Analysis of the preparation of In-doped CaZrO3 using a peroxo-oxalate complexation method

The wet chemical synthesis of CaZr_0.9In_0.1O_3-α powders via a peroxo-oxalate complexation method has been studied in detail using different techniques, i.e. TG-DTA, XRD, FT-IR, BET, SEM, EDX, and non-isothermal densification. Using these techniques, the different reaction steps in the calcination process have been clarified. After drying the precipitated complex at 150 °C for 3 h, a mixture of calcium oxalate and an amorphous zirconia phase is found. Between 200 and 450 °C, the calcium oxalate decomposes into calcium carbonate. In the temperature range 450±800 °C, the calcium carbonate decomposes into CaO, while a crystalline zirconia phase appears (CaZr₄O₉). In this temperature range, the formation of CaZrO₃ is already observed. Further increasing the calcination temperature to 1000 °C leads to a binary mixture of CaZrO₃ and CaIn₂O₄. When the calcination temperature is increased to around 1500 °C, the CaIn₂O₄ phase dissolves into the calcium zirconate to form the desired CaZr_0.9In_0.1O_3-α. All compacts sintered at 1550 °C for 10 h show single-phase CaZr_0.9In_0.1O_3-α, independent of the calcination temperature. The morphology of the sintered compacts, however, varies with the calcination temperature, due to the presence or absence of a reactive sintering step around 1300 °C. Powders calcined at 1000 °C show a larger grain size in the sintered compact than powders calcined at 1450 or 1550 °C.