Structure Determination and Relative Properties of Novel Cubic Borates MM‘<sub>4</sub>(BO<sub>3</sub>)<sub>3</sub> (M = Li, M‘ = Sr; M = Na, M‘ = Sr, Ba)

A series of novel borates, MM‘<sub>4</sub>(BO<sub>3</sub>)<sub>3</sub> (M = Li, M‘ = Sr; M = Na, M‘ = Sr, Ba), have been successfully synthesized by standard solid-state reaction. The crystal structures have been determined from powder X-ray diffraction data. They crystallize in the cubic space group <i>Ia</i>3̄<i>d</i> with large lattice parameters:  <i>a</i> = 14.95066(5) Å for LiSr<sub>4</sub>(BO<sub>3</sub>)<sub>3</sub>, <i>a</i> = 15.14629(6) Å for NaSr<sub>4</sub>(BO<sub>3</sub>)<sub>3</sub>, and <i>a</i> = 15.80719(8) Å for NaBa<sub>4</sub>(BO<sub>3</sub>)<sub>3</sub>. The structure was built up from 64 small cubic grids, in which the M‘ atoms took up the corner angle and the BO<sub>3</sub> triangles or MO<sub>6</sub> cubic octahedra filled in the interspaces. The isolated [BO<sub>3</sub>]<sup>3-</sup> anionic groups are perpendicular to each other, distributed along three 〈100〉 directions. The anisotropic polarizations were counteracting, forming an isotropic crystal. Sr and Ba atoms were found to be completely soluble in the solid solution NaSr<sub>4</sub><sub>-</sub><i><sub>x</sub></i>Ba<i><sub>x</sub></i>(BO<sub>3</sub>)<sub>3</sub> (0 ≤ <i>x </i>≤ 4). The photoluminescence of samples doped with the ions Eu<sup>2+</sup> and Eu<sup>3+</sup> was studied, and effective yellow and red emission was detected, respectively. The results are consistent with the crystallographic study. The DTA and TGA curves of them show that they are chemically stable and congruent melting compounds.