Chemical and structural effects on the high-temperature mechanical behavior of (1−x)(Na1/2Bi1/2)TiO3-xBaTiO3 ceramics

Abstract

Bismuth sodium titanate–barium titanate [(1−x)(Na1/2Bi1/2)TiO3-xBaTiO3, NBT-100xBT] is one of the most well studied lead-free piezoelectric materials due in large part to the high field-induced strain attainable in compositions near the morphotropic phase boundary (x = 0.06). The BaTiO3-rich side of the phase diagram, however, has not yet been as comprehensively studied, although it might be important for piezoelectric and positive temperature coefficient ceramic applications. In this work, we present a thorough study of BaTiO3-rich NBT-100xBT by ferroelastic measurements, dielectric permittivity, X-ray diffraction, and Raman spectroscopy. We show that the high-temperature mechanical behavior, i.e., above the Curie temperature, TC, is influenced by local disorder, which appears also in pure BT. On the other hand, in NBT-100xBT (x < 1.0), lattice distortion, i.e., tetragonality, increases, and this impacts both the mechanical and dielectric properties. This increase in lattice distortion upon chemical substitution is counterintuitive by merely reasoning on the ionic size, and is due to the change in the A-O bond character induced by the Bi3+ electron lone pair, as indicated by Raman spectroscopy.

Revealing the role of local stress on the depolarization of BNT-BT-based relaxors

“…2. For higher temperatures the average structure appears to be cubic in agreement with previous reports [8,46].…”

Remarkable impact of low BiYbO3 doping levels on the local structure and phase transitions of BaTiO3

“…This might be ascribed to the combined effect of Bi 3+ (promoting tetragonality) and Yb 3+ (promoting pseudocubicity) substitution at A- and B-sites of BaTiO 3 , respectively. 2 , 11 In contrast, the dielectric anomaly associated with the tetragonal-to-orthorhombic phase transition shifts dramatically towards lower temperatures with increasing Bi/Yb content. Indeed, it drops from ∼12 °C for undoped BT to ∼ –18 °C for x = 0.005 and subsequently to ∼–37 °C for x = 0.01, eventually merging (at x = 0.02) with the orthorhombic-to-rhombohedral phase transition, which remained almost independent of the Bi/Yb content.…”

“…Pokorny et al 10 demonstrated that site occupancy in doped BaTiO 3 can be analysed by Raman spectroscopy, in particular the appearance of an A 1g mode was postulated to be a sufficient proof to ascertain either the presence of a dopant in the B-site or the existence of a Ti vacancy. In Bi-substituted BaTiO 3 , Deluca et al 11 proved that the insertion of Bi 3+ into the BaTiO 3 lattice promotes tetragonal distortion due to the effect of the stereochemically active lone-pair of Bi 3+ . This effect, however, seems to be compensated if a large cation (such as Yb) is introduced on the B-site.…”

Structure of 3 at.% and 9 at.% Si-doped HfO2 from combined refinement of X-ray and neutron diffraction patterns

“…The calculations above that are based on simple arguments of ionic radii are, therefore, overly simplistic. In perovskite solid solutions such as (Na,Bi,Ba)TiO 3 and (Ba,Ca)TiO 3 , it has been shown that significant changes in ionicity between different cations and oxygen can result in anomalous lattice parameter changes and phase transition behaviors [35,36]. It is possible that a similar effect occurs in Si-doped HfO 2 .…”