Phase Relations and Physical Properties of Layered Pb-Containing Nd2MoO6 Compounds

The phase relations along the Nd2MoO6-PbO join of the ternary Nd2O3-MoO3-PbO system have been studied by means of solid-state synthesis in air. The samples with high Pb content underwent a reversible first-order phase transition near 820 degrees C. XRD analysis revealed two tetragonal phases, the high-temperature centric phase (I4(1)/acd) and the low-temperature acentric phase (I(2)m). In the region of the phase transition, the permittivity of the Pb-containing samples show a strong lambda-type anomaly and electrical conductivity increases sharply by one and half orders of magnitude. The conductivities of the Pb-containing samples reach 10(-2) S/cm at 850 degrees C, which is two orders of magnitude greater than the conductivity of pure Nd2MoO6. The conductivity in such compounds may be due to oxygen ions. A permittivity anomaly, existence of a piezoelectric effect, and the symmetry change from acentric I(2)m to centric I4(1)/acd may indicate an antiferroelectric nature of the phase transition.