Sr2(Mg1-xGax)Ge2</su b>O7+0.5x: Melilite-type oxygen ionic conductor associated with fivefold coordinated germanium and gallium

초록

We demonstrate a new type of oxygen ionic conductor, Sr-2(Mg(1-x)Ga5(x))Ge2O7+0.5x with a melilite-type structure. The oxygen-ion conductivity of Sr2Mg0.8Ga0.2Ge2O7.1 is measured as 10(-4) S/cm at 800 degrees C using both 2-probe ac impedance and 4-probe dc measurements, and hardly depends on Po-2 indicating that the main charge carriers are interstitial oxygen ions. Based on total energy calculations, it is suggested that a Ge4+ ion as well as Ga3+ contributes to the ionic conduction of interstitial oxygen through the coordination changes from fourfold to fivefold. (C) 2014 Elsevier B.V. All rights reserved.

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