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Highlights: [•] The conductivity increases as a function of factor dimensionality n. [•] After substituting the silicon remains in tetrahedral Site. [•] The Rietveld analysis confirms the substitution in the La site. [Copyright &y& Elsevier]

The preparation of (LaSr□)SiOO (0 ≤ x ≤ 2) samples with different amounts of cation vacancies is reported. Structure and unit-cell parameters were deduced by Rietveld analysis of XRD patterns. Structural features that enhance oxygen conductivity in Sr-doped apatites are discussed. Up to three components were detected in Si MAS-NMR spectra which change with the amount and distribution of cation vacancies. In general, oxygen conductivity increases with the amount of vacancies at La1 (6h) sites, passing through a maximum for x = 0.4. In the case of activation energy, a minimum is detected near x = 1.2, indicating that entropic and enthalpic change in different ways. The presence of cation vacancies should enhance oxygen hopping along c-axis; however, the analysis of the frequency dependence of conductivity suggests that oxygen motions are produced along three axes. [ABSTRACT FROM AUTHOR]