A new compound filled tungsten-bronze-type structure Ba2Na1 3xRExNb5O15 (trivalent rare-earth ions: RE3+ =Sc3+, Y3+, La3+, Gd3+, Yb3+ and Lu3+, with x = 0.02) has been prepared by selecting RE3+ ions without any absorption in the visible range. The effect of rare-earth addition oil micro-twin formation, that is to say, tetragonal-orthorhombic ferroelastic phase transition in barium sodium niobate was investigated and micro-twin formation could be suppressed by doping of smaller RE3+ ions such as Yb3+ and Lu3+ . All the samples exhibit an intense second harmonic generation signal under tunable IR pumping laser source, due to both the high values of the non-linear optical coefficients and the absence of absorption of additional RE ions in the visible range. (C) 2002 Elsevier Science B.V. All rights reserved.