In this investigation, X-ray diffractometry and C-13 NMR spectroscopy were used to characterize the effect of pH on the formation of gel and its thermal decomposition by the Pechini process. It was found that the major effect of pH was to destroy the esterification between citric acid (CA) and ethylene glycol, which in turn could influence Ba species and the formation of a mixed-metal CA complex. It was also found that barium carbonate was derived from the Ba species and was not related to the instability of Ba2Ti2O5CO3, but Ba2Ti2O5CO3 was formed by the thermal decomposition of a mixed-metal CA complex. Moreover, BaTiO3 formed via two routes, the reaction of BaCO3 with Ti species and thermal decomposition of Ba2Ti2O5CO3.