Doping effects on the electrical conductivity of bismuth layered Bi3TiNbO9-based ceramics

Single phase ${\mathrm{Bi}}_3\mathrm{Ti}\mathrm{Nb}{\mathrm{O}}_9$ (BTNO)-based ceramics, with ${\mathrm{Sr}}^{2+}$ replacing ${\mathrm{Bi}}^{3+}$ as an acceptor dopant and ${\mathrm{Nb}}^{5+}$ and ${\mathrm{W}}^{6+}$ replacing ${\mathrm{Ti}}^{4+}$ as donor dopants, were prepared by conventional solid-state reaction method. The conductivity increased with acceptor dopant and decreased with donor dopant. These results indicate that the dominant conduction mechanism of pure BTNO is $p$ type at low temperature range. Detailed investigations about the ${\mathrm{W}}^{6+}$ donor doped BTNO ceramics showed that when the doping amount $x>0.01$ , the conductivity increases with increasing donor doping amount, suggesting that the extrinsic conductivity changes from $p$ type to $n$ type at the low temperature region. The extrinsic conductivity range extends to higher temperature with the increase of donor doping amount. At high temperature range the intrinsic electrical conductivity activation energy is about $1.8\mathrm{eV}$ . This value is equal to half the band gap energy.