Speaker
Description
Nickel sesquioxide Ni2O3 also referred to as black nickel oxide is being recently increasingly used as a component of number of functional materials due to its photocatalytic activity. Yet, the compound remains poorly characterized and its crystal structure, which is a crucial starting point for understanding structure – property relationship, is unknown. The first attempt in 1961 to resolve its crystal structure from XRD diffractions was unsuccessful [1]. Since than the same diffraction pattern was reported on various occasions, but no further attempts have been made to resolve it. Here we focus on predicting the crystal structure and basic structure-related properties using ab initio modelling.
Our study is dedicated to theoretical prediction of crystal structure of Ni2O3 using two approaches. First, we model crystal structure of Ni2O3 in structural types commonly observed for other transition metal sesquioxides using DFT methods and evaluate their fitness to accommodate Ni2O3 [2]. Second, we use DFT modelling in conjunction with evolutionary algorithms (EA) to search for global minimum structure. The chemical formula Ni2O3 suggests presence of Ni3+ cations with formally d7 electronic configuration with possibility of both low-spin and high-spin state and various magnetic ordering patterns. Additionally, the elusive Ni3+ may show tendency to disproportionation to more stable Ni4+ and Ni2+ species. We address all these issues and here present results of thorough EA+(hybrid)DFT crystal structure search along with electronic and magnetic structure and lattice dynamics calculations. Furthermore, we evaluate thermodynamic stability of Ni2O3 in context of the binary Ni-O system and transition metal sesquioxides in general [3].
[1] P. S. Aggarwal and A. Goswami, National Chemical Laboratory 2-0770 (1961).
[2] M. Gašpárková, Diploma Thesis (2020): https://opac.crzp.sk/?fn=docviewChild0006F1F5
[3] M. Gašpárková, K. Tokár, M. Derzsi, manuscript in preparation (2021).
| Speaker Country | Slovakia |
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