Discovery of the origin of high oxygen permeability in praseodymium nickel oxide-based materials

October 30, 2012
Refined crystal structures of Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ, Pr2Ni0.75Cu0.25O4+δ, and Sr2Ti0.9Co0.1O4-δ, which were obtained by the Rietveld analysis of neutron-diffraction data taken at room temperature. Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ and Pr2Ni0.75Cu0.25O4+δ have the excess interstitial O3 atoms.

A team led by Prof. Masatomo Yashima from the Graduate School of Science and Engineering, Tokyo Institute of Technology and Prof. Tatsumi Ishihara from the International Institute for Carbon-Neutral Energy Research and the Faculty of Engineering of Kyushu University has discovered the origin of the high oxygen permeability in praseodymium nickel oxides containing gallium and copper, Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ.

Ionic conductors with high oxygen permeability and mixed conductors with both high oxygen permeability and high electron conductivity are indispensable in improving the efficiency of fuel cells and oxygen concentrators. Therefore, much effort has been devoted to the development of ionic and mixed conductors. Oxides with the K2NiF4-type structure have recently been identified as mixed conductors with high ionic conductivity.

Temperature dependence of the isosurface of nuclear density in (a–d) Pr2Ni0.75Cu0.25O4+δ and (e–h) Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ. O2 and O3 stand for the apical and interstitial oxygen atoms, respectively. × denotes the bottleneck with the minimum nuclear density on the O2-O3 diffusion path. (a) 25 °C , (b) 602 °C, (c) 807 °C, (d) 1011 °C, (e) 20 °C, (f) 605 °C, (g) 810 °C, (h) 1011 °C.

Prof. Ishihara's team has previously discovered a Ga3+- and Cu2+-containing praseodymium with the K2NiF4-type structure that exhibits high oxygen permeability. Prof. Yashima's group has visualized the diffusion pathways of oxide ions at an in a similar material, (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+δ. However, the roles of Ga3+ and Cu2+ in the high oxygen permeability of praseodymium nickel oxides and the relationship between interstitial oxygen and oxygen permeability have not been understood well.

The oxygen permeability and δ in three mixed conductors with the K2NiF4-type structure, Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ, Pr2Ni0.75Cu0.25O4+δ, and Sr2Ti0.9Co0.1O4-δ, were measured. Their crystal structures and nuclear and electron densities were analyzed by Rietveld and maximum-entropy methods using the neutron diffraction data obtained by the neutron diffractometer HERMES at the Institute for Materials Research, Tohoku University, located at the research reactor JRR-3M of the Japan Atomic Energy Agency, and using the synchrotron X-ray diffraction data collected by the high-resolution powder diffractometer installed at the BL-4B2 beamline of the Photon Factory, KEK. All the three compositions were confirmed to have the tetragonal K2NiF4-type structure (Fig. 1). Excess interstitial O3 oxygen atoms were observed in Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ and Pr2Ni0.75Cu0.25O4+δ, while Sr2Ti0.9Co0.1O4-δ does not have interstitial O3 atoms but oxygen defects.

The oxygen permeability of Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ is higher than those of conventional mixed conductors, while the oxygen permeability of Sr2Ti0.9Co0.1O4-δ is much lower. In this work the origin of the high oxygen permeability of Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ was found to be (1) a large amount of excess interstitial oxygen atoms formed by higher valence gallium ion Ga3+ and (2) higher mobility of apical oxygen due to longer and weaker copper-apical oxygen bond. At high temperatures between 600 ° and 1000 °C, the nuclear-density distribution of the interstitial O3 oxygen atom connected with that of apical O2 lattice oxygen atom. The connected nuclear densities indicate the oxide-ion diffusion pathway between the O3 and O2 atoms (Fig. 2). The nuclear density around the center of the interstitial O3 atom decreased with increasing temperature, while the minimum nuclear density on the O2-O3 path increased. The oxygen permeation rate increased with the minimum nuclear density, which indicates that the minimum nuclear density is an important parameter that governs the oxide-ion diffusivity.

The present work demonstrates a new concept in the design of interstitial-ion conductors with high oxygen permeability and can lead to the development of new ionic conductors for better solid oxide fuel cells and oxygen concentrators.

Explore further: Ceramic, heal thyself

Related Stories

Ceramic, heal thyself

April 17, 2008

A new computer simulation has revealed a self-healing behavior in a common ceramic that may lead to development of radiation-resistant materials for nuclear power plants and waste storage.

SSRL contributes to platinum-based catalyst design

August 15, 2012

( -- Researchers from two SLAC-Stanford joint institutes, the Stanford Institute for Materials and Energy Sciences (SIMES) and the SUNCAT Center for Interface Science and Catalysis, recently joined forces to investigate ...

Researchers probe invisible vacancies in fuel cell materials

August 22, 2012

( -- Knowing the position of missing oxygen atoms could be the key to cheaper solid oxide fuel cells with longer lifetimes. New microscopy research from the Department of Energy's Oak Ridge National Laboratory is ...

Recommended for you

Calcium channel blockers caught in the act at atomic level

August 24, 2016

An atomic level analysis has revealed how two classes of calcium channel blockers, widely prescribed for heart disease patients, produce separate therapeutic effects through their actions at different sites on the calcium ...

New electrical energy storage material shows its power

August 24, 2016

A powerful new material developed by Northwestern University chemist William Dichtel and his research team could one day speed up the charging process of electric cars and help increase their driving range.

Bio-inspired tire design: Where the rubber meets the road

August 24, 2016

The fascination with the ability of geckos to scamper up smooth walls and hang upside down from improbable surfaces has entranced scientists at least as far back as Aristotle, who noted the reptile's remarkable feats in his ...

Selecting the right house plant could improve indoor air

August 24, 2016

Indoor air pollution is an important environmental threat to human health, leading to symptoms of "sick building syndrome." But researchers report that surrounding oneself with certain house plants could combat the potentially ...

LiH mediates low-temperature ammonia synthesis

August 24, 2016

Nearly half of the world's population is fed by industrial N2 fixation, i. e., the Harbor-Bosch process. Although exergonic in nature, NH3 synthesis from N2 and H2 catalyzed by the fused Fe has to be conducted at elevated ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.