Strategies for the Optimisation of the Oxide Ion Conductivities of Apatite-Type Germanates
Strategies for the Optimisation of the Oxide Ion Conductivities of Apatite-Type Germanates
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DOI：
10.1002/fuce.201000020
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发表时间：
2011-02-01
期刊：
影响因子：
2.8
通讯作者：
Slater, P. R.
中科院分区：
文献类型：
--
作者：
Orera, A.;Baikie, T.;Slater, P. R.
近年来，磷灰石型锗酸盐La9.33+ xGe（6）O（26+ 3x/2）由于其高的氧离子电导率而引起了人们的极大兴趣。研究表明，关键的缺陷是导致部分GeO 4单元转化为GeO 5的氧化物离子。因此，在制备具有高缺陷浓度的高氧过量样品中存在很大的兴趣。然而，这种策略导致对称性从六方减少到三斜（x > 0.4），并因此导致低温下氧化物离子电导率降低。我们目前的掺杂策略，以稳定的六方晶格，同时保持高的氧含量。特别是，部分取代的La较小的稀土元素（Y，Yb）被证明是成功的，在制备x = 0.67的样品与六方对称，因此高电导率。此外，用Ti、Nb或W在Ge位点上掺杂已被证明是类似成功的，导致W掺杂的非常高的氧含量，例如。G. La10Ge5.5W0.5O27.5。然而，在Ti掺杂的情况下，有一些证据表明Ti周围的间隙氧化物离子的捕获。类似的掺杂策略对Pr，Nd锗酸盐（Pr/Nd）（9.33+x）Ge_6 O_（26 + 3 x/2）的影响的初步结果进行了讨论。
Recently, apatite-type germanates La9.33+ xGe(6)O(26+ 3x/2) have attracted considerable interest due to their high oxide ion conductivities. Research has shown that the key defects are oxide ion interstitials which lead to the conversion of some of the GeO4 units to GeO5. Consequently there has been a large interest in the preparation of high oxygen excess samples with high defect concentration. This strategy, however, leads to a reduction in symmetry from hexagonal to triclinic for x > 0.4, and consequently to reduced oxide ion conductivity at low temperatures. We present doping strategies to stabilise the hexagonal lattice, while maintaining high oxygen content. In particular, partial substitution of La by smaller rare earths (Y, Yb) is shown to be successful in preparing x = 0.67 samples with hexagonal symmetry and hence high conductivities. In addition, doping on the Ge site with Ti, Nb or W, has been shown to be similarly successful, leading to very high oxygen contents for W doping, e. g. La10Ge5.5W0.5O27.5. In the case of Ti doping, however, there was some evidence for trapping of the interstitial oxide ions around the Ti. Preliminary results on the effect of similar doping strategies on Pr, Nd germanates (Pr/Nd)(9.33+x)Ge6O26+3x/2, are also discussed.