Synthesis and dielectric characteristics of the layered structure Bi4−xRxTi3O12 (Rx=Pr, Nd, Gd, Dy)

Four Aurivillius type systems with generic formula Bi4−xRxTi3O12, where Rx=Pr, Nd, Gd, and Dy, have been synthesised to investigate the physical effects of Rx on the host lattice Bi4Ti3O12. Particularly we report here the crystallographic characteristics, as measured by X-ray, and the dielectric properties of the resulting compounds. The layered orthorhombic structures show variations of the a/b distortion comparable with that of Bi4Ti3O12. Impedance spectroscopy is used to display the electrical response over a wide temperature range, from room temperature up to 850 °C. The conductivity diminishes as the size of Rx grows; activation energies are reported. The rare earth concentration determines the ferroelectric characteristics of the compounds: for small x, they behave as typical ferroelectrics, but all of them tend to become relaxors when x grows. The structure seems to favour the appearance of ferroelectricity when the atomic size of the rare earth diminishes. SEM reveals microscopic composition fluctuations in all samples. Using the specimens as if they were the detectors of the electron microscope, we have determined the type of charge carrier involved in the conductivity phenomena.