Structural, dielectric and electrical properties of LiBa2X5O15 (X = Nb and Ta) ceramics

The polycrystalline complex tungsten–bronze (TB) type compounds LiBa2Nb5O15 (LBN) and LiBa2Ta5O15 (LBT) were prepared by a high-temperature solid-state reaction technique. X-ray diffraction (XRD) study confirmed the formation of single-phase orthorhombic compounds in the crystal system at room temperature. Microstructural analysis of the surface of the compounds by scanning electron microscopy (SEM) suggests that small grains are uniformly distributed on the surface of the samples. Detailed studies of the dielectric properties suggest that they have undergone a phase transition well above the room temperature. Measurements of electrical conductivity (dc) as a function of temperature confirm the semiconducting properties of the compounds much above the room temperature with negative temperature coefficient of resistance (NTCR) behaviour.