Dielectric, X-Ray, and Optical Study of Ferroelectric Cd2Nb2O7 and Related Compounds

Abstract

Single crystals of ${\mathrm{Cd}}_2$ ${\mathrm{Nb}}_2$ ${\mathrm{O}}_7$ have been grown, and dielectric, x-ray, and optical studies have been carried out on these above and below the ferroelectric Curie point. The x-ray analysis confirms the pyrochlore structure, and gives the oxygen parameter $x=0.305\mathrm{}$ at room temperature. The symmetry below the Curie point, -85°C, is uncertain, due to the very slight lattice distortion: $\frac{c}{a}$ is about 1.0005 if the ferroelectric phase is tetragonal. The spontaneous polarization along the cubic (111) axis is 6 microcoulombs/${\mathrm{cm}}^2$ at -180°C.