Oxide ion conduction in Nd-9.33(SiO4)(6)O-2 and Sr2Nd8(SiO4)(6)O-2 single crystals grown by floating zone method

Single crystals of Nd-9.33(SiO4)(6)O-2 and Sr2Nd8(SiO4)(6)O-2 oxide ion conductors with the oxyapatite structure were grown without any macroscopic defect by the floating zone method. The oxide ion conductivity of the Sr2Nd8(SiO4)(6)O-2 single crystal varied with the distance from its seed crystal along the growth direction, because of its changing deficiency in Sr content. Its stoichiometric portion had a lower electrical conductivity by about five orders of magnitude at 600 degreesC than the value for Nd-9.33(SiO4)(6)O-2 single crystal. Structural refinement of neutron diffraction data for powdered Nd-9.33(SiO4)(6)O-2 single crystal showed that the previous structure analysis was misleading. Cation vacancies were present only at 4f site and its channel oxygen site was fully occupied in space group of P6(3)/m. The oxygen had an anisotropic displacement along the channel in the refined oxyapatite structure. (C) 2003 Elsevier B.V. All rights reserved.