Mixed electronic and oxide ionic conduction and migration mechanisms in digermanate La2−xCaxGe2O7−x/2

Lu Liang; Xiaohui Li; Xiaoge Wang; Zhaoji Luo; Kun Lin; Qiang Li; Sihao Deng; Lunhua He; Xiaojun Kuang; Xianran Xing

doi:10.1039/D3DT00708A

Mixed electronic and oxide ionic conduction and migration mechanisms in digermanate La_2−xCa_xGe₂O_7−x/2†

Lu Liang,‡^a Xiaohui Li,

‡*^ab Xiaoge Wang,^c Zhaoji Luo,^d Kun Lin,^a Qiang Li,

^a Sihao Deng,^e Lunhua He,^e Xiaojun Kuang

^bd and Xianran Xing

*^a

Author affiliations

* Corresponding authors

^a Beijing Advanced Innovation Center for Materials Genome Engineering, Institute of Solid State Chemistry, University of Science and Technology Beijing, Beijing 100083, People's Republic of China
E-mail: lixiaohuiftd@126.com, xing@ustb.edu.cn

^b Guangxi Key Laboratory of Electrochemical and Magnetochemical Functional Materials, College of Chemistry and Bioengineering, Guilin University of Technology, Guilin 541004, People's Republic of China

^c College of Chemistry and Molecular Engineering, Peking University, Beijing National Laboratory for Molecular Science (BNLMS), Beijing 100871, People's Republic of China

^d MOE Key Laboratory of New Processing Technology for Nonferrous Metal and Materials, Guangxi Key Laboratory of Optical and Electronic Materials and Devices, Guangxi Universities Key Laboratory of Nonferrous Metal Oxide Electronic Functional Materials and Devices, College of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, People's Republic of China

^e Songshan Lake Materials Laboratory, Dongguan 523808, China; Spallation Neutron Source Science Center, Dongguan 523803, People's Republic of China

Abstract

Mixed electronic and oxide ionic conduction was enabled in digermanate-type La_2−xCa_xGe₂O_7−x/2 containing Ge₃O₁₀ chains and isolated GeO₄ units by substitution of La³⁺ with Ca²⁺. The structure and solid solution limit of Ca doped La₂Ge₂O₇ were studied by systematic experiments, including rotation electron diffraction (RED), X-ray diffraction (XRD) and neutron powder diffraction (NPD) experiments, etc. The preferred occupation of Ca²⁺ and oxygen vacancies was investigated by Rietveld analysis of the NPD data. The obtained conducting material La_1.925Ca_0.075Ge₂O_6.963 exhibits superior thermal stability and an order of magnitude improvement in conductivity compared to the parent La₂Ge₂O₇ (∼9 × 10⁻⁵ S cm⁻¹ at 1000 °C). BVEL calculations reveal that the oxygen vacancies were stabilized and transported within the framework of La₂Ge₂O₇ by sharing oxygen and oxygen exchange between the adjacent Ge₃O₁₀ chains and GeO₄ units, exhibiting a three-dimensional oxide ion transport nature.

Dalton Transactions

Mixed electronic and oxide ionic conduction and migration mechanisms in digermanate La_2−xCa_xGe₂O_7−x/2†

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Mixed electronic and oxide ionic conduction and migration mechanisms in digermanate La_2−xCa_xGe₂O_7−x/2

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