Semiconductor to metal transition in Ln2Mo3O9 compounds

Ln2Mo3O12 and Ce2Mo3O12.25 are reduced by hydrogen yielding Mo4+ oxides of the formula Ln2Mo3O9 (Ln = La, Ce, Pr, Nd, Sm, Gd and Dy). The new compound Ce2Mo3O9 has the same structure as other Ln2Mo3O9 compounds. All of the products are single phase materials and crystallize in a tetragonal scheelite type structure with Mo2O6 clusters. The IR spectra of the Ln2Mo3O9 oxides show two absorption bands. These compounds are black n-type semiconductors and exhibit Curie-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 °C.