Effect of some dopant elements on the low temperature formation of γ-Ce2S3

For the first time, it has been clearly shown that carbon is an excellent element to stabilize the gamma-phase of cerium sesquisulfide at a low temperature (around 800 degrees C) by using CS2. The most appropriate route is to use cerium molecular-complex precursors which contain some carbon (like acetate, succinate...), but this element can also be added to carbon-free precursors, such as nitrate. However, the gamma-phases so-obtained are dark or brown due to the presence of graphitic carbon. Silicon presents the same properties as carbon. Likewise, the use of phosphate precursors leads to the gamma-phase at low temperature (750-800 degrees C). However, during the thermal treatment under CS2, some phosphorus is lost from the solid-phase resulting in a progressive transformation of the gamma-phase into the alpha-phase. Contrary to the alpha-Ce2S3 phase, the residual monazite (CePO4) does not greatly affect the red color of gamma-Ce2S3. The same results are observed by using berate and, to a lesser extent, vanadate and arseniate precursors. One can assume that the stabilization of the gamma-phase is probably due to the insertion of a small amount of these dopants into the empty tetrahedral cavities of the gamma-Ce2S3 structure. (C) 2000 Elsevier Science S.A. All rights reserved.