SEMICONDUCTOR TO METAL TRANSITION IN LN(2)MO(3)O(9) COMPOUNDS

Ln(2)Mo(3)O(12) and Ce2Mo3O12.25 are reduced by hydrogen yielding Mo4 oxides of the formula Ln(2)Mo(3)O(9) (Ln = La, Ce, Pr, Nd, Sm, Gd and Dy). The new compound Ce2Mo3O9 has the same structure as other Ln(2)M o(3)O(9) compounds. All of the products are single phase materials and crystallize in a tetragonal scheelite type structure with Mo2O6 clust ers. The IR spectra of the Ln(2)Mo(3)O(9) oxides show two absorption b ands. These compounds are black n-type semiconductors, and exhibit Cur ie-Weiss Law behavior from 100K to 250K. Temperature dependence of the electrical properties of these compounds were measured for the first time, and a semiconductor-metal transition was found at about 250 degr ees C.