THE STABILIZATION OF GAMMA-CE2S3 AT LOW-TEMPERATURE BY HEAVY RARE-EARTHS

The use of some heavy lanthanide(III) elements allows the stabilizatio n of the gamma-phase of Ce2S3 synthesized in H2S at low temperatures ( 600 degrees C-800 degrees C). Among the lanthanides used, the best ele ment is dysprosium followed by holmium, erbium and terbium. The stabil ization is more pronounced when using mixed-precursors, either the cry stallized oxalate or other less crystallized complexes. However this s tabilization is only transitory: heating above 800 degrees C yields th e beta form. It is the first time that the gamma phase is observed at a lower temperature than the beta form. Due to the low temperatures an d the short treatment time no change of morphology is observed between the starting precursor and the final sulphide. (C) 1997 Elsevier Scie nce S.A.