(K1-xNax)2Al2B2O7 with 0≤x<0.6:: A promising nonlinear optical crystal

Up to about 60% K+ in K2Al2B2O7 (KABO), a well-known nonlinear optical material, can be substituted by Na+ with the structure type being retained. AlO4 tetrahedra and BO3 triangles in the Na-substituted compound tilt to adjust to the local distribution of alkali-metal atoms, which explains the large range of homogeneity. When the Na+ substitution is higher than 50%, the decomposition and volatility of KABO are strongly inhibited and the sample melts congruently at about 940 degrees C, which makes it possible to grow bulk crystals from the melt directly. The second harmonic generation property of KNaAl2B2O7 is close to that of KABO. Taking the crystal growth into account, (K1-xNax)(2)Al2B2O7 (0 <= X < 0.6) seems to be a more promising nonlinear optical material than KABO.