Crystal Structural Analyses of Ferrielectric Tetragonal (Bi_1/2Na_1/2)TiO₃–7%BaTiO₃ Powders and Single Crystals

Abstract

We have investigated the crystal structure of (Bi1/2Na1/2)TiO3–7%BaTiO3 (BNT–7%BT) by high-resolution neutron powder diffraction (NPD) and high-energy synchrotron radiation X-ray diffraction (SR-XRD) analyses. The NPD study revealed that the BNT–7%BT crystals have a single-phase tetragonal structure with P4b m symmetry. The crystal structure refined by the Rietveld method was found to be similar to the ferrielectric P4b m phase reported for BNT at a high temperature of 673 K. The SR-XRD analyses for single crystals of BNT–7%BT demonstrated that the P4b m phase remains as a stable phase in the crystals even after a high electric field is applied for poling, which is different from the structural analysis of ceramics by Ma et al. [Phys. Rev. Lett. 109 (2012) 107602].

Polarization twist in perovskite ferrielectrics

“…Unlike antiferroelectrics with a remanent polarization ( P r ) of zero25, the crystals have a certain P r . This apparent P r associated with the pinched hysteresis suggests that the crystals have the ferrielectric phase in space group P 4 bm at E  = 0, as revealed for BNT–7%BT powders by neutron diffraction structural analysis26.…”

“…In the poled state at E  = 0 kV/cm (Fig. 2a), all diffraction spots arise from a ferrielectric tetragonal structure in space group P 4 bm 222627. Among the fundamental hkl reflections from the pseudocubic cell, we detect 1/2{ o o e } superlattice reflections, where o denotes an odd number and e an even number.…”

High electromechanical strain and enhanced temperature characteristics in lead-free (Na,Bi)TiO3–BaTiO3 thin films on Si substrates

“…3(a)], and the P r value (13.3 C/cm 2 ) of the film is clearly large as compared to that of bulk P4bm phase. The induction of this large P r is likely to be linked to the fact that the crystal lattice of the P4bm phase of the film is distorted to a greater extent along the c -axis direction compared than in the bulk NBT–BT, i.e., the ( c / a ) pc of the film is 1.004, whereas the most accepted value for bulk is less than 1.001 46,47 . It is most likely that the distortion of the crystal lattice results not only from compressive stress caused by energetic particle bombardment in sputtering but also from deposition-induced defects such as defect dipoles 48 .…”

Polarization Rotation and Monoclinic Distortion in Ferroelectric (Bi0.5Na0.5)TiO3–BaTiO3 Single Crystals under Electric Fields

“…Transmission electron microscopy observations by Ma et al [28] have revealed that (1 − x)BNT-xBT ceramics without an application of E exhibit P4bm symmetry in the x range of 6%-10%. Neutron powder diffraction study conducted by Kitanaka et al [79] have reported direct evidence of tetragonal P4bm for BNT-7%BT powder. The P4bm phase has a P s of 4 μC/cm 2 [79] along <001> pc , as depicted in Figure 3b.…”

“…Neutron powder diffraction study conducted by Kitanaka et al [79] have reported direct evidence of tetragonal P4bm for BNT-7%BT powder. The P4bm phase has a P s of 4 μC/cm 2 [79] along <001> pc , as depicted in Figure 3b. It is suggested that the MPB between monoclinic Cc and tetragonal P4bm lies around x of 6%.…”