Strukturchemische und impedanzspektroskopische Untersuchungen an Mg2+-stabilisierten Na+/Pr3+-β″-Al2O3-Kristallen

Structural Chemistry and Impedance Spectroscopy of Mg²⁺ stabilized Na⁺/Pr³⁺-β″-Aluminas The structure with the ionic distribution in the conduction planes of a Pr³⁺-exchanged Mg²⁺ stabilized Na⁺-β″-alumina crystal, composition determined by electron microprobe analysis to Na_1.19Pr_0.13Mg_0.49Al_10.49O₁₇ (degree of exchange ξ = 25%, related to Na⁺ content), has been investigated by single crystal X-ray diffraction methods at room temperature (R3 m, Z = 3, a = 561.8(2) pm, c = 3 361.5(11) pm). Pr³⁺ is slightly shifted in the ab-plane from the centrosymmetric 9 d (mO) into a 18 h site. Na⁺ occupies 18 h as well as 6 c (BR) positions. Ionic conductivity data of Mg²⁺ stabilized Na⁺/Pr³⁺-β″-Al₂O₃ crystals with varying degree of exchange determined by impedance spectroscopy are given in an Arrhenius diagram. With growing Pr³⁺ content the conductivity σ decreases with increasing activation energy.