Phase formation in the BaB2O4-BaF2-BaO system and new non-centrosymmetric solid-solution series Ba7(BO3)4−xF2+3xCCDC 891832. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c2ce26122g

Detailed study of the BaB 2 O 4 -BaF 2 -BaO system resulted in the discovery of the new Ba 7 (BO 3 ) 4− x F 2+3 x solid solution belonging to the BaF 2 -Ba 3 (BO 3 ) 2 section. The distinguishing feature of the crystal structure of Ba 7 (BO 3 ) 4− x F 2+3 x phase is its extensive (BO 3 ) 3− ↔ 3F − anionic isomorphic substitution, confirmed by X-ray diffraction study of Ba 7 (BO 3 ) 3.51 F 3.47 ( x = 0.49) single crystals (space group P 6 3 ; a = 11.18241(11) Å, c = 7.23720(8) Å). The area of homogeneity for Ba 7 (BO 3 ) 4− x F 2+3 x solid solution spans between Ba 7 (BO 3 ) 3.35 F 3.95 and Ba 7 (BO 3 ) 3.79 F 2.63 compositions (0.21 < x < 0.65). Also, a new orthorhombic phase with a tentative composition of Ba 5 (BO 3 ) 3 F has been identified in XRD powder patterns and indexed with cell parameters a = 7.605 Å, b = 14.843 Å and c = 10.291 Å. The new non-centrosymmetric solid-solution series Ba 7 (BO 3 ) 4− x F 2+3 x with unique anionic isomorphic substitution has been discovered.