Theoretical and experimental investigation of Raman modes, ferroelectric and dielectric properties of relaxor Na0.5Bi0.5TiO3

Abstract

We use a combination of first-principles density functional theoretical analysis and experimental characterization to understand the lattice dynamics, dielectric and ferroelectric properties of lead-free relaxor ferroelectric Na0.5Bi0.5TiO3 (NBT) system. Vibrational spectrum determined through our calculations agrees well with the observed Raman spectrum, and allows assignment of symmetry labels to modes. The calculated Born effective charges reveal (a) two distinct types of Ti ions at the B-site with anomalous dynamical charges differing by up 1.6e, and (b) Na and Bi ions at the A-site exhibit disparate dynamical charges of about 1 and 5.5e, respectively. Thus, there exist hetero-polar activity at both A and B-sites in NBT, and disorder associated with these hetero-polar ions is responsible for its relaxor behaviour. Large dielectric response of NBT arises primarily from phonons, and specifically the modes involving Bi-O (109 cm−1) and Ti-O (246, 276 cm−1) vibrations, respectively.

Evidence for the suppression of intermediate anti-ferroelectric ordering and observation of hardening mechanism in Na1/2Bi1/2TiO3 ceramics through cobalt substitution

“…1(a) and 1(b)) in both NBT and NBT-Co samples indicate the presence of antiphase tilt system (i.e., a − a − a − ), which is accordance with the existing reports. 4,6,9 In addition, the lattice parameters extracted from the refinement studies indicate a clear variation in the lattice parameters due to Co substitution. The variation in Bragg peak position (i.e., 2θ ) accompanied with a shift towards lower degree of ≥3% observed in (024) plane (See Fig.…”

“…6,8 A similar behavior was observed in NBT ceramics by several authors. [6][7][8][9] In this context upon cobalt-ion substitution in NBT, a significant change in the dielectric behavior was observed in both C p vs. T…”

“…[6][7][8][9] The aforementioned features made them unique from other B-site disordered system such as PMN, PMN-PT etc. 10 It is well known from x-ray/neutron diffraction experiments, on cooling from high temperature prototypic cubic phase (Pm3m) it pass through a tetragonal phase i.e., P4bm (a o a o c + ) between ∼540…”

The dielectric and ferroelectric properties of (Ba0.5Sr0.5)TiO3-doped (Bi0.5Na0.5)TiO3 lead-free ceramics

“…Moreover, the composition-dependent T m moves to lower temperature gradually as the BST content is increased; the dielectric maximum also becomes smaller with respect to the increase of the BST content, simultaneously. According to the published data, T m of pure NBT is around 310 C, 38 while that of 7, 1750028 (2017) pure BST is around À40 C. 39 The introduction of BST especially Sr 2þ makes T m move towards lower temperature. Figure 6 shows the P-E hysteresis loops of BST-doped NBT ceramics.…”

Structural and electrical properties of bismuth magnesium titanate substituted lead-free sodium bismuth titanate ceramics

“…9E modes are both Raman and IR active and 5B 1 modes are silent. From [29][30][31]. On substitution of BMT in NBT an increase in frequency of the two modes namely 247 and 281 cm -1 related to TiO 6 octahedra vibration modes are noticed which may be due to the rotational change of the oxygen octahedra.…”