Planar faults in metastably retained hexagonal BaTiO$_{3}$.

Hot-pressed BaTiO$_{3}$ ceramic samples contain predominantly h-BaTiO$_{3}$ as determined by XRD, and with a trace amount of t-BaTiO$_{3}$ as revealed by TEM. Extended planar stacking faults (EPSF's) found ubiquitously in hot-pressed samples having the eligible fault vectors \textbf{\textit{R}}$_{F(I)}$ = (1/2)\textbf{c} + \textbf{p}$_{(I)}$ and \textbf{\textit{R}}$_{F(II)}$ = (n/6)\textbf{c} + \textbf{p}'$_{(II)}$, containing both \textbf{p}$_{(I)}$ = 1/3$\langle $2\underline {11}0$\rangle $, \textbf{p}'$_{(II)}$ = 1/3$\langle $10\underline {1}0$\rangle $, n = 1, 2, 4, and 5, and \textbf{c} = [0001], have been determined by contrast analysis using the 2$\pi $\textbf{\textit{g}}$^{.}$\textbf{\textit{R}}$_{F}$ = 0 or 2n$\pi $ criteria crystallographically, and the number of layers along \textbf{\textit{c}} confirmed by high-resolution imaging uniquely. Two general types of EPSF's are found; one group with only three vectors of the six degeneracies of the \textbf{p}-component $\langle $10\underline {1}0$\rangle $ eligible and the other with all six degeneracies of the \textbf{p}-component $\langle $2\underline {11}0$\rangle $ eligible for the fault vector. The latter is analogously a $\pi $-rotation fault (as in DO$_{19}$ intermetallics) that a rotation about [0001] by 180$^{o}$ (or 60$^{o})$ arrives at another eligible fault vector. The metastable retention of the high-temperature h-BaTiO$_{3}$ phase is discussed in favour of oxygen deficiency.