CRYSTAL-GROWTH AND STRUCTURAL INVESTIGATION OF THE NEW QUATERNARY COMPOUND MO1-XCRXALB WITH X=0.39

Single crystals of Mo(1-x)Cr(x)AIB (quaternary representative of UBC) were synthesized by the high-temperature metal-solution method using a luminium flux, chromium, molybdenum metals and boron powder as startin g materials. The mixture, with atomic ratio [Cr] / [Me] = 3, [B] / [Cr + Mo] = 1.5 and [Al] / [Cr + Mo] = 28, was heated to 1650 degrees C, soaked at this temperature for 5 h and then cooled to 1000 degrees C a t a cooling rate of 50 degrees Ch(-1). Under these conditions, Mo(1-x) Cr(x)AIB single crystals were obtained with maximum dimensions of abou t 0.1 X 0.1 X 1 mm(3) together with CrB2 and (Cr1-xMox)(3)B-4 crystals . Mo(1-x)Cr(x)AIB crystallizes in the orthorhombic space group Cmcm (N o. 63) with a = 3.1702(6) Angstrom, b = 13.948(2) Angstrom, c = 3.0743 (4) degrees and Z=4. The structural parameters of Mo(1-x)Cr(x)AIB were refined with a full-matrix least-squares program using single-crystal X-ray diffraction data. The molybdenum and chromium atoms occupy the same position with x = 0.39. The refinement converged at a conventiona l R(F-2) value of 0.029 for 856 reflections. The homogeneity range and the structural characteristics of Mo(1-x)Cr(x)AIB are discussed. Ther e is evidence that the early reported phase Mo7Al6B7 crystallizes in t he UBC-type structure.