Transformation‐Induced Twinning: The 90° and 180° Ferroelectric Domains in Tetragonal Barium Titanate

Abstract

Ferroelectric twin domains resulting from the cubic (c) to tetragonal (t) phase transformation at the Curie point TC≈130°C in pressureless‐sintered BaTiO3 ceramics, using TiO2‐excess powder, have been investigated using scanning and transmission electron microscopy. Both 90° and 180° domains were identified by spot splitting along characteristic crystallographic directions in the selected‐area diffraction patterns and/or from the shape of domain boundaries. Lamellar domains were found predominantly with the 90° types. The 180° domain boundaries mostly appeared wavy in shape, while the 90° ones, having sharpened ends, attained a dagger shape. Failure of Friedel's law in the non‐centrosymmetric t‐BaTiO3 was adopted to validate the existence of the 180° domains. The 90° domains with boundaries lying in are reflection–inversion twins, and the 180° domains lying in {100)t and }220)t are inversion twins. Convergent‐beam electron diffraction was performed to ensure that changing of the polar direction [001]t across the 90° and the 180° domain boundaries was consistent with the domain type. It was also used to confirm whether the 180°‐type walls are inversion domain boundaries produced by the loss of an inversion center when the cubic phase transforms into tetragonal symmetry. The formation of such ferroelectric domains is discussed with reference to the crystal symmetry reduction from (c‐phase) to P4mm (t‐phase) with a loss of mirror plane (m) and roto‐inversion axis upon c→t phase transformation.

Ferroelectric domain structure of lead-free potassium-sodium niobate ceramics

“…2(b), 3(a) and 3(b). Both, the lamellar and dagger-shaped 17 domains are 90 • type, as indicated in Fig. 3(a).…”

“…3(c) shows the 180 • domains. In this case, they adopt the watermark pattern 17 and are larger than the 90 • domains (3-10 m W × 20-40 m L). The main feature of 180 • domains is that the domain walls grow in a wavy form to reduce electrostatic energy when the head to tail coupling is violated.…”

“…These domains were previously observed in KNbO 3 and BaTiO 3 . 14, 16,17 Well-defined 90 • ferroelectric domains are arranged with square-net and herringbone structures similar to BaTiO 3 16,17 , the representative microstructures of them are shown in Figs. 2(b), 3(a) and 3(b).…”

“…The main feature of 180 • domains is that the domain walls grow in a wavy form to reduce electrostatic energy when the head to tail coupling is violated. [16][17][18] The origin of both, 90 • and 180 • domains is to minimize elastic and electrostatic energy, 14,16,17 respectively. Another feature observed is that most domains are of the 90 • type.…”

Dielectric and ferroelectric properties of BST ceramics obtained by a hydrothermally assisted complex polymerization method

“…Therefore the tetragonal distortion of BaTiO 3 ceramics below the T c is mostly compensated by the formation of 901 domains. The 901 and 1801 domains are typical domain configurations for BaTiO 3 ceramics with tetragonal symmetry [35][36][37]. The SEM micrograph of the fractured surface shown in Fig.…”