Substituted Na-based Layered Tellurates: Synthesis, Local Structure and Na-Dynamics
Abstract
Solid-state batteries are currently limited by low ionic conductivity compared to the liquid analogue, and improving ionic conductivity is a major concern for commercialization. This thesis focuses on the local structure and ionic conductivity mechanism of a solid-state electrolyte candidate (the layered oxide Na2Zn2TeO6). The Na content of layered materials is well known to influence conductivity and phase stability, and in this work this is changed by substituting the framework cations Zn and Te with Ga and Sb. The first work of this thesis establishes a reliable synthesis route for the substituted materials, ensuring and confirming homogeneous distribution of the substituent by nuclear magnetic resonance spectroscopy (NMR). The decreased Na content is found to increase local motion of Na, but this is not translated to long range motion of ionic conductivity. Decreasing the Na-content is therefore not enough to improve ionic conductivity. This work finally made an in-depth study of complex ordering schemes that may occur in multicomponent layered oxides. The real situation can indeed be very complex, compared to the rather simple average picture description.List of papers
Paper I. Effects of Ga Substitution on the Local Structure of Na2Zn2TeO6. Frida Sveen Hempel, Federico Bianchini, Bjørnar Arstad, and Helmer Fjellvåg. Inorg. Chem. 2022, 61, 13067−13076. DOI: 10.1021/acs.inorgchem.2c01431. The article is included in the thesis. Also available at: https://doi.org/10.1021/acs.inorgchem.2c01431 |
Paper II. Dynamics of Interlayer Na-Ions in Ga-Substituted Na2Zn2TeO6 (NZTO) Studied by Variable-Temperature Solid-State 23Na NMR Spectroscopy and DFT Modeling. Frida Sveen Hempel, Charlotte Martineau-Corcos, Federico Bianchini, Helmer Fjellvåg, and Bjørnar Arstad. ACS Phys. Chem Au 2023, 3, 4, 394–405. DOI: 10.1021/acsphyschemau.3c00012. The article is included in the thesis. Also available at: https://doi.org/10.1021/acsphyschemau.3c00012 |
Paper III. Superstructure of locally disordered Na2Zn2TeO6. Frida Sveen Hempel, Wojciech A. Sławiński, Bjørnar Arstad and Helmer Fjellvåg. To be published. The paper is not available in DUO awaiting publishing. |
Paper IV. Substitution mechanism and effect of Na-distribution on 125Te spectra in Na2+xZn2SbxTe1–xO6 layered O3-type oxides. Frida Sveen Hempel, Federico Bianchini, Helmer Fjellvåg and Bjørnar Arstad. To be published. The paper is not available in DUO awaiting publishing. |