High oxide-ion conductivity by the overbonded channel oxygens in Si-deficient La9.565(Si5.826□0.174)O26 apatite without interstitial oxygens
High oxide-ion conductivity by the overbonded channel oxygens in Si-deficient La9.565(Si5.826□0.174)O26 apatite without interstitial oxygens
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无间隙氧的缺硅 La9.565(Si5.826□0.174)O26 磷灰石中过度键合的沟道氧具有高氧化物离子电导率
DOI：
10.1039/c8ta02237b
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Takashi Ohhara
中科院分区：
文献类型：
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作者：
Kotaro Fujii;Masatomo Yashima;Keisuke Hibino;Masahiro Shiraiwa;Koichiro Fukuda;Susumu Nakayama;Nobuo Ishizawa;Takayasu Hanashima;Takashi Ohhara
磷灰石型稀土硅酸盐是极具吸引力的材料，由于其在 600 °C 以下具有极高的氧化物离子电导率，因此具有广泛的应用，例如在固体氧化物燃料电池中。间隙（过量）氧的存在被认为是磷灰石型材料具有高电导率的原因。相反，本研究通过单晶中子和X射线衍射分析、密度测量和从头算电子计算清楚地揭示了富LaLa9.565(Si5.826□0.174)O26中存在Si空位□而不是间隙氧。与 La9.333Si6O26 相比，La9.565(Si5.826□0.174)O26 具有较高的氧化物离子电导率，其主要原因是沿 c 轴的氧化物离子具有较高的迁移率（即较低的活化能）。过量的 La 阳离子会产生过度键合的沟道氧，导致其高度各向异性的原子位移和沿 c 轴的高氧迁移率。这一关于无间隙氧的过度键合效应的新发现将为更好的离子导体的设计打开一扇新的窗口。
Apatite-type rare-earth silicates are attractive materials with extensive applications such as in solid-oxide fuel cells due to their extremely high oxide-ion conductivity below 600 °C. The presence of interstitial (excess) oxygens has been believed to be responsible for the high conductivity of apatite-type materials. On the contrary, the present study clearly reveals the presence of Si vacancies □ instead of interstitial oxygens in La-rich La9.565(Si5.826□0.174)O26 using single-crystal neutron and X-ray diffraction analyses, density measurements and ab initio electronic calculations. Higher mobility (i.e., lower activation energy) of oxide ions along the c axis is a major reason for the high oxide-ion conductivity of La9.565(Si5.826□0.174)O26 when compared with that of La9.333Si6O26. Excess La cations yield overbonded channel oxygens, leading to their highly anisotropic atomic displacements and high oxygen mobility along the c axis. This novel finding of the overbonding effect without interstitial oxygens will open a new window for the design of better ion conductors.