Hydrothermal Synthesis, Crystal Structure, and Properties of CuAl2Si2O7(F,OH)2

Crystal Chemistry and Selected Physical Properties of Inorganic Fluorides and Oxide-Fluorides

“…In CuAl 2 Si 2 O 7 F 2 , , the AlO 4 F 2 octahedra are associated by one O–O edge into Al 2 O 6 F 4 dimers and into (010) corrugated [Al 2 O 6 F 2 ] layers connected by CuO 5 pyramids (Figure ). The structure of CuAl 2 Si 2 O 7 F 2 is also considered as a derivative from Al 2 SiO 4 F 2 topaz structure.…”

“…70 Sometimes, the elaboration of synthetic crystals precedes the discovery of the corresponding minerals: Na 3 La 2 (CO 3 ) 4 F 71 was grown in 1993, while the cerium analogue Na 3 Ce 2 (CO 3 ) 4 F 72 lukechangite was found in 1997. It is observed that OH − /F − substitution occurs and that the substitution rate increases when the elaboration temperature is decreased; at 680 °C, the presence of hydroxyl groups is ruled out in Ni 3 (BO 3 )F 3 , 73 80 on topaz seed, and the nocerites M 3 (BO 3 )F 3 (M = Fe, Co, Ni) 73 can be cited (see section 2.4.8). However, numerous fluoride carbonates or fluoride phosphates have been evidenced: rare earth phases, K 4 Ln 2 (CO 3 ) 3 F 4 (Ln = La−Gd), 81 3d transition metal phases, Mn 2 (PO 4 )F and Co 2 (PO 4 )F already cited, 66 and the first 3d transition metal fluoride carbonates, KCu(CO 3 )F, 82 BaM(CO 3 )F 2 83 (M = Mn, Co, Zn), and Ba 2 Co(CO 3 ) 2 F 2 .…”

“…The hydrothermal growth of fluoride silicates and fluoride borates is difficult. Nevertheless, Ba 2 Ti 2 Si 2 O 9 F 2 , CuAl 2 Si 2 O 7 F 2 , the epitaxy of CuAl 2 Si 2 O 7 (OH,F) 2 on topaz seed, and the nocerites M 3 (BO 3 )­F 3 (M = Fe, Co, Ni) can be cited (see section ). However, numerous fluoride carbonates or fluoride phosphates have been evidenced: rare earth phases, K 4 Ln 2 (CO 3 ) 3 F 4 (Ln = La–Gd), 3d transition metal phases, Mn 2 (PO 4 )F and Co 2 (PO 4 )F already cited, and the first 3d transition metal fluoride carbonates, KCu­(CO 3 )­F, BaM­(CO 3 )­F 2 (M = Mn, Co, Zn), and Ba 2 Co­(CO 3 ) 2 F 2 …”