SrTiO3 (100) epitaxial films with thicknesses of 3, 1 μm, and 250 nm were prepared on MgO (100) substrates by pulsed‐laser deposition. The electrical conductivities of the thin films were systematically investigated as a function of temperature and ambient oxygen partial pressure. This was made possible by using a specially designed measurement setup, allowing the reliable determination of resistances of up to 25 GΩ in the temperature range of 600°–1000°C under continuously adjustable oxygen partial pressures ranging from 10−20 to 1 bar. The capabilities of the measurement setup were tested thoroughly by measuring a SrTiO3 single crystal. The well‐known characteristics, e.g., the decline of the conductivity with a slope of –1/4 under reducing conditions and the opposite +1/4 behavior in oxidizing atmospheres, are found in the log(σ)–log(pO2) profiles of the epitaxial films. However, the p‐type conductivity decreases, and the n‐type conductivity increases with decreasing film thickness. This phenomenon is attributed to the charge carrier redistribution in the surface space charge layers. Owing to the high surface‐to‐volume ratio, the space charge layers play an important role in thin films.

Undoped BaTiO 3 ceramic samples with an average grain size of ϳ35 nm were prepared and the electrical properties investigated. The defect structure is dominated by acceptor impurities; therefore, the conductivity of nanocrystalline BaTiO 3 is of p-type. Comparing with microcrystalline BaTiO 3 , the conductivity of nanocrystalline BaTiO 3 is about 1 to 2 orders of magnitude higher and the activation energy remarkably lower, which is ascribed to a greatly reduced oxidation enthalpy in nanocrystalline BaTiO 3 ͑ϳ0.3 versus ϳ0.92 eV for microcrystalline BaTiO 3 ͒. respectively, either in bulk form or thin-film form, have been prepared and the electrical properties investigated. Among these nanocrystalline oxides, the most dramatic property changes were observed for nanocrystalline CeO 2 . Comparing with microcrystalline counterparts, nanocrystalline CeO 2 is characterized by an orders-of-magnitude enhanced n-type conductivity and a significantly reduced activation energy. This phenomenon was explained by a greatly reduced reduction enthalpy of nanocrystalline CeO 2 , and the grain-boundary sites of lower vacancy formation enthalpy were proposed to be the atomic-level origin of this behavior.1,2 However, Kim and Maier 5 proposed that the higher conductivity of nanocrystalline CeO 2 is due to the electron accumulation at the grain boundaries. With its comparatively high electronic bulk contribution and high density of grain boundaries, the grain boundaries in nanocrystalline CeO 2 can become electronically conducting and dominate the overall behavior.Nanocrystalline BaTiO 3 materials of high density have also been prepared in thin-film form with an average grain size of ϳ25 nm, 10 and in bulk form with an average grain size of ϳ70 nm, 11 respectively, and the ferroelectric properties characterized. It is found that the ferroelectricity is weakened and the dielectric constant is remarkably lower for nanocrystalline BaTiO 3 ceramics.11 The ferroelectric response is even absent when the grain size is 25 nm.10 In neutral to oxidizing atmospheres, acceptor-doped BaTiO 3 shows a p-type conductivity. 12,13 In this letter, the defect and transport properties of nanocrystalline BaTiO 3 ceramics, nominally undoped but actually doped with acceptor impurities, are characterized, featuring an enhanced p-type conductivity.BaTiO 3 powder with an average particle diameter of ϳ10 nm was synthesized through the hydrolytic decomposition of a barium-titanium-isopropoxide solution in a waterin-oil microemulsion, consisting of 10.47 wt. % of Tergitol NP35, 80.70 wt. % of cyclohexane, 6.04 wt. % of 1-octanol and 2.79 wt. % of ultrapure and degassed water. Since the reaction is confined to the ultrasmall space of individual aqueous micelles, this approach allows the formation of nanopowders.14 The Ti/ Ba ratio of the powder was determined to be 1.0035± 0.0004 by x-ray fluorescence spectroscopy. According to inductively coupled plasma mass spectroscopy analyses, the nominally undoped BaTiO 3 powder was actually doped with acceptor impurities ͑...

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In order to investigate the dominant charge transport mechanisms of doped SrTiO, thin films, high temperature measurements were performed under varying oxygen partial pressures. To meet specific demands of SrTiO, thin films, a common 4-point measuring setup was improved profoundly by full triaxial shielding and the use of a solid state oxygen pump (made of YSZ). This allowed a precise analysis in the temperature range from 700°C to 1000°C and at oxygen partial pressures (PO*) between bar and 1 bar. The conduction behavior of (doped) SrTiO, thin films, as a function of pO2, revealed characteristics that substantially differ from those of bulk ceramics and cannot be explained by point defect chemistry. Additionally, segregation effects have been observed which lead to a restructuring of the film's morphology to a significant extent.

This work presents the first systematic study of conductivity characteristics of alkaline earth titanates in the form of polycrystalline and heteroepitaxial thin films as well as nanocrystalline ceramics as a function of temperature (between 600 • C and 1000 • C) and continuously adjustable oxygen partial pressures ranging from 10 −20 bar to 1 bar. Compared to the well-known log σ -log pO 2 profiles of single crystals, the conductivity behavior of CSD-prepared, polycrystalline SrTiO 3 thin films with a feature size of about 50 nm differs radically. The most prominent characteristics are a sharp drop under reducing conditions followed by a broad plateau region. Tailored investigations on heteroepitaxial as well as polycrystalline thin films grown by PLD and especially by studies on nanocrystalline BaTiO 3 ceramics with a mean grain size of ≤100 nm allowed an unambiguous assignment of the described effects to the nanocrystalline morphology of the samples.