Rare-earth induced nonlinear structural evolutions in fluorite solid solution crystals

Abstract

The modification of chemical composition to improve desired material parameters is an effective method in materials science and engineering. In this work, Ca1-xSrxF2 solid solution is chosen as the subject. Nd3+ and Y3+ ions are used as dopants. We have found that spectral properties of Nd3+:Ca1-xSrxF2 and Nd3+,Y3+:Ca1-xSrxF2 crystals vary nonlinearly with the ‘x’. The X-ray diffraction (XRD) patterns and the density functional theory (DFT) calculations on Ca1-xSrxF2 solid solutions have ruled out the influence of matrix crystals on spectral properties. The rare-earth monomer centers of C4v or C3v symmetry, and the high order clusters are modeled. The calculated results show, that thermodynamic stabilities of the centers vary nonlinearly. Temperature-dependent dielectric losses and the results of projected density of states (pDOS) calculations also show nonlinear dependency. The nonlinearly evolved local structures from cubic to square antiprism sublattice cause the nonlinear variation of spectral properties. The methodology of rare-earth induced nonlinear structural evolutions is then proposed, which is useful for exploring new materials.