arXiv subjects

Lennart Singer

Publications and source records attributed to Lennart Singer.

2 recordsLinked to original sources

arXiv2026

Magnetism in antiperovskite (Li$_2$\textit{M})\textit{Ch}O (\textit{M} = Fe, Mn, Co; \textit{Ch} = S, Se) diluted magnets with fixed 1/3 filling: the key role of magnetic anisotropy

We report the magnetic properties of a series of lithium-rich antiperovskites (Li$_2M$)$Ch$O ($M$ = Fe, Co, Mn and $Ch$ = Se, S) where transition metal and lithium ions are randomly distributed on the X-sites of the X$_3$BA structure, thereby forming a strongly diluted magnetic sublattice. Our study hence enables us to investigate the evolution of magnetic order at fixed 1/3-filling -- which is in the vicinity but slightly above the percolation threshold -- upon variation of the spin size, the magnetic anisotropy, and the orbital configuration. The data imply the absence of a distinct Curie-Weiss behavior up to 350~K but show rather large and weakly temperature-dependent magnetic susceptibility. We observe clear signatures of long-range antiferromagnetic order evolving in the 1/3-filled and strongly diluted magnetic X-site lattice with increasing N\'eel temperatures from $T_{\rm{N}}\simeq 30$~K in (Li$_2$Mn)$Ch$O to $\simeq 50$~K in (Li$_2$Fe)$Ch$O and $70-90$~K in (Li$_2$Co)$Ch$O. Except for $M$ = Co, the chalcogenide has no sizable effect on $T_{\rm N}$. We conclude significant magnetic coupling and short-range magnetic correlations at well above $T_{\rm N}$ which is in line with the observation of a broad electron spin resonance signal at room temperature. The actual ordering temperatures are strongly diminished by magnetic dilution. While structural parameters such as the tolerance factor and bonding angles do not strongly affect $T_{\rm N}$, a key parameter is the magnetic anisotropy of the transition metals.

cond-mat.str-el↗

arXiv2024

Separating cationic and anionic redox activity in antiperovskite Li$_2$Fe)SO

Lithium-rich antiperovskite promise to be a compelling high-capacity cathode material due to existence of both cationic and anionic redox activity. Little is however known about the effect of separating the electrochemical cationic from the anionic process and the associated implications on the electrochemical performance. In this context, we report the electrochemical properties of the illustrative example of three different Li$_2$Fe)SO materials with a focus on separating cationic from anionic effects. With the high voltage anionic process, an astonishing electrochemical capacity of around 400~mAh/g can initially be reached. Our results however identify the anionic process as the cause of poor cycling stability and demonstrate that fading reported in previous literature is avoided by restricting to only the cationic processes. Following this path, our Li$_2$Fe)SO-BM500 shows strongly improved performance indicated by constant electrochemical cycling over 100 cycles at a capacity of around 175~mAh/g at 1~C. Our approach also allows us to investigate the electrochemical performance of the bare antiperovskite phase excluding extrinsic activity from initial or cycling-induced impurity phases. Our results underscore that synthesis conditions are a critical determinant of electrochemical performance in lithium-rich antiperovskites, especially with regard to the amount of electrochemical secondary phases, while the particle size has not been found a crucial parameter. Overall, separating and understanding the effects of cationic from anionic redox activity in lithium-rich antiperovskites provides the route to further improve their performance in electrochemical energy storage.

cond-mat.mtrl-sci↗