Thermal expansion behaviour in the oxygen deficient perovskites Sr2BSbO5.5 (B=Ca, Sr, Ba). Competing effects of water and oxygen ordering

Low‐energy Sr2MSbO5.5 (M = Ca and Sr) structures show significant distortions near oxygen vacancies

“…The significant distortions seen in neutron pair distribution analysis [ 12 ] of Sr 2 MSbO 5.5 , with M = Ca and Sr, have been computationally verified to be lower‐energy structures than the undistorted systems. The trend in lattice sizes is the same as the experiment, [ 12,15 ] even though the computational lattice sizes are expanded. The computational distortions feature trigonal bipyramids and square pyramids around the smaller ions with adjacent oxygen vacancies and square pyramids or distorted trigonal bipyramids and edge‐sharing polyhedra variations of pentagonal bipyramids for larger ions in agreement with neutron pair distribution analysis.…”

“…[ 9–11 ] However, some oxygen‐deficient perovskite systems do show significant rearrangements around oxygen vacancies. [ 12–15 ] A neutron pair distribution analysis [ 12 ] study of the double perovskite Sr 2 MSbO 5.5 (M = Ca and Sr) found that multiple structures where oxygen vacancies drastically altered the local geometry of the system could explain the same neutron‐scattering measurements.…”

“…However, Sr 2 MSbO 5.5 with Sr(II), M(II) and Sb(V) needs 5.5 oxygen ions to balance the positive charge. Some experimental studies [ 12,15 ] suggest that there can be significant lattice distortions around the oxygen vacancies in Sr 2 MSbO 5.5 , (M = Ca and Sr). Previous work [ 12 ] showed that neutron pair distribution analysis was consistent with either oxygen ions moving toward a vacancy, causing a square pyramid to trigonal bipyramid distortion as shown in Figure 2, or a 45° rotation of a SbO 6 octahedron allowing oxygen ions to form pentagonal bipyramids in the adjacent octahedra as shown in Figure 3.…”

“…In this study, structures that are inspired by the large lattice distortions seen in experimental studies of the double perovskites Sr 2 MSbO 5.5 ,(M = Ca and Sr), [ 12,15 ] along with traditional double perovskite structures, are optimized. Candidate structures are optimized to consider whether the trigonal bipyramidal distortion (Figure 2) or the 45° SbO 6 rotation distortion (Figure 3) or a 45° SbO 5 rotation (Figure 4) is the most likely rearrangement.…”

Removal of Methylene Violet from Aqueous Solutions Using BaSr2NbO5.5

“…Methyl violet 10B (MV) is known in medicine as Gentian violet and is the active ingredient in a Gram stain, used to classify bacteria [16]. It is used as a pH indicator, with a range between 0 and 1.6.…”