The Effect of Tartaric and Citric Acid as a Complexing Agent on Defect Structure and Conductivity of Copper Samarium Co-doped Ceria Prepared by a Sol-Gel Auto-Combustion Method

Abstract

A copper samarium co-doped ceria (CSDC) (Cu0.01Sm0.19Ce0.80O2-δ) nanoparticles were synthesized via a sol-gel auto-combustion of metal nitrates with two different complexing agents including tartaric acid (TA) and citric acid (CA). A reference sample was metal nitrates in deionized water (DI). TGA/DSC of gels reveals endothermic reaction for CSDC/DI but exothermic behavior for CSDC/TA or CSDC/CA during oxide formation. The CA route exhibits the highest energy release since it has extensive formation of metals-citrate. From SEM, the as-synthesized morphologies of DI, TA and CA routes show porous sheet-like, fluffy-like and foamy-like structure, respectively. XRD patterns of calcined CSDCs denote a cubic fluorite structure. The average particle sizes from TEM vary in the range of 30-32 nm. The relative oxygen vacancy (VO) concentrations for calcined and sintered CSDCs from Raman analysis are as follow; CSDC/CA>CSDC/TA>CSDC/DI. Moreover, segregation of (Ce and/or Sm)2O3 and CuO can be observed in Raman spectra for calcined and sintered CSDCs. The oxides of copper segregate mostly in sintered CSDC/CA. The XPS results confirm that Ce3+/Ce4+ coexist, and in addition, the Ce3+ represent Ce3+-VO and/or Ce2O3 segregation. The Ce3+ in sintered CSDCs suggest the existence of Ce3+-VO for CSDC/DI and CSDC/CA; however, Ce3+ implied coexisting of Ce3+-VO and Ce2O3 segregation for CSDC/TA. The relative densities of sintered CSDC/DI, CSDC/TA and CSDC/CA are 82.78%, 95.51% and 97.98%, respectively. The enthalpy of association increases with the increasing of porosity and metal oxide segregation. Segregation of CuO increases CSDC/CA’s association enthalpy at low temperature but it does not affect high temperature conductivity of CSDC/CA. The high total conductivity of 0.0271 S/cm was achieved for CSDC/CA at 600 °C.