Multi-scale structural analysis of the A-site and oxygen deficient perovskite Sr₁₁Mo₄O₂₃

Abstract

The long range average crystal structure, as well as the short and medium range structural features, of the A-site deficient and oxygen deficient perovskite SrMoO have been determined. Rietveld refinement of synchrotron X-ray and neutron powder diffraction data show that this compound is cubic with space group Fd3[combining macron]m and a lattice parameter of a = 16.4108 Å. These findings contradict earlier reports of a tetragonal crystal structure. SrMoO appears to be isostructural with BaWO, except that the disordered coordination environment around one of the Mo sites seems to be a mixture of octahedral and square pyramidal instead of octahedral and tetrahedral. The short and medium range structural features have been inspected using the neutron pair distribution function (PDF). Short range correlations between the oxygen polyhedra surrounding the Mo(2) atom exist to avoid short O-O contacts. A model has been constructed which contains such correlations and is verified by reverse Monte Carlo (RMC) modeling of the PDF. The RMC refinements also give the distribution of inter-atomic distances in this compound which reveals how the various atomic positions are correlated and over what length scales. These results are important for understanding the ionic conduction pathways.

Synthesis conditions impact on Sr11Mo4O23 electroceramic: crystal structure, stability and transport properties

“…1) exhibit subtle differences, suggesting that SMO11 presents a lower symmetry than SMO14. The diffraction pattern of Sr 11 Mo 4 O 23 treated at 1400 C can be indexed with a cubic symmetry in the Fd 3m space group, as previously reported by King et al 20 This pattern was properly tted with this cubic model with a unit-cell parameter of 16.3982(2) A. Fig.…”

“…[17][18][19] On the other hand, King et al presented novel structural evidences and reported Sr 11 Mo 4 O 23 as cubic (Fd 3m), the difference between both materials only residing in the annealing temperature. 20 In addition, in a recent work, Kharton et al studied the ionic conductivity and also observed the mass changes with temperature. 21 So far, the physicochemical reasons behind these changes remain unknown.…”

New examples of non-cooperative octahedral tilting in a double perovskite: phase transitions in K3GaF6

“…Very recently Rb 3 AlF 6 was reported to have the same structure as -K 3 AlF 6 at room temperature (Rakhmatullin et al, 2020). There are also a few oxide and oxyfluoride compounds which have structures based on non-cooperative octahedral tilting (Bramnik et al, 2000;King et al, 2010King et al, , 2012King et al, , 2017Stö ger et al, 2010;Fry & Woodward, 2013).…”