Two New Barium Borate Fluorides ABa₁₂(BO₃)₇F₄ (A = Li and Na)

Two new barium borate fluorides LiBa12(BO3)7F4 and NaBa12(BO3)7F4 are obtained by spontaneous crystallization from high-temperature flux. The two compounds are isostructural and crystallized into the tetragonal system, I4/mcm space group, with unit cell parameters of a = 13.5709(6) Å, c = 14.9908(13) Å for LiBa12(BO3)7F4 and a = 13.6443(9) Å, c = 15.021(2) Å for NaBa12(BO3)7F4. Isolated Li/NaF4–BO3 units formed by Li/NaF4O square pyramids and B3O3 groups sharing the O5 atom are found occupying the octagonal tunnels built by Ba and BO3 groups along the c axis. High mobility of Li+ ion is observed in the LiBa12(BO3)7F4 single crystal by ac impedance measurements at different temperatures.