Dielectric and IR spectroscopy
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THz science and technology
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Light and neutron scattering
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Theory and simulations |
Solid-state materials science
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Liquid crystals |
About us
Main activities of Department of Dielectrics cover experimental and theoretical investigations of high-permittivity insulators like liquid crystals, ferroelectrics, multiferroics, piezoelectrics, semiconductor nanostructures, and low-loss materials.
- Dielectric and IR spectroscopy
- THz science and technology
- Light and neutron scattering
- Theory and simulations
- Solid-state materials science
- Liquid crystals
The most significant fresh scientific results of our deparment are listed in the section Highlights.
Charged domain walls in BaTiO3 crystals emerging from superdomain boundaries
Petr Bednyakov and Jirka Hlinka observed a transient domain structure with multiple superdomains whose boundaries transform into charged domain walls in BaTiO3 [Adv. Electron. Mater. 9, 2300005 (2023)]. These superdomains highlighted the inside front cover of the June issue of Advanced Electronic Materials.
Abstract: Previous experiments with barium titanate crystals [1,2] have shown that electric field applied in the vicinity of its ferroelectric phase transition can be used to introduce peculiar ferroelectric domain walls, persisting to the ambient conditions: head-to-head charged walls compensated by the 2D electron gas. The present in situ optical observations [3] allow the documentation of the early stage of this poling process in which the cubic and ferroelectric phases coexist, the latter being broken into multiple martensitic superdomains, separated by superdomain boundaries. It is revealed that the transient superdomains are subsequently converted into the regular ferroelectric domains, while the superdomain boundaries transform into the desired charged domain walls. In order to assign the observed transient domain patterns, to understand the shapes of the observed ferroelectric precipitates and their agglomerates as well as to provide the overall interpretation of the recorded domain formation process, the implications of the mechanical compatibility of the coexisting superdomain states are derived in the framework of the Wechsler–Lieberman–Read theory. These results also suggest that both the electric conductivity and interlinked motion of the superdomain boundaries and phase fronts are involved in the transport of the compensating charge carriers toward the charged domain wall location.
The inside front cover of the June issue of Advanced Electronic Materials illustrated by a transient domain structure with multiple superdomains containing bundles of stripe ferroelastic subdomains in BaTiO3 [3].
References
[1] P. S. Bednyakov, T. Sluka, A. K. Tagantsev, D. Damjanovic, N. Setter,
Formation of charged ferroelectric domain walls with controlled periodicity,
Sci. Rep. 5, 15819 (2015).
[2] P. Bednyakov, T. Sluka, A. Tagantsev, D. Damjanovic, N. Setter,
Free-carrier-compensated charged domain walls produced with super-bandgap illumination in insulating ferroelectrics,
Adv. Mater. 28, 9498 (2016).
[3] P. S. Bednyakov and J. Hlinka,
Charged domain walls in BaTiO3 crystals emerging from superdomain boundaries,
Adv. Electron. Mater. 9, 2300005 (2023).
Jan Petzelt is ranked #8 in Czech Republic among Best Materials Science Scientists
According to the 2nd edition of Research.com ranking, Jan Petzelt holds the 8th place in the Czech Republic and the overall 3564th place in the Ranking of Best Scientists in the field of Materials Science 2023.
Jan Petzelt is an internationally accepted authority in solid state physics. Throughout his long career in the Department of Dielectrics at the Institute of Physics of the Czech Academy of Sciences he has contributed to development of physics of dielectric materials. His scientific publications have more than 7000 citations (h-index 56). Since the 1990s he has focused on the investigation of application-attractive materials, particularly ferroelectric thin films and ceramics, relaxor ferroelectrics, novel ferroelectric nanocomposites with considerable dielectric properties and their broadband dielectric spectroscopy.
