Crystal structure and electrical properties of bismuth sodium titanate zirconate ceramics

Abstract

Lead-free bismuth sodium titanate zirconate (Bi0.5Na0.5Ti1-xZrxO3 where x = 0.20, 0.35, 0.40, 0.45, 0.60, and 0.80 mole fraction) [BNTZ] ceramics were successfully prepared using the conventional mixed-oxide method. The samples were sintered for 2 h at temperatures lower than 1,000°C. The density of the BNTZ samples was at least 95% of the theoretical values. The scanning electron microscopy micrographs showed that small grains were embedded between large grains, causing a relatively wide grain size distribution. The density and grain size increased with increasing Zr concentration. A peak shift in X-ray diffraction patterns as well as the disappearance of several hkl reflections indicated some significant crystal-structure changes in these materials. Preliminary crystal-structure analysis indicated the existence of phase transition from a rhombohedral to an orthorhombic structure. The dielectric and ferroelectric properties were also found to correlate well with the observed phase transition.

Analytic Study of Phase Shift Crystal Structure and Temperature Dependent Dielectric Properties of Modified Synthesis One System Ceramics Using BNT-BZT

“…In general, increasing Zr concentration in BNT-BZT ceramics caused a gradual drop off in dielectric constant with a slight drop off in dielectric loss. This behavior was in agreement with other systems with isovalent additives [4]. In addition, the replacement of larger Zr ions may also cause the dipoles to be poorly induced due to limited ionic movement.…”

“…Therefore, for this BNT-BZT solid solution ceramic system, the structure changed from rhombohedral to orthorhombic when the Zr concentration exceeded 0.6-mole fraction [5]. The exact phase-transition composition is currently being investigated [4]. The entire BNT-BZT ceramics had trial density values in the range of 5.8 -6.11g/cm3.The difference in sintering behavior could also be noted from the microstructure of BNT-BZT ceramics.…”

“…It seemed that the effect of ionic size and limited ionic movement in the perovskite structure of this compound had a greater influence on the dielectric properties than the change in the crystal structure in their unit-all dimensions. [4] [5]. The hysteresis loops were finding at the maximum applied electric field of 20 × 10 3 V/cm and a frequency of 50 Hz and some degree of domain reorientation might also be the cause of unfortunate hysteresis loops for these compositions [6].…”

“…All reflection peaks systematically shifted to lower than 2θ angles for the existence of Zr. Additional the shift, intensities of some diffraction peaks such as (012) and (202) were reduced, indicating that lattice distortion alongside unit cell expansion has occurred [4]. The enhancement of the XRD patterns was conceded out.…”

“…Figure 3 shows the refined pattern for the Zr composition equal to 0.2 -0.8 in XRD patterns. BNT-BZT ceramics containing Zr from 0.2 -0.6 overcome a rhombohedral structure with improved lattice parameters [4]. The rise in the value of interaxial angle caused the structure to be close to cubic, which resulted in the vanishing of certain reflections.…”