Structural, dielectric and electrical properties of NaBa2X5O15 (X = Nb and Ta) ceramics

Polycrystalline samples of NaBa2X5O15 (X = Nb and Ta), i.e., NaBa2Nb5O15 (NBN) and NaBa2Ta5O15 (NBT), members of tungsten bronze family, were prepared using a high-temperature solid-state reaction technique. A preliminary structural (XRD) analysis of these compounds shows the formation of a single-phase orthorhombic structure at room temperature. The scanning electron microscopy (SEM) provides information on the quality of the samples and uniform grain distribution over the surface of the sample. Detailed studies of the dielectric properties suggest that they have undergone a phase transition well above the room temperature. Measurement of electrical conductivity (dc)/resistivity as a function of temperature suggests that compounds have semiconducting properties above the room temperature with negative temperature coefficient of resistance (NTCR) behavior.