Top five of his most cited publications:
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Z. Kutnjak J. Petzelt, and R. Blinc,
The giant electromechanical response in ferroelectric relaxors as a critical phenomenon,
Nature 441, 956 (2006). -
S. Kamba, D. Nuzhnyy, M. Savinov, J. Šebek, J. Petzelt, J. Prokleška, R. Haumont, and J. Kreise,
Infrared and terahertz studies of polar phonons and magnetodielectric effect in multiferroic BiFeO3 ceramics,
Phys. Rev. B 75, 024403 (2007). -
J. Petzelt, T. Ostapchuk, I. Gregora, I. Rychetský, S. Hoffmann-Eifert, A. V. Pronin, Y. Yuzyuk, B. P. Gorshunov, S. Kamba, V. Bovtun, J. Pokorný, M. Savinov, V. Porokhonskyy, D. Rafaja, P. Vaněk, A. Almeida, M. R. Chaves, A. A. Volkov, M. Dressel, and R. Waser,
Dielectric, infrared, and Raman response of undoped SrTiO3 ceramics: Evidence of polar grain boundaries,
Phys. Rev. B 64, 184111 (2001). -
S.Kamba, V. Porokhonskyy, A. Pashkin, V. Bovtun, J. Petzelt, J. C. Nino, S. Trolier-McKinstry, M. T. Lanagan, and C. A. Randall,
Anomalous broad dielectric relaxation in Bi1.5Zn1.0Nb1.5O7 pyrochlore,
Phys. Rev. B 66, 054106 (2002). -
J. Hlinka, T. Ostapchuk, D. Nuzhnyy, J. Petzelt, P. Kuzel, C. Kadlec, P. Vanek, I. Ponomareva, and L. Bellaiche,
Coexistence of the phonon and relaxation soft modes in the terahertz dielectric response of tetragonal BaTiO3,
Phys. Rev. Lett. 101,167402 (2008).
About the Research.com ranking
The mission of Research.com is to create an academic platform that cares about the quality of research to inspire young researchers to contribute to the advancement of science. The 2nd edition of Research.com ranking of the best researchers in the discipline of Materials Science is based on data consolidated from multiple data sources including OpenAlex and CrossRef. The bibliometric data for evaluating the citation-based metrics were gathered on 21. 12. 2022. Position in the ranking is based on D-index (Discipline H-index) metric, which only includes papers and citation values for an examined discipline. The ranking includes only leading scientists with D-index of at least 40 for academic publications made in the area of Materials Science.
Karel Tesař received the Stanislav Hanzl award
Karel Tesař, a PhD student at the Department of Dielectrics and at the Faculty of Nuclear Sciences and Physical Engineering, won the Stanislav Hanzl award which is presented to best students of the Czech Technical University in Prague on the occasion of the International Student Day (on November 17, 2022).
The aim of the Stanislav Hanzl award is to reward students for their excellent results in studies and scientific, professional and other important student activities. The award was presented to nine students in the Bethlehem Chapel by the rector of the Czech Technical University (CTU) in Prague, doc. RNDr. Vojtěch Petráček, CSc., and doc. Antonín Pokorný, Chairman of the Board of Trustees of the Stanislav Hanzel Foundation.
The Stanislav Hanzl Foundation was founded in 1997 in honor of the first rector of the Czech Technical University (CTU) in Prague after November 1989, prof. Ing. Stanislav Hanzl, CSc. Professor Hanzl served as rector until his death in June 1996. The aim of the endowment fund is to support studies and students of study programs accredited at the faculties and university institutes of CTU in Prague. The fund receives financial resources in the form of subsidies, donations and contributions from collaborating organizations, businesses, and professional associations as well as individuals, especially former students - graduates of the faculties of CTU in Prague.
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Best three places in the FZU Photo Competition 2022 taken by our department
Alexey Bubnov won the
FZU Photo Competition 2022.
by his beautiful image of liquid crystal texture.
Manas Ranjan Parida received the 2nd place for his SEM image of V2O5 nanoflower,
Fedir Borodavka & Vladimir Pushkarev got the 3rd place for their artistic picture of a superlattice roll.
Best photos from Department of Dielectrics placed in top ten of the FZU Photo Competition 2022:
1st place, Alexey Bubnov: Observing liquid crystal textures in polarized light microscope.
