Hydrogen-induced changes in electrical conduction properties of perovskite SmNiO₃ thin film

抄録

[Introduction]

Perovskite ReNiO₃ (Re=rare-earth) is known to display a metal-insulator transition with temperature change except for Re=La, and this is accompanied by a structural phase transition [1]. Furthermore, recently, it was reported that the electrical resistance of SmNiO₃(SNO) thin films increases by hydrogenation with Pt catalysts [2]. When hydrogenated ReNiO₃ is denoted as ReNiO₃H_x, this increase in resistance was thought to be due to the Mott transition, in which the eg orbital of Ni ion becomes half-filled due to the electron donation to Ni from hydrogen when x=1.

There is a previous study [3] that investigated the relationship between the hydrogen concentration and electrical resistance, but the hydrogen concentration was measured after the hydrogenated sample was exposed to air, which may have resulted in hydrogen desorption. We investigated the relationship between the resistance and hydrogen concentration by performing hydrogenation without exposing the sample to the atmosphere, and the results showed that the resistance increased for x < 0.5 and then decreased for x~1 [4]. However, a problem is that the studies used Pt catalysts, and the hydrogen concentration in the sample was not uniform.

[Problem & Purpose]

The purpose of this study is to elucidate the mechanism of hydrogen-induced changes in electrical conduction properties from the viewpoints of rare earths and hydrogen concentration. To overcome this problem, experiments without Pt catalysts were conducted to investigate the relationship between hydrogen concentration and electrical resistance.

[Experiment]

SmNiO₃ thin films epitaxially grown on an LaAlO₃ substrate by pulsed laser deposition were used in this study. Hydrogenation, electrical resistivity, and hydrogen concentration were measured in situ without exposure to air to minimize hydrogen desorption. For uniformly hydrogenate the sample, atomic hydrogen exposure was used for hydrogenation, and depth profile of hydrogen concentration was measured by nuclear reaction analysis (NRA).

[Results & Discussion]

Atomic hydrogen exposure increased the electrical resistance, and NRA experiments indicated that hydrogen concentrations were increasing. The experimental results show that the electrical resistance increases rapidly at a hydrogen concentration of x~0.5 (Figure), and the temperature dependence of the electrical resistance also changes to an Arrhenius-type one. From the analysis of the Arrhenius plot, its pre-exponential factor, and activation energy were mapped to hydrogen concentration. We will discuss the electronic mechanism by comparing the previous results with those of the previously performed results on NdNiO₃ thin films.

[References]

[1] J. B. Torrance et.al., Phys. Rev. B 45 8209(R) (1992)

[2] J. Shi et al. Nat Commun 5, 4860 (2014).

[3] J. Chen et al. Nat Commun 10, 694 (2019).

[4] I. Matsuzawa et al., Phys. Rev. Mater. in press (2023)