Solid-State Electrochemical Protonation of SrCoO_2.5 into H_xSrCoO_2.5 (x = 1, 1.5, and 2)

Abstract

Among many transition-metal oxides (TMOs), strontium cobalt oxide (SrCoO x ) is a promising active material for advanced memory devices due to the versatile valence state of cobalt ions. Several SrCoO x -based electrochemical devices have been proposed, but solid-state protonation from SrCoO 2.5 to H x SrCoO 2.5 (x = 1, 1.5, and 2) at room temperature has not been demonstrated thus far due to the absence of an appropriate solid electrolyte. Here, we demonstrate a solid-state electrochemical protonation of SrCoO 2.5 using mesoporous amorphous 12CaO• 7Al 2 O 3 (CAN) film as the solid electrolyte. The crystalline phase discretely changed from SrCoO 2.5 to HSrCoO 2.5 (phase A), H 1.5 SrCoO 2.5 (phase B), and H 2 SrCoO 2.5 (phase C) through formation of an intermediate phase of H 1.25 SrCoO 2.5 . H 1.5 SrCoO 2.5 (phase B) was colorless transparent and showed weak ferromagnetism. The present results indicate that the CAN film can be used as the solid electrolyte for the protonation treatment of TMOs.

Voltage Control of Patterned Metal/Insulator Properties in Oxide/Oxyfluoride Lateral Perovskite Heterostructures via Ion Gel Gating

“…We attribute this latter phase to hydrogenated H x SrFeO 2.5 , which has been reported once in ionically-gated strontium ferrite [4] as well as in several studies involving the analogous H x S-rCoO 2.5 system. [12][13][14] While we do not quantify the hydrogen content, x, in these films, previous studies with cobaltite films reported an ≈4.2% c-axis lattice parameter expansion on SrTiO 3 substrates upon incorporation of one equivalent of hydrogen, as measured by time-of-flight secondary ion mass spectrometry, [13,55] in excellent agreement with the lattice expansion we observe in these films (3.8%). Future studies could investigate the quantitative hydrogenation of ferrite films by this method.…”

“…In the ubiquitous field-effect transistor, for example, this is achieved by applying an electric field across a gate insulator interfaced with the active material to modulate the interfacial charge-carrier population. However, due to the high carrier densities and short screening lengths also effective, such as in the case of voltage-driven shuttling of hydrogen [4,[12][13][14][36][37][38] and nitrogen. [39] Importantly, in contrast to electrostatic gating, these electrochemical effects are not limited by an interfacial electrostatic screening length.…”

“…Electrochemical control of oxygen vacancies using ionic gating has thus been demonstrated to tune the electronic, magnetic, and/or optical properties of cobaltites, [ 7,12,13,21–27 ] manganites, [ 23,28,29 ] nickelates, [ 30,31 ] and ferrites, [ 8,24,32–34 ] to name just a few examples in the field of oxide perovskites, as well as phenomena stemming from interlayer interactions in perovskite vertical heterostructures [ 33,35 ] and properties of various other oxides. [ 1 ] While this oxygen vacancy modulation is a key pathway toward electrochemical control of properties in oxides, electrochemical manipulation via other ions is also effective, such as in the case of voltage‐driven shuttling of hydrogen [ 4,12–14,36–38 ] and nitrogen. [ 39 ] Importantly, in contrast to electrostatic gating, these electrochemical effects are not limited by an interfacial electrostatic screening length.…”

“…[1,2,9] However, particularly effective control over magnetic, electronic, and optical function can also be realized through electrochemical gating of perovskites, in which the interfacial electric field reduces and oxidizes the perovskite through the removal and re-insertion of oxygen ions. The precise mechanism of this electrochemistry has not been explained in full, although hypothesized mechanisms point to either molecular oxygen [10,11] or water [7,[12][13][14] as the source and sink for the lattice O 2− . Electrochemical gating of this nature has attracted particular attention for neuromorphic, [1,2,15,16] magneto-ionic, [1,2,[17][18][19] and electrochromic [20] device applications.…”

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

“…The magnetic behaviors (M−H & M−T curves) demonstrate that the magnetization of the B-SCO film (∼42 nm) is rather weak (Figure 2a) with only small uncompensated magnetic moments and a tiny coercive field, consistent with previous reports. 35,36 By contrast, the M-SCO film has significant ferromagnetism (note that the thickness of M-SCO is approximately 24 nm due to corrosion by an acid). For a freshly prepared M-SCO film, the magnetic hysteresis loop gives the saturated magnetization M S approximately 1.01 μ B / Co (the same order of magnitude as that of the SrCoO In addition to the significant improvement of ferromagnetism, the electrical conductance of M-SCO also shows an abrupt increase than that of B-SCO, as demonstrated by the resistance−temperature (R−T) relationship in Figure 2b.…”