Low-Cost, Multifunctional, and Sustainable Sodium Sulfido Ferrate(II)

Abstract

We introduce Na2[Fe3S4], comprising anionic layers, synthesized by a simple and straightforward solid-state method based on the fusion of binary sulfides of abundant sodium and iron. The structure crystallizes in a trigonal lattice with honeycomb cavities, as well as 25% of statistical iron vacancies in the crystal structure. The compound depicts high dielectric constants from 998 to 1850 at a frequency of 1 kHz depending on the sintering temperature, comparable with benchmark dielectric materials. According to the complex electrochemical impedance results, the compound depicts an electrical conductivity at ambient temperature. Optical investigations reveal a band gap of 1.64 eV, which is in agreement with an electronic band gap of 1.63 eV computed by density functional theory calculations. Magnetometry results reveal an antiferromagnetic behavior with a transition at 120 K. These findings introduce Na2[Fe3S4] as a sustainable multifunctional material with potential for a variety of electronic and magnetic applications.

Optical and Electrical Properties of A3[VS4] (A = Na, K) Synthesized via a Straightforward and Scalable Solid-State Method

“…The sintering process can enhance the bulk density of the samples, thereby increasing the ionic conductivity. 51 A different measurement temperature or other measurement parameters, such as the applied voltage, not reported in the literature, might be additional reasons for the observed difference in conductivity values, as well as the reported impurities of previous samples. While some compounds containing alkali metals, oxygen, and vanadium, such as Na 3 [VO 4 ], 17 NaVO 3 , 52 and K 2 [V 3 O 8 ], 53 are recently reported as promising candidates for the electrode materials of the alkali metal ion batteries (σ ≈ 0.1–10 mS·cm –1 ), 1 and 2 display ionic conductivity values comparable with some vanadium-containing materials such as ZrV 2 O 5 and Ag 3 Sc 2 [VO 4 ] 3 .…”

“…Here, the pellets were sintered at 673 K, while the samples in the literature were not reportedly sintered. The sintering process can enhance the bulk density of the samples, thereby increasing the ionic conductivity . A different measurement temperature or other measurement parameters, such as the applied voltage, not reported in the literature, might be additional reasons for the observed difference in conductivity values, as well as the reported impurities of previous samples.…”