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Control of PbO loss and Reduced hysteresis model

There will be two presentations representing Noliac at the “2017 Joint IEEE ISAF-IWATMD-PFM Conference” in Atlanta, USA, in May 7-11.
Control of PbO loss and Reduced hysteresis model

Control of PbO loss during sintering of PZT
Martin Safar, PhD student at University of Birmingham, UK, will present the results of his research done at Noliac Ceramics. He will hold a presentation titled “Control of PbO loss during sintering of PZT: laboratory vs industry”. Martin Safar explains the research:

- At high sintering temperatures, PZT loses mass in a form of PbO vapour, which may lead to undesirable changes in the material’s structure and properties. The use of a lead oxide-containing powder bed is one of the ways to prevent the PbO loss. In my experiments, I’ve encountered some issues with conventionally used powder beds, when using long industrial sintering programmes on a laboratory scale. This has led me to a series of experiments, where I have compared a number of different powder beds. I’ve chosen the one that mostly suits the industrial sintering programme and is able to repeatedly produce single-phase material with good properties.

The presentation will take place:

  • Tuesday, May 9, 2017, 4:00pm - 4:15pm
  • Session: Processing optimization

Find an abstract of Martin Safar’s research paper below

Reduced hysteresis model for real-time control systems
Charles Mangeot, Senior R&D Engineer at Noliac A/S, will present his paper “Reduced hysteresis model and temperature dependency of multilayer piezo actuators” at a poster session. Charles Mangeot explains:

- When operating piezoelectric multilayer actuators in a closed-loop system, creep and hysteresis can affect the performance and stability of the control loop. It is possible to use a model-based approach to improve that; however, for many applications it is critical to adapt the model characteristics to the operating temperature to achieve consistent performance, leading to very complex models. To reach an accurate model of hysteresis, a Preisach model is often used. This research aims at reducing the complexity of such a model in order to be able to implement it in simple real-time control systems. The result is a model with only five parameters, which could lead to several benefits such as reduction of hysteresis, faster response of a control loop or sensorless temperature estimation.

The poster presentation will take place:

  • Tuesday, May 9, 2017, 12:00pm - 2:00pm
  • Session: ISAF Group IV

Find an abstract of Charles Mangeot’s research paper below 

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Abstract: Martin Safar “Control of PbO loss during sintering of PZT: laboratory vs industry”

The relatively low melting point of lead oxide (approx. 900 °C) has always presented an issue in the processing of lead zirconium titanate (PZT) piezoelectric ceramics. The loss of PbO at high sintering temperatures (up to 1300 °C) can cause undesirable changes in stoichiometry, phase composition and electrical properties of the final ceramic product. In high-volume production, the PbO loss per piece is low, with a small excess of lead oxide in the initial powder composition, it is usually sufficient to keep sintered samples in enclosed crucibles. Small-scale lab processing requires better atmosphere control, usually implemented by surrounding the sample in a lead oxide-containing powder bed. Such control is required in order to prepare samples for detailed composition- microstructure- property studies.

In this work, a typical industrial sintering program with slow heating rate and long dwell (4 hours) was used to sinter a small number of hard PZT samples at 1260 °C in a laboratory furnace. It was found that conventionally used powder beds such as PZT or PbZrO3 mixed in different ratios with ZrO2 were either difficult to separate from the crucible/samples or not able to sufficiently prevent the loss of PbO. Excessive PbO loss was indicated by the presence of ZrO2 secondary phase in sintered samples using the scanning electron microscope (SEM). Weight loss of individual samples, and their resulting electrical properties, varied depending on the composition and particle size of the powder bed. An alternative powder bed consisting of ZrO2 sand reacted with PbO was found to sufficiently reduce the PbO loss in the samples (no secondary phase detected) while being easily separated from both the samples and crucible after sintering, and maintaining good piezoelectric properties in the sintered samples.

Abstract: Charles Mangeot “Reduced hysteresis model and temperature dependency of multilayer piezo actuators”

Piezoelectric multilayer actuators are widely used in the field of micro-positioning and nano-positioning plus in applications that require a fast and accurate movement such as hydraulic valves. Unfortunately, the control of these actuators is difficult due to their non-linear response. Creep and hysteresis are two phenomena that can affect the performance and stability of a control loop. In addition, for many applications it is critical to adapt a model characteristics to the ambient temperature to achieve consistent performance.

A common approach to reach an accurate model of hysteresis is to use a Preisach model and an interesting research area lies in reducing the complexity of such models. A previous paper focused on the measurement of the hysteresis response in terms of polarization P versus voltage U, through the application of a unipolar sinusoidal signal of decreasing amplitude combined with a measurement using a Sawyer-Tower circuit. A clear shift of the Preisach density with temperature was observed. To match these measurements, a simplified model is proposed. It is composed of:

  • a linear density (parameters b, d) along the diagonal of the Preisach plane and
  • a Gaussian-Gaussian density centered on the origin with two independent standard deviations.

Therefore it is proposed that the P-U response of an actuator can be modeled by five parameters. Where P is the model output, U is the voltage input and γ_αβ represents the hysteron elements that can take values from the set {0,1}. This model was applied to the experimental data using a solver. The reconstruction of the major hysteresis loop shows a good fit with the experimental data.

Several observations can be drawn. As observed previously, the linear part of the model (parameters b and d) increases with temperature. The peak value of the Gaussian distribution a increases also with temperature, but the standard deviations c1 and c2 both decrease following a similar trend.

The Preisach approach is a phenomenological model, so it is not related to physical phenomena. Nevertheless, the increase in linearity can be interpreted by the higher proportion of polarized material (intrinsic effect) while the decrease in Gaussian density can be interpreted by the higher mobility of the domain walls at high temperature (extrinsic effect).

With only five parameters, this model is simple enough to be used in real-time control systems and could lead to several benefits such as reduction of hysteresis, faster response or sensorless temperature estimation.

More about the Joint IEEE ISAF-IWATMD-PFM Conference 
The Joint IEEE ISAF-IWATMD-PFM Conference consist of three symposiums/workshops: 

  • IEEE International Symposium on Applications of Ferroelectrics (ISAF)
  • International Workshop on Acoustic Transduction Materials and Devices (IWATMD)
  • Piezoresponse Force Microscopy Workshop (PFM)

The conference aims to bring together leaders from academia, national laboratories and industrial research and development sectors, to discuss the recent advancements in the science and technology of ferroelectric and dielectric materials. The topics will range from theory and modelling of the materials to the development of new applications and devices. The conference takes place at the Georgia Institute of Technology's campus in Atlanta.

Read more about the Joint IEEE ISAF-IWATMD-PFM Conference

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