Christian Pithan

Enhancement of p-type conductivity in nanocrystalline BaTiO3 ceramics

Undoped BaTiO3 ceramic samples with an average grain size of ∼35nm were prepared and the electrical properties investigated. The defect structure is dominated by acceptor impurities; therefore, the conductivity of nanocrystalline BaTiO3 is of p-type. Comparing with microcrystalline BaTiO3, the conductivity of nanocrystalline BaTiO3 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 BaTiO3 (∼0.3 versus ∼0.92eV for microcrystalline BaTiO3).

Nanocomposite thin films for miniaturized multi-layer ceramic capacitors prepared from barium titanate nanoparticle based hybrid solutions

In the present work a flexible approach for the wet chemical processing of nanocomposite functional thin films is demonstrated. Barium titanate (BTO) based nanocomposite thin films for future miniaturized multi-layer ceramic capacitors are chosen as model systems to introduce the concept of “hybrid solutions” which consist of stabile mixtures of reverse micelle derived BTO nanoparticle dispersions and conventional molecular precursor solutions of either the same (BTO:BTO) or a specifically different material such as zirconia (BTO:ZrO2). While in the case of using BTO:BTO hybrid solutions an interesting mode of microstructure control is found, the use of BTO:ZrO2 hybrid solutions with various BTO : ZrO2 ratios leads to nanocomposite films. BTO:BTO hybrid solutions yield columnar grown films with excellent permittivities up to 1050 with a significantly reduced number of coating steps at 700 °C. Low values of the temperature coefficient of capacitance are realized in the BTO–ZrO2 nanocomposite thin films. The observed dielectric behavior of these films is explained based on the formation of a core–shell type microstructure on the nanoscale. A detailed high resolution transmission electron microscopy study combined with Raman spectroscopy and X-ray diffraction gives evidence for the proposed BTO–ZrO2 nanocomposite character of these thin films.

Microemulsion mediated synthesis of nanocrystalline BaTiO3: possibilities, potential and perspectives

Abstract The present study gives an overview on the potential, possibilities and perspectives that the synthesis of functional materials, such as BaTiO3, with microemulsions as the reaction medium offers. Well defined nanocrystalline particles in the form of powders for further ceramic processing, as well as stable colloidal dispersions for the preparation of coatings may be obtained. The paper describes the formation, phase behaviour and stabilization of microemulsions and related water/oil/surfactant systems that may be used as a nanoreactor during particle formation. The reaction principles of microemulsion mediated synthesis are outlined and some examples of structural aspects, revealing size effects in these systems are implemented using advanced characterization techniques, such as Raman spectroscopy. Finally, the preparation of mesoscopic layers, covering the thickness gap between thin film and thick film technology, is demonstrated.