التفاصيل البيبلوغرافية
| العنوان: |
Structure of crystalline and amorphous materials in the NASICON system Na1+xAlxGe2−x(PO4)3. |
| المؤلفون: |
Gammond, Lawrence V. D., Auer, Henry, Mendes Da Silva, Rita, Zeidler, Anita, Ortiz-Mosquera, Jairo F., Nieto-Muñoz, Adriana M., Rodrigues, Ana Candida M., d'Anciães Almeida Silva, Igor, Eckert, Hellmut, Benmore, Chris J., Salmon, Philip S. |
| المصدر: |
Journal of Chemical Physics; 8/21/2021, Vol. 155 Issue 7, p1-23, 23p |
| مصطلحات موضوعية: |
AMORPHOUS substances, CRYSTAL structure, MAGIC angle spinning, NUCLEAR magnetic resonance, SUPERIONIC conductors |
| مستخلص: |
The structure of crystalline and amorphous materials in the sodium (Na) super-ionic conductor system Na1+xAlxGe2−x(PO4)3 with x = 0, 0.4, and 0.8 was investigated by combining (i) neutron and x-ray powder diffraction and pair-distribution function analysis with (ii) 27Al and 31P magic angle spinning (MAS) and 31P/23Na double-resonance nuclear magnetic resonance (NMR) spectroscopy. A Rietveld analysis of the powder diffraction patterns shows that the x = 0 and x = 0.4 compositions crystallize into space group-type R 3 ̄ , whereas the x = 0.8 composition crystallizes into space group-type R 3 ̄ c. For the as-prepared glass, the pair-distribution functions and 27Al MAS NMR spectra show the formation of sub-octahedral Ge and Al centered units, which leads to the creation of non-bridging oxygen (NBO) atoms. The influence of these atoms on the ion mobility is discussed. When the as-prepared glass is relaxed by thermal annealing, there is an increase in the Ge and Al coordination numbers that leads to a decrease in the fraction of NBO atoms. A model is proposed for the x = 0 glass in which super-structural units containing octahedral Ge(6) and tetrahedral P(3) motifs are embedded in a matrix of tetrahedral Ge(4) units, where superscripts denote the number of bridging oxygen atoms. The super-structural units can grow in size by a reaction in which NBO atoms on the P(3) motifs are used to convert Ge(4) to Ge(6) units. The resultant P(4) motifs thereby provide the nucleation sites for crystal growth via a homogeneous nucleation mechanism. [ABSTRACT FROM AUTHOR] |
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