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Lead barium niobate (PBN or PbxBa1–xNb2O6) is a promising tungsten bronze ceramic system that has a morphotropic phase boundary between the orthorhombic and tetragonal phases at x
0.63, where the spontaneous polarization (Ps
60–70 mC/cm2) and other ferroelectric properties are known to be higher. However, even textured PBN60 ceramics have low Ps (23.9 mC/cm2) and piezoelectric charge coefficient (d33
236 pC/N) as compared to the single crystal counterparts. The aim of this study is to control powder processing, green body formation, and sintering conditions to enhance both densification and electrical properties. Therefore, samples were prepared by tape casting methods using single phase PBN60 and reactive mixture of PbNb2O6 and BaNb2O6 powders. Three wt% excess PbO was found to be necessary for densification. Our results showed that undoped PBN60 ceramics reached Ps ¼ 33 mC/cm2, d33 ¼ 305 pC/N, and had a Tc ¼ 340–350  C. These results are much higher than the reported values in the literature, which can be attributed to the careful ceramic processing such as tape casting (e.g., homogenous green structure), annealing (e.g., control of excess grain boundary phase), and liquid phase sintering (e.g., higher densification). I. INTRODUCTION

Lead barium niobate (PBN or PbxBa1–xNb2O6) is a promising tungsten bronze ceramic system which has a morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases at x
0.63, where the spontaneous polarization and other ferroelectric properties are known to be higher.1,2 The polar axis is along [010] and [100] on the orthorhombic (mm2) phase while it is along [001] on the tetragonal (4mm) phase.3 Since PBN60 (x ¼ 0.60) is located near a MPB, this composition has been extensively studied in the single crystal form due to its attractive ferroelectric properties such as a very high spontaneous polarization (Ps
60–70 mC/cm2) and a high Curie temperature (Tc
320  C).4–7 There is a scarcity of polycrystalline ceramic studies on PBN60 compositions in the literature. Neurgaonkar et al.8 prepared dense (95% relative density) PBN60 ceramics using 6 wt% excess PbO with and without La modification by a hot forging technique. They obtained anisotropic properties parallel and perpendicular to the hot forging direction without any texture quantification. The highest properties were reported to be Ps ¼ 23.9 mC/cm2 and the piezoelectric strain coefficient d33 ¼ 236 pC/N in PBN60 without La addition. Venet et al.9 also fabricated dense (96% relative density) PBN60 ceramics by hot forging a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0284 J. Mater. Res., Vol. 25, No. 11, Nov 2010

http://journals.cambridge.org

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and obtained anisotropic properties; however, a Ps
9 mC/cm2 was measured. Chandramouli et al.10 prepared Ce-doped PBN60 ceramics by a conventional sintering method. They reached 98% relative densification in 3 wt% excess PbO containing samples. They reported enhanced d33 ¼ 318 pC/N in 6 m