Guest Editorial

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The 14^th European Meeting on Ferroelectrics (EMF) looks back to over 50 years of its history. For the second time, the meeting took place in Switzerland after the EMF-3, which was held at the ETH Zurich in 1975, chaired by K. A Müller and W. J. Merz, and published in Ferroelectrics Volumes 12–14 (1976). This time, the meeting took place at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in July 2019, 44 years later. EPFL is the younger sister institute of ETH, celebrating its 50 years of existence in 2019. The conference venue was the new Swiss Tech Convention Center on the EPFL campus.

For the first time, EMF was joint together with the International IEEE Symposium on Applications of Ferroelectrics (ISAF), and the International Conference on Electroceramics (ICE). The idea was to extend the conference in direction of applications, which are most dynamic in the USA and in Japan. Ferroelectricity is also a topic in ICE, but more importantly, ionic point defects and their migration are central topics in ICE, and have been extensively studied for a couple of years also in ferroelectrics. In addition, two smaller workshops were part of the joint conference, the Piezosensitive atomic Force Microscopy workshop PFM, and the International Workshop on Piezoelectric MEMS (IWPM). The first one because PFM techniques play a central role in modern studies of ferroelectrics, and the second one because piezoelectricity is becoming very important in microtechnology. From the acronyms of the five joint meetings, ISAF-EMF-ICE-IWPiM-PiFM, the short name of the joint conference was derived as f²c $\pi$ ² , symbolizing a powerful conference on ferroelectrics, ceramics and piezoelectrics, hinting as well to their physical background.

      

The conference attracted 859 scientists from all over the world, and thus can be considered as a big success. The largest country delegations came from Germany and USA (100 each), followed by Japan, Switzerland, China, and South Korea. Grouping into larger entities, we count 458 participants from Europe, 252 from Asia and Australia, 106 from North America, 33 from the Near East, and 10 from South America. The distribution of given papers per country is slightly different: 95 abstracts are from the USA, 87 from Germany, 85 from China, 66 from Japan, 55 from South-Korea, 49 from France, 48 from Switzerland, and 46 from the United Kingdom. From the 935 abstracts received, 838 were scheduled in the program. The addition of the last two conferences reinforced topics on thin films, functional surfaces and nano characterization. They were well reflected in the types of exhibiting companies: Six companies can be assigned to the area of functional characterization, four to the thin film area, and an equal number to the area of atomic force microscopy. From remaining exhibitors, two represented bulk materials, and two piezo-MEMS applications.

The participants had to assign their abstracts to one of the meetings. The EMF-14 received roughly half the contributions as compared to the EMF-13 (Porto, 2015). This can be well explained by the nature of the joint meetings having some internal competition. Works on thin films and MEMS applications were partially absorbed by IWPM, studies with piezo-AFM techniques were partially presented in PAFM, and many application-oriented contributions were absorbed by ISAF. Nevertheless, the joint conference model roughly doubled the participation as compared to a simple ISAF meeting and multiplied by a factor 2.3 the number of delegates as compared to a simple EMF, as the previous one. In total, we had more scientists from Europe (458) than participants at the previous EMF (366). All these number show that there is an advantage to join conferences from time to time. Given that ISAF is in Europe every three years, and EMF has a period of 4 years, the combination ISAF-EMF can be realized only every 12 years.

        

The feedback from participants and exhibitors was excellent. We had good interactions among scientists engaged in the different activities. It became also evident that the architecture of the convention center was ideal for this purpose. One prominent scientist even wrote us that the 2019 meeting was the best EMF ever. Indeed, the meeting demonstrated very well that the field of ferroelectrics is as vital as before and is able to renew interest and activities thanks to new topics, materials, and applications.

The conference demonstrated that ferroelectricity is a very vital field, not showing signs of age as one would assume soon 100 years after its discovery. The secret of ferroelectricity lies in its wide range of phenomena on the microscopic level and of applications. In the first article published in the journal Ferroelectrics in 1970, R. E. Nettleton wrote that “Since almost any experiment which can be performed on a crystal is possible in a ferroelectric, particularly if we include specimens rendered semiconducting by doping or reduction, the subject of ferroelectricity embraces most of the solid state physics.” The aspect of applications was mention by A. von Hippel in his forward to the first issue of Ferroelectrics (1970): “In this stormy age of man’s expanding mind, science and engineering have become firm allies on the search for new knowledge and its applications”. This is even more true today, as the storm became a hurricane. He mentions the dipole ordering in ferroelectric phase transitions as a universal phenomenon that is promising deeper molecular insights and surprising uses, among which the transducers for medical applications, and dipolar ordering for memories. Müller and Merz remarked in their guest editorial of 1975, that classic problems in ferroelectrics are “still” of considerable interest. About the conference program, they underlined that they sought a balance of classical properties of ferroelectrics, physics of phase transitions, and applications related to electro-optics and holography. What changed tremendously over the last 50 years are our tools for synthesizing materials, particularly as thin films, instruments for structural and chemical analysis, techniques for functional characterization and ab-initio calculations based on density functional theory (DFT). For this reason, a refinement of knowledge in molecular phenomena in ferroelectrics, and new insights into domain wall properties were still possible during the recent years. The research on the coexistence of ferroelectricity and ferromagnetism advanced also very much due to studies at thin films and improved understanding by DFT simulations. We see that thin film structures, properties and applications are increasingly important in our field. Not only because of applications in microtechnology, but also because materials can be grown in metastable states. The trend for more thin film research is visible in the changes from EMF-13 to EMF-14: Crystals are investigated in a steady percentage of works (9%), but thin films take now a larger portion increasing from 8 to 15%.

