Modified BiFeO 3 -PbTiO 3 Morphotropic Phase Boundary (MPB) Piezoelectric Ceramics for High Temperature and High Power A
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Modified BiFeO3-PbTiO3 Morphotropic Phase Boundary (MPB) Piezoelectric Ceramics for High Temperature and High Power Applications JinRong Cheng1,2 and L.Eric Cross1 1 Materials Research Institute, The Pennsylvania State University University Park, PA 16802 2 School of Materials Science and Engineering, Shanghai University Shanghai 201800, P.R.China ABSTRACT BiFeO3-PbTiO3 (BF-PT) crystalline solutions have been modified by La3+, Ga3+ and Ba2+ substituent. The modified BF-PT had morphotropic phase boundary (MPB), at which the ferroelectric rhombohedral phase transferred to the tetragonal symmetry. The piezoelectric properties at the MPB were strongly depended on different substituents. The modified BF-PT system showed the insulation resistivity up to 1012 Ω⋅cm at room temperature. Lanthanum played a critical role making BF-PT softer to be poled to the piezoelectric state. Ga provided BF-PT additional polarization and breakdown strength with La substituent. In the system with La3+, Ga3+ and Ba2+ simultaneously, addition of Ba enhanced dielectric and piezoelectric activity. It was flexible to tailor BF-PT by using different substituents. In the vicinity of MPB, the Curie temperature Tc was above 385oC of BF-PT for La ≤10 at%, whereas the d33 constant was as high as 295 pC/N for one with La of 20 at%. The modified BF-PT revealed comparable performances to conventional Pb(Zr,Ti)O3 (PZT) ceramics, but in significantly lead reduced forms. INTRODUCTION Pb(Zr,Ti)O3 (PZT) is a strategically important material on which rests sonar and medical ultrasonic imaging technologies. [1,2] However, the high lead content of PZT is the disadvantage due to the ecological restriction to the usage of lead. A lot of efforts have been done to look for an alternative to conventional piezoelectric ceramics [3-5]. To date, no MPB piezoelectrics has been developed that has the potential to replace PZT for acoustic materials applications. BiScO3PbTiO3 (BS-PT) was the interesting one with excellent piezoelectric properties, however, the scandium source was expensive and the lead content was required to be >60 at% [6]. BiFeO3PbTiO3 was in great interest due to the existence of MPB and the significant lead reduced content [7]. For many years, the difficulty to develop BF-PT system lied in the conductivity caused by the easy change of Fe3+ to Fe2+[8-9]. Most recently, we discovered that BF-PT could be good insulating materials as normal piezoelectric ceramics with addition of dopant. In this investigation, systematical experiments has been carried out to modify BF-PT with Ga3+ only in Fe3+ site, La3+ and Ga3+ in Bi3+ and Fe3+ site respectively, and La3+ and Ga3+ with Ba2+ in Pb2+ site. For each set composition, the ceramics were fabricated and characterized for different PbTiO3 concentrations, and the MPB compositions were determined according to the abnormal in both structural and electrical properties. The MPB of the modified BF-PT was identified, and their dielectric and piezoelectric properties were measured and discussed. EXPERIMENT Modifie
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