Klaus Reichmann

Characterisation of LaNi1 − xCoxO3 as a possible SOFC cathode material

The perovskite with nominal composition LaNi0.6Co0.4O3 was evaluated for the use as a possible solid oxide fuel cell (SOFC) cathode. Thick film layers, printed and fired on yttria stabilised zirconia (YSZ) electrolyte, exhibit good characteristics, i.e. a porous microstructure, a temperature expansion coefficient of 11.9 × 10−6/K, and low, temperature independent, sheet resistivity. However, LaNi0.6Co0.4O3 reacts with YSZ at lower temperatures than other perovskites which are usually used for SOFC cathodes.

Bismuth Sodium Titanate Based Materials for Piezoelectric Actuators

The ban of lead in many electronic products and the expectation that, sooner or later, this ban will include the currently exempt piezoelectric ceramics based on Lead-Zirconate-Titanate has motivated many research groups to look for lead-free substitutes. After a short overview on different classes of lead-free piezoelectric ceramics with large strain, this review will focus on Bismuth-Sodium-Titanate and its solid solutions. These compounds exhibit extraordinarily high strain, due to a field induced phase transition, which makes them attractive for actuator applications. The structural features of these materials and the origin of the field-induced strain will be revised. Technologies for texturing, which increases the useable strain, will be introduced. Finally, the features that are relevant for the application of these materials in a multilayer design will be summarized.

Weak-relaxor behaviour in Bi/Yb-doped KNbO3 ceramics

Weak-relaxor behaviour was observed in K1−xBixNb1−xYbxO3 ceramics with x = 0.20 and x = 0.30. According to x-ray diffraction analysis, the crystal structure of these ceramics can be described by the cubic centrosymmetric Pm3¯m space group; however Raman spectroscopy reveals both the occurrence of local lattice distortions and the disruption of the long-range ferroelectric order. The local lattice strain caused by the larger Yb3+ combined with the presence of Bi3+, which lone-pair of electrons induces further local distortions, gives rise to polar nanoregions (PNRs). Nevertheless, the interaction between the PNRs appears weak and proper relaxor behaviour does not develop.

Morphology and electrical properties of SrTiO3-films on conductive oxide films

Abstract The effect of various electrically conductive oxides on the morphology and the electrical properties of SrTiO 3 films (STO) was investigated by means of scanning electron microscopy, impedance analysis and leakage current measurement (DC). LaNiO 3 (LNO), La 0.5 Sr 0.5 CoO 3 (LSCO) and La 0.7 Sr 0.3 MnO 3 (LSMO) as electrically conductive oxides were deposited on platinized silicon wafers by chemical solution deposition (CSD) via the propionate route. Subsequently a film of STO was deposited by CSD of an acetate based precursor solution. Platinum contacts were sputtered onto the STO film to act as top electrodes. The STO films in these multilayer structures showed significant differences to STO films grown directly on the platinized substrate with respect to morphology as well as to the electrical properties.

Formation of Images and Surface Relief Gratings in Photosensitive Polymers Containing SCN Groups

Poly(4-vinylbenzyl thiocyanate) (PVBT) and a copolymer of styrene and 4-vinylbenzyl thiocyanate (PST-co-VBT) were assessed as dual-tone imaging systems. These polymers change their refractive index under deep UV irradiation as a result of the photoisomerization of SCN to NCS groups. Subsequent modification of the illuminated zones with gaseous amines grave thiourea groups via an addition reaction. The post-exposure modification of the film with gaseous amines produced large increasese of the film thickness (formation of negative images). This effect was utilized to produce surface relief gratings. Using contact lithography with λ + 193 and 248 nm, gratings with periods Λ = 300 and Λ = 600 nm were obtained. Under selected experimental conditions, a nucleophilic substitution (S N ) of the SCN units in the unirradiated zones by amines was achieved (formation of positive images). Gratings of these types are of general interest for the setup of organic lasers based upon the principle of distributed feedback (DFB) as well as for holographic recordings.

NTC Ceramics: Past, Present and Future

In contrast with metals, the resistivity of ceramics decreases with increasing temperatures. This phenomenon was first discovered in 1833 by Faraday and remained a mere scientific curiosity until 1930, when Samuel Ruben proposed the fabrication of a pyrometer device, which explored the negative temperature coefficient (NTC) of resistance exhibit by Cu2O. Eight decades later, NTC ceramic thermistors constitute an important business segment for most electroceramic manufacturers. Here, we present a review of the most significant scientific and technological advances, which lead to the enormous commercial success of NTC thermistors. This review concludes with an outlook into future possible applications of NTC ceramics, providing that some current technological shortcomings (such as ageing) are resolved.

Strength and Fractography of Piezoceramic Multilayer Stacks

Modern low-voltage piezoelectric actuators consist of a stack of piezoceramic layers (PZT) with metallic electrodes in between. Due to the use of these parts in automotive applications, a big but sensitive market is opened. During application mechanical stresses are an inherent loading of these electro-mechanical converter components. Therefore some strength of the actuators is necessary to guarantee a demanded life time. Bending and tensile tests were performed on commercial components to measure the strength in axial direction. Fracture surfaces were investigated with the methods of fractography to get information about the weakest links in the microstructure.

The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT)

The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La3+ donor-doped, Fe3+ acceptor-doped and La3+/Fe3+-co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.

Effect of Isovalent B-Site Doping on Structural and Electrical Properties of Bismuth-Sodium-Titanate

Samples exhibiting substitution of Titanium in Bismuth-Sodium-Titanate (BNT) by isovalent Zirconium, Tin and Germanium (Bi0.5Na0.5Ti(1-x)DxO3 with D = Zr, Ge and Sn and x = 0.0025; 0.0050; 0.01; 0.02; 0.04; 0.08) were investigated with respect to microstructure, relative permittivity, loss factor and polarization. The substituents differ in mass, ionic radius and d-electron configuration. The shift of transitions observed in plots of permittivity and loss factor vs. temperature indicate the influence of the ionic radius. The occurrence of a pinched hysteresis loop at ambient temperature in the Sn-doped samples and the absence of any pinching in the hysteresis loops of Zr-and Ge-doped samples give rise to the assumption that this feature of polarization is connected to the ionic radius combined with the d10 electron configuration of Sn4+.

Investigation of reactions between BaTiO3 and La(Ni,Co)O3 by diffusion couples

The diffusion of cations and the formation of compounds at the interface of diffusion couples of BaTiO3 and LaNi0.6Co0.4O3 have been investigated by scanning electron microscopy and energy dispersive X-ray spectroscopy. The firing conditions have been varied with respect to firing temperature, firing time and heating rate. At the interface between BaTiO3 and LaNi0.6Co0.4O3 a layer of a perovskite type compound with varying composition is formed. Ti and La ions diffuse preferentially towards the reaction layer from the BaTiO3 and the LaNi0.6Co0.4O3, respectively. A consequence of the preferred diffusion of Ti towards the reaction layer is a depletion of Ti and the enrichment of Ba within the BaTiO3 adjacent to the interface causing the formation of overstoichiometric BaTiO3 (with respect to Ba), which is known to exhibit pronounced grain growth inhibition. The zone of reduced grain size is found to reach approximately 200 μm into the BaTiO3 bulk.