First-principle investigation of doping effects on mechanical and thermodynamic properties of Y₂SiO₅

We investigate the variation of elastic stiffness moduli and the thermodynamic properties of yttrium orthosilicate (Y₂SiO₅, YSO) under various doping concentrations of Eu³⁺ ions. The model is based on a low temperature approximation (T<<θ_D), and the plane-wave density functional theory (DFT) is used to carry out the calculations. The results show that the Eu³⁺ ions primarily occupy the Y₁ site of the basic molecule for all applied concentrations. The overall shear, bulk, and Young's moduli exhibit a decreasing trend with increasing Eu³⁺ concentration. The overall anisotropy shows a very small increase with increasing concentration. The Debye temperature as well as the Grünesien parameter for each concentration are predicted. Lastly, the predicted heat capacity at constant volume is calculated and compared to experimental values. Our study reveals that there is almost linear relationship between concentration and mechanical properties of YSO. The decrease of the Grünesien parameter with concentration increase might decrease the anharmonic effects in YSO, although this effect is small. In addition, the change in heat capacity with concentration rise is negligible.