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anion

Ca. O. Al. anion.

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anion

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  1. Ca O Al anion We present thermodynamic data for microporous calcium aluminates (CAAL) with a common formula [Ca12Al14O33-]2+(2e-), (01), that represent, as recently highlighted in a Science publication by Matsuishi et al. 2003, a new class of electrides (see picture). The capability of CAAL to confine and effectively emit electrons arises from the unique microporous structure of the parent CAAL ionic conductor [Ca12Al14O32]2+(O2-), characterized by small interconnecting channels. We employed high temperature calorimetry to study the opposite process, i.e. oxidation of electron-rich samples to eliminate these electrons and obtain a stoichiometric compound. The enthalpies of oxidation and formation for electron-rich, as well as the stoichiometric compound, relative to the most stable Energetics of Microporous Materials,DMR 0101391 Formation and Oxidation Energetics of Microporous Calcium Aluminates: a New Class ofElectrides and Ionic ConductorsAlexandra Navrotsky, Thermochemistry Facility and NEAT ORU, UC Davis annealed calcium aluminate are measured. The study supports the idea that the oxidation of the stoichoimetric Ca12Al14O33 sample results in formation of extra-framework ions (O2 and O). The unique structure of CAAL is able to stabilize both oxygen ions and electrons in cages at room temperature and, at the same time, provide the environment for ion and electron conductivity. The latter is strongly related to framework-ion vacancy geometry and ion-framework bonding, which is reflected in oxidation energetics. The thermochemical study of [Ca12Al14O33-]2+(2e-) samples presented provides not only insight into energetics of electron–framework binding and formation of extra-framework ions, but also sets the stage for future theoretical studies of electride-type structures and the search for new electrides. Postdoc Olga Trofymluk, originally from the Ukraine, contributed to this work. CAAL samples were synthesized by graduate student Yoshitake Toda under supervision of Prof. Hideo Hosono at Tokyo Institute of Technology, Japan.

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