Microstructure and electrical properties of Mn-modified bismuth-layer Na 0.25 K 0.25 Bi 2.5 Nb 2 O 9 Ceramics Xiang-Ping Jiang, Xin-Jia Wang ⇑ , Jia-Xin Wen, Chao Chen, Na Tu, Xiao-Hong Li Jiangxi Key Laboratory of Advanced Ceramic Materials, Department of Material Science and Engineering, Jingdezhen Ceramic Institute, Jingdezhen 333001, China article info Article history: Received 19 July 2012 Accepted 29 July 2012 Available online 4 August 2012 Keywords: Bismuth layer-structured Piezoelectric ceramics Microstructure Na 0.25 K 0.25 Bi 2.5 Nb 2 O 9 abstract Bismuth layer-structured ferroelectric ceramics Na 0.25 K 0.25 Bi 2.5 Nb 2 O 9 +xmol% MnCO 3 (NKBN–Mn) were synthesized by a traditional solid-state reaction. The effects of Mn addition on the microstructure and electrical properties of ceramics have been investigated in details. It was found that the ceramics possess a pure phase of bismuth oxide layer-type structure. The Curie temperature T c gradually decreases from 653 to 624 °C with increasing the Mn modification. The electrical properties of NKBN-based ceramics are improved significantly by the addition of Mn. The piezoelectric constant d 33 , dielectric loss tan d, mechanical quality factor Q m and remanent polarization P r for the NKBN ceramics with 3.0 mol% MnCO 3 modification were found to be 25 pC/N, 0.28%, 2817, 14.50 lC/cm 2 , respectively, together with the high T c (643 °C) and stable piezoelectric properties, demonstrating that the Mn modified NKBN-based ceramics are the promising candidates for high-temperature applications. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Since the first report by Aurivillius, bismuth layer-structured ferroelectrics (BLSFs) has been investigated extensively [1]. They are composed of pseduo-perovskite (A m1 B m O 3m+1 ) 2 blocks inter- leaved with bismuth oxide (Bi 2 O 2 ) 2+ layers along the c-axis and have a general formula of (Bi 2 O 2 ) 2+ (A m1 B m O 3m+1 ) 2 . In the for- mula, A is a mono-, di-, or trivalent ion (or their combination), B is a combination of tetra-, penta-, and hexavalent ions, e.g., Fe 3+ , Ti 4+ , Nb 5+ , Ta 5+ , or W 6+ , and m is the number of BO 6 octahedral (m = 1–5) [2–4]. Owing to the high Curie temperature (T c ), the BLSFs are widely used in high- temperature piezoelectric devices [5]. In addition, they possess low temperature coefficients of dielectric, piezoelec- tric properties and resonant frequency, low aging rate, and strong anisotropic electromechanical coupling factors, making them suit- able for pressure sensors and trapped energy filter, etc. [6–8]. Therefore, the BLSFs, such as Bi 4 Ti 3 O 12 , Bi 3 NbTiO 9 , CaBi 2 (Nb,Ta) 2 O 9 , M 0.5 Bi 4.5 Ti 4 O 15 (M = Li,Na,K), M 0.5 Bi 2.5 Nb 2 O 9 (M = Li, Na, K), CaBi 4 Ti 4 O 15 , and SrBi 2 Ta 2 O 9 have attracted much attention recently [2–18]. However, large coercive field E c , which may be caused by the two-dimensional orientation restriction of rotation of the sponta- neous polarization, makes the BLSFs difficult to be poled and their piezoelectric properties are not desirable [2,8]. To improve the pie- zoelectric activities of BLSFs, grain orientation techniques, such as hot-forging (HF), templated grain growth (TGG), and spark plasma sintering (SPS), have been attempted in improving the piezoelec- tric activities of BLSFs. Using the grain orientation techniques, the d 33 can be significantly improved (>20 pC/N). But high cost lim- its their applications in industrial practice. An alternative method is to introduce modification elements. It was found that the d 33 of the BLSFs can exceed 15 pC/N by replacing an A and/or the B site cation using the traditional solid-state reaction [6–9,15]. Na 0.25 K 0.25 Bi 2.5 Nb 2 O 9 (NKBN) is one of the most studied com- pounds among the bismuth-based layered ceramics because of its high T c (650 °C) and lead-free nature [7,17]. To further en- hance the piezoactivity, the LiCe-modified M 0.5 Bi 4.5 Ti 4 O 15 /M 0.5- Bi 2.5 Nb 2 O 9 (M = Li, Na, K) ceramics with excellent electrical properties have been fabricated by the conventional solid-state processing, the mechanisms of A-site substitution have been well studied [2,6–8,17]. However, little attention has been paid to M 0.5- Bi 2.5 Nb 2 O 9 (M = Li, Na, K) ceramics with B-site substitution. It is well known that MnCO 3 is one of the most interesting and effective additives in improving the piezoelectric activities of perovskite structure ceramics [4,18–21], because of Mn ions have multiva- lence: Mn 2+ , Mn 3+ and Mn 4+ . It was reported that the doping of Mn ions are used to substitute the B-site cations in the perov- skite-type ABO 3 ferroelectric materials, and it has been demon- strated that Mn doping is an effective way to increase the electric resistivity and improve the piezoactivity of the materials. Based on these considerations, in the present work, ordinarily fired Mn-modified NKBN ceramics were prepared by a traditional solid- state reaction, and their phase, microstructure, and electrical prop- erties were investigated in details. 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.07.135 ⇑ Corresponding author. Tel./fax: +86 798 8499237. E-mail address: wangxinjia1120@163.com (X.-J. Wang). Journal of Alloys and Compounds 544 (2012) 125–128 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom