In recent years, large effort has been put into the development and characterization of new colossal-ε' materials. For example, the recent discovery (1,2) of "colossal" values of the dielectric constant, ε', up to about 10 5 in CaCu 3 Ti 4 O 12 (CCTO) has aroused tremendous interest and a huge number of publications deals with its investigation and optimization. Aside of the extensively investigated CCTO, there are also some reports of other colossal-ε' materials (e.g., refs. (3,4,5,6,7)), mainly transition metal oxides. While there is no clear definition, the term "colossal" typically denotes values of ε' > 10 4 . Such materials are very appealing for the further miniaturization of capacitive components in electronic devices and also in giant capacitors that may replace batteries for energy storage.Of course, colossal dielectric constants are also found in ferroelectrics where close to the phase transition very large values are reached. However, ferroelectrics are characterized by a strong temperature dependence of ε' around their critical temperature, which restricts their applicability. In contrast, CCTO and other materials stand out due to their colossal-ε' values being nearly constant over a broad temperature range around room temperature. But in all these materials a strong frequency dependence is observed, revealing the signature of relaxational contributions, namely a steplike decrease of ε' above a certain, temperaturedependent frequency, accompanied by a peak in the dielectric loss. Intrinsic relaxations are commonly observed, e.g., in materials containing dipolar molecules, which reorient in accord with the ac field at low frequencies, but cannot follow at high frequencies. However, the extensive investigations of CCTO, have quite clearly revealed that the observed relaxation features are due to a nonintrinsic effect, termed Maxwell-Wagner (MW) relaxation (8,9,10). It arises from heterogeneity of the sample, which is composed of a bulk region with relatively high conductivity and one or several relatively insulating thin layers. The equivalent circuit describing such a sample leads to a relaxation-like frequency and temperature dependence (10). The insulating layers can arise, for example, from surface effects (e.g., depletion regions of Schottky diodes at the electrodes) or internal barriers (e.g., grain boundaries). However, this is rather irrelevant from an application point of view (e.g., external surface layers are used to enhance the capacitance in ferroelectrics-based multi-layer ceramic capacitors). Thus, although in CCTO the exact mechanism is not yet finally clarified, the interest in this material is still high. This is, amongst others, demonstrated by the fact that since its discovery in 2000, twelve socalled "highly-cited" papers on this topic have appeared (source: ISI Web of Science, Nov. 2008). Unfortunately, at room temperature the relaxation in CCTO leads to a decrease of ε' in the MHz region and around GHz only values of the order of 100 are observed (8,11,12). In contrast, electron...

The design and development of the next-generation power-efficient CIGS solar cells are at the research forefront due to their potential applications in renewable energy. Due to rich fundamental properties such as chemical and physical structures of the CIGS layer, cell scaffolding, and its promising applications like low cost, easy integration, and high efficiency, the CIGS-based solar cell systems are of considerable interest and received tremendous attention. In this article, we review the CIGS solar cells from the point of view of structural engineering. We explain the intrinsic parts of crystalline, optical, and electronic structures of the CIGS absorber layer up to the extrinsic part of the cell multilayer structure. For intrinsic structure, we primarily review the modification of the crystallinity or chemical composition of the CIGS and the effects that these modifications have on the physical properties such as the adjustment of the bandgap grading, effect of impurity or doping, selenization, oxidation processes, and the surface morphology and structure orientation. For extrinsic structure, the effect of substrates, electrical back contact, windows, n-buffer, grid, and antireflection layers will be discussed further, as well as the possibility of their tandem use with other solar cell thin films.

The reactivities of several oxide materials (OM) in direct contact with BSCCO powder has been tested at a temperature of approximately 845 • C in air. The OM such as BaZrO 3 , SrCO 3 , MgO and ZrO 2 showing little or no reactivity with BSCCO were mixed (10 wt%) with a BSCCO precursor powder and used for monocore tapes made by a standard powder-in-tube technique. The microstructure of the BSCCO+OM cores was analysed by SEM and XRD and the transport current properties-critical current, pinning force and resistance up to 16 T-were measured as a function of the magnetic field for various orientations with respect to the ab plane. The OM used influenced the electrical properties of the Bi-2223 phase in different ways. This is because the oxides react with BSCCO during the heat treatment and simultaneously affect the 2212 → 2223 phase transformation as well as the Bi-2223 grain growth and grain connectivity. Submicrometre commercial SrCO 3 powder was evaluated as the best material from all those tested, for resistive barriers in Bi-2223/Ag tapes.

Some of the technical problems that appear are obtaining solar cell parameters from I-V curve measurement data. One simple method is using linear graphical fit at zero current or voltage conditions. Although the accuracy of the obtained values is acceptable, other problems may arise regarding the number of parameters which could be obtained. We report a comparison between manual or graphical fit and fit using Shockley's equation. The single I-V curve under the lighting was inferred to obtain the intrinsic parameters of the solar cells' performance. The fittings were performed using the nonlinear equation of Shockley by determining some initial values of fittings such as R s , R sh , n, I 0 , I ph , and T. In the case of the Shockley equation fit, the iteration was performed several times to obtain the least possible inferred parameters. We have successfully obtained a better result of nonlinear Shockley fitting compared to the manual linear fit.

The phenomenon in the classroom where teachers are still limited space to train and to improve students' creative thinking skills (CTS) on the topic of material elasticity is the main reason for this research. Information on improving students' creative thinking skills in material elasticity topics by implementing problem based learning model (PBL) in learning is also limited. Previous research has not revealed any effort related to improving students' creative thinking skills on material elasticity topics by comparing two different learning models. Therefore this study aims to reveal differences in student learning outcomes on material elasticity materials in PBL and conventional models. Based on the research results obtained information that students 'creative thinking skills scores using PBL model is higher compared with that of conventional learning. It also revealed at each meeting that the CTS indicator of students are always improve. It can be concluded that PBL is very effective in training and improving students' creative thinking skill in physics learning. Thus PBL can be recommended in improving students' creative thinking skills.