Characterisation of competing orders in dielectric oxides

Dielectric oxides exhibit many intriguing properties. For example, ferroic materials are central to developing transducers due to their ability to convert energy owing to the presence of coupled orders. In particular, lead-based perovskite relaxor-ferroelectric single crystal have attracted great attention in recent years, with exceptional piezoelectric and dielectric responses reported. Suitable for high-power industrial and underwater SONAR ultrasonic applications due to their high energy density, the performance of these materials has been linked to compositional disorder and short-range order but the mechanism is not yet well-understood. In general, coupling and competition of different orders can result in thought provoking physics and, in this work, this link was investigated by studying the fundamental behaviour of complex ferroelectrics and multiferroics. Polarised neutrons were used to characterise the magnetic ground state of Cu3Nb2O8, addressing an issue in the literature regarding the microscopic ordering mechanism. Furthermore, muon techniques were used to study the composition and magnetic structure of the relaxor-multiferroic Pb(Fe1/2Nb1/2)O3 which provided insight into the role of disorder and random fields. This work was then extended to study the Mn distribution and valence in doped Pb(In1/2Nb1/2)O3 - Pb(Mg1/3Nb2/3)O3 - PbTiO3. These materials are indicated to be amongst the highest performance piezoelectric but the microscopic mechanisms are not fully understood. This raised the question of best practice in material comparison, with unbiased comparison of transduction materials desired. To address this, a new method was developed to quantify the energy density of piezoelectric materials, which was verified in silico to be independent of a single use case or application. Overall, this work extends the understanding of three complex ferroelectric and multiferroic systems using fundamental characterisation methods with a foundation in applications

Progress Towards the Miniaturization of an Ultrasonic Scalpel for Robotic Endoscopic Surgery Using Mn:PIN-PMN-PT High Performance Piezocrystals

Mn:PIN-PMN-PT piezocrystals are under consideration for potential use in miniaturised ultrasonic scalpels for robotic minimally-invasive surgery where small size and light weight may be advantageous. Electromechanical coupling coefficient k > 0.9 for both [001] and [011] poled Mn:PIN-PMN-PT was calculated, confirming the well-recognized higher efficiency of this material when compared to standard piezoceramics. Novel transducer design strategies have been explored, and outcomes are discussed. The introduction of components with additional compliance in a standard d 31 mode transducer has been shown to drop the resonant frequency of the first longitudinal mode by more than 17%, with more than 75% improvement in tip/blade displacement. Results suggest that the combination of high performance piezocrystals with highly compliant components may be a useful route to follow to achieve our miniaturisation target

Progress Towards Piezocrystal and Pb-Free Piezoceramic Performance Prediction for High Power Ultrasound Devices

The full piezoelastoelectric matrices for 4mm Mn: PIN-PMN-PT piezocrystal (TRS Technologies, PA, USA) and 6mm piezoceramic PIC 700 (PI Ceramics, Lederhose, Germany) have been obtained through resonant ultrasound spectroscopy combined with an optimisation algorithm based on the Levenberg-Marquardt (LM) and Nelder-Mead (NM) approaches using exact cube samples. Both methods have been found to converge, and differences in the solutions are reported. Laser Doppler vibrometry (LDV) has been used to validate the material characterisation method via shape mode reconstruction and comparison with finite element analysis (FEA). Reconstructed results are in good agreement with experimental data. Temperatures above ambient and uniaxial pressure have been found to affect the first mode resonant frequency by up to approximately 5% for PIC 700, and 15% for Mn: PIN-PMN-PT

Full set of material properties of lead-free PIC 700 for transducer designers

The impact of Pb on the environment and human health and recent restrictions on its use in electronic devices are generating demand for Pb-free piezoelectric materials. Examples are now available commercially, but the full elastic-piezoelectric-dielectric (EPD) matrices needed for device design, including over a range of operating conditions, have not yet been published. The standard IEEE EPD matrix measurement method needs four sample geometries, making it inconvenient and increasing errors. Here, we present an alternative method combining resonant ultrasound spectroscopy with optimization algorithms to measure the EPD matrix from a single exact cube sample. The Levenberg–Marquardt (LM) and Nelder–Mead (NM) optimizations are compared in refining the independent parameters. Both give convergent solutions, but the LM algorithm is more accurate and efficient. The single-sample approach was used to obtain results from Pb-free Na 1/2 Bi 1/2 TiO 3 (PIC 700, PI Ceramics, Lederhose, Germany) piezoceramic ( ∞ mm sample symmetry) characterized with the standard IEEE method at ambient temperature and with the single-sample method at ambient temperature and additionally up to 80 °C. The results are validated with the laser Doppler vibrometry via mode shape reconstruction and comparison with finite-element analysis (FEA). They demonstrate that convenient measurement of the EPD matrix of Pb-free materials with temperature dependence is possible, providing a crucial capability for the adoption of these materials in devices

A Measure of Energy Density to Quantify Progress in Pb-free Piezoelectric Material Development

The negative environmental impact of Pb has led to an increased demand for Pb-free electronics. This is particularly important in ultrasonic transducers where Pb-based piezoelectric materials, primarily ceramic PZT, are the dominant choice. Naturally for Pb-free materials to become a viable option, the performance must match that of the current standard. However, present comparison methods and figures of merit for piezoelectric materials are based on specific use cases which can lead to disparate results. In the work described here, a new measure is developed for the performance of a piezoelectric material, based on its energy density. This was achieved by developing a generalized electromechanical coupling factor derived from first principles and defined at zero frequency. It encompasses all conversion mechanisms allowed by symmetry and so avoids any resonance/geometry effects which obscure the pure material response. Comparison between Pb-free materials using this new coupling factor are made within the con of PZT and high performance piezocrystal and were validated using finite element analysis. Whilst no Pb-free materials currently match the level of PZT/single crystal by this method, it is shown that the new figure of merit is independent of geometry and other spatial effects and thus allows a fully unbiased comparison between materials. Hence it defines a universal measure against which Pb-free material development may be traced

High-Power Characterization of d32-Mode Mn:PIN-PMN-PT Piezoelectric Single Crystals at Different Temperatures

Mn:PIN-PMN-PT plates: [011]-poled (mm2 symmetry, d 32 -mode) were characterized at high-power excitation levels and at different temperatures. A bespoke high-power measurement system was utilized to acquire the electrical impedance at resonance. Results have shown that the resonant frequency/anti-resonant frequency downshifts with increasing driving voltage and temperature

Can Mn: PIN-PMN-PT piezocrystal replace hard piezoceramic in power ultrasonic devices?

No abstract available

Full-property Measurement for Piezoelectric Devices through Applied Artificial Intelligence

The piezoelectric effect is the most common means to excite power ultrasonics tools. However, the standard characterisation of piezoelectric materials is costly and complicated, particularly because of the need for multiple samples supporting only one or two modes each, with different poling requirements. These issues are of increasing importance because of the growing need for new piezoelectric materials, for example, lead-free. Moreover, the requirement for highly efficient finite element analysis (FEA) to design these tools demands precise, cheaper and easier material characterisation methods. This paper presents progress towards an innovative, simple characterisation approach. It is based on implementing machine learning-assisted global optimisation combined with FEA, using a single electrical impedance spectroscopy (EIS) measurement on a miniature sample. This solution may lead not only to considerable savings on costly material samples but also to save on experimental equipment and the training of engineers and materials scientists to use it. The technique also avoids difficulty in poling as no materials with large thicknesses are needed. Our approach is based on using an optimisation algorithm to fit an experimental EIS measurement with FEA. So far, surrogate model-assisted differential evolution for antenna synthesis (SADEA) and Levenberg-Marquardt (LM) algorithms have been studied for [001]-poled PZ54 (CTS Ferroperm, Kvistgaard, Denmark) as a reference, with SADEA showing the best results. The results are promising but there is still a need to achieve a better fit between the FEA and measurements and this is under investigation, via improvements in the optimisation process and implementation of complex piezoelectric material properties

Towards Miniature Single Sample Characterisation (MSSC) of Piezoelectric Material with a Single Experimental Measurement

No abstract available