Synthesis, processing and microstructural characterization of CaSnO3 and SrSnO3 ceramics

A thorough study of CaSnO3 and SrSnO3 with respect to their synthesis, proc essing and microstructural characterization has been made. In order to esta blish a standard methodology for mass manufacturing with identical and bene ficial microstructure and reproducible electrical characteristics, differen t synthesis routes were adopted. Evolution of microstructure which is intim ately related to the envisaged properties in the ceramics, was closely and systematically followed in terms of sintering over a wide range of temperat ures and soak time. By using an alternative precursor (nitrate instead of c arbonate) with favorable decomposition kinetics, the temperature of compoun d formation by solid-state route was lowered by a significant margin of 200 degrees. In the case of the self-heat-sustained (SHS) method, the final co mpound was found to have formed via two-step reaction between molten tin an d metal nitrate. In CaSnO3, a dense microstructure with near zero porosity and uniform grain size could be developed by sintering at 1200 degrees C up to 48 h, while the solid-state derived SrSnO3 could be sintered to about 8 5-90% density relative to that of the green compact at 1350 degrees C/24 h. In the case of SHS technique, small grain size and a narrower particle siz e distribution was an interesting feature of the sintered samples. Sinterin g at 1350 degrees C for soak-time 48<t less than or equal to 60 h was found to be the most suitable schedule to obtain dense microstructure in CaSnO3 with average grain size similar to 1 mu m and, theoretical densification wi th larger grain size (3-5 mu m) could be achieved by sintering at 1600 degr ees C for 2 h. The SHS-derived SrSnO3 had very dense (relative density simi lar to 95%) microstructure after sintering at 1350 degrees C for soak-time in the range 12 h<t less than or equal to 24 h; sintering at higher tempera ture such as 1600 degrees C even for 2 h was found to be deleterious. Citra te-complex synthesis route yielded very fine, homogeneous and reactive subm icron sized CaSnO3 powder, with microstructure benign for making gas sensin g devices. (C) 1999 Elsevier Science S.A. All rights reserved.