Ferroelectric perovskite-type barium copper niobate: BaCu1/3Nb2/3O3

Unusual crystal structure evolution, multiple phase boundaries and phase coexistence in (1 - x)Ba(Cu1/3Nb2/3)O3-(x)PbTiO3 perovskite solid solution

Exploring the functionalities of materials requires a profound understanding of the crystal structure. In this paper, room temperature crystal structures of a new solid solution (1 - x)Ba(Cu1/3Nb2/3)O3-(x)PbTiO3 have been investigated in the entire compositional span and different crystallographic phases and phase coexistence regions have been discovered. The confirmation of the symmetry of these crystal structures has been done with the help of Rietveld analysis of the high-resolution XRD data. Despite both the end components, Ba(Cu1/3Nb2/3)O3 and PbTiO3, having tetragonal (P4mm) symmetry, new cubic and monoclinic phases have been discovered for the intermediate compositions with multiple phase boundaries. The composition region 0.05 ≤ x ≤ 0.55 exhibits a cubic crystal structure and increasing PbTiO3 concentration to 0.62 results in a unique coexistence of two tetragonal phases with different tetragonalities. This transformation is mediated by coexisting cubic and tetragonal phases, for 0.59 and 0.60. The crystal structure of the solid solution later transforms into coexisting monoclinic and tetragonal phases for a wider compositional span i.e., 0.65 ≤ x ≤ 0.85. This composition region is very fascinating, as two phenomenologically different monoclinic structures have been observed in it. Finally, a tetragonal phase at x = 1 is achieved through the mediation of two coexisting tetragonal phases, for the region 0.85 < x ≤ 0.975. The evolution of different crystallographic structures and the coexisting phases are critically comprehended using the variations in the lattice parameters and unit cell volume. The presence of multiple phase boundaries spread across a wide range of compositions makes this solid solution very intriguing and a viable choice for exploring different properties with compositional tuning.

Spectroscopic and electrical studies on Nd(3+), Zr(4+) ions doped nano-sized BaTiO3 ferroelectrics prepared by sol-gel method

Lead free ferroelectric ceramics in the form of Ba(1-3x)Nd(2x)Ti(1-y)ZryO3 ((where x=0.025, y=0 (BT1), 0.025 (BT2), 0.05 (BT3)) were prepared using sol-gel method. The surface morphology and the orientation of grains of the present ceramics were examined using Field Emission Scanning Electron Microscope (FESEM) images. The effect of Nd(3+), Zr(4+) ions content on the BaTiO3 was studied using Raman and Fourier Transform Infrared (FTIR) spectroscopies. From the Raman analysis the band observed at ∼838 cm(-1) was attributed due to the presence of Nd(3+)-barium vacancy pairs. The FTIR studies suggested that the addition of Nd(3+) ions in A-site of BaTiO3 (ABO3) perovskite create lattice distortion by forming A-site vacancies and Zr(4+) ions in B-site of BaTiO3 induce the lattice distortion by forming ZrO6 octahedra in the place of TiO6 octahedra. Dielectric measurements of the samples were done at different frequencies from RT-150°C. Charge transportation phenomenon is explained using DC conductivity, which is found to increase with temperature.