Oxide ion conduction in Ba, Ca and Sr doped apatite-type lanthanum silicates

Effect of Sr and Al or Fe co-doping on the sinterability and conductivity of lanthanum silicate oxyapatite electrolytes for solid oxide fuel cells

“…In contrast, alkaline earth (Ca, Sr, Ba) doped samples containing oxygen excess all exhibited high oxide conductivities (e.g. s at 700 C ¼ 8.74 Â 10 À3 S cm À1 for La 9 Sr(SiO 4 ) 6 O 2.5 , versus 3.26 Â 10 À4 S cm À1 for La 9.33 , 0.67 Si 6 O 26 ) [22]. These results also show that oxygen excess is more important than cationic vacancies to achieve good oxide-ion conductivity of lanthanum silicate oxyapatite.…”

Synthesis and characterization of Al3+ and M (M = W6+, In3+, Nb5+, Mg2+) co-doped lanthanum silicate oxy-apatite electrolytes

“…The cationic substitutions on the La site with other rare earth elements [15e17] or alkaline earth elements [18e23] have been investigated. The samples containing oxygen excess exhibit high oxygen ion conductivity, which indicates that oxygen excess is more important than cationic vacancies to achieve good oxide-ion conductivity of oxy-apatite lanthanum silicate [21].…”

Synthesis and characterization of calcium and iron co-doped lanthanum silicate oxyapatites by sol–gel process for solid oxide fuel cells

“…The intensity of the La 2 SiO 5 second phase of LCSFO(SSP) is lower than that of LSFO(SSP) synthesized under identical conditions and temperatures, indicating that doping Ca on the La site for LSFO oxyapatite can further retard the formation of the La 2 SiO 5 secondary phase. However, as shown previously, phase pure lanthanum silicate apatite-type powders synthesized by SSP can be formed at temperature above 1500 C [29,41]. Fig.…”

“…Fig. 1c is the XRD patterns of LCSFO powders synthesized by SGP at the temperatures of 700e1000 C. The oxyapatite phase starts to form at 700 C and the complete formation of apatite phase for LCSFO(SGP) powders occurs at 750 C. This is substantially lower than complete phase formation temperature of~1500 observed for the lanthanum silicates such as La 10 Si 6 O 27 and La 9 Ba 1 Si 6 O 26.5 synthesized by SSP route [29,41]. La 2 SiO 5 was not detected.…”

“…Direct evidences for the importance of the silicate units were obtained from the solid state 29 Si NMR studies, which shows a close correlation between the silicon environment and the observed oxide-ion conductivity [20]. The computer modeling studies also indicated the importance of the silicate substructure in aiding the motion of the oxide ions down the channels in the oxyapatites.…”