Versatile and Highly Efficient Controls of Reversible Topotactic Metal–Insulator Transitions through Proton Intercalation

Abstract

The ability to tailor a new crystalline structure and associated functionalities with a variety of stimuli is one of the key issues in material design. Developing synthetic routes to functional materials with partially absorbed non-metallic elements (i.e., hydrogen and nitrogen) could open up more possibilities for preparing novel families of electronically active oxide compounds. Here, we introduce a fast and reversible uptake and release of hydrogen in epitaxial ABO3 manganite films through an adapted low-frequency inductively coupled plasma technology. Compared with traditional dopants of metallic cations, the plasma-assisted hydrogen implantations not only produce reversibly structural transformations from pristine perovskite (PV) phase to a newly found protonation-driven brownmillerite (BM) one, but also regulate remarkably different electronic properties driving the material from a ferromagnetic metal to a weakly ferromagnetic insulator for a range of manganite(La1-xSrxMnO3) thin films. Moreover, a reversible perovskite-brownmillerite-perovskite (PV-HBM-PV') transition is achieved at a relatively low temperature (T ≤ 350°C), enabling multi-functional modulations for integrated electronic systems. The fast, low-temperature control of structural and electronic properties by the facile hydrogenation/dehydrogenation treatment substantially widens the space for exploring new possibilities of novel properties in proton-based multifunctional materials.

Hydrogen Control of Double Exchange Interaction in La0.67Sr0.33MnO3 for Ionic–Electric–Magnetic Coupled Applications

“…The film was still ferromagnetic, with a smaller magnetic moment of 0.9 μ B /Mn at 10 K and 0.3 T (blue lines in Figure 1c,d), which differs from that of the oxygen‐driven transition into an antiferromagnetic insulator. [ 15,22 ] The slightly larger coercive field (blue line in the inset) might be attributed to the pinning of the magnetic domains by the non‐ferromagnetic regions in the film. [ 15 ] Although annealing the SrTiO 3 substrate in hydrogen also generated a magnetic signal, we confirmed that its value was negligible compared with that of the LSMO (Figure S2, Supporting Information).…”

“…At first glance, the metal–insulator transition observed in this study seems similar to the oxygen‐driven transition. [ 15 ] Although metal‐to‐insulator transitions occur when annealing LSMO films in a reducing environment (for example, in hydrogen (our work) or under a vacuum [ 15 ] ), we also successfully recovered the physical properties of the AG films by annealing the AH film in a reducing environment again (argon [our work]), rather than in an oxidizing environment (for example, oxygen [ 7,8,15,22 ] ). Furthermore, a much lower T a of 200 °C compared with the oxygen‐driven transition (>500 °C) [ 15 ] provides insight into hydrogen‐driven control because the much smaller size of the hydrogen ions enables faster hopping in an oxide, with a lower activation energy of 0.3–0.8 eV [ 24,25 ] (e.g., 0.8–1.0 eV for oxygen ions).…”

“…This persistent structure was distinct from the oxygen‐driven topotactic transition from perovskite to brownmillerite. [ 15,22 ]…”

“…[ 30 ] Our comparatively small lattice volume expansion should prevent device delamination, which may occur in the oxygen‐driven topotactic transition owing to the extremely large volume expansion (6.6–8.4%). [ 22 ]…”

Defects in complex oxide thin films for electronics and energy applications: challenges and opportunities

“…275 Similar reversible phase transformations mediated by hydrogen and oxygen ions was also observed in VO 2 , ZnO, WO 3 , SrRuO 3 , La 1Àx Sr x MnO 3 , La 0.7 Sr 0.3 MnO 3 /SrIrO 3 superlattice films, etc. 18,164,[276][277][278][279][280][281] Water was also used as a gating medium for achieving hydrogen doping. 282 The ionization of water to form H + and OH À occurs when a bias voltage over 1.23 V is applied between an electrode and TMOs in water.…”