Phase Relations and Physical Properties of Layered Pb‐Containing Nd 2 MoO 6 Compounds

The phase relations along the Nd 2 MoO 6 –PbO join of the ternary Nd 2 O 3 –MoO 3 –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 °C. XRD analysis revealed two tetragonal phases, the high‐temperature centric phase ( I 4 1 / acd ) and the low‐temperature acentric phase ( I $\bar {4}$ 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 °C, which is two orders of magnitude greater than the conductivity of pure Nd 2 MoO 6 . 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 $\bar {4}$ 2 m to centric I 4 1 / acd may indicate an antiferroelectric nature of the phase transition.