Search

A lead-free series of 1−x(K0.4Na0.6Nb0.96Sb0.04O3)-x(Bi0.5 K0.5TiO3) (0.00 ≤ x ≤ 0.07) composites were prepared by the conventional solid-state reaction route. Rietveld's refined XRD pattern revealed phase transitions from orthorhombic (Amm2) to rhombohedral (R3m) and rhombohedral to tetragonal (P4mm) with x = 0.03 and 0.05 content of (Bi0.5K0.5TiO3). SEM images reveal that the microstructure consists of small, randomly oriented, well-inter-linked, and non-uniform-shaped grains. Dielectric study indicates that Curie temperature (TC) decreases from 340 to 160 °C as the BKT content increases from x = 0.00 to 0.07 and the first transition temperature shifts below room temperature. The complex modulus plots exhibited two semicircles, confirming the ceramics' presence of bulk grain and grain boundary. The impedance and modulus plots confirm the presence of a non-Debye type of relaxation in the ceramics. The ac conductivity increases with a rise in the temperature, confirming negative temperature coefficient resistance (NTCR) behavior. Therefore, conductivity may increase due to the charge carrier hopping rate or the oxygen vacancies (V″O). [ABSTRACT FROM AUTHOR]

In the present report, Ce3+ modified SnO2 compositions [Sn(1−y)CeyO2, for y = 0, 0.05, and y = 0.10, where y is wt.% of Ce3+] were synthesized via co-precipitation and their physicochemical properties were investigated. Crystal structure studies were carried out by using Rietveld refinement which confirmed high phase-purity and rutile-type tetragonal crystallinity with a P42/mnm space group (space group no. 136) for all samples. Fourier transform infrared (FTIR) spectroscopy depicted the antisymmetric vibrations of Sn-O-Sn and stretching vibration of Sn-O, which were confirmed by bends located at 636 cm−1, and 460 cm−1, respectively. All the compositions showed a strong hump at ~ 300 nm in the ultra-violet (UV) region and the peak shifts slightly towards the blue region with increasing Ce3+content. Transmission electron microscopy (TEM) micrographs depicted pseudospherical particles with an average particle diameter of 12.84 ± 0.17 nm, 15.55 ± 0.31 nm, and 16.52 ± 0.36 nm for y= 0, 0.05, and 0.10, respectively. High-resolution transmission electron microscopy (HRTEM) images confirmed tetragonal crystallinity for all the compositions. Dielectric studies illustrated that on increasing the concentration of Ce3+ in the host SnO2, the value of dielectric permittivity increased. The value of tanδ is maximum for pristine SnO2. The variation of ac conductivity was due to Maxwell–Wagner type interfacial polarization. For all the compositions, a sharp hump centered at ~ 407 nm was observed in the photoluminescence spectrum, which may be attributed to the presence of oxygen anion vacancies. [ABSTRACT FROM AUTHOR]