Molecular dynamics study on defect structure of rare earth-doped thoria

希土類ドープトリアの欠陥構造に関する分子動力学的研究

逢坂 正彦  ; 安達 淳*; 黒崎 健*; 宇埜 正美*; 山中 伸介*

Osaka, Masahiko; Adachi, Jun*; Kurosaki, Ken*; Uno, Masayoshi*; Yamanaka, Shinsuke*

希土類をドープしたトリアの欠陥構造に関して、分子動力学法を用いて評価を行った。Th, Gd及びOイオンに部分イオン性二体ポテンシャルを用い、パラメータは経験的に決定した。欠陥構造を仮定し、格子定数へ与える影響を評価した。Gd濃度が0-45%、温度が1273Kまでの分子動力学計算により格子定数の変化を求めた。また1273Kにおける酸素の拡散係数を計算した。計算結果を実験と比較・検討することにより、Gd-酸素空孔-Gd型のクラスターが欠陥構造として確からしいことがわかった。

A molecular dynamics study on the defect structure of rare earth-doped thoria was carried out. The partially ionic two-body potential was used with empirically obtained parameters for Th, Gd and O ions in the fluorite structure. Four types of defect structures were assumed and their effects on the lattice parameter were investigated; i.e., oxygen vacancy point defect, Gd-Gd pair, singly charged Gd-vacancy cluster and neutral Gd-vacancy-Gd cluster. Molecular dynamics simulations were carried out with Gd fractions and temperatures ranging from 0 to 45 % and from 298 to 1200 K, respectively. Diffusion coefficients of O ion in the Gd-doped thoria having various Gd fractions were also calculated at 1273 K. Comparison of the calculated results with the experimental ones lead to the conclusion that Gd-oxygen vacancy-Gd type cluster is the most likely defect structure in the Gd-doped thoria.