Thermal analysis of metal organic precursors for functional oxide preparation: Thin films versus powders

Abstract

The thermal decomposition of several metal organic precursors, used in the preparation of YBa 2 Cu 3 O 7-x superconducting coated conductors (Cu acetate, Cu, Y and Ba trifluoroacetates and Ce propionate) is analyzed by means of several thermoanalytical techniques (TG/DTA, MS and DSC). In all cases, the metal organic precursors deposited as thin films decompose differently than powders from the same precursors. In thin films, decomposition is facilitated by the easier transport of reactive gas from the surrounding atmosphere and by the easier out-diffusion of volatile products. Consequently, films decompose at lower temperature and are more sensitive to the presence of any residual reactive gas in the furnace. Good thermal contact with the substrate is also shown to minimize overheating in films and avoid combustion processes that are otherwise often observed during the thermal decomposition of powders. Finally, the formation and stability of intermediate products towards the oxide formation, such as metal fluorides, differs in films because of the easier gas exchange. With respect to powders, these compounds are much less stable in films, where their decomposition temperature can be lowered by several hundreds of degrees Celsius. While in some cases the behaviour of films can be predicted by analyzing varying masses of precursor powders, this is not always the case. Therefore, thermal analysis carried out on films is recommended to avoid erroneous conclusions about materials preparation drawn from powders.

Thermal decomposition of yttrium propionate: film and powder

“…4C). Since both powder and film are obtained from the same solution, this difference can be attributed to the fact that films are much more sensitive to residual atmospheres than powders [21,39]. The effect of the residual oxygen was confirmed by increasing the flow of nitrogen in the TG; the higher the nitrogen flow, the higher the amount of 3-pentanone and the smaller the formation of propionic acid.…”

“…In powders, due to the slow intra-particle oxygen transport [21], the local atmosphere near particles is almost inert and process β shifts to higher temperatures. This shift of process β favors the occurrence of α, to the point that in N 2 β is almost suppressed; we observe a long plateau before decomposition starts and the volatiles observed correspond to route α (Fig.…”

“…However, it has been stated that powders can behave differently than films [9,[21][22][23][24][25] due to different gas and heat transport phenomena between the two. Therefore, an in-situ study of the thermal processes that lead to YBCO tape synthesis is of fundamental interest to reveal the actual kinetics and mechanism occurring in films.…”

Study of a sol–gel precursor and its evolution towards ZnO

“…As depicted in Figure 6, the Ink undergoes a very pronounced mass-loss process ( to: a) the more difficult gas exchange, and consequently slower decomposition rate 43 , in a bulky sample (necessary for TG experiments) than for the layer needed for powder XRD; and b) the long stabilization time required for each in-situ XRD measurement, so the time in each temperature has an important role.…”

Measuring thermal conductivity of powders with differential scanning calorimetry

“…For relative densities below 80% and small particle sizes (< 100 µm) heat-flow is governed by interparticle contact resistance [4]. This surprising behaviour renders metallic powders as insulating as ceramic powders [5,1] and has significant consequences for the combustion synthesis of materials [3,6,7,8] and for thermal insulation [9]. As such, the low thermal conductivity of powders reduces DSC analysis accuracy as a result of the thermal gradients that develop inside the sample [10].…”