Structure, phase transition behaviors and electrical properties of Nd substituted aurivillius polycrystallines Na_0.5Nd_xBi _2.5-xNb₂O₉ (x = 0.1, 0.2, 0.3, and 0.5)

New high temperature Aurivillius piezoelectrics Na_0.5Nd _xBi_2.5-xNb₂O₉ (NDBNx, x = 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 A2₁am [a = 5.48558(8) Å, b = 5.46326(9) Å, c = 24.8940(4) Å, and Z = 4 for NDBN0.2 and a = 5.46872(5) Å, b = 5.46730(5) Å, c = 24.80723(25) Å, and Z = 4 for NDBN0.5], at room temperature. The refinement results and Raman spectroscopy of NDBNx 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 NDBNx. The ferroelectric to paraelectric phase transition temperature (T _c) of NDBNx 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 NDBNx.