Structure and dielectric properties of new niobates Sr5LnTi3Nb7O30

Two new niobates Sr5LaTi3Nb7O30 and Sr5YTi3Nb7O30 were synthesized by using high temperature solid state reaction in the SrO-Ln(2)O(3)-TiO2-Nb2O5 system. The crystal structure and dielectric properties were characterized by using X-ray powder diffraction, scanning electron microscope and dielectric measurements. The results show that Sr5LaTi3Nb7O30 belongs to paraelectric phase of fully filled tetragonal tungsten bronze structure at room temperature with unit cell parameters: a = 1. 233 60 (4) nm, c = 0. 388 01 (2) nm. The room temperature dielectric constant (epsilon(r)) of Sr5LaTi3Nb7O30 ceramic reached 466 combined with a low dielectric loss of 0. 005 at 1 MHz. While Sr5YTi3Nb703o belongs to ferroelectric phase of fully filled tetragonal tungsten bronze structure at room temperature with unit cell parameters: a = 1. 228 80 (4) nm, c = 0. 387 05 (2) nm. Sr5YTi3Nb7O30 has significant relaxor behaviors, and the phase transition from ferroelectric to paraelectric occurred at temperature 260 degreesC and frequency 10 kHz. The room temperature relative dielectric constant (epsilon(r)) of Sr5YTi3Nb7O30 ceramic reached 290 at 1 MHz.