Dr. Mario Quilitz

Hochauflösungs-TEM/STEM spektroskopiert und bildet Strukturen atomar aufgelöst ab. Mit einer Mikrofluid-Probenkammer eignet sich das Elektronenmikroskop auch für In-situ-Untersuchungen zu lebens- und materialwissenschaftlichen Fragen.

Nanoscaled ZnO was synthesized by an electrochemical process using zinc or Al-alloyed zinc electrodes in an aqueous system with acetic acid as a conductive salt. Depending on the synthetical parameters, the precipitated precursor solids were found to consist of various compounds such as zincite, presumably δ-Zn(OH)2, β1-Zn(OH)2, ε-Zn(OH)2, Zn5(CO3)2(OH)6 and, in case an Al-alloyed electrode was used for the synthesis, Zn0.71Al0.29(OH)2(CO3)0.145·xH2O. The intermediate solids served as precursors for the subsequent thermal treatment resulting in zincite powders with various morphologies. Depending on the processing conditions, zincite was formed between 100 and 260 °C with a mean crystallite size between 6 and 25 nm. Selected zincite powders were pressed to pellets, sintered at temperatures between 900 and 1,100 °C and characterized by measurements of the electrical bulk conductivities, yielding values up to 1.69 S cm−1 in samples with 1.24 wt% Al. Comparison with samples prepared by precipitation methods showed that the latter had values of up to 44 S cm−1.

Transparent semiconducting ITO:Ti thin films, prepared by a sol-gel process, has been deposited by spin-coating technique onto alkali-free glass substrates. The as-coated films were annealed in ambient air at 550 °C for 1 h and further annealed in a reducing atmosphere. The influences of the Ti content in the sol on the surface morphology, microstructure, optical properties and electrical resistivity have been investigated. These properties were found to depend on the Ti content in the coating sol. Ti addition led to dense smooth layers with larger crystallite size (20–30 nm). Double layers synthesized with Ti:ITO = 0.53 wt% and submitted to reducing treatment in forming gas exhibited the lowest sheet resistance R□ = 60 Ω□ with an average transmittance of 87% at 550 nm.

Nanoscaled hydroxyapatite (n-HAp) was prepared by a wet chemical precipitation method, pressed to pellets and sintered at various temperatures between 900 and 1200°C. With input stoichiometries of Ca/P ratios between 1.4 and 2.0, compositions in the substoichiometric range of Ca/P between 1.45(1) and 1.62(3) were determined after preparation. After sintering, final values of the Ca/P ratio between 1.45(8) and 1.66(4) were found. Capacitances and dielectric losses were determined in the frequency range between 20 Hz and 1 MHz and dielectric constants calculated from the capacitances. Dependencies of the dielectric properties on the composition, as well as on sintering temperature and frequencies were investigated. The dielectric constants generally tend to increase with increasing Ca-content. Different behaviour was observed for low frequencies (below 103 Hz) and for compositions far from the stoichiometric point of hydroxyapatite (Ca/P: 1.67). Comparable results were found for dielectric losses.

Nanoscaled so called indium tin oxide In2O3:Sn (ITO) with a specific BET surface area of 50 m2/g to 60 m2/g was prepared via an electrochemical method in an aqueous system containing ammonium acetate as conductive salt. As an intermediate product of the synthesis nanocrystalline In(OH)3 is obtained which serves as a precursor for the subsequent calcinations accompanied by tin doping resulting in ITO powders with various tin concentrations. Its phase transitions and the reduction behaviour of hydroxide to oxide during the calcination process in air flow and forming gas atmosphere of N2 to H2 ratio of 95 to 5 respectively, have been investigated by high temperature X-ray diffraction, TG/DSC/MS, HRTEM and SEM analysis. Depending on the atmosphere dehydration of tin doped In(OH)3 started at 150 °C, cubic ITO solid solution formed between 190 °C and 300 °C. The total weight loss of the hydroxide of approx. 21% occurred mainly below 360 °C and the burn-out of organic components mainly between 308 °C and 316 °C. The results of DSC and MS analyses were in good agreement with the results of the X-ray diffraction. In addition, the products have been characterized by EDX associated with TEM, XPS, ICP-AES, BET analysis and 119Sn Mössbauer spectroscopy. Completely reacted samples of ITO have been processed to pellets, calcined and sintered in the temperature range between 900 °C and 1100 °C and characterized by measurements of the electrical conductivities of bulk and surface in the reduced as well as in the oxidized state giving values up to 1400 Scm−1.

In this study, we demonstrated that the electrochromic properties of silica/polyaniline nanocomposite films are superior to those of films made of pure polyaniline. The silica/polyaniline composite particles were synthesized using an inverse microemulsion method. The composite material was deposited on the FTO-coated glass by a spin coating. To compare the electrochromic properties with the pure polyaniline film, characterizations such as cyclovoltammetry, visible transmittance spectroscopy, and color contrast measurements were performed on both the films. The comparison showed an increase of durability for the composite film. This stability enhancement in the composite film was ascribed to the suppression of the formation of highly oxidized forms such as pernigraniline. This suppression is believed to come from the protective effect of silica in the composite nanoparticles.

Nanosized BaTiO3 powders with a specific surface area of 60-75 m2/g have been prepared by precipitation of a titanium ester with Ba(OH)2 solution at temperatures less than 100 °C. The effects of the Ba(OH)2 concentration, isopropanol mixing with water as a solvent, the Ba:Ti ratio and surface modifiers on the surface area, the particle size, the crystalline phase, the agglomeration and aggregation degree of the synthesized powders as well as dielectric properties of sintered pellets have been investigated. The properties of the obtained powders have been characterized with XRD, BET, TG-DTA, ICP-AES, HRTEM and dilatometer. A high concentration of Ba(OH)2 can increase the agglomeration and aggregation degree of the particles while the addition of isopropanol in water is beneficial for lowering it. To obtain stoichiometrical barium titanate, the ratio of Ba:Ti should be 1.1. The leaching of barium ions during processing can be limited by washing the powder with ammonia solution at pH 10.2. A BaTiO3 ceramic (95.8% of the theoretic density) has been fabricated by sintering the powders at 1250 °C for 2 h.