The wet chemical synthesis of CaZr 0.9 In 0.1 O 32a 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 densi®cation. Using these techniques, the different reaction steps in the calcination process have been clari®ed. After drying the precipitated complex at 150 ³C for 3 h, a mixture of calcium oxalate and an amorphous zirconia phase is found. Between 200 and 450 ³C, the calcium oxalate decomposes into calcium carbonate. In the temperature range 450±800 ³C, the calcium carbonate decomposes into CaO, while a crystalline zirconia phase appears (CaZr 4 O 9 ). In this temperature range, the formation of CaZrO 3 is already observed. Further increasing the calcination temperature to 1000 ³C leads to a binary mixture of CaZrO 3 and CaIn 2 O 4 . When the calcination temperature is increased to around 1500 ³C, the CaIn 2 O 4 phase dissolves into the calcium zirconate to form the desired CaZr 0.9 In 0.1 O 32a . All compacts sintered at 1550 ³C for 10 h show single-phase CaZr 0.9 In 0.1 O 32a , 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 ³C. Powders calcined at 1000 ³C show a larger grain size in the sintered compact than powders calcined at 1450 or 1550 ³C.