Advances in Applied Ceramics: Structural,Functional and Bioceramics

There has been a surge of interest in polymer–clay nanocomposites over the past decade. This review surveys these new materials with emphasis on the debate surrounding interaction mechanisms and the behaviour of intercalated polymer in clay galleries. Swelling properties, high cation exchange capacities, high aspect ratio and large surface area give smectite clays the new role of high performance filler for thermoplastic or thermosetting polymers for the creation of intercalated or exfoliated nanocomposites. These nanocomposites can be prepared by three routes: in situ polymerisation, solution methods, or melt processing. Modification of either clay or polymer can change the type of polymer–clay composite. X-ray diffraction and transmission electron microscopy are often employed as the main characterisation techniques to establish the state of the clay. A very low volume fraction of clay significantly improves the mechanical and barrier properties of the pristine polymer, which makes these nanocomposites very promising materials.

The electrical properties of Ba_1–xSr_xSn_0·15Ti_0·85O₃ (BSST) (x=0, 0·03, 0·06, 0·09) ceramics synthesised by the precursor solution method were investigated by impedance spectroscopy in the temperature range from room temperature to 500°C. SEM micrographs show the grain distribution. Nyquist plots reveal the presence of a bulk effect for x=0 and of bulk and grain boundary effects for x=0·03, 0·06 and 0·09. Variation in bulk ac conductivity as a function of frequency demonstrates that the compounds exhibit Arrhenius type electrical conductivity. The ac activation energy increases with increasing Sr concentration.

Aqueous gelcasting with a low toxicity monomer system has attracted increasing attention. The present study attempts to enhance the flexural strength of green bodies gelcast from a low toxicity hydroxyethyl methacrylate (HEMA) system by introducing an appropriate amount of the water soluble polymer polyvinylpyrrolidone (PVP). The rheological properties and gelling characteristics of PVP–HEMA/Al₂O₃ suspensions were examined. In addition, the flexural strength and microstructure of the gelcast green and sintered bodies are discussed.

The aim of this work was to study the effect of Nd³⁺ doping on the structural, dielectric and electrical properties of Pb(SnTi)O₃ ceramics, to give materials with the general formula (Pb_1–xNd_x)(Sn_0·45Ti_0·55)^1–x/4O₃(x=0, 0·05, 0·07, 0·1). These materials were synthesised using a conventional high temperature solid state reaction technique. X-ray diffraction studies at room tempera- ture revealed orthorhombic symmetry, and uniform grain size distribution throughout the surface of the samples for x=0·05–0·1 was observed by SEM. Study of the dielectric behaviour of compounds as a function of temperature shows that with increasing concentration of Nd³⁺ the dielectric constant maximum decreases; transition temperature T_c shifts to lower temperatures for x=0–0·07 but increases again at x=0·1. It is observed that at each concentration of Nd³⁺ the dielectric constant ϵ′ reaches a maximum at the same Curie temperature for all three test frequencies (1, 10, 100 kHz), which reveals the non-relaxor ferroelectric behaviour of these materials.

Zinc oxide containing either Ni or Co dopants in various proportions has been investigated. Only zincite phase was found by XRD analysis. Incorporation of Ni or Co into the ZnO structure resulted in a marked shift in the XRD peaks. Remarkable microstructural uniformity was obtained by the addition of 1 mol-% of either Ni or Co oxides. Densification was achieved through atomic diffusion along grain boundaries. All samples showed non-linear I–V dependence. Ni concentration had a non-monotonic effect on breakdown voltage and the non-linear coefficient decreased with increasing Ni content. In contrast, breakdown voltage and non-linear coefficient increased with increasing CoO content.