Diffuse scattering in Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3 relaxor solid solutions

Abstract

Pb(In 1/2 Nb 1/2 )O 3 (PIN) and Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) are complex perovskites with the chemical formula A(B' x B" 1-x )O 3 . The electrically balanced 1:1 B-site cation ordered domains, of which directions are along <111>, can form in PIN. In contrast, since the 1:2 stoichiometric cation ratio is the chemical nature of PMN. Antiferroelectricity and sharp phase transition can be observed in the highly ordered PIN; whereas the incompletely ordered and disordered PIN are relaxors, which exhibit diffuse phase transition and slim polarization hysteresis loop. Since the 1:1 order-disorder behaviour in PIN-PMN as well as other complex perovskite materials plays a central role in influencing the physical properties [1][2][3], TEM studies were carried out to investigate the various structural ordering. In addition to the superstructure reflection ½ ½ ½ given by 1:1 B-site ordering, the forbidden reflections ½ ½ 0 and diffuse streak and scattering are observed in selected-area electron diffraction (SAED) patterns, shown in Figure 2. The intensity of the features other than Bragg reflections depends on the composition of PIN, similar to the size of B-site ordered domains. The ½ ½ 0 reflections indicates that the crystal structure of the solid solutions have a lower symmetry than Fm-3m. Diffuse streaks along <110>* are observed in all major zone axes, indicating the presence of either planar defects or shortrange ordering along the directions. The ordered domains and the electrical properties of the ceramics suggest that the occurrence of diffuse streaks can be contributed by the large amount of short-range antiparallel polarization [5], polar nanoregions (PNRs) [6], various kind of nanoscale 1:1 ordering [4] and APBs. Relaxor behavior is given by the short-range polarization or polar nanoregions. The directions of the polarization can be in different crystallographic directions but still be stabilized and electrically balanced by the APBs. These are the consequence of three cations in the B-site and the source of random-field. However, the origin of these diffuse streak and scattering in SAED patterns is not fully understood [6,7].