The effect of native defects on the domain structure of has been investigated. To reduce the number of native defects, two methodologies have been adopted: firstly, co-doping with Mg; and secondly, the addition of to the congruent melt. When grown from congruent melts, has a multi-domain nature. Co-doping with Mg changes the domain structure, although the crystals are still multi-domain. On addition of , single-domain crystals are obtained. The change in domain structure brought about by doping with Mg is due to compensation of the stoichiometric defects. On the other hand, reduction in the number of intrinsic defects due to change in the Li/Nb ratio in the crystal as a result of the addition of to the melt is responsible for the mono-domain structure.