Lattice distortions and piezoelectric properties in (Bi_3.25Nd_{0.75− x}Eu_x)Ti₃O₁₂ nanoplates with a- and b-axis orientations

Abstract

a- and b-axis-oriented (Bi3.25Nd0.75− x Eu x )Ti3O12 (BNEuT, x = 0–0.75) films of 3.0 µm thickness were fabricated on conductive Nb:TiO2(101) substrates containing 0.79 mass % Nb by high-temperature sputtering at 650 °C, and their structural and piezoelectric characteristics were investigated. The room-temperature remanent polarization (2P r) and effective piezoelectric coefficient (d 33) values for the BNEuT films exhibited maxima of 87 µC/cm2 and 15 pm/V, respectively, at x = 0.10, which were approximately 1.3 times larger than those (2P r = 65 µC/cm2 and d 33 = 12 pm/V) of the nondoped (Bi3.25Nd0.75)Ti3O12 (BNT) nanoplate. The BNEuT film with x = 0.10 had a high a-axis orientation judging from the X-ray diffraction measurement and the observation of the phase image by piezoresponse force microscopy. It is shown that adequate Eu3+ doping of BNT nanoplates produces a larger displacement magnitude of the octahedra than that in the nondoped BNT nanoplate, resulting in an improvement of piezoelectric properties in addition to the ferroelectricity.

Effects of post-annealing temperature and micropillar shape on physical properties of micropillar-type multiferroic composite thin films

“…15) In our previous study, we have successfully fabricated a-axis oriented (Bi 3.25 Nd 0.65 Eu 0.10 )Ti 3 O 12 (BNEuT) nanoplates with a unique nanoplate structure and large remanent polarization (2P r = 66 μC cm −2 ) at room temperature. [16][17][18] The MF composite films were fabricated by utilizing the gaps in the nanoplate structure, 19,20) but the ME effect could not be clearly observed due to the small amount of ferromagnetic material introduced in the small gaps. Therefore, ferroelectric micropillar structure controlled sizes of gaps were fabricated by reactive ion etching (RIE).…”

Structural, Magnetic and Electric Characteristics of Multiferroic CoFe₂O₄/BNEuT Composite Thin Films Produced by Non-aqueous Sol-gel Process

“…In our previous studies, we succeeded in achieving heteroepitaxial growth of (Bi 3.25 Nd 0.65 Eu 0.10 )Ti 3 O 12 (BNEuT) nanoplates with a strong a-axis orientation by high-temperature sputtering on conductive single-crystal Nb:TiO 2 (101) substrates containing 0.79 mass% Nb [12][13][14]. This material is promising as a ferroelectric template for fabricating nanopillar MF composite devices, since it exhibited a large room-temperature remanent polarization (2P r ) of 66 C/cm 2 and a high surface porosity of 24%.…”

Effects of deposition temperature on characteristics of ferroelectric Sr2Bi4Ti5O18nanoplates fabricated by RF sputtering

“…In recent years, lead-free bismuth layer-structured ferroelectrics (BLSFs) [1][2][3][4] have attracted much attention as promising alternatives to lead zirconium titanate (PZT) 5,6) for ferro-and piezoelectric device applications. In previous studies, we succeeded in achieving heteroepitaxial growth of (Bi 3.25 Nd 0.75 )Ti 3 O 12 (BNT) nanoplates with strong aand baxis orientations, [7][8][9] and (Bi 3.25 Nd 0.75¹x Eu x )Ti 3 O 12 (BNEuT, x = 0-0.075) nanoplates with a strong a-axis orientation, 10,11) by high-temperature sputtering using conductive singlecrystal Nb:TiO 2 (101) substrates with 0.79 mass % Nb. Moreover, high-resolution cross-sectional transmission electron microscopy (TEM) images showed that for a BNEuT epitaxial layer with x = 0.10, good long-range lattice matching was achieved between the BNEuT unit cell and seven lattice units of the underlying Nb:TiO 2 substrate.…”

“…Moreover, high-resolution cross-sectional transmission electron microscopy (TEM) images showed that for a BNEuT epitaxial layer with x = 0.10, good long-range lattice matching was achieved between the BNEuT unit cell and seven lattice units of the underlying Nb:TiO 2 substrate. 10,11) It is known that the crystal structure of BLSF compounds consists of stacked (Bi 2 O 2 ) 2+ layers and (A m¹1 B m O 3m+1 ) 2¹ perovskite block layers, where A represents ions with charge states of +1 to +3, B represents ions with charge states of +4 to +6, and m is the number of BO 6 octahedra in the block layer along the c-axis. As for the relation between the m number and the major polarization of the BLSF compounds, it is known that when m is an odd number greater than 3, significant macroscopic polarization due to ionic displacement appears along the a-axis direction, which is the major polarization axis.…”

“…As for the relation between the m number and the major polarization of the BLSF compounds, it is known that when m is an odd number greater than 3, significant macroscopic polarization due to ionic displacement appears along the a-axis direction, which is the major polarization axis. 12) We have previously reported the results of studies on the growth of epitaxial films with a high a-axis orientation, and the formation of a nanoplate structure, for BLSFs such as BNT [7][8][9] and BNEuT 10,11) with m = 3. BLSF compounds with m = 5, represented by the general formula A 2 Bi 4 Ti 5 O 18 (ABTO, A = Ba, Sr, and Ca), which consist of stacked (Bi 2 O 2 ) 2+ and (A 2 Bi 2 Ti 5 O 16 ) 2¹ layers, have received considerable attention because of their high potential for use in ferroelectric, piezoelectric, and multiferroic applications.…”