ABSTRACT
This chapter presents a review on the field of clean energy, including materials, crystal structure, electron/nuclear-density distribution, and diffusional pathway of mobile ions. The electron /nuclear-density analysis based on the maximum-entropy method (MEM) and MEM-based pattern fitting using neutron and synchrotron powder diffraction data is powerful to investigate the diffusional pathway of mobile ions and the chemical bonding of materials for clean energy. Structural disorder and/or diffusional pathways of mobile oxide ions and copper cations have been visualized in various fluorite-type materials (ceria solid solution,
Ce0.93Y0.07O1.96; bismuth oxide solid solution, Bi1.4Yb0.6O3; yttrium tantalum oxide, Y0.785Ta0.215O1.715; copper iodide, CuI; ceriazirconia, CexZr1-xO2 (x = 0.12, 0.5 and 1.0)) and perovskite-type and perovskite-related materials ((La
LaGaO3, La0.6Sr0.4CoO3-d, La0.4Ba0.6CoO3-d, La0.6Sr0.4Co0.8Fe0.2O3-δ, La0.64(Ti0.92Nb0.08)O2.99). The diffusional pathway of mobile ions through the interstitialcy or interstitial mechanism has also been investigated in Pr2(Ni0.75Cu0.25)0.95Ga0.05O4+δ, Pr2Ni0.75Cu0.25O4+δ, (Pr0.9La0.1)2(Ni0.74Cu0.21-Ga0.05)O4+δ, and La9.69(Si5.70Mg0.30)O26+δ. Electron-density analysis of visible-light photocatalysts enables the visualization of covalent and ionic bonds. The covalent bonding makes the bandwidth wider and the band gap narrower, which leads to the visible-light response of these materials. We also describe the electron-density analysis of a visible-light photocatalyst (Ga0.885Zn0.115)(N0.885O0.115). 8.1 Introduction
Ionic conducting ceramic materials are keys for the clean energy, because the electrolyte and cathode materials for solid oxide fuel cells require the high ionic conductivity and the ionic-electronic mixed conductors are used for oxygen separation membrane [1-7]. The nuclear/electron-density distribution obtained by the maximum-entropy method (MEM) analysis of neutron, X-ray and synchrotron X-ray diffraction data enables the visualization of diffusional pathways of mobile ions and anisotropic/anharmonic atomic thermal motions in ionic conducting ceramic materials [5, 6, 8, 9]. In this review, I describe the results of MEM analyses for various ionic conducting ceramic materials.
