Text

theses

Bismuth based piezoelectric ceramics such as 0.88Bi1/2Na1/2TiO3 – 0.08Bi1/2K1/2TiO3 – 0.04BaTiO3 (BNKBT88) are a promising lead-free candidate with moderate piezoelectric properties for use in in transducers, multilayer actuators (MLA), and piezoelectric transformers. This dissertation focuses on three areas of piezoelectric research: i) development of a BNT-based co-fired actuator with copper metal electrodes sintered at low temperature and in controlled oxygen atmosphere, ii) study the effect of A-site non-stoichiometry in BNKBT ceramics and improvement of the electrical resistivity in Bi-deficient composition for a high power transducer application, and iii) development of a prototype bridge transducer with a novel electrode pattern utilizing d33 for enhanced energy generation. i) Compatibility of Bi-based ceramics and copper electrodes was demonstrated by co-firing BNKBT88 ceramics with copper electrodes at 900oC in controlled atmosphere with an oxygen partial pressure of 6.1x10-8 atm. A combination of additives for low temperature sintering was used for firing at 900oC in air or controlled atmosphere with minimal effect on the piezoelectric properties of BNKBT88 compared to sintering at 1150oC. The oxygen atmosphere was controlled during sintering by mixing carbon dioxide and a hydrogen-nitrogen mixture. To keep the concentration of oxygen within the narrow range necessary for the coexistence of Cu metal and Bi2O3, the BNKBT88 samples were placed inside of a rectangular alumina boat and covered with a custom drilled alumina plate. A mixture of copper metal powder and cuprous oxide (Cu2O) were placed adjacent to the samples inside of the alumina boat to release or absorb excess O2. BNKBT88 ceramics were successfully co-fired with internal and surface Cu metal electrodes. ii) The effect of non-stoichiometry of A-site cations in BNKBT88 was studied. Hardening and softening of piezoelectric properties has been observed. The most notable effect is that the mechanical quality factor, which is an essential figure of merit for high power application, is as high as 1200 for the Bi-deficient composition compared to 150 for the unmodified composition. Multilayer bismuth deficient BNKBT88 with co-fired copper metal electrodes is candidate for use in a lead-free piezoelectric transformer. iii) A prototype novel lead zirconate titanate (PZT) bridge transducer based on the cymbal design has been developed for energy harvesting from impact loading by vehicle- induced deformations on pavement. Efficient transfer of mechanical energy from the road to the piezoelectric transducers embedded beneath the surface is achieved through mechanical coupling of the transducer and the pavement. A busy highway can be used as a source of electrical power where the harvested energy can be transmitted to the electrical grid or used to power streetlights. The novel transducer is also a highly sensitive detector that has the potential to be used to monitor vehicles on a roadway. The novel transducers generate energy to power electronic circuitry, including wireless transmitters for real-time traffic monitoring, without requiring external cables. A network of self-powered piezoelectric sensors could be installed in any roadway to control the flow of traffic on a highway or enable the communication of autonomous vehicles with the road. A novel electrode design is used to polarize the piezoelectric ceramic along its length, effectively utilizing d33 mode for enhanced energy generation. The effective piezoelectric coefficient d33ef was measured to be 19,000pC/N using a modified Berlincourt method. Horizontal poling increases energy and output voltage considerably. A prototype module with 64 bridge transducers was fabricated and loaded repeatedly with a pneumatic piston to simulate vehicle loading on a busy highway. Each loading of 600 lbs on the prototype transducer module generates 0.83 mJ of energy. Loading under simulated traffic conditions with 500 lbs at 5 Hz generated 2.1 mW at a resistive load of 330 kOhm. An impedance matching circuit utilizing a step down switch-mode DC-DC “buck” converter was used to power a series of LEDs.

ETD_8633

Ph.D.

Includes bibliographical references

by Gregory Yesner

doi:10.7282/T3MK6H4T

ETD doctoral

The author owns the copyright to this work.