Solid solubilities of (La Nd,)2(Zr,Ti)2O7 phases deduced by neutron diffraction

Time-of-flight powder neutron diffraction has been performed on oxides with composition (La1−xNdx)2Zr2O7 and Nd2(Zr1−xTix)2O7, where image, 0.2, 0.4,…1.0, in order to determine the solid solution behaviour across each series. Between La2Zr2O7 and Nd2Zr2O7, a cubic pyrochlore phase is observed (image, image). A linear decrease in the lattice parameter from 10.8047 to 10.6758 Å indicates complete miscibility of the two end-members. For the same series, the image oxygen x-parameter increases from 0.3313 to 0.3348, suggesting increased distortion of the 6 coordinate B sites and reduced distortion of the 8 coordinate image sites. There is limited solubility of Nd2Ti2O7 in Nd2Zr2O7. Exsolution of a monoclinic phase (image, image) rich in Nd2Ti2O7 is observed at approximately image. The compositional range over which a solid solution exists is more extensive than that which has been previously reported. The solubility of Nd2Zr2O7 in Nd2Ti2O7 is very low.