New soft chemical routes to ferroelectric materials

A new soft chemical route has been developed in the first part of this thesis for synthesis of relaxor ferroelec tric, (1 -~)Pb(Mg~~-,Nb~~~)O~-xPbTi0~ [(I -x)PMN-xPT] (x = 0.10, 0.35) ceramics. This polyethylene glycol-based method shows some very interesting features. It allows the sol-gel reactions to be performed at room temperature, eliminating reflux steps usually required in sol-gel processes. Moreover, it does not require excess amounts of lead starting material to compensate for lead oxide loss during sintering as is usually the case in conventional synthesis. The effect of a trio1 molecule, l , l , 1-tris(hydroxy)methylethane (THOME), a known complexing agent for binding together metal ions in solutions, has also been studied. Well-sintered 0.90PMN-O.1OPT and 0.65PMN-0.35PT ceramics were prepared in a single heat-treatment step of the precursor powder. The use of THOME gives excellent dielectric and ferroelectric properties in stoichiometric 0.90PMN-O.lOPT ceramics sintered at 1050 "C. A room temperature dielectric constant, &IRT of -25,000 is observed at 1 kHz in this ceramic which is the highest value obtained so far in ceramics of the same composition. A 5% mol excess of lead in the sol-gel process without THOME improves the formation of the perovskite phase but degrades the dielectric properties. The 0.65PMN-0.35PT ceramics prepared with THOME and stoichiometric amounts of lead, and sintered at 1040 "C show pure perovskite phase and very good dielectric and ferroelectric properties (&lRT >5,000, -27,000, and = 21 p~/cm2). In the second part of this work, pure perovskite ferroelectric SrBi2Ta209 (SBT) ceramics have been synthesized by two new soft chemical techniques: a sol-gel process and a co-precipitation method. The sol-gel derived ceramics show denser and more homogeneous microstructure, and E\u27,,, and P~,RT values (950 and 7.6 p~lcm2, respectively) higher than in ceramics prepared under the same conditions by the coprecipitation method. These values are also higher than in ceramics prepared by solid state reactions. The superior dielectric and ferroelectric properties of the sol-gel synthesized SBT ceramics are attributed to a more homogeneous microstructure with a better distribution of grain orientations, which eliminates the preferential grain orientation along the [00B]-direction

Children's perceptions of obesity as explained by the common sense model of illness representation

Purpose – The aim of this paper is to qualitatively examine the ways in which primary school children, aged between 7 and 12, perceive various facets of obesity as defined by the common sense model of illness representation (CCM). Design/methodology/approach – The study was qualitative in nature. Semi-structured interviews were conducted with 33 children on all dimensions of the CSM. Twenty four children were normal weight and nine were overweight. A drawing task formed the methodology for the “identity” section of the interview. Findings – Although children identified food intake as a main cause of obesity, almost half did not name sedentary behaviours as a cause of obesity. Duration (timeline) of obesity was regarded by most children as reliant on a person’s undertaking of positive health behaviours. Normal weight children were found to list more severe consequences of obesity than the overweight group. It was found that experience contributed to the detailed knowledge of overweight children’s perceptions of cures of obesity. Overweight children also spoke of personal incidents of barriers to cures. Practical implications – The findings suggest that the CSMs can be used to classify children’s perceptions of obesity. Future childhood obesity interventions can utilise these findings to create campaigns and strategies that are more consistent with children’s understandings of this condition. Originality/value – To the authors’ knowledge, no previous study has examined children’s perceptions of obesity beyond perceived causes

Children's understandings of mediated health campaigns for childhood obesity

Purpose – The purpose of this paper is to investigate children’s understandings of the intent and importance of current media initiatives designed to target childhood obesity. Semi-structured interviews were analysed using qualitative content analysis, for the responses of overweight and normal weight children. Design/methodology/approach – In total, 33 children were interviewed, 24 of normal weight and nine overweight. They were shown two print and four television advertisements from the New South Wales Health Department web site that were popularly broadcast between 2003 and 2007. Children were then asked if they had seen the advertisement prior to the interview, and their understanding of the intent and importance of the advertisements. Findings – Most children in both weight groups recalled seeing five out of the six presented advertisements prior to interview. The main themes identified were ‘‘Health Maintenance’’ and ‘‘Illness Prevention’’ for five of the six advertisements. Overweight children were more numerous in their detection of a health message as opposed to normal weight children, who mostly commented on the safety aspect of advertisement six. Practical implications – Future evaluations of mediated health campaigns should go beyond recording simple recall of campaign material and investigate instead the understandings of target groups. Mediated health campaigns should also specify messages to particular target groups, as they appear to be most likely to facilitate behaviour change. Originality/value – Mediated health campaigns are mostly evaluated quantitatively rather than by qualitative means. In addition, no study has evaluated the views of overweight and normal weight children with regards to these health campaigns