Synthesis and Characterization of New Mixed-Metal Triple-Layered Perovskites, Na2La2Ti3-xRuxO10(x≤ 1.0)

Abstract

The properties of the triple-layered Ruddlesden−Popper oxide Na2La2Ti3O10 have been modified by substituting ruthenium for titanium. Polycrystalline samples of ruthenium-doped sodium lanthanum titanium oxide, Na2La2Ti3-xRuxO10 (x = 0.25, 0.50, 0.75, 1.0), were prepared by heating the binary oxides at 1000 °C for 24 h under flowing argon. An upper limit to the degree of substitution was found at x = 1.0. The phases were structurally characterized by Rietveld analysis of X-ray powder diffraction data. Ruthenium cations are found to exhibit site preferences for the inner-layer octahedral sites, although not to the complete exclusion of the outer layer. A second-order Jahn−Teller effect is thought to influence the site selectively while providing an upper limit to the extent of ruthenium doping. There is spin-glass-like cusp in the magnetic susceptibility of the heavily doped (x = 1.0) phase that was not observed with the lighter doping levels. The oxides displayed high electrical resistivity (7.6 × 103 ≤ ρ ≤ 3.1 × 106 Ω cm), which decreased with increasing ruthenium content. The electronic behavior is consistent with that of narrow d-band oxides in which there are contributions from both disorder and electron correlation; accordingly, the oxides can be classified as disordered Mott insulators.