A key word search among the titles allows for a rough comparison of f²c$\pi$ ² with EMF 2015. Ferroelectricity is without surprise the most mentioned phenomena. The mentioned material type is most frequently a ceramic. Thin films surpassed the single crystals. Issues related to domains are studied with a constant effort. Phase transitions are somewhat less mentioned in the titles. What is strongly increasing are interfaces and heterostructures (maybe somewhat overestimated due to ICE topics). BiFeO₃ is investigated more frequently. This is, however, also true for PZT, probably due to the maturity of PZT thin films for MEMS. Lead free is still a growing topic. The recently discovered ferroelectricity in thin films of hafnia and related materials is a completely new topic and not mentioned in 2015. This holds also for the piezoelectric AlScN thin films. Common point of hafnia and AlScN is that they display their desired properties only in the form of thin films. Organic materials seem to increase on a low level. Halide ferroelectrics are newly mentioned. The most investigated effect apart of ferroelectricity is piezoelectricity. Multiferroics, and coupled magnetic materials are somewhat less studied, but compete with piezoelectricity concerning the size of the research activity. The coupling to mechanical parameters is increasingly investigated. Photovoltaic and other photonic applications were very well represented at the conference (×3 with respect to 2015). The electrocaloric effect is getting more popular. Studies on phononics are increasing on a low level. We also observed an increase in microstructural issues by defects and oxygen vacancies, which is also reflected by an increased mentioning of microscopical techniques. Astonishingly, calculations from first principles decreased in the absolute numbers, and even more in the relative portion. Possibly, the field is already too much harvested.

The program committees selected excellent speakers to cover some novel insights and new trends. From the 10 plenary talks, two were selected by EMF. We mention here all of them. Jean-Marc Triscone from Geneva University (EMF) opened the plenary talks and the technical program of the joint conference with his insights in the structural and electronic coupling at oxide interfaces and induced interfacial ferroelectricity. Javier Junquera from the University of Cantabria (EMF) spoke on topological phases in ferroelectric materials, showing how to combine density functional theory with a judicious selection of the essential physics in the problem. Kenji Uchino from PennState University (ISAF) pointed out the importance of critical length scales in ferroelectrics and the fractal aspect of ferroelectric domain patterns. Yun Liu (ISAF) from the Australian National University taught us the importance of structure and phase transitions for finding new and improving existing ferroelectric materials. Uwe Schröder from Namlab (ISAF) presented a new ferroelectric material in the form of doped Hafnium Oxide thin films, its applications in nonvolatile memories, negative capacitance elements, and neuromorphic networks. Peter Mardilovich from XAAR plc, Cambridge, (IWPM) spoke about the first mass market for PZT thin film microdevices in ink jet printing. Property engineering of electroceramic materials was in the focus of Satoshi Wada’s research at the University of Yamanashi (ISAF). He spoke on the importance of interface control and strain-gradient regions. Will Chueh from Stanford University (ICE) outlined the role of point defects on the strength of metal-oxygen bonds in the lithium metal oxides. Geoffrey Beach of MIT (ICE) introduced a novel method for tuning magnetism through ionic switching. Sergei Kalinin from the Oak Ridge National Laboratory (PFM) presented results on electrochemical phenomena at surfaces of ferroelectrics and presented approaches to engage big data and deep learning in image interpretation of transmission electron microscopy.

We had several special and social activities. Twelve tutorial lectures were given by world class experts on the Sunday preceding the conference. In the evening of the same day, we had a student reception on a nice terrace overlooking the campus. An expert Jury nominated 30 PhD students before the conference to participate in the final round of a student competition award. The Jury selected 10 works for the awards, 5 for ISAF, 2 for ICE, and one for each of EMF, IWPM and PFM. In addition, we had a student pitch competition. All the prizes were given in a small ceremony during the conference dinner on Thursday evening. Last but not least, we also had a very well visited women in science event in one of the lunch breaks. As a special event of the scientific program, there was a special session on the photovoltaic effect in ferroelectrics to honor Prof. Vladimir Fridkin for his pioneering contributions to this field.

I would like to thank all who helped setting up the program, who helped in the organization, the plenary speakers as well as the invited speakers, and the tutorial instructors. Particularly, I would like to thank the program chair of EMF, Marin Alexe, and the chairs of the other meetings for their strong engagement in getting plenary and invited speakers to the conference: Geoff Brennecka and Julia Glaum from ISAF, Harry Tuller and Jennifer Rupp from ICE, Neus Domingo and Patrycja Paruch from PFM, and Isaku Kanno from IWPM. My cordial thanks go also to my colleague Dragan Damjanovic, who made an extraordinary job in putting the overall program together. Finally, I would also like to thank our university EPFL and the IEEE society for their support.

Only a minority of conference papers are published in these issues of Ferroelectrics (27 papers out of 160). However, they give an interesting representation of the meeting. We would like to express our warmest thanks to all the participants who contributed to this publication, and to the Taylor & Francis Group with Dr. George W. Taylor and Dr. Deborah J Taylor who made this issue possible. We hope that these proceedings may be useful to researchers in ferroelectrics, multiferroics, and beyond.

The next EMF is planned to take place in 2023, in Katowice, Poland. We are sure that the vast interdisciplinary frontier of ferroelectric materials and their uses will continue to produce surprising and important results, for which we are looking forward with serenity and joy.

Paul Muralt
EMF-14 Chairman
Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland