Electrochemical oxidation of hematite (α-Fe 2 O 3 ) nano-particulate films at 600 mV vs. Ag + /AgCl reference in KOH electrolyte forms a species at the hematite surface which causes a new transition in the upper Hubbard band between the Fe(3d)-O(2p) state region and the Fe(4sp)-O(2p) region, as evidenced by oxygen near edge x-ray absorption fine structure (NEXAFS) spectra. The electrochemical origin of this transition suggests that it is related with a surface state. This transition, not known for pristine α-Fe 2 O 3 is at about the same x-ray energy, where pristine 1% Si doped Si:Fe 2 O 3 has such transition. Occurrence of this state coincides with the onset of an oxidative dark current wave at around 535 mV -a potential range, where the tunneling exchange current has been previously reported to increase by three orders of magnitude with the valence band and the transfer coefficient by a factor of 10. Oxidation to only 200 mV does not form such extra NEXAFS feature, supporting that a critical electrochemical potential between 200 and 600 mV is necessary to change the electronic structure of the iron oxide at the surface. Decrease of the surface roughness, as suggested by visual inspection, profilometry and x-ray reflectivity, points to faceting as potential structural origin of the surface state.

An approximately 125 nm thick pulsed laser deposited blue, nonstoichiometric WO 3Àδ film grows on TiO 2 (110) in the [220] direction. Oxidative treatment at 400 °C turns the film color from blue to yellow and improves the film quality considerably, as shown by improvement of the Kiessig oscillations in the X-ray reflectometry curves. Detailed analysis of resonant valence band photoemission spectra of the as-deposited nonstoichiometric blue film and oxidized yellow film suggests that a transition near the Fermi energy originates from the nonstoichiometry, i.e., oxygen deficiency, and insofar poses electronic defect states that partially can be eliminated by heat treatment in oxygen. The defects of the as-deposited blue film seem to be located throughout the film, except for the top surface due to exposure to oxygen in ambient air. Thermal after-treatment under oxygen heals the defects in the bulk, whereas residual defect states appear to remain near the filmÀsubstrate interface. Potential strain at the substrateÀfilm interface due to lattice mismatch may be one origin for the remanence of the defect states in the bulk.

In a three-step development process CaCu 3 Ti 4 O 12 -based bulk ceramic pellets, tape-casted multilayer ceramic laminates, and multilayer ceramic capacitors with cofired electrodes were fabricated. The sintering behavior, microstructure, electrical resistivity, and dielectric properties were studied. At a firing temperature of 1050°C, an effective permittivity of about e 0 = 60 000 and 10 000 was observed for sintered pellets and multilayer laminates, respectively. The typical grain growth observed in pellets is suppressed in multilayer laminates. Impedance spectroscopy was employed to show that the bulk grain resistivity is similar in pellets and multilayer laminates, but the grain-boundary resistivity is higher in pellets. Tapes were processed into multilayer capacitors with Ag/Pd electrodes and cofired at 1050°C. All three types of samples, pellets, laminates, and capacitors were also processed with a glass additive, in which case they can be cofired at a lower temperature of 900°C. In glass-containing pellets, the temperature dependence of permittivity is weak and exhibits X7R characteristics for frequencies below % 60 kHz. Our results demonstrate the high potential of CaCu 3 Ti 4 O 12 for application in monolithic as well as in integrated multilayer capacitors.A. Feteira-contributing editor Manuscript No. 34996.

The influence of sintering temperature and dwell time on the microstructure formation and dielectric properties of CaCu3Ti4O12 ceramics was investigated. For sintering temperatures of 1050 and 1100 °C significant differences in the CaCu3Ti4O12 ceramic microstructure and the segregation of a CuOx-rich phase towards the grain boundary (GB) areas were observed with increasing dwell time. In addition to the formation of a semiconducting bulk and insulating grain boundary phase the segregated CuOx forms an intergranular phase, and the effects of this phase on the dielectric properties are rather intriguing. At sintering temperature below 1050 °C only small amounts of CuOx segregate, whereas sintering above 1050 °C (e.g., 1100 °C) leads to increased evaporation of the CuOx. Therefore, the effects of the CuOx-rich intergranular phase upon the dielectric properties are felt strongest in samples sintered at 1050 °C. Such effects are discussed in terms of microstructural variations due to liquid phase sintering behavior facilitated by the TiO2-CuOx-eutectic, which appears to be melted at high sintering temperature prior to evaporation of CuOx at prolonged dwell times at the highest sintering temperatures (1100 °C).