Large Electric Field-Induced Strain Response Under a Low Electric Field in Lead-Free Bi1/2Na1/2TiO3-SrTiO3-BiAlO3 Ternary Piezoelectric Ceramics

Abstract

Bismuth-based lead-free ceramics are some of the most promising candidates for actuator applications due to their large strain response. Despite the large strains in bismuth-based piezoelectric ceramics, there still remain challenges regarding their utilization in practical applications. For instance, a relatively high operating field is required to obtain the large strain properties. In this work, lead-free Bi 1/2 Na 1/2 TiO 3-SrTiO 3-BiAlO 3 (BNT-ST-BA) ternary piezoelectric ceramics are proposed as materials that could enhance the electromechanical strain performance under low driving field. We found that the highest normalized strain d 33 * value of 707 pm/V was achieved at a relatively low electric field of 3 kV/mm from 2 mol.% BA-modified BNT-ST ceramics. We suggest that the naturally induced nonergodicities in the ergodic relaxor generate internal stress. This induced internal stress is responsible for the excellent strain properties of this material. We believe that the materials synthesized in this study are promising candidates for actuator applications.

Field-induced Strain Property of Lead-free Ferroelectric Ceramics Based on Sodium Bismuth Titanate

“…传感和储能等电子器件 [1] 。其中，压电驱动器可用作 超声波清洗机、汽车喷油器以及镜头用超声波电机 等，具有广阔的市场前景，已成为当前研究热点 [1][2] 。 目前含铅压电驱动器材料锆钛酸铅 Pb(Zr1-xTix)O3(PZT)在商业应用中占据主要市场，但由于铅 元素对人体健康和环境都具有极大的危害，已被多 国限制使用。因此，亟需开发高性能、环境友好的无 铅铁电陶瓷材料以取代传统铅基压电陶瓷材料。 目前， 关于无铅压电材料和应变性能研究主要集中于三类 铁电材料：钛酸铋钠(Bi0.5Na0.5)TiO3(BNT)、钛酸钡 BaTiO3(BT)和铌酸钾钠(K0.5Na0.5)NbO3(KNN) [3] 。 优化 工艺与晶粒尺寸、陶瓷织构化以及通过化学掺杂构造 准同型相界(MPB)等是提高陶瓷场致应变性能的有 效方式 [4] 。 通常，KNN 基铁电陶瓷的压电系数 d33 仅有 80 pC/N，通过优化工艺可达 125 pC/N 左右，进一步调 控 K 和 Na 的化学计量比，即 K/Na 为 48/52 时，d33 可及 160 pC/N [5] 。其次，通过化学掺杂构造 KNN 基 陶瓷的 MPB，也能提升陶瓷的压电性能。2018 年 Lv 等 [6] 通过掺杂构造(0.99-x)KNNS-0.01SZ-xBNZ 陶瓷， 使其在 MPB 处压电系数 d33 可达 450 pC/N 且应变值 在 0.148%~0.16%范围内。此外，多晶体陶瓷织构化 也能显著优化陶瓷应变性能 [7] 。2004 年，Saito 等 [8] 通 过掺杂 Li、Ta 和 Sb 等元素，在 MPB 处得到<001>方 向织构的 KNN 基铁电陶瓷，该陶瓷的 d33 高达 416 pC/N 且 d33*为 750 pm/V。然而，由于 K 元素极易挥 发， 普通烧结很难得到致密陶瓷， 极大地阻碍了 KNN 基铁电陶瓷的实际应用 [9] 。BT 是最早发现的无铅铁 电材料，优化应变性能方法与 KNN 类似 [10] 。2018 年 Zhao 等 [11] 构造(1-x-y) BaTiO3-yCaTiO3-x(BaZr1-zHfz)O3(BT-yCT-xBZHz)陶瓷，在 MPB 处获得堪比铅 基陶瓷的压电性能： d33=500 pC/N 与 d33*=1100 pm/V。 再者，优化晶粒尺寸和取向也是有效途径。Tan [12] 等 对 BT 陶瓷晶粒尺寸与应变关系研究发现，在晶粒尺 寸为 4.5 μm 时，场致应变最佳。此外，Zhao 等 [13] 发 现，BT 作为籽晶的 BZT-BCT 织构陶瓷，可在极低电 场 E=20 kV/cm 时，得到 0.153%的应变值，d33*可达 767 pm/V。即便如此，目前 BT 基陶瓷场致应变仍然 较低(0.1%~0.2%)，且居里温只有 120 ℃，因此用作 压电驱动器件并不具有显著优势。2007 年，张善涛课 题组 [14] [15] 。通过对 0.92BNT-0.06BT-0.02KNN 陶瓷场致应变原理研究发现， 这主要源于室 温下电场诱导非极性弛豫-极性铁电相转变 [16] 。基于 上述研究，降低 MPB(II)相界温度 Td 至室温来优化应 变性能不失为有效思路，主要手段包括构造钙钛矿型 多组元固溶体、离子掺杂以及调节非化学计量比等。 如 2013 年，Hao 等 [17] 制备 BNT-BKT-KNN 陶瓷，得 到应变值 S=0.48%且 d33* = 600 pm/V。Chen 等 [18] 将 [19][20] 。 此外， 同样为钙钛矿结构的 NN 也 能有效提高 BNT 基陶瓷的应变性能 [21][22] 高 [24] 。 此外， 温度的进一步升高使得 PNRs 活性更高， 从而电场诱导弛豫-铁电相转变所需要克服的势垒也 相应地升高，导致相同电场下场致应变值下降 [26]…”

