Porous Piezoelectric Single Crystal Sensors (POPSICALS)
Lead Research Organisation:
University of Bath
Department Name: Mechanical Engineering
Abstract
Piezoelectric materials generate an electrical charge in response to mechanical stress. These properties make them important materials for pressure sensors, medical transducers and vibration energy harvesters and the market is estimated to be £28 billion by 2025. Current commercial materials are based on dense ceramics since they generate a high charge in response to mechanical stress. However, they have a range of disadvantages.
(i) current materials are lead-based, such as lead zirconate titanate (PZT), and generate over 2500 tons of lead electronic waste per annum,
(ii) existing materials are high density and high stiffness, leading to poor impedance matching with biological tissue or water,
(iii) the high permittivity of dense materials leads to poor performance for sensing and harvesting since performance indicators are inversely proportional to permittivity,
(iv) ceramic elements can only be produced in limited geometries since they are made by pressing ceramic powders and subsequent high-temperature sintering.
POPSICALS will overcome the disadvantages of existing ceramics by developing a new manufacturing process based on a magnetic field enhanced freeze-casting process to create single crystal-like lead-free porous piezoelectric materials. This will combine the high piezoelectric charge coefficients of single-crystal materials with the low permittivity, low density and low stiffness of porous materials.
(i) current materials are lead-based, such as lead zirconate titanate (PZT), and generate over 2500 tons of lead electronic waste per annum,
(ii) existing materials are high density and high stiffness, leading to poor impedance matching with biological tissue or water,
(iii) the high permittivity of dense materials leads to poor performance for sensing and harvesting since performance indicators are inversely proportional to permittivity,
(iv) ceramic elements can only be produced in limited geometries since they are made by pressing ceramic powders and subsequent high-temperature sintering.
POPSICALS will overcome the disadvantages of existing ceramics by developing a new manufacturing process based on a magnetic field enhanced freeze-casting process to create single crystal-like lead-free porous piezoelectric materials. This will combine the high piezoelectric charge coefficients of single-crystal materials with the low permittivity, low density and low stiffness of porous materials.
| Description | The project has shown that it is possible to produce aligned single-crystal seeds using directional freeze casting where the seed crystals are frozen; this is clear new knowledge that can be exploited for future research. After removing the ice crystals by freeze drying, the aligned seed crystals can be heat treated to form a more robust material and the porous aligned material can also be infiltrated with a polymer to provide greater mechanical flexibility; this has been demonstrated. This alignment of the material enables highly textured materials to be produced, which can exhibit high piezoelectric properties related to applications such as energy harvesting, sensing and SONAR applications. The project has led to collaboration with Imperial College London who are able to coat the seed crystals with magnetic particles, this can be used to further align the seed crystals to produce a greater level of texturing - we have submitted a joint publication in this area to disseminate this new knowledge and method.. |
| Exploitation Route | The key outcomes are that this can form textured materials, and the key point is that the directional freezing is relatively simple and could be scaled up. One potential area of interest is the manufacture of piezoelectric materials for hydrophones/SONAR applications. The only other approach to produce such aligned seed crystals is a process known as tape casting; this is a slow layer-by-layer process and can only form limited geometries and sizes. The approach developed in this work has the potential to provide a more commercially viable route due to its relative simplicity and scalability; in addition, since the process involves a simple process pf directional freezing, there is potential for complex geometries to be produced by freezing in a three-dimensional printed mould. |
| Sectors | Aerospace Defence and Marine Electronics |
| Description | We have had discussions with a company (located in UK and Europe) who are interested in using freeze casting to manufacture ceramics for high-temperature filters, such as filtering molten metals. In this regard, the interest it to use the porosity left by the ice when it is removed to provide the pores that would be used in high-temperature filtration. After a visit to the University of Bath by the company to discuss and view the process, we are considering initial informal trials of the freezing process and then seeking funding, for example, by impact acceleration or by industry funding. |
| First Year Of Impact | 2025 |
| Sector | Manufacturing, including Industrial Biotechology |
| Description | Academic Collaboration with Imperial College London |
| Organisation | Imperial College London |
| Country | United Kingdom |
| Sector | Academic/University |
| PI Contribution | Collaboration in terms of the characterisation of ferroelectric materials by the University of Bath. |
| Collaborator Contribution | Supply of aligned materials which are textured using magnetic fields to produce ferroelectric materials. |
| Impact | Initial stages and joint publications expected. Training of PhD and Postdoc from Bath and Imperial due to different skill sets. |
| Start Year | 2023 |