LiBa2AlO4: A new lithium barium aluminate having an oxygen tetrahedral framework

Single-crystal grains of the new oxide LiBa2AlO4 were obtained from a sample that had been partially melted by heating a compact of a binary oxide powder mixture having a Li:Ba:Al molar ratio of 4:5:1 ​at 1173 ​K. Single-crystal X-ray diffraction analysis demonstrated that this oxide had a trigonal superstructure (hexagonal lattice with a ​= ​5.7879(2) Å and c ​= ​13.2456(6) Å, space group P3121) formed by an ordered Li and Al arrangement. The c-axis period in this structure was found to be approximately twice as long as that in BaZnO2, the space group of which is also P3121, and a three-dimensional framework constructed by sharing all vertices of Li- and Al-centered oxygen tetrahedra. This structure can be derived from the perovskite (ABO3)-type structure via the orderly replacement of BO6 octahedra with LiO4 and AlO4 tetrahedra. Polycrystalline samples of LiBa2AlO4 were synthesized by heating compacts having stoichiometric compositions at 1173 ​K. The relative dielectric constant and dielectric loss values observed for a polycrystalline sample at room temperature were 8.3 and 0.004, respectively. The second harmonic generation intensities for LiBa2AlO4 and BaZnO2 were found to be 4.4 and 19.4 times greater than the value for quartz, respectively.