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)(2)Zr2O7 and Nd-2(Zr1-xTix)(2)O-7, where x = 0, 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 (Fd (3) over barm, Z = 8). A linear decrease in the lattice parameter from 10.8047 to 10.6758 angstrom indicates complete miscibility of the two end-members. For the same series, the 48f 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 A sites. There is limited solubility of Nd2Ti2O7 in Nd2Zr2O7. Exsolution of a monoclinic phase (P2(l), Z = 8) rich in Nd2Ti2O7 is observed at approximately x = 0.56. 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. (c) 2004 Elsevier Inc. All rights reserved.