Frequency and thermal studies of dielectric permittivity and Raman analysis of Ba0.97La0.02Ti0.98Nb0.016O3

Abstract

The dielectric properties of polycrystalline ceramic Ba0.97La0.02Ti0.98Nb0.016O3 (BLTi0.98Nb0.016), elaborated by a molten-salt reaction, were methodically characterized. Phase purity, structure and crystallinity were examined with X-ray diffraction at room temperature, demonstrating pure phase with tetragonal symmetries and a P4/mmm space group for our sample. The frequency and temperature dependence of the dielectric properties showed an excellent response. The real part of permittivity and dielectric tangent decreased with increasing frequency. This can be clarified by Maxwell-Wagner type of polarization as per with Koop’s theory. The temperature dependence of the dielectric properties was examined in the frequency range 1 kHz to 1 MHz. Mostly, these three regions of dielectric relaxations are begun from phase transitions beginning: a cubic-paraelectric to a tetragonal-ferroelectric “C” (at the Curie temperature Tc), after that to an orthorhombic-ferroelectric “T → O” (at TT → O), and lastly to a rhombohedral-ferroelectric “O → R” (at TO → R) resembling to those of pure Barium titanate (BaTiO3, BT). To clarify the dielectric phenomenon, the Curie-Weiss law is investigated. This method is used to describe the ferro–paraelectric transition. The degree of disorder of the Ba0.97La0.02Ti0.98Nb0.016O3 was assessing via the modified Curie-Weiss law. The Raman spectrum was measured at room-temperature, and their variation related to the chemical composition, which affirmed the tetragonal structure for Ba0.97La0.02Ti0.98Nb0.016O3.