Abstract
Lead-free 0.94Na0.5Bi0.5TiO3–0.06Ba1+xTiO3 (NBT–0.06B1+xT) ceramics (0.0 ≤ x ≤ 0.03) were synthesized by a conventional solid-state reaction process. X-ray diffraction shows that the compositions are at the morphotropic phase boundary where rhombohedral and tetragonal phase coexist. Grain size slightly changes with the increase of Ba2+ content and reaches the minimum at x = 0.02. The depolarization temperature (T d ) decreases with the extra Ba2+ content but the lowest T d was obtained at x = 0.01–0.02. The pyroelectric coefficient (p) was measured as a function of Ba2+ content, and increased from 2.90 × 10−4 to 3.54 × 10−4 C m−2 °C−1, and from 55.3 × 10−4 to 740.7 × 10−4 C m−2 °C−1 for x = 0.00 and 0.02 at RT, and depolarization temperature (T d ) respectively. The pyroelectric coefficient (p) shows a large increase with rising the temperature and reaches the maximum value at the depolarization temperature (T d ). The figures of merits of F i , F v and F D have all been improved with the addition of extra barium. These improved pyroelectric properties indicate that NBT–0.06B1+xT is a promising material for pyroelectric applications or a wide range of temperature.
Highlights
At present the most widely used ferroelectric materials are lead-based ceramics such as PZT and PZT-based multicomponent ceramics due to their superior piezoelectric and electrical properties, but there are two serious environmental problems arising from the fabrication of lead-containing materials: atmospheric pollution caused by PbO vapour during ceramic fabrication, and the difficulty in removing lead during component recycling
The absence of other phase indicates that NBT– 0.06B1?xT lattices have either absorbed the extra amount of Barium (Ba2?), and formed the NBT–0.06B1?xT ceramic solid solutions [17, 18] or the amount of the second phase is too small to be tested by X-Ray Diffraction (XRD)
The coexistence of both rhombohedral and tetragonal phases in NBT–0.06B1?xT ceramics proves that the sample structures are at morphotropic phase boundary (MPB), which was consistent with what was reported in literature [12, 14, 19]
Summary
At present the most widely used ferroelectric materials are lead-based ceramics such as PZT and PZT-based multicomponent ceramics due to their superior piezoelectric and electrical properties, but there are two serious environmental problems arising from the fabrication of lead-containing materials: atmospheric pollution caused by PbO vapour during ceramic fabrication, and the difficulty in removing lead during component recycling. Pyroelectric ceramic materials are becoming increasingly on high demand in variety of industrial applications such as sensors, infrared detectors, thermal cameras, gas detectors, microelectronic devices, as well as actuators, transducers, medical devices, airplanes and spacecraft [6]. These materials could have a large pyroelectric coefficient (polarization change vs temperature change) at a phase transition temperature. NBT exhibits two structural phase transitions: the first one (Td) from a ferroelectric rhombohedral to a tetragonal phase (*260–350 °C) and the second one (Tc) from a tetragonal phase to a paraelectric cubic phase (520–540 °C) These phase transition temperatures are well above room temperature. In NBT-based systems, there is a weakly polar intermediate phase [8],
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