Relationship between structural and dielectric properties of Zn-substituted Ba5CaTi2−xZnxNb8O30 tetragonal tungsten bronze

Abstract

Ba₅CaTi_2−xZn_xNb₈O₃₀ ceramics (x = 0, 0.04, and 0.08) were synthesized by a conventional solid-state reaction method at 1300 °C for 6 hours. The effects of the Ti/Zn ratio on structural and dielectric properties were studied by changing the value of x. The pure phase formation of all prepared Ba₅CaTi_2−xZn_xNb₈O₃₀ compositions was confirmed by X-ray diffraction. The refinement of the (XRD) data by the Rietveld method confirmed the tetragonal crystal structure with the space group P4bm at room temperature. Scanning electron microscopy (SEM) showed that the Ba₅CaTi_2−xZn_xNb₈O₃₀ ceramics have good sinterability, low porosity and uniform distribution of grains of unequal size over the entire surface in all the samples. The average grain size is in the range of 1.3 to 1.6 μm. The frequency-dependent dielectric properties were examined by complex impedance spectroscopy in the temperature range of 50 °C to 420 °C where a structural phase transition was observed for all the samples.