  Large single crystals of the double-perovskite Ba$_2$ScNbO$_6$ were grown
from the melt for the first time. With a lattice parameter at room temperature
of 4.11672(1) \r{A}, this cubic double-perovskite has an excellent lattice
match to BaSnO$_3$, PbZr$_{0.9}$Ti$_{0.1}$O$_3$, LaInO$_3$, BiScO$_3$, and
other perovskites of contemporary interest. Differential thermal analysis
showed that Ba$_2$ScNbO$_6$ melts at 2165$\pm$30{\deg}C in an inert atmosphere.
Competitive grain growth was visualized by energy dispersive Laue mapping.
X-ray diffraction rocking curve measurements revealed full width at half
maximum values between 21 and 33 arcsec for 002 and 004 reflections. The
crystals were sufficiently large to yield (100)-oriented single-crystal
substrates with surface areas as large as 10 x 10 mm$^2$.
