Synthesis and electrical conductivity of La10Si5.5B0.5O27 + δ (B = In, Si, Sn, Nb) ceramics

Abstract Apatite-type lanthanum silicates doped with different multivalent cations at the Si site, La 10 Si 5.5 B 0.5 O 27 +  δ ( B  = In, Si, Sn, Nb) ceramics, are synthesized via the high temperature solid state reaction process. X-ray diffraction and complex impedance analysis are used to analyze crystal structure and electrical conductivity of La 10 Si 5.5 B 0.5 O 27 +  δ ceramics. Both La 10 Si 5.5 In 0.5 O 26.75 and La 10 Si 5.5 Nb 0.5 O 27.25 ceramics consist only of a hexagonal apatite structure with a space group P 63/ m , however, La 10 Si 6 O 27 and La 10 Si 5.5 Sn 0.5 O 27 ceramics are composed of a hexagonal apatite structure and a small amount of second phase La 2 SiO 5 . The measured total conductivity of each composition gradually increases with increasing temperature from 673 K to 1173 K, which follows the Arrhenius behavior. Lanthanum silicates doped with trivalent In 3+ or pentavalent Nb 5+ cations at the Si 4+ site have a higher total conductivity than undoped lanthanum silicate, however, La 10 Si 5.5 Sn 0.5 O 27 ceramic doped with tetravalent Sn 4+ cations at the Si 4+ site exhibits a comparable total conductivity to undoped La 10 Si 6 O 27 ceramic. La 10 Si 5.5 In 0.5 O 26.75 and La 10 Si 5.5 Nb 0.5 O 27.25 ceramics have a total conductivity of 1.75 × 10 − 2  S·cm − 1 and 1.23 × 10 − 2  S·cm − 1 at 1073 K, respectively, which are considerably higher than that of undoped La 10 Si 6 O 27 . At temperature of 773 K, La 10 Si 5.5 In 0.5 O 26.75 ceramic has the highest total conductivity of 8.92 × 10 − 4  S·cm − 1 .