Local Electronic Structure and Protonic Conductivity in Perovskite-Type Oxide, SrZrO3 (original) (raw)

Local electronic structures around hydrogen and acceptor ions in perovskite-type oxide, SrZrO3

Solid State Ionics, 2000

Local electronic structures around hydrogen and acceptor ions in SrZrO are simulated by the DV-Xa molecular orbital 3 method. In pure SrZrO , there is a band gap of about 6 eV between the O-2p valence band and the Zr-4d conduction band, 3 in agreement with experiments. When Y or Sc is doped into SrZrO , an acceptor level appears just above the valence band. 3 When hydrogen is introduced into SrZrO , a donor level appears below the conduction band. Also, an oxygen ion vacancy 3 makes the defect level below the conduction band. It is shown that charge compensation takes place among these acceptor, donor and defect levels. In addition, local electronic structure around hydrogen is found to change largely with the acceptor dopants, Sc and Y. For example, the metal-oxygen bond strength changes in the order, Y-O , Zr-O , Sc-O, which probably modifies the thermal vibrational amplitude of oxygen ions near hydrogen, and affects protonic conductivity in the doped SrZrO .

Short-Range Structure of Proton-Conducting Perovskite BaIn x Zr 1- x O 3- x /2 ( x = 0−0.75)

Chemistry of Materials, 2008

In a systematic study we investigate the effect of dopant level and hydration on the short-range structure of the proton conducting perovskite-type oxide BaInxZr1−xO 3−x/2 (x = 0 − 0.75), using infrared and Raman spectroscopy. The results show that doping leads to significant local distortions of the average cubic structure of these materials. By increasing the In concentration from x = 0 to x = 0.75 new bands appear and grow in intensity in both the IR and Raman spectra, showing that the local distortions become successively more and more pronounced. The structural distortions are largely uncorrelated to the presence of oxygen vacancies, but instead are mainly driven by the size difference between the In 3+ and Zr 4+ ions, which leads to displacements of the cations and to tilting of the (In/Zr)O6 octahedra. Based on our results, we suggest that there is a threshold between x = 0.10 and x = 0.25 where the local structural distortions propagate throughout the whole perovskite structure. Comparison of our spectroscopic data with the proton conductivity reported for the same materials indicates that the presence of extended structural distortions are favorable for fast proton transport.

Comparison of proton conduction in KTaO3 and SrZrO3

Chemical Physics, 2007

In the present paper, the authors focus on proton conduction pathways in a cubic perovskite KTaO 3 and an orthorhombic perovskite SrZrO 3 . Density functional theory with a generalized gradient approximation is used to find proton binding sites. The nudged elastic band method is used to find transition states between minima. With this potential energy map of binding and transition states, adjacency matrices and their analogs identify four types of conduction paths in KTaO 3 . Distortions from these paths are seen in SrZrO 3 . In both cases, the lowest energy path has an intraoctahedral transfer rate-limiting barrier. A Fourier analysis of the OH stretch in ab initio molecular dynamics simulations revealed a strongly redshifted OH stretch in SrZrO 3 relative to KTaO 3 . Hence, an orthorhombic system with a lowest energy conduction path limited by an intraoctahedral barrier can exhibit a redshifted OH stretch.

Tritium conductivity and isotope effect in proton-conducting perovskites

Journal of the …, 1999

High temperature protonic-conducting oxides based on the perovskite structure have been studied extensively since their discovery in 1981. The hydrogen and deuterium isotope conductivities in these oxides have been evaluated 2,3 recently, and their potential application as hydrogen separation membranes has been discussed. However, there are no reported studies on the tritium ion-conduction in these perovskites. In this paper, we report the hydrogen (H), deuterium (D), and tritium (T) conductivities of three protonic conducting perovskites, viz. SrZr 0.9 Yb 0.1 O 2.95 , BaCe 0.9 Yb 0.1 O 2.95 , and SrCe 0.95 Yb 0.05 O 2.975 . The conductivity of tritium ions through these perovskites not only gives fundamental information regarding the hydrogen transport in these perovskites, but also allows for the exciting possibility of tritium separation using these oxides as an electrochemical membrane.

Proton conduction in layered perovskite oxides

Solid State Ionics, 1994

Investigation of the electrical conductivity behavior of layered perovskite oxides, H2Ln2Ti3Om (Ln = La, Nd, Sm and Gd), has revealed that the materials exhibit moderate conductivity (~ 10-5 O-z cm-~ at 400°C) in hydrogen atmosphere, that is likely to be protonic in origin. It is suggested that the anion-deficient layered perovskite, Ln2Ti3Ogrq, formed in situ by dehydration, may interact with water vapor in hydrogen atmosphere in a manner analogous to that of yttria-doped BaCeO3 and SrCeO3 giving rise to the protonic conductivity. HLa2Ti2NbOlo and HCa2Nb30]o possessing a slightly different layered perovskite structure, exhibit a higher conductivity (~ 10-4 10-3 ~-~ cm-]) under the same conditions.

High oxide ion and proton conductivity in a disordered hexagonal perovskite

Nature Materials

Oxide ion and proton conductors, which exhibit high conductivity at intermediate temperature, are necessary to improve the performance of ceramic fuel cells. The crystal structure plays a pivotal role in defining the ionic conduction properties and the discovery of new materials is a challenging research focus. Here we show that the undoped hexagonal perovskite Ba7Nb4MoO20 supports pure ionic conduction with high proton and oxide ion conductivity at 510 °C (the bulk conductivity is 4.0 mS cm-1) and hence is an exceptional candidate for application as a dual-ion solid electrolyte in a ceramic fuel cell which will combine the advantages of both oxide ion and proton conducting electrolytes. Ba7Nb4MoO20 also showcases excellent chemical and electrical stability. Hexagonal perovskites form an important new family of materials for obtaining novel ionic conductors with potential applications in a range of energy-related technologies.

Ionic conductivity in new perovskite type oxides: NaAZrMO6 (A=Ca or Sr; M=Nb or Ta)

Materials Chemistry and Physics, 2008

New oxides of the type, NaAZrMO 6 (M = Ca or Sr; M = Nb or Ta), have been prepared by the solid-state reaction technique. Phase identification by powder X-ray diffraction (XRD) shows that NaCaZrMO 6 has orthorhombic perovskite type structure (Pnma) and NaSrZrMO 6 has cubic perovskite type structure (Pm3m). The grain morphology observation by scanning electron microscope (SEM) shows well-sintered grains. ac impedance spectra and electrical conductivity measurements in air, oxygen and nitrogen atmospheres indicate that they are probable oxide ion conductors with ionic conductivities of the order of 10 −3 S cm −1 at 750 • C.