Wilhelmus Cornelis Keur

Mechanochemical synthesis of BaTiO3, Bi0.5Na0.5TiO3 and Ba2NaNb5O15 dielectric ceramics

Abstract In the last years, mechanochemical alloying has been proven to be an important technology for the synthesis of intermetallic compounds. This technology has recently been used as a new route for the synthesis of inorganic compounds. The use of mechanochemical synthesis opens possibilities for the synthesis of complex systems at low temperatures. In this paper we discuss the preparation of the powders BaTiO3, Bi0.5Na0.5TiO3 and Ba2NaNb5O15 by mechanochemical synthesis. Phase formation is studied by X-ray powder diffraction. Since partly amorphous powders are obtained the crystallisation behaviour is further investigated by high temperature X-ray powder diffraction. Ceramic pellets have been sintered starting from as-milled powders as well as prefired powders. Microstructure and dielectric properties are characterised.

The electrical and optical properties of thin layers of nano-sized antimony doped tinoxide particles

For the use in anti-static films on glass or polymeric substrates, transparent conductive layers can be prepared by spinning an aqueous suspension of nano-sized antimony-doped tinoxide (ATO) particles. These layers have a resistivity which is substantially higher than that of homogeneous ATO layers which are deposited by physical vapour deposition techniques. By curing the films to temperatures up to 700 °C, the resistivity of the particle layer can be decreased by two or three decades. Because the nano-sized particles are prepared by a low-temperature process a different mechanism can contribute to this decrease in resistivity. Possible effects which may influence the conductivity are sintering of the particles, change of the bulk material and the presence of an insulating layer at the outside of the particles. This decrease can be explained by the presence of an insulating antimony-rich layer on the outside of the particles, the thickness of which is reduced when the layer is cured. At temperatures above 350 °C, sintering of the particles also highly influences the decrease in resistivity. At temperatures above 700 °C, the resistivity is increased due to segregation of the antimony to the surface of the particle.

A 6Li, 7Li and 59Co MAS NMR study of rock salt type LixCoO2 (0.48≤x≤1.05)

Abstract Low temperature (LT, 400°C) and high temperature (HT, 900°C) Li x CoO 2 samples were synthesised with Li/Co ratios between 0.8 and 1.05. These samples were characterised by XRD, chemical analysis, 6 Li, 7 Li and 59 Co MAS NMR. 7 Li MAS NMR of the Li x CoO 2 -T 400 samples (LT) showed a single resonance line at −0.9 ppm, characteristic of lithium in an octahedral coordination. A somewhat narrower resonance at the same position was observed in the 7 Li MAS NMR spectra of the Li x CoO 2 -T 900 samples synthesised with a Li/Co ratio ≤0.95. The Li x CoO 2 -T 900 samples synthesised with a Li/Co ratio >0.95 showed several new lithium resonances, containing up to 35% of the signal intensity. The resonance positions of these new resonances indicate the presence of a paramagnetic cobalt species in the material. The 59 Co MAS NMR spectra of the Li x CoO 2 -T 900 samples revealed a spinning sideband manifold centred at ≈14 250 ppm for x ≤0.95 and three overlapping spinning sideband manifolds at ≈14 285, ≈14 260 and ≈14 230 ppm for Li/Co ratios >0.95. Compared to the Li x CoO 2 -T 900 samples the Li x CoO 2 -T 400 samples all showed one resonance with an increased line width. These resonance positions are typical for Co 3+ octahedrally coordinated by oxygen. No quadrupole induced shift is observed as a function of the external field (measurements performed at 14.1 and 7.05 T), indicating an undistorted octahedral coordination of cobalt in the materials studied. Chemical extraction of lithium with H 2 SO 4 leads to the formation of lithium that can not be detected with NMR. Electrochemical extraction of lithium, on the other hand, leads to a low field shift of the lithium resonance of 60–120 ppm, depending on the amount of lithium removed. Electrochemical intercalation (discharging) of the samples results in the reappearance of the original lithium spectra, showing the excellent reversibility of the charge/discharge process. Partly charged samples are characterised by signals in the range of 120–60 ppm and a signal at −0.9 ppm, indicating that part of the lithium remains in an unchanged environment. The dependence of the chemical shift on the amount of lithium removed is due to an rapid exchange process.

Amalgams for fluorescent lamps: Part II: The systems Bi–Pb–Hg and Bi–Pb–Au–Hg

Abstract In nowadays compact fluorescent lamps, having coolest spot temperatures in the range 60–130°C, amalgams based on the eutectic Bi–In and Bi–Pb–Sn alloys are used to control the mercury vapour pressure inside the lamp. The consequence of the trend towards smaller and more attractive compact fluorescent lamps is that the amalgam temperature increases. In this paper the materials and thermodynamic properties of the amalgams Bi–Pb–Hg and Bi–Pb–Au–Hg are described. The mercury vapour pressure measurements show that these amalgams can be used for controlling the optimal mercury vapour pressure inside fluorescent lamps at temperatures in the range 60–150°C. In the ternary Bi–Pb–Au system the new ternary compound BiPb 3 Au has been found for which the crystal structure and melting point have been determined. The results of XRD, EPMA, DTA and mercury vapour pressure measurements are combined to formulate a thermodynamic model for the mercury activity in both liquid and solid Bi–Pb–Hg and Bi–Pb–Au–Hg.

Sol-gel, modified sol-gel, and metallo-organic decomposition techniques for complex oxide films: Materials processing and applications

Publisher Summary This chapter discusses the processing of thin oxide films via sol–gel, modified sol–gel, and metallo-organic decomposition (MOD). The special feature of sol–gel, modified sol–gel, and MOD processes is their low temperature depositions, which show more than 500 oC lower processing temperatures than the conventional ceramic sintering techniques and thus offer the compatibility of ceramic materials with substrates such as glass, glass-ceramic, and ceramic as well as silicon. The processing of thin films is relevant for microelectronic applications. These films include conductive oxides such as RuOx and dielectric thin films. Various types of precursor systems developed worldwide have been reported together with the growth of thin films and their typical performance. Dielectric films are developed for applications of thin film miniaturized capacitors, multifunctional modules, or ferroelectric nonvolatile memories. The relevance of these techniques for electroceramic films is demonstrated in the chapter in addition to the growth of thin films via different routes.