Preparation, structure and dielectric properties of (Ba1−xSrx)2NaNb5O15 ceramics

In this study the tungsten–bronze type tetragonal (Ba1−xSrx)2NaNb5O15 system as a kind of lead-free ferroelectric ceramics has been synthesized by low-temperature combustion method. Microstructure and dielectric properties of (Ba1−xSrx)2NaNb5O15 system were also investigated. X-ray diffraction (XRD) study confirms the formation of single-phase tetragonal compounds in the crystal system at room temperature. The TEM photograph shows that the particles synthesized by low-temperature combustion method are uniform with an average particle size of 30 nm in diameter. Microstructure analysis of the surface of the compounds by scanning electron microscopy (SEM) suggests that small grains distribute uniformly on the surface of the samples. The dielectric constant (ɛ) and tangent loss (tan δ) of the samples have been measured as a function of both frequency (0–1 GHz) and temperature (0–500 °C). Detailed studies of the dielectric properties suggests that they have undergone a phase transition well above the room temperature and it is also found that the compositions with x = 0.6 have the lowest phase transition temperature (Tc) and the highest dielectric constant at Tc under 100 kHz. Moreover, the (Ba1−xSrx)2NaNb5O15 synthesized by low-temperature combustion method have better dielectric properties than those prepared by the solid-state reaction.