Synthesis, crystal growth and structure investigations of rare-earth disilicates and rare-earth oxyapatites

Abstract

The rare-earth disilicates RE2Si2O7 (RE = La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Y) and the rare-earth oxyapatites RE9.33□0.67(SiO4)6O2 (RE = La, Nd and Eu) were synthesized in solid-state reactions at temperatures from 1050 to 1500°C. Single crystals of the disilicates Ho2Si2O7, Er2Si2O7 and Y2Si2O7 and of the oxyapatites Eu9.33□0.67(SiO4)6O2 and Dy9.33□0.67(SiO4)6O2 were grown in a flux growth mode in the temperature interval 1260-960°C from a flux containing Bi2O3 and V2O5. Purity of single crystals and reaction products was investigated by X-ray single-crystal and powder-diffraction techniques. X-Ray single-crystal diffraction analyses are reported on Ho2Si2O7 and EuVO4. Ho2Si2O7 type D is monoclinic P21/c with Z=4 and a=4.6868(5), b = 10.8618(12), c=5.5872(5)Å, β= 95.993(7)°. EuVO4 is tetragonal. I41/amd with Z=4 and a= 7.2480(9), c = 6.3778(10) Å. Neutron powder diffracton analyses are reported on Er2Si2O7, Ho2Si2O7 and Y2Si2O7 all of type D structure and on the oxyapatites La9.33□0.67(SiO4)6O2 and Nd9.33□0.67(SiO4)6O2. The type D structure is monoclinic with P21/c and Z=4. Er2Si2O7 has a=4.6943(4), b=10.8097(10), c = 5.5646(4)Å, β=96.037(4)°. Ho2Si2O7 has a=4.6929(5), b= 10.8627(12), c=5.5895(5) Å, β= 96.017(4)°. Y2Si2O7 has a=4.6916(4), b = 10.8521 (10), c = 5.5872(5) Å, b = 96.040(3)°. The rare-earth oxyapatite structure is hexagonal with P63/m and Z=I. La9.33□0.67(SiO4)6O2 has a = 9.7259(10) and c= 7.1899(3)Å, and Nd9.33□0.67(SiO4)6O2 has a = 9.5731(8) and c=7.0336(2)Å. © Acta Chemica Scandinavica 1997.