title: Efficiency and characterisation comparison between various compositions of conventionally sintered PZT ceramics for piezoelectric energy harvesting
Creators: name: Garcia Caballero, Veronica Lizeth
Publisher: name: University of Glasgow
Year: 2024

description: Amongst the available kinetic energy harvesting methods, piezoelectric devices have gained popularity due to their prolonged service life, as well as their reduced maintenance, weight and size. Lead zirconate titanate, also known as PZT, is one of the most common piezoelectric ceramics used worldwide. When left undoped, changing the proportions of TiO2 and ZrO2 in the material will result in different proximities to the morphotropic phase boundary (MPB), which is thought to be where the best piezoelectric properties are exhibited. Additionally, the purity of the parent oxides used in the preparation of PZT has been found to have a direct effect not only on its properties but also on its fabrication cost.

To identify the effects of varying these properties, this dissertation presents and discusses the work done to compare the efficiency and characteristics of ten different compositions of PZT disks sintered through a two-stage conventional ceramic method. The disks were fabricated using two grades of purity for the parent oxides, and three different chemical compositions. Six of the sets were made using the same grade of purity for the main PZT disk and the lead zirconate (PZ) atmosphere that was used to compensate the PbO loss that occurs near ~888°C. The other four were sintered using the opposite grade of purity for the PZ atmosphere. Three of these were for the high-purity compositions and one for the samples made with the lowest concentration of TiO2 and lower-grade starting powders.

The ten sets were physically characterised using their densities, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Energy Dispersion Analysis (EDS). The samples were processed to achieve smooth parallel surfaces and functionally characterised after applying silver electrodes on their faces. The disks were poled along their thickness using 4kV/mm for 15min at ~100°C, prior to measuring their piezoelectric constants, electromechanical coupling factor, mechanical quality factor and acoustic impedance. The lower purity (LP) PZT samples registered higher densities and seemingly behaved as hard ceramics, resisting polarization and exhibiting lower permittivities and Curie points.

Although the highest piezoelectric coefficients (d33 &gt; 310pC/N) were measured from the higher purity (HP) PZT samples, the highest coupling factors (kp &gt; 54%) were obtained from compositions that were made with the LP chemicals or used LP PZ disks, suggesting that the presence of the LP components had a positive effect in the energy conversion.

After coupling the samples as energy harvesters, controlled impact tests were done at two different frequencies for approximately 12s each to obtain their I-V curves. The highest average output power density was achieved by the samples with the highest TiO2 made with LP PZT and PZ (43.7μW/cm3 at ~6 hits/s and ~28.4μW/cm3 at 14 hits/s). This further supports the positive effects the LP chemicals can have, not only offering similar properties as the HP counterparts but also implicating major cost reductions when fabricated in bulk for large-scale commercial use, whilst their higher densities anticipate a better response to the expected conditions associated with their use.