownmillerite SrCoO 2.5 ( BM- SCO), is insulating and an antiferromagnet. Moreover, BM- SCO exhibits oxygen vacancy channels (OVCs) that in thin films can be oriented either horizontally ( H -SCO) or vertically ( V -SCO) to the film’s surface. To date, the orientation of these OVCs has been manipulated by control of the thin film deposition parameters or by using a substrate-induced strain. Here, we present a method to electrically control the OVC ordering in thin layers via ionic liquid gating (ILG). We show that H -SCO (antiferromagnetic insulator, AFI) can be converted to P -SCO (ferromagnetic metal, FM) and subsequently to V -SCO (AFI) by the insertion and subtraction of oxygen throughout thick films via ILG. Moreover, these processes are independent of substrate-induced strain which favors formation of H -SCO in the as-deposited film. The electric-field control of the OVC channels is a path toward the creation of oxitronic devices.

Mechanisms of Hysteresis and Reversibility across the Voltage-Driven Perovskite–Brownmillerite Transformation in Electrolyte-Gated Ultrathin La0.5Sr0.5CoO3−δ

“…13 Building on the ability to thermally cycle between P and BM in thin-film perovskite cobaltites, 55,56 recent work in ionic-liquid/ion-gel/ionic-conductor-based transistors established electrical cycling (i.e., gating) between these phases. [11][12][13][14]16,[19][20][21][24][25][26][27]31 As illustrated in Figure 1(b), ionic-liquid/gel-based transistors achieve reduction of P SrCoO 3−δ to BM SrCoO 2.5 under positive V g (left panel), and oxidation of BM SrCoO 2.5 to P SrCoO 3−δ under negative V g (right panel), [11][12][13][14]16,[19][20][21][24][25][26][27]31 the requisite O for the latter likely deriving from electrochemical splitting of H 2 O in the ionic liquids/gels. 2,4,13,19 This cycling is nonvolatile, and intrinsically power-efficient due to low electrochemical gate current (I g ).…”

The Dynamics of Oxygen Ion Exchange in Epitaxial Strontium Cobaltite Bilayers

“…[11] The reversible transition between epitaxial thin-film BM-SCO and PV-SCO has been accomplished through the use of oxidizing environments and elevated temperatures (≈200-500 °C) [11,15,16] both with and without an external bias, [17,18] as well as by solid-state and ionic liquid gating. [19][20][21][22] A schematic of an iontronic device utilizing the reversible transition (i.e., moving of the interface) between epitaxial BM-SCO and PV-SCO under oxidizing and reducing conditions is shown in Figure 1.…”

Reversal of Anomalous Hall Effect and Octahedral Tilting in SrRuO3 Thin Films via Hydrogen Spillover

“…[31] Various methods have been used to carry out the hydrogenation that include hydrogen spillover, [27,28,[32][33][34][35] electrolyte gating, [24][25][26] and ionic liquid gating. [29,[36][37][38] Ionic liquid gating of an oxide layer involves the formation of an electric double layer at the surface with large electric fields that can result in significant electrostatic tuning of the carrier charge density [39] but which can also lead to oxygen vacancy formation, [40][41][42] as well as hydrogen inter calation that typically arises from water dissolved in the ionic liquid. [36][37][38] Therefore, to unambiguously unravel the effect of hydrogen on the physical property of SRO films, a method that introduces hydrogen alone is desired.…”