Clarification on phase transition behaviors by local strain engineering in Bi1/2Na1/2TiO3–SrTiO3‐based ternary ceramics

“…Furthermore, it was reported that a large normalized strain ( S max / E max ) of about 600 pm/V under a relatively low field (4 kV/mm) was obtained in BNT–ST ceramics of MPB regions 16–19 . This abnormally large strain in BNT‐based (or BNT–ST) ceramics is associated with the reversible electric‐field‐induced phase transition from an ergodic relaxor (ER) to a ferroelectric (FE) 20–24 . Recently, several studies have suggested that exploring ternary systems can result in discovering a high‒performance piezoelectric in BNT–ST ceramics.…”

“…The BiMeO 3 ‐modifying effects have been intensively studied for phase transition behaviors and electromechanical strain properties of BNT‐based binary ceramics. More precisely, it was reported that a phase transformation from normal ferroelectrics to a relaxor with a significant disruption of the long‐range ferroelectric order is induced by adding a small amount of BiMeO 3 (e.g., Me = Al) into BNT‐based binary ceramics 22,32–34 . Furthermore, it is noted that the tolerance factor t of BiMeO 3 is strongly dependent on the B‐site ion (Me).…”

“…[16][17][18][19] This abnormally large strain in BNT-based (or BNT-ST) ceramics is associated with the reversible electric-field-induced phase transition from an ergodic relaxor (ER) to a ferroelectric (FE). [20][21][22][23][24] Recently, several studies have suggested that exploring ternary systems can result in discovering a high-performance piezoelectric in BNT-ST ceramics. As a result, a maximum strain of 0.27% at 4 kV/mm for BNT-ST-AgNbO 3 , 25 a high strain of 0.24% with 4 kV/mm at low sintering temperature for BNT-ST-LiNbO 3 , 26 a large strain of 0.239% under ultralow driving field of 3 kV/mm for BNT-ST-KTaO 3 , 24 and so on have been published.…”

“…More precisely, it was reported that a phase transformation from normal ferroelectrics to a relaxor with a significant disruption of the long-range ferroelectric order is induced by adding a small amount of BiMeO 3 (e.g., Me = Al) into BNT-based binary ceramics. 22,[32][33][34] Furthermore, it is noted that the tolerance factor t of BiMeO 3 is strongly dependent on the B-site ion (Me). Therefore, it is suggested that bismuth-based compounds BiMeO 3 as an end member of BNT-ST-based ternary systems can be a promising candidate for studying the phase transition behavior due to the relation between the phase boundary and the tolerance factor t of the end member.…”