Synthesis, Crystal Growth and Structure Investigations of Rare-Earth Disilicates and Rare-Earth Oxyapatites.

Recent progress on synthesis, multi-scale structure, and properties of Y–Si–O oxides

“…Synthesis of powders and sintering of bulk ceramics Christensen et al 39 Ogura et al 41 Parmentier et al 28 Seifert et al 40 Kumar 43 Aparicio et al 44 Sun et al Leonyuk et al 48 Zhang et al 49 Gü nther and Georg 50 Pang et al 51 Hartenbach et al , etc., via the hydrothermal method. [35][36][37][38] In this process, layered clay, saponite or smectits, is suspended in Y(NO 3 ) 3 solution, and then heated to 300uC or above in a hydrothermal tank for several days.…”

Ionic conductivity of apatite-type rare-earth silicates prepared by mechanical milling

“…it becomes very difficult to avoid the formation of the very stable and non-conductive RE 2 SiO 5 (1:1, SiO 2 :RE 2 O 3 ) and RE 2 Si 2 O 7 (2:1) silicates with both having a detrimental effect on the electrical properties of the title materials. However, pure polycrystalline RE 9.33 (SiO 4 ) 6 O 2 materials have been readily obtained by firing at high temperature (1400 • C) stoichiometric mixtures of the corresponding oxides [26]; interestingly, attempts to grow single crystal disilicates Eu 2 Si 2 O 7 and Dy 2 Si 2 O 7 by a flux method on Bi 2 O 3 and V 2 O 5 melts starting from the corresponding stoichiometry, were unsuccessful yielding in both cases case apatite-type RE 9.33 (SiO 4 ) 6 O 2 crystals [26].…”

“…1/(r RE + r O )] thus, reaching a minimum in the series for RE = La. It has been argued that as the RE cation size decreases, the apatite crystal network shows less tendency to accommodate structural distortions around the channel oxygen sites with either "trapping" of the interstitial ions or reducing their concentration as well as blocking of the conduction pathway all having a detrimental effect on the activation energy for migration and conductivity [26]. As shown in Fig.…”

Polymorphism in the Lu2−xYxSi2O7 system at high temperatures

“…␥-Y 2 Si 2 O 7 . 20 All the reflections could be fitted on the basis of a monoclinic unit cell with space group P2 1 /c, corresponding to the crystal structure of the ␥-rare earth disilicates. 20 The lattice parameters as a function of Y content are shown in Fig.…”