E. Hatzikraniotis

Science education research in the knowledge-based society

1: Theoretical and Methodological Approaches to Science Education Research.- Presidential Address: What can we reasonably expect of research in science education?.- Constructivism in science education: The need for a clear line of demarcation.- Overviews of the Research Presented at ESERA 2001.- On the methodology of phenomenography as a science education research tool.- Conversation Theory and self-learning.- Analysis of video data of secondary school science students.- Longitudinal studies - providing insight into individual themes in science learning and students views of their own learning.- Changing referential perspective in science classroom discourse.- 2:Learning and Understanding Science.- Students positions in physics education. A gendered perspective.- Situated conceptions and obstacles. The example of digestion/excretion.- About some of the difficulties in learning Thermodynamics at the University Level.- Metacognitive Experiences in the Domain of Physics: Developmental and Educational Aspects.- How children reason from data to conclusions in practical science investigations.- Mechanistic reasoning on the concept of wave surface, and on the Huygens principle.- Atomic Physics in Upper Secondary School: Layers of Conceptions in Individual Cognitive Structure.- The electric current on its way to our house and the parallel connection of the electric appliances: primary students (11-12) representations.- Detailed Investigation of Professional Physicists Solving Physics Tasks.- Learning from writing in secondary science: A case study of students composing strategies.- Seventh-grade pupils epistemic views in the context of model-based instruction.- Nonlinear Analysis of the Effect of Working-Memory Capacity on Student Performance in Problem Solving.- The Nature Of Growth In Childrens Science Understandings: Insights From A Longitudinal Study.- HOCS Problem solving Vs. LOCS exercise solving: What do college science students prefer?.- 3 :Teaching and Communicating Science.- Science and Technology Education: A high priority political concern in Europe.- A mesoscopic model of liquids for teaching fluids statics.- The importance of weightlessness and tides in teaching gravitation.- Making decisions about biological conservation issues in peer group discussion.- Discourse in the laboratory: quality in argumentative and epistemic operations.- Modelling the evolution of teaching -learning sequences: From discovery to constructivism.- Nonlinear Physics in Upper Physics Classes: Educational Reconstruction as a Frame for Development and Research in a Study of Teaching and Learning Basic Ideas of Nonlinearity.- Promoting Understanding through Representational Redescription: an exploration referring to young pupils ideas about gravity.- Different types of classroom debates on biotechnology. Are these simply an exercise in rhetoric or do they encourage a well-founded critical attitude?.- 4: Science Education and Information and Communication Technologies.- WISE Research - Promoting International Collaboration.- Research about the use of information technology in science education.- Physics Learning and Microcomputer Based Laboratory (MBL) - Learning effects of using MBL as a technological and as a cognitive tool.- Phenomenographical Approach to Design for a Hypertext Teachers Guide to MBL.- Application of a framework appropriate for a multilevel assessment of educational multimedia software in science (FEVES).- Brain Research in Science Education Research.- Computer modelling and simulation in science lessons: using research into teachers transformations to inform training.- 5: Science Teachers: Knowledge and Practices.- Exploring science teachers pedagogical content knowledge.- Relating research in didactics and actual teaching practice: impact and virtues of critical details.- Transforming the Standard Instrument for Assessing Science Teachers Self-Efficacy Beliefs (STEBI) For Use in Denmark.- Teachers confidence in primary science and teacher-student interactions.- Teachers views and attitudes towards the communication code and the rhetoric used in press science articles.- Science teachers perceptions of the current situation of planetary emergency.- 6: International Research and Development Projects.- A European Research Project for New Challenges in Science Teacher Training.- Quality Development Projects in Science Education.- Video-Based Studies on Investigating Deficiencies of School Science Teaching.- Authors Index.

Solid-State Synthesis and Thermoelectric Properties of Sb-Doped Mg2Si Materials

Sb-doped magnesium silicide compounds have been prepared through ball milling and solid-state reaction. Materials produced were near-stoichiometric. The structural modifications have been studied with powder x-ray diffraction. Highly dense pellets of Mg2Si1−xSbx (0xa0≤xa0xxa0≤xa00.04) were fabricated via hot pressing and studied in terms of Seebeck coefficient, electrical and thermal conductivity, and free carrier concentration as a function of Sb concentration. Their thermoelectric performance in the high temperature range is presented, and the maximum value of the dimensionless figure of merit was found to be 0.46 at 810xa0K, for the Mg2Si0.915Sb0.015 member.

Seebeck and thermal conductivity analysis in amorphous/crystalline β-K2Bi8Se13 nanocomposite materials

In this work, ball milling is applied on β-K2Bi8Se13 compounds in order to explore the potential of the process for the fabrication of nano-based material. Polycrystalline β-K2Bi8Se13, synthesized from melt, was ball milled under inert atmosphere. Powder x-ray diffraction showed a significantly increased disorder with ball milling time. TEM studies confirmed the presence of nanocrystalline material in an amorphous matrix, suggesting the development of crystalline/amorphous β-K2Bi8Se13 nanocomposite material via ball milling process. Seebeck coefficient and thermal conductivity were analyzed based on the effective medium theory and show a significant contribution of a nanocrystalline phase.

