The novel oxy-sulfide glassy ionic conductors Na4P2S7-xOx 0 ≤ x ≤ 7: Understanding the features of static and dynamic cations

• Published in: Solid state ionics Vol. 402; p. 116363
• Main Authors: Shastri, Ananda, Rons, Nathan, Ding, Qing-Ping, Kmiec, Steven J., Olson, Madison, Furukawa, Yuji, Martin, Steve W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 01.12.2023; Elsevier
• Subjects: Activation energy; Distribution of activation energies; Ionic conduction; MATERIALS SCIENCE; Nuclear magnetic resonance; Sodium glass; Ionic conduction; Sodium glass; Distribution of activation energies; Nuclear magnetic resonance; Activation energy
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2023.116363

We present a 23Na nuclear spin dynamics model for interpreting nuclear magnetic resonance (NMR) spin-lattice relaxation and central linewidth data in the invert glass system Na4P2S7-xOx, 0 ≤ x ≤ 7. The glassy nature of this material results in variations in local Na+ cation environments that may be described by a Gaussian distribution of activation energies. A consistent difference between the mean activation energies determined by NMR and DC conductivity measurements was observed, and interpreted using a percolation theory model. From this, the NaNa coordination number in the sodium cation sublattice was obtained. These values were consistent with jumps through tetrahedral faces of the sodium cages for the sulfur rich glasses, x < 5, consistent with proposed models of their short range order (SRO) structures. From NMR spin-echo measurements, we determined the NaNa second moment M2 resulting from the NaNa magnetic dipole interaction of nearest neighbors. Values of M2 obtained as a function of sodium number density N were in agreement with models for uniform sodium distribution, indicating that these invert glass systems form so as to maximize the average NaNa distance. A simple Coulombic attraction model between Na+ cation and X (=S−, O−) anion was applied to calculate the activation energy. In the range 1.5 ≤ x ≤ 7, an increase in activation energy with increasing oxygen content x occurred, and was consistent with the decrease in average anionic radius, and the increase in Coulombic attraction. For small oxygen additions, 0 ≤ x ≤ 1.5, the suggested minimum at low oxygen concentration seen in the activation energies obtained from DC conductivity data is not evident in the model. •Sodium glasses show promise as energy storage devices for wind/solar energy farms.•Nuclear dynamics was used to determine distributions of activation energies.•Sodium - sodium coordination number is consistent with face jumps through tetrahedral cages.•Sodium cations are uniformly distributed over the glass composition range.