SYNTHESIS AND STRUCTURE CHARACTERISTICS OF THE NEW TERNARY BORIDE (V1-XNBX)(2)B-3

The new ternary compound (V1-xNbx)(2)B-3 was synthesized by both singl e crystal and polycrystalline methods. It belongs to the V2B3-type str ucture, which crystallizes in the orthorhombic space group Cmcm (No. 6 3), with Z = 4. The unit cell parameters of the ternary compound vary in the ranges 3.1086-3.162 Angstrom, 18.5817-19.107 Angstrom and 3.011 4-3.086 Angstrom for a, b and c respectively, with the V/Nb ratios in the starting materials varied from 3 to 1/2. The crystal structure of one representative single crystal of (V1-xNbx)(2)B-3 was studied by si ngle crystal X-ray diffractometry. The structure refinement converged at an R(F-2) value of 0.042 for 1165 reflections. For the single cryst al studied, the composition calculated from the refinement was (V0.82N b0.18)(2)B-3. In the crystal structure of (V0.82Nb0.18)(2)B-3, 73.9% o f the niobium atoms occupy the V(1) position, while the remaining atom s occupy the V(2) position. The influence of the V/Nb ratio in the sta rting materials on the formation of the (V1-xNbx)(2)B-3 compound and t he unit cell parameters is discussed.