Electron paramagnetic resonance on impurity copper ions in sodium trititanate with a hierarchical two-level architecture

Abstract

The results of studies of electron paramagnetic resonance on impurity copper ions in sodium trititanate (Na₂Ti₃O₇) with a hierarchical two-level architecture, potentially suitable for use as negative electrodes of sodium-ion batteries, are presented. The main emphasis in the work was placed on the identification of magnetically different centers of the impurity copper ion, establishing the positions of these centers in the crystal lattice, determining the nature of their distributions in the volume of the sample, and elucidating the charge compensation mechanism for aliovalent substitutions. For Cu²⁺ ions in positions of Ti⁴⁺ substitution, the degree of a spin density delocalization from the bottom d_{x2 − y2} orbital to the σ-orbitals of the nearest equatorial oxygen ions was estimated.