Electrical and structural properties of Nb-doped SrTiO 3 ceramics J. Karczewski & B. Riegel & M. Gazda & P. Jasinski & B. Kusz Received: 27 January 2009 / Accepted: 6 May 2009 / Published online: 20 May 2009 # Springer Science + Business Media, LLC 2009 Abstract Niobium-doped strontium titanate synthesized via conventional solid-state reaction has been studied. Influence of niobium content on the lattice parameters and electrical conductivity has been reported. Various reduction conditions have been investigated. For samples reduced in hydrogen at 1400°C, a transition from thermally activated to metallic behavior has been observed. Maximum electri- cal conductivity (ca. 55 Scm -1 at 650°C) has been observed for the SrTi 0.98 Nb 0.02 O 3-δ sample. The relation of electrical conductivity with the porosity of the samples has been shown. Keywords Electrical conductivity . Nb-doped Strontium titanate . Anode materials . Solid oxide fuel cell 1 Introduction The NiO and yttria-stabilized zirconia (YSZ) cermet (Ni- YSZ) commercially used as an anode material for solid oxide fuel cells (SOFC) suffers some fundamental limita- tions. It seems to be necessary to discover a new anode material overcoming the disadvantages of Ni-YSZ. Fergus has compared a variety of the oxide anode materials [1]. Perovskites based on the strontium titanate seem to be one of the most competitive choices. They can be used as an anode material for solid oxide fuel cells (SOFC) working at high as well as at intermediate temperatures. Such perovskite materials present a very good stability over working cycles in various atmospheres [2, 3], have large triple phase boundary [2, 4] and are chemically and thermally compatible with the electrolyte [2–5]. Moreover, they eliminate some fundamental problems of cermet anodes: deposition of carbon when using hydrocarbon fuels and poisoning by sulphur [2, 6, 7]. The SrTiO 3 is an example of the perovskite family of general formula ABO 3 . Its total electrical conductivity can be increased by doping a rare earth element into the A sublattice or a transition metal into the B sublattice [8–10]. Doped strontium titanates have been investigated since early 1980’ s, although most of the oldest works deal with the lanthanum doping [11–15]. Later, the yttrium addition to the pure strontium titanate and the deficiency on the strontium site has been examined [7, 8, 16, 17]. Recently, the attention has been paid again to the niobium doping into the B sublattice [18–21], where Nb 5+ substitutes Ti 4+ , bringing more oxide ions or more electrons into the system. Niobium-doped samples have several significantly im- proved properties [8, 16, 18–20], depending on where the oxygen incorporates in the structure and to which extent the extra charge of Nb 5+ is compensated. Either the cation vacancies are created in order to fulfill the electroneutrality condition or there must be excessive oxygen ions occupy- ing the interstitial oxygen positions in perovskites. It is reported that probably the strontium vacancies are predom- inant defects in the donor-doped SrTiO 3 [22]. For equal number of A-site and B-site cations in ABO 3 the effect would be a creation of a strontium oxide phase. According to the Kröger-Vink notation it can be written, that if J Electroceram (2010) 24:326–330 DOI 10.1007/s10832-009-9578-7 J. Karczewski (*) : B. Riegel : M. Gazda : B. Kusz Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Gdansk, Poland e-mail: ja_kubek@wp.pl P. Jasinski Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Poland