2nd place, Manas Ranjan Parida: Scanning electron microscope image of V2O5 nanoflower.
3rd place, Fedir Borodavka & Vladimir Pushkarev: Artistic picture of a PbTiO3/SrTiO3 superlattice roll under a laser beam combining various experimental data (Raman, GPA, SXOM, and PFM maps).
4th place, Alexey Bubnov: Observing liquid crystal textures in polarized light microscope.
7th place, Vladimíra Novotná: When an organic material is crystalizing.
New Research Professor in Department of Dielectrics
We are happy to announce that Stanislav Kamba has received the Research Professor degree for his outstanding and o riginal scientific work in condensed matter physics, presented in his dissertation: Soft-mode spectroscopy of ferroelectrics and multiferroics.
Stanislav Kamba is a world-wide known expert in the field of high-frequency dielectric spectroscopy, especially in studies of soft phonons in ferroelectric and multiferroic materials. He made a fundamental contribution to understanding of the properties of hydrogen-bonded ferroelectrics, lead-based relaxor materials, and the mechanism of phase transitions in multiferroic materials. His dissertation, titled: Soft-mode spectroscopy of ferroelectrics and multiferroics, presents results which are outcomes of his research done and/or led by him in the Department of Dielectrics for the last 25 years.
(photo after the Czech Academy of Sciences).
About the degree Research Professor:
The scientific degree "Research Professor" (abbreviated as Res. Prof. or DSc.) was established by a resolution of the twenty-first session of
the Academy Assembly convened on December 18, 2002. The Academy awards the scientific degree of Research Professor to scientists
in recognition of their outstanding and original scientific work, contributing to the advancement of research in a specific scientific field and
characterizing the awardee as a scientist of recognizing stature.
(see more details)
Paving the way to a 3-state thermal switch using antiferroelectric Pb(Zr1-xTix)O3
We propose a novel approach of phase-control in Pb(Zr0.95Ti0.05)O3 (PZT95/5) based on the thermal behavior of its phases. Our results show the possibility to thermally switch among three states near room temperature using small temperature gradients by heating-cooling cycles at slow rates. Thus, PZT95/5 ceramics are potential materials for room temperature device applications [Acta Materialia, 119208 (2023), online].
Pb(Zr1-xTix)O3 with very high content of Zr shows an antiferroelectric ground state and possesses an exceptional property: the coexistence of several built-in structural instabilities at high temperatures. This leads to the possibility of their successive condensation on cooling to trigger a sequence of phase transitions, instead of reaching directly the antiferroelectric state, as in pure PbZrO3. This peculiar behaviour is more pronounced in compositions near the antiferroelectric morphotropic phase boundary and the tricritical point around room temperature, as Pb(Zr0.95Ti0.05)O3 (PZT 95/5), where three phases are energetically available.
Raman scattering experiments performed out of the thermodynamical equilibrium revealed a complex and hysteretic thermal behaviour of the phase transition dynamics, due to the inhomogeneous microstructure and the coexistence of regions with different phases within the samples. A way to control the thermal development of these different phases is to selectively condense the different instabilities by an external parameter such as temperature, hence creating a sequence of phase transitions instead of a direct phase transition.
Figure: Scheme of thermal switching using the three near-room-temperature phases of PZT 95/5.
Our results, obtained under many different experimental conditions and specific pre-history, suggest that ceramics with composition near PZT 95/5 are potential materials for novel 3-state thermal switches. An innovative approach of phase-control is proposed, based on the thermal behaviour of the intermediate polar states observed and using small temperature gradients by appropriate heating-cooling cycles around room temperature.
Reference:
[1] E. Buixaderas, C. Milesi-Brault, P. Vaněk, J. Kroupa, F. Craciun, F. Cordero, C. Galassi,
Peculiar Dynamics of Polar States at the Morphotropic Phase Boundary of Antiferroelectric Pb(Zr1-xTix)O3,
Acta Materialia, 119208 (2023), online.
