A random field Potts model is used to establish the spatial relationship between the nanoscale distribution of charged chemical defects and nanoscale polar domains for the perovskite-based relaxor materials lead magnesium niobate (PMN) and lead scandium tantalate (PST). The random fields are not set stochastically but are determined initially by the distribution of B-site cations (Mg,Nb) or (Sc,Ta) generated by Monte Carlo NNNI-model simulations for the chemical defects. An appropriate random field Potts model is derived and algorithms developed for a 2D lattice. It is shown that the local fields are strongly correlated with the chemical domain walls and that polar nanodomains tend to nucleate about the latter. The evolution of the polar domains as a function of decreasing temperature is simulated for the two cases of PMN and PST. The dynamics of the polar clusters is also discussed. The results are used in an accompanying paper (H. Qian and L.A. Bursill, Int. J. Mod. Phys.B10, 2007, 1996) in order to predict the temperature and frequency dependence of the dielectric response of these two relaxors.
As an emerging energy storage technology, Na-CO2 batteries with high energy density are drawing tremendous attention because of their advantages of combining cost-effective energy conversion and storage with CO2 clean recycle and utilization. Nevertheless, their commercial applications are impeded by unsatisfactory electrochemical performance including large overpotentials, poor rate capability, fast capacity deterioration, and inferior durability, which mainly results from the inefficient electrocatalysts of cathode materials. Therefore, novel structured cathode materials with efficient catalytic activity are highly desired. In this review, the latest advances of catalytic cathode materials for Na-CO2 batteries are summarized, with a special emphasis on the electrocatalysts for CO2 reduction and evolution, the formation and decomposition of discharge product, as well as their catalytic mechanism. Finally, an outlook is also proposed for the future development of Na-CO2 batteries.
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