Compressive-Strain-Facilitated Fast Oxygen Migration with Reversible Topotactic Transformation in La_0.5Sr_0.5CoO_x via All-Solid-State Electrolyte Gating

Abstract

Modifying the crystal structure and corresponding functional properties of complex oxides by regulating their oxygen content has promising applications in energy conversion and chemical looping, where controlling oxygen migration plays an important role. Therefore, finding an efficacious and feasible method to facilitate oxygen migration has become a critical requirement for practical applications. Here, we report a compressive-strain-facilitated oxygen migration with reversible topotactic phase transformation (RTPT) in La0.5Sr0.5CoO x films based on all-solid-state electrolyte gating modulation. With the lattice strain changing from tensile to compressive strain, significant reductions in modulation duration (∼72%) and threshold voltage (∼70%) for the RTPT were observed, indicating great promotion of RTPT by compressive strain. Density functional theory calculations verify that such compressive-strain-facilitated efficient RTPT comes from significant reduction of the oxygen migration barrier in compressive-strained films. Further, ac-STEM, EELS, and sXAS investigations reveal that varying strain from tensile to compressive enhances the Co 3d band filling, thereby suppressing the Co–O hybrid bond in oxygen vacancy channels, elucidating the micro-origin of such compressive-strain-facilitated oxygen migration. Our work suggests that controlling electronic orbital occupation of Co ions in oxygen vacancy channels may help facilitate oxygen migration, providing valuable insights and practical guidance for achieving highly efficient oxygen-migration-related chemical looping and energy conversion with complex oxides.

Strain-Induced Uphill Hydrogen Distribution in Perovskite Oxide Films

“…Ionic control of transition-metal oxides (TMOs) has become an effective pathway to tune functionalities including magnetic, − electronic, − optical, − thermoelectric, , and catalytic performances. − As the smallest ion, H + (proton) is naturally endowed with high mobility, excellent reversibility, prominent modulation effect, and broad applicability to binary and complex oxides. − In recent years, increasing efforts have been put into developing facile hydrogenation methods − and discovering novel properties in protonated phases. − Owing to the tight relationship between hydrogen (doping) concentration, lattice, and electronic structure, understanding the migration mechanism and detecting the spatial distribution of H + are necessary for finely tailoring the physical properties on a microscopic scale and enhancing the reaction efficiency of the energy-conversion process in protonic ceramic fuel cells. ,,− A typical example is the construction of reconfigurable NdNiO 3 electronic devices (artificial neurons, synapses, and memory capacitors) via the sensitivity of electronic properties to the local distribution of H + …”

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

“…Related effects have also been proposed for topotactic resistive random access memory devices. 57,58 By the above means, electrochemical gating of epitaxial films of compounds such as SrCoO 3−δ , [11][12][13][14]16,[19][20][21][24][25][26][27]31 SrCo 1−x Fe x O 3−δ , 19 and La 1−x Sr x CoO 3−δ 18,22,23,29 has been intensively studied. In terms of the structure, both ex situ and operando studies of V g -controlled P ↔ BM transformations have been performed, via transmission electron microscopy 14,21,22,24,27,29 and X-ray diffraction (XRD), [11][12][13]16,[18][19][20][21][22][23][24]27,29 significantly advancing the understanding of this (first-order 18 ) topotactic transition.…”

“…In terms of the structure, both ex situ and operando studies of V g -controlled P ↔ BM transformations have been performed, via transmission electron microscopy 14,21,22,24,27,29 and X-ray diffraction (XRD), [11][12][13]16,[18][19][20][21][22][23][24]27,29 significantly advancing the understanding of this (first-order 18 ) topotactic transition. 18,56,59 Interestingly, some studies, particularly on SrCoO 3−δ , present clear evidence for tristate gating between P SrCoO 3−δ , BM SrCoO 2.5 , and hydrogenated HSrCoO 2.5 , 13,25,31 while others, particularly on La 1−x Sr x CoO 3−δ , evidence bistate gating between P and BM phases; 18,22,23,29 this difference is not yet understood. In terms of electronic transport, accompanying V g -induced metal−insulator transitions have been observed through temperature (T)-dependent resistivity (ρ) measurements, 13,18,21,23 leading to room-temperature ρ modulations up to 10 5 in SrCoO 3−δ and La 1−x Sr x CoO 3−δ .…”

“…It is now understood that this can be achieved via ionic liquids and gels, − solid electrolytes, ,− and ionic conductors, ,− utilizing these media to control the insertion/extraction of various chemical species into/out of target materials they are interfaced with. These species include oxygen ions/vacancies (O/V O ), − H ions, ,− ,,,,,,, Li ions, ,, N ions, , F ions, etc., inserted/extracted into/from a variety of target materials, spanning metals, − ,,,, oxides, − ,− ...…”

“…By the above means, electrochemical gating of epitaxial films of compounds such as SrCoO 3−δ , − ,,− ,− , SrCo 1– x Fe x O 3−δ , and La 1– x Sr x CoO 3−δ ,,, has been intensively studied. In terms of the structure, both ex situ and operando studies of V g -controlled P ↔ BM transformations have been performed, via transmission electron microscopy ,,,,, and X-ray diffraction (XRD), − ,,− ,, significantly advancing the understanding of this (first-order) topotactic transition. ,, Interestingly, some studies, particularly on SrCoO 3−δ , present clear evidence for tristate gating between P SrCoO 3−δ , BM SrCoO 2.5 , and hydrogenated HSrCoO 2.5 , ,, while others, particularly on La 1– x Sr x CoO 3−δ , evidence bistate gating between P and BM phases; ,,, this difference is not yet understood.…”