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A systematic study on the site occupancy of rare-earth cations in Ba-rich and Ti-rich BaTiO3 fired in reducing atmosphere is performed. The corresponding lattice relaxation is used as an indicator of site occupancy and, to a lesser extent, defect structures. Accurate lattice parameters are obtained from X-ray diffraction data that is analyzed with the maximum likelihood method to account for correlated errors in the c and a lattice parameters. Comparisons of lattice volume as a function of ionic radius of the dopant reveals three regimes, with the intermediate sized cations (0.087 nm \leqslantr \leqslant0.094 nm where r is the ionic radius in six-fold coordination) demonstrating amphoteric behavior (occupying A- or B-sites). Defect chemistry analysis of site occupancy links the importance of metal vacancy ratios and oxygen vacancy concentrations with site occupancy. The trends predicted from the defect chemistry analysis are consistent with the observed lattice relaxations.

Air-fired barium titanate samples doped with cerium, neodymium, samarium, gadolinium, dysprosium, erbium, or ytterbium were examined by electron paramagnetic resonance (EPR). Reducing atmosphere-fired europium-doped barium titanate was also investigated with EPR. Each dopant was studied in both Ba- and Ti-rich (Ba/Ti = 1.01, 0.99) samples. Point charge calculations were used to predict the EPR spectrum of each lanthanide in A- and B-sites. Different EPR spectra are expected for A- versus B-site substitution when Ce3+, Sm3+, Dy3+, and Yb3+ are the dopants. The experimentally observed Ba/Ti doping behavior of Ce3+ in BaTiO3 suggests that as a 3+ cation it is on the A-site. No EPR active signal was observed for Sm3+ in BaTiO3. Eu2+ and Gd3+, as previously discussed in the literature, were found to be an A-site dopant and amphoteric, respectively. Dy3+ was found to be a B-site dopant with an EPR signal intensity suggesting amphoteric behavior, whereas Yb3+ showed only B-site occupancy. Nd3+ and Er3+ could not easily be assigned to a particular site by EPR methods alone. We also discuss the lanthanide dopant's effect on the observed levels of titanium vacancies, barium vacancies, and Mn2+ impurities.

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Electric-field-assisted sintering of ceramic materials is under considerable attention during recent years. The current research is reviewed with a focus on mechanism research. Research of the mass transfer mechanisms in flash sintering (FS) is under debate during recent years. The research yields three main proposed mechanisms: nucleation due to movement of charged defects, Joule heating runaway, and electrochemical reactions. These are critically presented and discussed. Unlike FS, the mechanism of field-assisted sintering technologies (FAST) of ceramics is well agreed upon. However, recent studies challenge even this perception with new approaches, which are presented here. New technological and methodological developments in both FS and FAST/spark plasma sintering are also presented.

In this study, we present the positive effect of 1,10phenanthroline as an electrolyte additive that is strongly adsorbed on activated carbon electrodes, thereby adding effective redox activity to their initially capacitive interactions with electrolyte solutions. We obtain a stable capacitance of 320 F/g for the negative electrode and 190 F/ g electrode for full symmetric supercapacitor cells, operating up to 3.4 V in nonaqueous media, during many thousands of cycles. This corresponds to a specific capacity of 180 (mA h)/g electrode . The high voltage and capacity of these systems can pave the way for developing high-energy-density pseudocapacitors that may be able to compete with battery systems. We explored the mechanisms of the electrode interactions using electrochemical tools, including impedance spectroscopy.

This paper discusses the application of evolutionary programming methods to the problem of analyzing impedance spectroscopy results. The basic approach is a "direct-problem" one, i.e., to find a time constant distribution function that would create similar impedance results as the measured ones, within experimental error. Two complementary methods have been applied and are discussed here: Genetic Algorithm (GA) and Genetic Programming (GP). A GA can be applied when a known (or desired) model exists, whereas GP can be used to create new models where the only a-priori knowledge is their smoothness and their non-negativity. GP is tuned to prefer relatively noncomplex models through penalization of unnecessary complexity.

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