Textured Bi_1/2Na_1/2TiO₃‐BaTiO₃ Lead‐Free Films with Enhanced Piezoelectric Property and Depolarization Temperature

Abstract

largest usable strain shown in BNT-based solid solutions make them the most feasible lead-free materials for actuator applications. [1e,2] The major challenge for the technological application of BNT-based systems is the relatively low depolarization temperature (T d ), which is in the range from 80 to 100 °C for 0.94Bi 1/2 Na 1/2 TiO 3 -0.06BaTiO 3 (BNT-BT6). The thermal depolarization in BNT-based materials leads to a pronounced reduction of macroscopic electrical properties at T d , including the piezoelectric coefficient d 33 , the remanent polarization (P r ), and the negative strain (S neg ). [1d,3] As a consequence, the T d determines the maximum working temperature. Various approaches have been attempted to increase the T d . [4] Stress induced either by direct loading [4b] or by constructing composite structure [4a,d] is found to effectively increase the T d and broaden the temperature range in which the thermal depolarization takes place. It is believed that the stress, especially a uniaxial stress, can stabilize the ferroelectric long-range order and modulate the relaxor-toferroelectric (RE-FE) phase transition.In traditional ferroelectric thin films, the effect of stress on the phase transition temperature has been systematically studied. [5] Compared with bulk ceramics, it is much easier to introduce stress in thin films by modulating the properties of the sample and the substrate or the buffer layer, such as the thermal expansion coefficient and the lattice parameter. An efficient enhancement in Curie temperature (T c ) has been found by inducing the in-plane stress in several ferroelectric materials, such as PbTiO 3 and BaTiO 3 . [5,6] The enhancement of T c in ferroelectric perovskites has been explained by Devonshire thermodynamic formalism and interpreted as a stabilization of the long-range ferroelectric order. [6a,7] Through strain engineering, the in-plane stress could not only increase the T c but also enhance the ferroelectric properties of BaTiO 3 thin films. [8] It is worth mentioning that the stress-induced stabilization of the long-range ferroelectric order is only applicable to the case when the stress is perpendicular to or along the polarization vectors. Consequently, to enhance the phase transition temperature by modulating the in-plane stress, the film with specific orientations is preferred.Based on the analysis above, it is expected that the stabilization of long-range ferroelectric orders through Future microelectromechanical systems will need environmentally friendly lead-free piezoelectrics in the form of thin films, like Bi 1/2 Na 1/2 TiO 3 (BNT); however, its application is limited due to the relatively low depolarization temperature (T d ). In this work, not only enhanced piezoelectric properties, but also higher T d , are achieved in (001)-textured 0.94Bi 1/2 Na 1/2 TiO 3 -0.06BaTiO 3 (BNT-BT6) thin films on widely used platinized Si wafers with a LaNiO 3 buffer layer. The piezoelectric coefficient a 33,eff is increased by 65% to 43 pm V −1 in the textured films fr...

Enhanced ferroelectric properties in BiAlO3 modified lead‐free Mn‐doped Bi0.5(Na0.8K0.2)0.5TiO3 thin films

“…22 Moreover, the simple preparation process and low cost of LNO make it a good substitute for Pt electrodes. 23 In this work, the Mn-doped (1-x)Bi 0.5 (Na 0.8 K 0.2 ) 0.5 TiO 3 -xBiAlO 3 (Mn:BNKT-xBA) films on lanthanum nickelate coated silicon (LNO/Si) substrates were investigated. We explored the effects of using LNO electrodes and introducing Mn 3+ into the structure of the film.…”

“…Lanthanum nickelate (LNO) is a low‐resistivity perovskite material with good electrical and chemical stability and similar lattice matching, which makes it ideally suitable for the seed layer of perovskite films 22 . Moreover, the simple preparation process and low cost of LNO make it a good substitute for Pt electrodes 23 …”

Polarization Rotation Control Domain Dynamic Response Modulates Piezoelectric Properties of Lead‐Free Thin Films

“…The development of high-performance lead-free piezoelectric films is not only the key to the development of miniaturized devices and integration, but also the need to achieve green development. [1][2][3][4][5] Depending on the piezoelectric response including intrinsic (polarization extension and polarization rotation) and extrinsic (domain wall) contributions, [6] appropriate modification strategies are adopted to improve the piezoelectric properties, such as enhanced lattice internal contributions, [7] domain reconstruction, [8] phase boundary engineering, [9] defect treatment, [10,11] etc. Polarization rotation acts as the main intrinsic contribution, especially in crystal structures with large piezoelectric anisotropy.…”

Crystal structure, ferroelectric and piezoelectric properties of epitaxial (1−x)(Bi0.5Na0.5)TiO3–x(Bi0.5K0.5)TiO3 films grown by hydrothermal method

“…It is generally known that the electrical properties of piezoelectric materials can be improved obviously around the phase boundary of solid solutions. Hence, there are many works focused on the combination of rhombohedral BNT and other perovskite compounds, such as (Bi 0.5 Na 0.5 )TiO 3 -BaTiO 3 (BNT-BT), [12][13][14] (Bi 0.5 Na 0.5 )TiO 3 -SrTiO 3 (BNT-ST), [15][16][17] (Bi 0.5 Na 0.5 ) TiO 3 -NaNbO 3 (BNT-NN), 18) and (Bi 0.5 Na 0.5 )TiO 3 -(Bi 0.5 K 0.5 ) TiO 3 (BNT-BKT). [19][20][21] (1−x)(Bi 0.5 Na 0.5 )TiO 3 -x(Bi 0.5 K 0.5 )TiO 3 [(1−x)BNT-xBKT] is a solid solution of (Bi 0.5 Na 0.5 )TiO 3 (BNT) with R3c rhombohedral symmetry and (Bi 0.5 K 0.5 )TiO 3 (BKT) with P4mm tetragonal symmetry.…”