Hexagonal BaTiO$_{3}$ can be stabilized by alloying the titanium sites with other transition metals. (Dickson, 1961) The pure structure has been grown at 1853K and cooled to room temperature. (Akimo, 1994)
The data for this structure was taken 263K.
Space group $Amm2$ #38 does not specify the origin of the $z$-axis. We set it by taking $z_{1} = 0$, putting the barium atom at the origin.
$\frac{1}{2}a \,\mathbf{\hat{x}}- b y_{4} \,\mathbf{\hat{y}}+c z_{4} \,\mathbf{\hat{z}}$
(4e)
O II
References
G. Shirane, H. Danner, and R. Pepinsky, Neutron Diffraction Study of Orthorhombic BaTiO$_{3}$, Phys. Rev. 105, 856–860 (1957), doi:10.1103/PhysRev.105.856.
J. G. Dickson, L. Katz, and R. Ward, Compounds with the Hexagonal Barium Titanate Structure, J. Am. Chem. Soc. 83, 3026–3029 (1961), doi:10.1021/ja01475a012.
A. W. Hewat, Structure of rhombohedral ferroelectric barium titanate, Ferroelectrics 6, 215–218 (1974), doi:10.1080/00150197408243970.
J. Akimoto, Y. Gotoh, and Y. Oosawa, Refinement of Hexagonal BaTiO$_{3}$, Acta Crystallogr. Sect. C 50, 160–161 (1994), doi:10.1107/S0108270193008637.
Found in
R. T. Downs and M. Hall-Wallace, The American Mineralogist Crystal Structure Database, Am. Mineral. 88, 247–250 (2003).
First cited in
H. Eckert, S. Divilov, M. J. Mehl, D. Hicks, A. C. Zettel, M. Esters, X. Campilongo, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 4, Comp. Mat. Sci. 240, 112988 (2024). (doi=10.1016/j.commatsci.2021.110450)