A new tungsten-bronze type structure Ba2Na1-3xRxNb5O15, where R was a trivalent rare-earth ion (Sc3+, Y3+, La3+, Gd3+, Yb3+, Lu3+) and x was 0.02, was prepared by selecting R3+ ions with no absorption in the visible range. The effect of rare-earth additions upon micro-twin formation was investigated, and it was found that micro-twin formation could be suppressed by doping with smaller R3+ ions, such as Yb3+ or Lu3+.

Synthesis, Crystal Growth and Second Harmonic Generation Properties of Trivalent Rare-Earth Doped Non-Linear Tungsten–Bronze-Type Structure Ba2Na1-3xRExNb5O15 (RE = Sc, Y, La, Gd, Yb and Lu). A.Yoshikawa, H.Itagaki, T.Fukuda, K.Lebbou, A.El Hassouni, A.Brenier, C.Goutaudier, O.Tillement, G.Boulon: Journal of Crystal Growth, 2003, 247[1-2], 148-56