Intercalation studies in bismuth selenide

Abstract We investigated the possibility of using Bi2Se3 as an intercalation cathode in solid state ionic devices by the insertion of lithium into this material. The results presented in this paper show that lithium insertion occurs either by chemical or by electrochemical treatment, introducing additional layers perpendicular to the c axis, with a periodicity of about 60 A, as has been revealed by transmission electron studies. The variation of the carrier concentration owing to the transfer of charge from the lithium intercalant was probed by the combined measurement of the conductivity, Hall effect and plasma frequency. Two effects are noticeable and worth commenting on, these being a decrease of the mobility and an increase in the effective mass resulting from the increase of the lithium content. Both of these effects may have a common origin, being the result of the displacement of the Fermi level owing to the charge transfer or possibly the result of more drastic effects on the band structure owing to the filling of van der Waals voids by lithium. Finally, the electrochemical kinetics, at least in the limited range in which they were performed, proved to be completely reversible, whilst side reactions were not observed.

Lattice thermal conductivity of K2(Bi1−zSbz)8Se13 solid solutions

The family of solid solutions of the type β-K2(Bi1−zSbz)8Se13u200a(0<z⩽1) was studied with respect to thermal conductivity as a function of temperature and stoichiometry. At low temperature, the variation of lattice thermal conductivity with composition shows a transition from a typical crystalline to glasslike behavior. Analysis of the high-temperature data shows a contribution due to the mixed occupation of Bi/Sb crystallographic sites as well as an additional contribution due to point defects.

Τhe Effect of Ge on Mg2Si0.6−xSn0.4Gex Materials

In this work, we investigate the influence of the introduction of Ge on the thermoelectric properties of Bi-doped quaternary Mg2Si0.6−xSn0.4Gex alloys. Mg2Si0.58−xSn0.4Bi0.02Gex materials were fabricated by a low temperature reaction method, followed by hot pressing. Structure and phase composition of the obtained hot-pressed pellets were observed by x-ray diffraction. Morphology and chemical composition were monitored by scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy. The results indicate a natural tendency of the material to phase separate into Si-rich, Sn-rich, and Ge-rich regions, which seem to become finer in size with Ge concentration. The compounds have been characterized by electrical conductivity, Seebeck coefficient, and thermal conductivity measurements in the temperature range of 300–823xa0K. The effect of Ge in the lattice thermal conductivity is discussed in terms of solid solution formation as well as effective medium theory.

Lattice thermal conductivity of K2(Bi1−zSbz)8Se13K2(Bi1−zSbz)8Se13 solid solutions

The family of solid solutions of the type β-K2(Bi1−zSbz)8Se13u200a(0<z⩽1) was studied with respect to thermal conductivity as a function of temperature and stoichiometry. At low temperature, the variation of lattice thermal conductivity with composition shows a transition from a typical crystalline to glasslike behavior. Analysis of the high-temperature data shows a contribution due to the mixed occupation of Bi/Sb crystallographic sites as well as an additional contribution due to point defects.

Comparing Doping Methodologies in Mg 2 Si/AgMg System

Morphological and optical characterizations for the Mg2Si samples doped with Ag are presented. Two different doping methodologies with silver, namely in situ and ex situ doping, were studied for the case of Mg2Si of self-propagating high-temperature synthesis. Electron microscopy measurements in both scanning and transmission configurations verified the presence of AgMg precipitates embedded in the Mg2Si matrix and similar results were also yielded by FTIR spectroscopy. Finally, the dependence of silver content in both forms of dopant and inter-metallic constituent is studied upon doping technology.

Inhomogeneities and Effective Mass in Doped Mg2Si

Magnesium silicide (Mg2Si)-based materials are promising candidates as thermoelectric components for mid-temperature range (500–900xa0K) energy conversion. Many different approaches for determining the parabolicity of the conduction band have been suggested in the literature, while the values of the effective mass m*dL reported, lie between 0.46 and 1.1 m0. The aim of this work is to contribute in elucidating the discrepancy observed in the effective mass values of the lower conduction band of highly doped Mg2Si and examine whether this discrepancy could be attributed to the method of determination or to the sample’s characteristics. We present the results of effective mass calculations at room temperature (RT) by applying different experimental methods and models (parabolic and non-parabolic) in two different groups of samples; one yielding profound inhomogeneities (Sb-doped) and one yielding homogeneous (Bi-doped) samples. Concluding this analysis, it seems that the lower conduction band of Mg2Si is more likely described as non-parabolic. Comparing the two groups of samples, our analysis indicated that the effective mass may be significantly underestimated for samples with dopant and content-modulated composition.

Macro and Micro-Scale Features of Thermoelectric PbTe (Br, Na) Systems: Micro-FTIR Spectroscopy, Micro-Seebeck Measurements, and SEM/EDX Observations

In this work, n-type and p-type PbTe doped with Br and Na, respectively, were thoroughly examined to determine the effect of the dopant on microstructure. Macro and micro homogeneity of the samples were studied by means of micro-Fourier-transform infrared (micro-FTIR) spectroscopy, micro-Seebeck measurements, and scanning electron microscopy with energy-dispersive x-ray analysis (SEM/EDX). SEM/EDX observations showed the samples were not single-phase materials—second phases were created by inclusions that disturbed the coherence of the matrix and, subsequently, drastically affected the Seebeck coefficient. In a micro-scale study, local variations of sodium content were detected in Na-doped samples; in Br-doped samples a second, PbBr2, phase was observed in the PbTe matrix. A direct effect of matrix dopant on Seebeck coefficient and plasmon frequency for the Br-doped and Na-doped samples was observed by use of the three complementary techniques.