Structure Evolution and Electrical Properties of Y 3+ -Doped Ba 1 – x Ca x Zr 0.07 Ti 0.93 O 3 Ceramics Hairui Liu, ‡ Qiang Li, ‡,† Yuanyuan Li, ‡ Nengneng Luo, ‡ Jaeshik Shim, ‡ Jinghan Gao, ‡ Qingfeng Yan, ‡ Yiling Zhang, § and Xiangcheng Chu § ‡ Department of Chemistry, Tsinghua University, Beijing 100084, China § State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China Lead free piezoelectric ceramics of Y 3+ -doped Ba 1 – xCa x Zr 0.07 Ti 0.93 O 3 with x = 0.05, 0.10, and 0.15 were pre- pared. Composition and temperature-dependent structural phase evolution and electrical properties of as-prepared ceram- ics were studied systematically by X-ray diffraction, Raman spectroscopy, impedance analyzer, ferroelectric test system, and unipolar strain measurement. Composition with x = 0.10 performs a good piezoelectric constant d 33 of 363 pC/N, coer- cive field E c of 257 V/mm, remanent polarization P r of 14.5 lC/cm 2 , and a Curie temperature T m of 109°C. High-res- olution X-ray diffraction was introduced to indicate presence of orthorhombic phase. Converse piezoelectric constant d 33 * of x = 0.10 composition performed better temperature stability in the range from 50°C to 110°C. That means decreasing ortho- rhombic–tetragonal phase transition temperature could be an effective way to enlarge its operating temperature range. I. Introduction P IEZOELECTRIC materials generating a higher voltage induced by mechanical strain (and vice versa) attract sig- nificant scientific attention owing to its applications on sen- sor and actuation. 1 However, lead contamination and its restrictions encourage scientists to replace lead-based piezo- electrics with environmental-friendly piezoelectrics. Recently, high piezoelectric performance of Ba(Zr 0.2 Ti 0.8 )O 3 –50 (Ba 0.7 Ca 0.3 )TiO 3 (BZT–50BCT) ceramics have been reported by Ren et al. 2 as one of the most promising candidates for lead-free piezoelectrics. Nevertheless, previous work on Ba 1Àx Ca x Zr y Ti 1-y O 3 (BCZT) 3–5 demonstrated that lower Curie temperature T m and poorer temperature stability lim- ited its potential applications. Bao et al. 6 have achieved a modified composition with higher T m of 114°C, and pro- posed a almost vertical morphotropic phase transition (MPB) region, where compositions with both high d 33 and high T m could be achieved. Furthermore, Y 3+ -doped, 7 Ho 3+ -doped, 8 and Dy 3+ -doped 9 Ba 0.99 Ca 0.01 Ti 0.98 Zr 0.02 O 3 ceramics, reported by Li et al., revealed improved tempera- ture stabilities. Extensive researches have been conducted on the origin of excellent piezoelectric performance of BZT–50BCT. It was proposed 2 that this enhanced performance was attributed to coexistence of tetragonal (T) and rhombohedral (R) phase in MPB region. The flatten free energy made polarization switching easier. Then, based on transmission electron microscopy and convergent beam electron diffraction, Gao et al. 5 observed coexistence of R and T nanodomains, sup- porting above-mentioned MPB opinion. However, some abnormal discoveries about electrical performance throw doubt upon that mechanism. 10–12 Recently, Haugen et al. 13 have reported phase evolution of BZT–50BCT from À100°C to 150°C by high-resolution XRD and Rietveld method. In that work, coexistence of R and T phase was believed in the range from 20°C to À25°C, and presented anomalies were explained by changes in phase contents. However, all these conclusions were based on XRD peaks at around 2h = 16.8°, 20.6°, 23.8°, and 25.3°, rather than at around canonical 2h = 45°, which are always used to clarify phase evolution near MPB region. 14 In addition to that, for BaTiO 3, 15 poly- morphic phase transition (PPT), corresponding to ortho- rhombic (O) phase, is thought to be a possible reason for electrical anomalies. Li et al. 16 also described presence of PPT in BCZT system. Thus, whether O phase appears in this system should be confirmed. It is well-known that A-site or B-site substitution could lead to significant changes in structure and properties. Y 3+ doping will improve temperature stability and densities 17 of BCZT. Based on previous investigations, this work will focus on influence of Ca 2+ content on structural phase evolution and electrical properties of Y 3+ -doped Ba 1Àx Ca x Zr 0.07- Ti 0.93 O 3 system. Structural phase evolution, dielectric, piezo- electric, and ferroelectric responses were discussed by combing XRD, scanning electron microscope (SEM), and Raman spectrum with the electrical performance. II. Experimental Procedure Y 3+ -doped Ba 1Àx Ca x Zr 0.07 Ti 0.93 O 3 ceramics with x = 0.05, 0.10, and 0.15 were prepared via conventional mixed oxides route. BaCO 3 (99%), TiO 2 (99.99%), CaCO 3 (99%), ZrO 2 (99.99%), and Y 2 O 3 (99.99%) were used as raw materials. After weighed according to stoichiometric ratio, Ba 1Àx- Ca x Zr 0.07 Ti 0.93 O 3 powders were ball-milled for 4 h with agate balls and alcohol. After drying, mixed powders were calcined at 1350°C for 4 h. As-calcined powders were milled again for 4 h, and then mixed with 0.1 mol% Y 2 O 3 . Then the mixtures were ball-milled, dried and calcined at 1350°C for 4 h again. The as-prepared powders were mixed with 5 wt% polyvinyl alcohol (PVA), and then pressed into disks of 10 mm diame- ter. After burning off PVA, samples were sintered at 1450°C for 4 h. To measure electrical properties, silver electrodes were fired on both surfaces of samples. XRD patterns of as-prepared ceramics at room tempera- ture were recorded by a diffractometer (D8 ADVANCE; Bru- ker Inc., Karlsruhe, Germany) using CuK a (k = 1.5406  A) radiation. XRD patterns at various temperatures were implemented on crushed ceramic powders of x = 0.10 by a diffractometer (X’Pert PRO MPD; PANalytical B.V., Almelo, the Netherlands) with CuK a radiation. Raman S. Zhang—contributing editor Manuscript No. 34194. Received December 1, 2013; approved February 10, 2014. † Author to whom correspondence should be addressed. e-mail: qiangli@mail.tsin- ghua.edu.cn 2076 J. Am. Ceram. Soc., 97 [7] 2076–2081 (2014) DOI: 10.1111/jace.12900 © 2014 The American Ceramic Society J ournal