Evaluation on the crystal structure of ningyoite using XRD analysis and DFT calculation

Suzuki, Chikashi ; Osaka, Masahiko  ; Nakagiri, Toshio  

In order to evaluate uranium migration behavior in Ningyo-toge area, we are examining the stability of uranium minerals using DFT calculation. As the first step, we investigated the crystal structure and unit cell composition of ningyoite with its structural details unclear, which is a major uranium mineral there. We analyzed the reported XRD pattern of ningyoite to evaluate a crystal structure of ningyoite using XRD analysis code. This XRD analysis indicates that the distance between U atoms is along axis. We constructed the structure of [CaU(PO)] with three U or Ca atoms aligned along axis on the basis of this examination, and conducted structural optimization with this structure as initial one using DFT calculation. The theoretical XRD pattern has the maximum peak near 30, which the reported XRD pattern of ningyoite has. This result suggests that the structure of ningyoite is based on that of [CaU(PO)].