Experiment and First-Principles Calculations of A2Mg2TeB2O10 (A = Pb, Ba): Influences of the Cosubstitution on the Structure Transformation and Optical Properties.

Two new A2Mg2TeB2O10 (A = Pb, Ba) compounds have been synthesized by the high temperature solution method. A2Mg2TeB2O10 (A = Pb, Ba) crystallize in the same space group Cmca and feature a 3D [B2TeMg2O10]4- framework structure. A2Mg2TeB2O10 (A = Pb, Ba) can be regarded as the cosubstitution of Na2RE2TeB2O10 (RE = Y, Dy-Lu), which crystallize in a different space group, P21/c. The discussion on the structure transformation from A2Mg2TeB2O10 (A = Pb, Ba) to Na2RE2TeB2O10 (RE = Y, Dy-Lu) indicates that the cosubstitution of two cations with different valence states can change the dimension of cation groups in the crystal structure, which can further alter the arrangements of the anion groups. Furthermore, the band gap and birefringence have been changed after the cosubstitution. The influences of the cosubstitution on the band gap and birefringence have been discussed through first-principles calculations and structure comparison. In addition, the IR spectra and TG-DSC curves of title compounds were studied.