  We report a study of properties of Mn-doped NBT-6%BT single crystals. We show
that tetragonal single domain states can be stabilized by poling along a [001]
direction. For carefully prepared crystals, the piezoelectric coefficient d33
can reach 570 pC/N. When poled along non-polar directions, the crystals exhibit
ferroelectric domain structures consistent with tetragonal micron-sized
domains, as revealed by optical observation and Raman spectroscopy. The
multidomain crystals have lower d33 values, 225 and 130 pC/N for [011] and
[111]-oriented crystals respectively. This trend is commented on from a
domain-engineering perspective.
