Interstitial Oxygen in Perovskite-Related Sr_6–2xNb_2+2xO_11+3x

Abstract

Solid solutions of perovskite-related compounds Sr6–2x Nb2+2x O11+3x (0.103 ≤ x ≤ 0.333) were synthesized at 1523 K in air. The crystal structures were determined and refined by a combined powder X-ray and neutron Rietveld method (Fm3̅m, a = 8.3103Å, Z = 2, R p = 4.02%, wR p = 5.63%, χ2 = 4.44, 23 °C, for example, with x = 0.103). According to the Fourier synthesis map analysis, a new structural model, which includes interstitial oxygen, is proposed for the title compounds. The metal atoms fully occupy the A or B-sites of the perovskite (ABO3) structure. The pure Nb site and the mixed Sr/Nb site form a rock-salt type ordering in the B-site. The oxygen atoms and anionic vacancies are distributed statistically over the normal (O1 at 24e site) and interstitial positions (O2 at 48h site), and the occupancies for the interstitial sites are 8.5–15.4%. According to the electrical conductivities as functions of temperature and oxygen partial pressure under dry and wet air, the compounds are predominant oxide ion conductors at high temperatures and proton conductors as well at lower temperatures under wet air. The total conductivity increases with increasing strontium content, or decreasing oxygen content but increasing site occupancy at the interstitial oxygen site.

Drastic Differences between the Local and the Average Structures of Sr2MSbO5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

“…The average crystal structures and conductivities of several A 2 BB ′O 5.5 compounds which have very large B -site cations have been reported previously. − These compounds all have ideal cubic double-perovskite average structures with space group Fm -3 m and no long-range ordering of the oxygen vacancies. They also share a tendency to absorb water to form hydrated compounds.…”

Synthesis and Properties of Charge-Ordered Thallium Halide Perovskites, CsTl+0.5Tl3+0.5X3 (X = F or Cl): Theoretical Precursors for Superconductivity?

“…The appearance of an interstitial anion (as Cl2 in our case) has been observed in some oxygen-containing double perovskites with large B-site cations (as Tl 1+ in our case), such as Sr 2 (Sr 1-x M 1+x )O 6 (B = Nb, Ta) and Sr 2 MSbO 6 (M = Ca, Sr, Ba). [25][26][27] The large B-site cation causes non-harmonic atomic displacements that drives some oxygen to interstitial site and leaves oxygen vacancies in the original positions.…”

Sr4AlNbO8: A new crystal structure type determined from powder X-ray data

“…Sr 4 AlNbO 8 was synthesized by a solid-state reaction from a nominal mixture of high-purity SrCO 3 [4], Sr 6À2x Nb 2+2x O 11+3x (xE0.23) [5], and Sr 2 AlNbO 6 [1].…”

“…1) with the space group and the initial unit cell parameters known from the previous work [ impurity phases. The atomic parameters for the impurities were adopted from values found in the literature [1,[3][4][5]. At the beginning, a structural model with only a dummy atom at an arbitrary position in the unit cell was used.…”