The subsolidus phase equilibria of the Li2O-Ta2O5-B2O3, K2O-Ta2O5-B2O3 and Li2O-WO3-B2O3 systems have been investigated mainly by means of the powder X-ray diffraction method. Two ternary compounds, KTaB2O6 and K3Ta3B2O12 were confirmed in the system K2O-Ta2O5-B2O3. Crystal structure of compound KTaB2O6 has been refined from X-ray powder diffraction data using the Rietveld method. The compound crystallizes in the orthorhombic, space group Pmn2(1) (No. 31), with lattice parameters a = 7.3253(4) angstrom, b = 3.8402(2) angstrom, c = 9.3040(5) angstrom, z = 2 and D-calc = 4.283 g/cm(3). The powder second harmonic generation (SHG) coefficients of KTaB2O6, and K3Ta3B2O12 were five times and two times as large as that of KH2PO4 (KDP), respectively. (C) 2008 Elsevier Ltd. All rights reserved.