Graduate Thesis Or Dissertation
 

Development of new high-temperature piezoelectric perovskite ceramics

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/x346d7792

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  • Lead zirconate titanate (PZT) is the dominant ferroelectric material in the market due to its excellent piezoelectric properties, relatively high Curie transition temperature (T[subscript C]), low cost, etc. However, because of emerging applications with requirements for high temperature (T[subscript C] > 400 °C) ferroelectrics, researchers are increasingly looking at alternative materials to replace PZT. A number of ternary Pb-based solid solutions were developed to find ferroelectric ceramics with a TC above 400 °C, with piezoelectric properties similar to PZT. For high temperature applications, PbTiO₃-BiScO₃ (PT-BS) based ternary solid solutions were developed. The best results were found in the PT-BS-Bi(Ni₁/₂Ti₁/₂)O₃ (PT-BS-BNiT) ternary system where a number of compositions exhibited low field piezoelectric coefficients (d₃₃) between 300 and 450 pC/N, high field coefficients (d33*) between 300 and 900 pm/V, Curie temperatures (T[subscript C]) between 300 and 450 °C, and electromechanical coupling factors (k[subscript p]) up to ≈ 0.3. Additionally, the low field d₃₃ increased with increasing temperature in all compositions and with the highest recorded value of d₃₃ ≈ 1200 pC/N. In a number of compositions (mainly those with diffuse phase transitions), the decrease in properties occurred not at T[subscript C] but at a lower temperature called the depolarization temperature (T[subscript d]). For the PT-BS-BNiT ternary, the value of T[subscript C] decreased as BNiT content increased while at the same time, the separation between T[subscript d] and T[subscript C] increased with increasing BNiT content. In PT-BS rich compositions, a shift from a first order phase transition to more relaxor-like transitions were observed in BNiT rich compositions. This behavior is attributed to a break down in long-range order induced by poling treatment and to a large occupancy of Bi on the A-site of the perovskite unit cells allowing the persistence of a tetragonal distortion despite the loss of polarization (the order parameter of normal ferroelectric materials).
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