Abstract
Apatite-type lanthanum silicates doped with different multivalent cations at the Si site, La10Si5.5B0.5O27+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 La10Si5.5B0.5O27+δ ceramics. Both La10Si5.5In0.5O26.75 and La10Si5.5Nb0.5O27.25 ceramics consist only of a hexagonal apatite structure with a space group P63/m, however, La10Si6O27 and La10Si5.5Sn0.5O27 ceramics are composed of a hexagonal apatite structure and a small amount of second phase La2SiO5. The measured total conductivity of each composition gradually increases with increasing temperature from 673K to 1173K, which follows the Arrhenius behavior. Lanthanum silicates doped with trivalent In3+ or pentavalent Nb5+ cations at the Si4+ site have a higher total conductivity than undoped lanthanum silicate, however, La10Si5.5Sn0.5O27 ceramic doped with tetravalent Sn4+ cations at the Si4+ site exhibits a comparable total conductivity to undoped La10Si6O27 ceramic. La10Si5.5In0.5O26.75 and La10Si5.5Nb0.5O27.25 ceramics have a total conductivity of 1.75×10−2S·cm−1 and 1.23×10−2S·cm−1 at 1073K, respectively, which are considerably higher than that of undoped La10Si6O27. At temperature of 773K, La10Si5.5In0.5O26.75 ceramic has the highest total conductivity of 8.92×10−4S·cm−1.
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