Britholites with the general formula Ca10-xLnx(PO4)6-x(SiO4)xF2, (0≤x≤6) are considered to be promising matrices for the confinement of the by-products in the nuclear industry. A thermodynamic study showed tha...Britholites with the general formula Ca10-xLnx(PO4)6-x(SiO4)xF2, (0≤x≤6) are considered to be promising matrices for the confinement of the by-products in the nuclear industry. A thermodynamic study showed that the stability of these compounds de-creased as the substitution rate increased. The present work was an attempt to gain more information about the structural changes in-duced by the substitution, in order to understand the observed stability decrease. The samples were successfully synthesized as a sin-gle-phase apatite by a solid-state reaction between 1200 and 1400 °C. The structural refinement indicated that the La3+ions preferen-tially occupied the 6(h) sites. A progressive shift of F-along the c-axis outside its ideal position occurred as a result of the substitution increase. This might be the cause of the observed stability decrease, especially as the energies of the La-O, La-F and Si-O bonds are higher than those of Ca-O, Ca-F and P-O. The distribution of La3+ between the two non-equivalent sites was confirmed by the charge distribution method.展开更多
文摘Britholites with the general formula Ca10-xLnx(PO4)6-x(SiO4)xF2, (0≤x≤6) are considered to be promising matrices for the confinement of the by-products in the nuclear industry. A thermodynamic study showed that the stability of these compounds de-creased as the substitution rate increased. The present work was an attempt to gain more information about the structural changes in-duced by the substitution, in order to understand the observed stability decrease. The samples were successfully synthesized as a sin-gle-phase apatite by a solid-state reaction between 1200 and 1400 °C. The structural refinement indicated that the La3+ions preferen-tially occupied the 6(h) sites. A progressive shift of F-along the c-axis outside its ideal position occurred as a result of the substitution increase. This might be the cause of the observed stability decrease, especially as the energies of the La-O, La-F and Si-O bonds are higher than those of Ca-O, Ca-F and P-O. The distribution of La3+ between the two non-equivalent sites was confirmed by the charge distribution method.