Structure, Phase Transition Behaviors and Electrical Properties of Nd Substituted Aurivillius Polycrystallines Na_0.5Nd_<i>x</i>Bi_{2.5–<i>x</i>}Nb₂O₉ (<i>x</i> = 0.1, 0.2, 0.3, and 0.5)

New high temperature Aurivillius piezoelectrics Na_0.5Nd_<i>x</i>Bi_{2.5–<i>x</i>}Nb₂O₉ (NDBN<i>x</i>, <i>x</i> = 0.1, 0.2, 0.3, and 0.5) with Nd substitution for Bi at the A site were synthesized using a solid state reaction process. Crystal structures of NDBN0.2 and NDBN0.5 were refined with the Rietveld method with powder X-ray diffraction, and they crystallized in the orthorhombic space group <i>A</i>2₁<i>am</i> [<i>a</i> = 5.48558(8) Å, <i>b</i> = 5.46326(9) Å, <i>c</i> = 24.8940(4) Å, and <i>Z</i> = 4 for NDBN0.2 and <i>a</i> = 5.46872(5) Å, <i>b</i> = 5.46730(5) Å, <i>c</i> = 24.80723(25) Å, and <i>Z</i> = 4 for NDBN0.5], at room temperature. The refinement results and Raman spectroscopy of NDBN<i>x</i> verified that Nd occupied both the A site in the perovskite layers and the cation site in the (Bi₂O₂)²⁺ layers. The Nd substitution induced an enhancement in cation disordering between the A site and the (Bi₂O₂)²⁺ layer and an increase in the degree of the relaxation behavior for NDBN<i>x</i>. The ferroelectric to paraelectric phase transition temperature (<i>T</i>_c) of NDBN<i>x</i> ranged from 735 to 764 °C. Furthermore, the isovalent substitution of Nd for Bi had a great influence on microstructure (grain size and shape), defect concentration (mainly oxygen vacancies), preferred grain orientation (texture), and distortion of the octahedron. The coaction between these effects determined the structure characteristics, phase transition behaviors, and electrical properties of NDBN<i>x</i>

Large electrostrain in Bi_1/2Na_1/2TiO₃-based relaxor ferroelectrics: A case study of Bi_1/2Na_1/2TiO₃-Bi_1/2K_1/2TiO₃-Bi(Ni_2/3Nb_1/3)O₃ ceramics

(1-x)(0.8Bi Na TiO -0.2Bi K TiO )-xBi(Ni Nb )O (BNKT-xBNN) solid solution ceramics were fabricated by high temperature solid-state reaction method. All the compositions possess relaxor ferroelectric features, among which the ergodic BNKT-0.02BNN exhibits large repeatable electrostrain value S = 0.51% at electric field of 65 kV/cm, with high piezoelectric stain coefficient d ∗ of 890 pm/V at 45 kV/cm, while the non-ergodic compositions present unrepeatable large strain response. Based on the electric field-composition phase diagram, the repeatability of strain response in ergodic compositions can be attributed to the reversible electric-field-induced phase transition. In addition, the effects of BNN contents on the macroscopic strain properties are explored by analyzing the existing states of the polar regions with corresponding thermal evolutions and electric-field-induced phase transitions. This research is expected to guide the design of lead free relaxor ferroelectric materials with desired electrostrain properties. 1/2 1/2 3 1/2 1/2 3 2/3 1/3 3 uni 3