Hydrogen-Induced Topotactic Phase Transformations of Cobaltite Thin Films

Area of Science:

• Materials Science
• Solid-State Chemistry
• Thin Film Physics

Background:

• Ion migration in complex oxide thin films offers tunable properties for advanced applications.
• Direct hydrogenation for modulating physical properties remains underexplored compared to reduction processes.

Purpose of the Study:

• To investigate an unusual mechanism for hydrogen-induced topotactic phase transitions in perovskite La_0.7Sr_0.3CoO₃ thin films.
• To understand the atomic-scale role of hydrogen in these transitions via direct hydrogenation.
• To explore the impact of hydrogenation temperature on magnetic and electronic properties.

Main Methods:

• Annealing of La_0.7Sr_0.3CoO₃ thin films in a pure hydrogen gas environment at various temperatures.
• Analysis of topotactic phase transformations using experimental techniques (specific techniques not detailed in abstract).
• Density functional theory (DFT) calculations to elucidate the mechanism of phase transition.

Main Results:

• Topotactic phase transformation from perovskite (P) to hydrogenated-brownmillerite (H-BM) phase induced at temperatures as low as 220 °C.
• Higher hydrogenation temperatures (320-400 °C) hindered the progression toward more reduced phases.
• DFT calculations indicate hydroxyl bond formation, lowering oxygen vacancy formation energy and facilitating P to H-BM transition.

Conclusions:

• Hydrogen acts as a key element in low-temperature topotactic phase transitions in complex oxides.
• This research presents a pathway for low-temperature modulation of complex oxide thin films using hydrogen.
• Potential applications in neuromorphic computing are suggested due to tunable magnetic and electronic properties.