Structural study of the Lu2Si2O7–Sc2Si2O7 system

Different compositions in the Lu2Si2O7–Sc2Si2O7 system have been synthesized following the ceramic method. All XRD patterns are compatible with the thortveitite structure (β-RE2Si2O7 polymorph). Unit cell parameters change linearly with composition, which indicates a complete solid solubility of Sc2Si2O7 in Lu2Si2O7. 29Si MAS NMR spectra show a decrease of the 29Si chemical shift with increasing Sc content. A correlation reported in the literature to predict 29Si chemical shifts in silicates is applied here to obtain the theoretical variation in 29Si chemical shift values in the system Lu2Si2O7–Sc2Si2O7 and the results compare favourably with the values obtained experimentally. The FWHM values of the 29Si MAS NMR curves indicate a random distribution of Lu and Sc in the structure of the intermediate members. Finally, the IR study of the system confirms the solubility of Sc2Si2O7 in Lu2Si2O7, showing the splitting of several modes in the intermediate members and a linear shift of the frequency on going from one end-member to the other.