TY - JOUR
T1 - Crystal Structure of Apatite Type Rare-Earth Silicate (Sr2RE2)(RE6)(SiO4)6O2 (RE=La, Pr, Tb, Tm, and Y)
AU - Leu, Lii-Cherng
AU - Thomas, Sherin
AU - Sebastian, Mailadil Thomas
AU - Zdzieszynski, Swavek
AU - Ubic, Rick
PY - 2011/8/1
Y1 - 2011/8/1
N2 - The crystal structures of apatite-type (Sr 2 RE 2 )(RE 6 )(SiO 4 ) 6 O 2 (RE=La, Pr, Tb, Tm, and Y) ceramics prepared by conventional solid-state processing has been examined. The phase and structure analysis was carried out using powder X-ray diffraction (XRD) and transmission electron microscopy. Electron diffraction and Rietveld structure refinement of XRD data indicated that (Sr 2 RE 2 )(RE 6 )(SiO 4 ) 6 O 2 (RE=La, Pr, Tb, and Y) has a typical oxyapatite-type structure, A I 4 A II 6 (BO 4 ) 6 O 2 in space group P 6 3 / m (No. 176), where the A I site is shared equally and randomly by Sr and RE ions, A II is occupied by RE ions only, and B is occupied by Si. As the metaprism twist angle in this lanthanide series should increase as the size of RE decreases, the unrealistically low metaprsim twist angle for (Sr 2 Tm 2 )(Tm 6 )(SiO 4 ) 6 O 2 suggested that the hexagonal metric of apatite might not be sustained and the symmetry reduced to monoclinic, space group P 2 1 / m (No. 11), in order to compensate for the shorter Tm–O bond length. The P 2 1 / m model for (Sr 2 Tm 2 )(Tm 6 )(SiO 4 ) 6 O 2 also yields a better fit and improvement in bond valence as compared with P 6 3 / m model.
AB - The crystal structures of apatite-type (Sr 2 RE 2 )(RE 6 )(SiO 4 ) 6 O 2 (RE=La, Pr, Tb, Tm, and Y) ceramics prepared by conventional solid-state processing has been examined. The phase and structure analysis was carried out using powder X-ray diffraction (XRD) and transmission electron microscopy. Electron diffraction and Rietveld structure refinement of XRD data indicated that (Sr 2 RE 2 )(RE 6 )(SiO 4 ) 6 O 2 (RE=La, Pr, Tb, and Y) has a typical oxyapatite-type structure, A I 4 A II 6 (BO 4 ) 6 O 2 in space group P 6 3 / m (No. 176), where the A I site is shared equally and randomly by Sr and RE ions, A II is occupied by RE ions only, and B is occupied by Si. As the metaprism twist angle in this lanthanide series should increase as the size of RE decreases, the unrealistically low metaprsim twist angle for (Sr 2 Tm 2 )(Tm 6 )(SiO 4 ) 6 O 2 suggested that the hexagonal metric of apatite might not be sustained and the symmetry reduced to monoclinic, space group P 2 1 / m (No. 11), in order to compensate for the shorter Tm–O bond length. The P 2 1 / m model for (Sr 2 Tm 2 )(Tm 6 )(SiO 4 ) 6 O 2 also yields a better fit and improvement in bond valence as compared with P 6 3 / m model.
UR - https://scholarworks.boisestate.edu/mse_facpubs/68
UR - https://doi.org/10.1111/j.1551-2916.2011.04388.x
M3 - Article
JO - Journal of the American Ceramic Society
JF - Journal of the American Ceramic Society
ER -