PHASE-RELATIONS IN THE AL-TA SYSTEM - ON THE TRANSLATIONAL SYMMETRIESOF AL3TA2 AND ALTA

The Al-Ta system was reinvestigated preparatively in the range 0.15 < x(Ta) < 0.85. The translational symmetries of two phases referred to a s Al3Ta2 and AlTa were determined by means of X-ray powder diffractome try in combination with electron diffraction. The lattice parameters O f Al3Ta2 (f.c.c., cF) and AlTa (primitive monoclinic, mP) are a = 1915 .80(3) pm and a = 1486.5(3) pm, b = 986.3(2) pm, c = 986.2(2) pm and b eta = 99.98(2)-degrees respectively. The phase relations are discussed and previously reported data are critically reviewed.