Phase relations of the Li2O–Ta2O5–B2O3 and Li2O–WO3–B2O3 systems and promising nonlinear optical compounds in K2O–Ta2O5–B2O3 system

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 Pmn21 (No. 31), with lattice parameters a = 7.3253(4) Å, b = 3.8402(2) Å, c = 9.3040(5) Å, z = 2 and Dcalc = 4.283 g/cm3. 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.