Growth and Optical Properties of LixNa1–xBa12(BO3)7F4 Fluoride Borates with “Antizeolite” Structure

Studied LixNa1–xBa12(BO3)7F4 (P42bc) solid solution belongs to the new class of “antizeolite” borates with [Ba12(BO3)6]6+ 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 LixNa1–xBa12­(BO3)7F4 structure. Distinctive feature of LixNa1–xBa12­(BO3)7F4 crystals is their deep purple color, which is due to both hole-type and electron-type centers. Crystals are characterized by linear dichroism effect.