via a direct solid state reaction. This requires some prior Traditional exploration of phase diagrams is dominated by knowledge of the phase diagram, including the positions the annealing of reaction products formed from high temperaof the eutectics closest to the phase in question, to optimize ture reactions. In this paper we present an alternative approach, the cooling sequence and other reaction conditions (1, 2).
based on the low temperature crystallization of amorphous
Much recent effort in solid state synthesis has been direaction intermediates, which is ideally suited for the study rected at the low temperature synthesis of compounds, in of incongruently melting compounds. Within the vanadium part due to the traditional dominance of high temperature selenium phase diagram we demonstrate the ability to prepare methods in preparing new materials. Low temperature synthe incongruently melting compounds V 2 Se 9 and V 5 Se 4 using the thesis methods allow the preparation of many new comaverage composition of the amorphous reaction intermediate to pounds and structure types which are metastable or unstacontrol phase nucleation. We also present evidence for a new, ble at higher temperatures. Low temperature synthesis is kinetically stable vanadium selenide near the composition V 0.8 Se which disproportionates into a mixture of VSe 2-x and V 5 Se 4 typically accomplished by using low temperature eutectics upon annealing at 500ุC. The compounds V 5 Se 8 and V 3 Se 4 as solvents for the reactants or through the use of hydrowere not observed to nucleate from any of the amorphous thermal growth conditions. These exploratory synthesis intermediates, regardless of their overall composition. ยฉ 1996 efforts depend to a large degree upon intuition and insight, Academic Press, Inc.
since very little is known concerning the reaction mechanisms, the higher order phase diagram of the product, or the even more complex reacting systems that include the