Growth and Optical Properties of Li_xNa_1–xBa₁₂(BO₃)₇F₄ Fluoride Borates with “Antizeolite” Structure

Abstract

Studied LiNaBa(BO)F (P4bc) solid solution belongs to the new class of "antizeolite" borates with [Ba(BO)] cation pattern, which contains channels filled by anionic clusters. Optical-quality crystals were grown from the compositions with different sodium-lithium ratio. The results of Rietveld refinement based on powder data demonstrate linear increase of parameter a and unit cell volume with Na/(Na + Li) ratio in cation site. Parameter c is less sensitive to the changes in stoichiometry, which is consistent with channel topology of LiNaBa(BO)F structure. Distinctive feature of LiNaBa(BO)F crystals is their deep purple color, which is due to both hole-type and electron-type centers. Crystals are characterized by linear dichroism effect.

BaO−B2O3 system and its mysterious member Ba3B2O6

“…Both structures of the Ba 3 (BO 3 ) 1.8 F 0.6 intermediate member 29 and reported here Ba 3 (BO 3 ) 2 end-member of Ba 3 (BO 3 ) 2-x F 3x solid solution demonstrate a pronounced tetragonal pseudosymmetry, corresponding to the P4 2 /mbc space group. The potential tetragonal symmetry of Ba 3 (BO 3 ) 2-x F 3x solid solution is broken by~0.5% difference between the a and b axes of the unit cell.…”

“…It was found that the ability of the [Ba 12 (BO 3 ) 6 ] 6+ cationic pattern to accommodate intrachannel assemblages is not limited by the (BO 3 ) 3− versus F − variations. We identify the same cation pattern in the Li x Na 1−x Ba 12 (BO 3 ) 7 F 4 ( P 4 2 bc ) solid solution, where channels are filled with (BO 3 ) 3− anions and (LiF 4 ) 3− and (NaF 4 ) 3− clusters . Thus, in order to exclude possible incorporation of solvent elements in the channels, we grew crystals without solvent from the composition with a slight excess of B 2 O 3 .…”

“…All the (BO 3 ) 3– groups in Ba 3 B 2 O 6 are oriented perpendicular to the channel axis (Figure A) being compatible with the centrosymmetric space group. In contrast, another solid solution based on [ Ba 12 (BO 3 ) 6 ] 6+ cation pattern Li x Na 1– x Ba 12 (BO 3 ) 7 F 4 crystallizes in the tetragonal non‐centrosymmetric space group ( P 4 2 bc ) . The cubic sections of structural channels in Li x Na 1– x Ba 12 (BO 3 ) 7 F 4 are occupied by planar [(Li,Na)F 4 ] 3– clusters (Figure B) so that the cation of each cluster electrostatically attracts the oxygen atom of the neighbor (BO 3 ) 3– group, causing its orientation along the channel axis and losing of the inversion center.…”

“…Crystals of Li x Na 1– x Ba 12 (BO 3 ) 7 F 4 are characterized by a linear dichroism effect. The presence of a linear dichroism effect in these crystals makes them applicable for using as polarization filters and attenuators …”

“…We identify the same cation pattern in the Li x-Na 1Àx Ba 12 (BO 3 ) 7 F 4 (P4 2 bc) solid solution, where channels are filled with (BO 3 ) 3À anions and (LiF 4 ) 3À and (NaF 4 ) 3À clusters. 29 Thus, in order to exclude possible incorporation of solvent elements in the channels, we grew crystals without solvent from the composition with a slight excess of B 2 O 3 . It was impossible for us to grow crystals from the stoichiometric melt because of the heating furnace limits.…”