The crystal structure of Ca5(PO4)2SiO4 (Silico-Carnotite)

摘要: The crystal structure of Ca5(PO4)2SiO4 (silico-carnotite) has been determined from 3358 x-ray diffraction data collected by a counter method and refined toR w =0.038,R=0.045, in space group Pnma. unit cell parameters area=6.737 (1) A,b=15.508 (2) A andc=10.132 at 24°C;Z=4. observed density is 3.06 the calculated 3.03 g · cm−3. contains about 2.5% V2O5 as an impurity. bond lengths within tetrahedral anions suggest that substitution or disorder PO4 3−, SiO4 4− possibly VO4 3− occurs among anion sites. some relationship to Ca5(PO4)3OH, predominant inorganic phase human body, but suggests Ca5(PO4)3OH type may not be stable without OH positions being filled. more closely related K3Na(SO4)2 (glaserite) if it considered there are systematic cation vacancies Ca5(PO4)2SiO4. This consistent with view glaserite-type account for solid solutions between Ca2SiO4 Ca3(PO4)2 CaNaPO4.