Crystal Structure of Apatite Type Rare-Earth Silicate (Sr2RE2)(RE6)(SiO4)6O2 (RE=La, Pr, Tb, Tm, and Y)

Abstract

RE 5 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 5 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 P6 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 P2 1 /m (No. 11), in order to compensate for the shorter Tm-O bond length. The P2 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 P6 3 /m model. P. Davies-contributing editor

Crystal Structure and Microwave Dielectric Properties of LiRE9(SiO4)6O2 Ceramics (RE = La,Pr,Nd,Sm,Eu,Gd, and Er)

“…The twist angle varies in the range 23.48°–25.96°. The observed range in the values of twist angle is compatible with previous studies of many apatites . The variation in lattice parameters and unit‐cell volume as a function of RE 3+ ionic radius (coordination number = 9) are shown in Figs.…”

“…Scientific reports show that the crystal structure of most of the oxy apatites including the lithium apatites belongs to the space group P 6 3 / m (No: 176) with hexagonal symmetry . Figure (a) shows XRD pattern of LiRE 9 (SiO 4 ) 6 O 2 (La, Pr, Nd, Sm, Eu, Gd, and Er) ceramics calcined at 950°C for 10 h. The XRD patterns of all the compositions were indexed using the similar pattern of LiLa 9 (SiO 4 ) 6 O 2 in the ICDD file, no: 32‐ 0567.…”

“…They can find a wide variety of potential applications in catalysis, solid oxide fuel cells, solid‐state lasers, photoluminescence, and bio materials . The possibility of occupancy of various types of atoms in different sites created enormous interest in their crystal structures . Among the various apatites investigated so far, the silicate oxy apatites are found to be thermally stable compared with other apatites due to their high melting point .…”

“…reported the microwave dielectric properties of SrRE 4 Si 3 O 13 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, Yb, and Y) ceramics. A detailed investigation of crystal structure of this series has also been reported; however, microwave dielectric properties of most of the oxy apatites remain still unknown. In this study, the microwave dielectric properties of Li RE 9 (SiO 4 ) 6 O 2 (RE = La, Pr, Nd, Sm, Eu, Gd, and Er) ceramics are reported for the first time.…”

Infrared photoluminescence of sol–gel spin-coated films of rare-earth activated lanthanum silicate

“…The excess negative charge can be compensated by replacing part or all of the cations by trivalent rare earths. Partial replacement leads to the family of compounds NaLn 3 Ln 6 Si 6 O 24 O 2 and Sr 2 Ln 2 Ln 6 Si 6 O 24 O 2 [16]. Complete replacement by rare earths requires cation vacancies to maintain charge balance.…”