  We have grown cubic centimetre-size crystals of YBa2Cu3Ox suitable for
neutron studies, by a top-seeded melt-growth technique. Growth conditions were
optimized with an eye toward maximizing phase purity. It was found that the
addition of 2% Y2BaCuO5 and 0.5% Pt (by mass) were required to prevent melt
loss and to obtain the highest crystallinity. A neutron diffraction study on a
mosaic of six such crystals found that the final Y2BaCuO5 concentration was 5%,
while other impurity phases comprised less than 1% by volume. The oxygen
content was set to x=6.5, the crystals were detwinned and then carefully
annealed to give the well-ordered ortho-II phase. The neutron study determined
that 70% of the mosaic's volume was in the majority orthorhomic domain. The
neutron (0,0,6) and (1,1,0) rocking curve widths were ~1 degree per crystal and
\~2.2 degrees for the mosaic, and the oxygen chain correlation lengths were
>100 A in the a- and b-directions and ~50 A in the c-direction.
