We report the first in-situ powder X-ray diffraction (PXRD) study of the BaCO3-CeO2-In2O3 and CeO2-In2O3 systems in air over a wide range of temperature between 25 and 1200 degrees C. Herein, we are investigating the formation pathway and chemical stability of perovskite-type BaCe1-xInxO3-delta (x= 0.1, 0.2, and 0.3) and corresponding fluorite-type Ce1-xInxO2-delta phases. The potential direct solid state reaction between CeO2 and In2O3 for the formation of indium-doped fluorite-type phase is not observed even up to 1200 degrees C in air. The formation of the BaCe1-xInxO3-delta perovskite structures was investigated and rationalized using in-situ PXRD. Furthermore the decomposition of the indium-doped perovskites in CO2 is followed using high temperature diffraction and provides insights into the reaction pathway as well as the thermal stability of the Ce1-xInxO3-delta system. In CO2 flow, BaCe1-xInxO3-delta decomposes above T=600 degrees C into BaCO3 and Ce1-xInxO2-delta, Furthermore, for the first time, the in-situ PXRD confined that Ce1-xInxO2-delta decomposes above 800 degrees C and supported the previously claimed metastability. The,maximum In-doping level for CeO2 has been determined using PXRD. The lattice constant of the fluorite-type structure Ce1-xInxO2-delta follows the Shannon ionic radii trend, and crystalline domain sizes were found to be dependent on indium concentration.