Ba4r2sn4nb6o30 (R = La, Nd, Sm) Lead-Free Relaxors With Filled Tungsten Bronze Structure

Ba4R2Sn4Nb6O30 (R = La, Nd, Sm) lead-free relaxor ceramics were prepared by a standard solid-state reaction process. The B-site substitution effects of Sn4+ on crystal chemistry, dielectric, and ferroelectric nature were systematically discussed. Tetragonal tungsten bronze compound in space group P4/mbm was confirmed as the major phase for each composition. With decreasing temperature, a broad peak with strong frequency dispersion was observed for both the dielectric constant (epsilon ') and dielectric loss (tan delta), which could be well described by the Vogel-Fulcher relation. Raman analysis revealed the transformation of the internal vibration modes, demonstrating the modification effects of Sn4+ on the crystal chemical environment owing to its d(10) electron configuration. The ferroelectrically inert Sn4+ in B sites acted as disturbing centers which weakened the dipole coupling and the long-range ferroelectric order, and subsequently led to the suppression of ferroelectric transition and the enhancement of relaxor behavior.