Study of the formation of SrCuO2 from Sr2CuO3 and CuO by X-ray thermodiffractometry

The formation of SrCuO2 from Sr2CuO3 + CuO has been investigated by X-ray thermodiffractometry and differential thermal analysis in different atmospheres between room temperature and 1000 degrees C. The overall process implies the formal insertion of one copper-oxygen chain into the structure of Sr2CuO3 to give the characteristic double chains of SrCuO2. In air atmosphere this does not take place directly; instead, starting at temperatures of ca. 300 degrees degrees C the following reactions take place: (1) Sr2CuO3 + CuO+ (1-x) CO2 --> (1-x) SrCO3 + Sr1+xCu2O3 and (2) Sr2CuO3 + CuO --> (1-x) SrO + Sr1+xCu2O3. The relative extent of(1) and (2) depends on the quantity of CO2 present in the synthetic air used for the experiment, reaction (2) taking place only under flowing air atmosphere. The formation of SrCO3 could not be totally avoided in spite of the many rigorous precautions taken during the experiment in flowing air. Between 700 and 1000 degrees C the product SrCuO2 is formed, being the major phase after 1h 30' at 1000 degrees C. On the other hand, under a static air atmosphere, the oxycarbonate Sr2CuO2CO3 is formed at 889 degrees C. Finally, in an experiment performed in pure CO2, only the decomposition reaction Sr2CuO3 + CO2 --> SrCO3 + CuO takes place starting at 289 degrees C, and no SrCuO2 is formed.