Realizing Metastable Cobaltite Perovskite via Proton-Induced Filling of Oxygen Vacancy Channels

Abstract

The interaction between transition-metal oxides (TMOs) and protons has become a key issue in magneto-ionics and proton-conducting fuel cells. Until now, most investigations on oxide−proton reactions rely on electrochemical tools, while the direct interplay between protons and oxides remains basically at simple dissolution of metal oxides by an acidic solution. In this work, we find classical TMO brownmillerite SrCoO 2.5 (B-SCO) films with ordered oxygen vacancy channels experiencing an interesting transition to a metastable perovskite phase (M-SCO) in a weak acidic solution. M-SCO exhibits a strong ferromagnetism (1.01 μ B /Co, T c > 200 K) and a greatly elevated electrical conductivity (∼10 4 of pristine SrCoO 2.5 ), which is similar to the prototypical perovskite SrCoO 3 . Besides, such M-SCO tends to transform back to B-SCO in a vacuum environment or heating at a relatively low temperature. Two possible mechanisms (H 2 O addition/active oxygen filling) have been proposed to explain the phenomenon, and the control experiments demonstrate that the latter mechanism is the dominant process. Our work finds a new way to realize cobaltite perovskite with enhanced magnetoelectric properties and may deepen the understanding of oxide−proton interaction in an aqueous solution.

Strain-Induced Uphill Hydrogen Distribution in Perovskite Oxide Films

“…Therefore, the uphill distribution does not necessarily depend on the method to introduce hydrogen, which can be maintained in the absence of an electric field. This is also the first successful attempt of hydrogenation to perovskite oxides via metal-alkaline treatment, which avoids the use of electric gating or H 2 gas at high temperatures. , Note that metal-acid processing can also inject hydrogen into NNO via proton–electron codoping, but acid will inevitably corrode the surface of oxides. , Since most perovskite oxides are stable in alkaline conditions, the metal-alkaline protocol provides opportunities for exploring new hydrogenated phases of perovskite oxides.…”

“…25,27 Note that metal-acid processing can also inject hydrogen into NNO via proton−electron codoping, 55 but acid will inevitably corrode the surface of oxides. 8,56 Since most perovskite oxides are stable in alkaline conditions, the metal-alkaline protocol provides opportunities for exploring new hydrogenated phases of perovskite oxides.…”

“…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 + …”

Protonation-Induced Colossal Lattice Expansion in La2/3Sr1/3MnO3

“…It has been proven that strongly correlated oxides, including SrCoO x , , ReNiO 3 (Re = rare-earth metals), ,, La 1– x Sr x MnO 3, , and VO 2, − can accommodate significant amounts of hydrogen, leading to substantial changes in the lattice and d-band electron filling. These changes, in turn, can induce quantum phase transitions and result in remarkable alterations in the electrical and magnetic properties.…”

Highly efficient and fast modulation of magnetic coupling interaction in the SrCoO2.5/La0.7Ca0.3MnO3 heterostructure

“…Very recently, an acid solution with rich protons has been reported to trigger the rapid phase transition within seconds, 17,18 which is attributed to the migration of the active oxygen species into the materials assisted by protons. The brownmillerite SrCoO 2.5 (B-SCO) with an oxygen-vacancies channel exhibits an oxygen-dependent topotactic phase transition.…”