Preferred Site Occupation of Doping Cation and Its Impact on the Local Structure of V$_2$O$_5$

Cation doping is an effective method to alter the local structure and electronic state of V$_2$O$_5$. While it remains a great challenge to experimentally understand whether the dopingcations prefer to replace the V ions or reside between the V$_2$O$_5$ layers, namely, substitutional or interstitial positions. In this work, cation-doped V$_2$O$_5$ with different elements M (M = Mn, Ni, and Fe) were synthesized via a hydrothermal method since V and M ions can uniformly distribute in the solution to obtain a homogeneous target material. The impact of doping cations on the local structure of V$_2$O$_5$ is revealed. Multitechniques demonstrate the existence of a small portion of V$^{4+}$ in the doped samples resulting from the electronic structure change of V. Although the results do not directly certify where the doping cations lie in the V2O5 structure, all information together provide a hint that the doping cations may prefer to reside on the interstitial positions rather than the substitutional positions