SYNTHESIS AND STRUCTURES OF CARRIER DOPED TITANATES WITH THE RUDDLESDEN-POPPER STRUCTURE (SR0.95LA0.05)(N+1)TINO3N+1 (N = 1, 2)

Carrier doping in Srn+1TinO3n+1 (n = 1, 2) was conducted by the substi tution of La for Sr and the simultaneous introduction of oxygen vacanc ies. Single-phase products of (Sr0.95La0.05)(n+1)TinO3n+1-delta(n = 1, delta = 0.05; n = 2, delta = 0.125) were synthesized by the solid-sta te reaction of Sr2TiO4 (or Sr3Ti2O7), La2O3 and Ti. When TiO2 was used as one of the starting compounds to maintain oxygen stoichiometry, co mpounds with higher n were observed besides the object phases. Structu ral refinement by Rietveld analysis revealed that the a-axis expands w hile the c-axis contracts with La doping. The contraction of the c-axi s is attributed to a shortened (Sr,La)-O distance, since the TiO6 octa hedra elongated in both a and c directions with doping. The change in the structure is discussed on the basis of the size of the substitutin g ion. The resistivity of the single-phase products was semiconducting with a very weak temperature dependence down to 80 K. (C) 1998 Elsevi er Science B.V. All rights reserved.