Application of HfO2 thin films in non-volatile memories – a review
We review main factors in preparation of HfO2 thin films and their physical properties which are important for applications in high-density resistive random access memories and ferroelectric memories [Small 18, 2107575 (2022)].
Ultrathin films of HfO2 become ferroelectric although bulk crystals are paraelectric. In this review we describe how grain size, thermal stress, dopants, oxygen vacancies, film thickness, annealing process and electrodes influence dielectric properties of HfO2, which are important for applications in high-density resistive random access memories and ferroelectric memories. We also discuss how to achieve superlative performance with high-speed reliable switching, excellent endurance and retention.
Figure: Dependence of crystal structure of HfO2 on the thin film thickness, strain and electrodes.
[1] W. Banerjee, A. Kashir, and S. Kamba, Hafnium Oxide (HfO2) – A Multifunctional Oxide: A Review on the Prospect and Challenges of Hafnium Oxide in Resistive Switching and Ferroelectric Memories, Small 18, 2107575 (2022).
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Multidomain ordered metal–ferroelectric superlattices
By combination of advanced experimental techniques and phase-field simulations, we found that electric dipoles in superlattices, composed of layers of a ferroelectric material separated by thin metallic spacers, form an unusual pattern of nanoscale domains that order in three dimensions. These ferroelectric multidomain ordered superlattices exhibit an outstanding dielectric response and their engineered modulated structural and electronic properties can be controlled using electric field [Nat. Mater. 20, 495 (2021)].
Figure:
Two-dimensional base motif of the ferroelectrically ordered PbTiO3–SrRuO3 superlattices as seen by
(a-d) phase-field simulations and (e,f) transmission electron microscopy:
(a) electric polarization showing ferroelectric domain structure in two PbTiO3 layers separated by SrRuO3 spacers
(b) gradient energy density coming from domain walls and boundaries between layers,
(c-f) in-plane (exx) and out-of-plane (ezz) strain components demonstrating correlations between ferroelectric PbTiO3 layers.
The arrows in (a,b) panels show direction of electric polarization forming characteristic flux-closure patterns.
[1] M. Hadjimichael, Y. Li, E. Zatterin, G. A. Chahine, M. Conroy, K. Moore, E. N. O’ Connell, P. Ondrejkovic, P. Marton, J. Hlinka, U. Bangert, S. Leake, and P. Zubko, Metal–ferroelectric supercrystals with periodically curved metallic layers, Nat. Mater. 20, 495 (2021).
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Ferroelectric and antiferroelectric phases in liquid crystalline compounds with terphenyl in the molecular coere
We designed a new type of antiferroelectric liquid crystalline structure with terphenyl in the molecular core and two lactate units attached to the chiral chain [J. Mol. Liq. 336, 116267 (2021)].
For the series of compounds, we studied the mesomorphic properties by various experimental techniques and confirmed the phase identification by x-ray measurements. For selected homologues we proved the antiferroelectric phase with orthoconic properties existing in a wide temperature interval including the room temperatures. Valuable optical properties with the tilt angle about 45 degrees promised a big potential for applications.
Figure: Texture of the liquid crystalline compound with a terphenyl in the molecular core in antiferroelectric phase without field (left picture) and under applied electric field (right picture). The scale, orientation of polariser (P) and analyser (A) are presented. In the centre, there is a model of the studied molecule in the optimised conformation.
[1] N. Podoliak, M. Cigl, V. Hamplová, D. Pociecha, and V. Novotná, Multichiral liquid crystals based on terphenyl core laterally substituted by chlorine atom, J. Mol. Liq. 336, 116267 (2021).
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New material for 5G mobile networks
Epitaxial strained thin films of (SrTiO3)n-1(BaTiO3)1SrO were found to be a promising new material for mobile network of the 5th generation [Nature Mater. 19, 176 (2020)].
Epitaxial strained thin films of (SrTiO3)n-1(BaTiO3)1SrO were grown on DyScO3 substrates using molecular beam epitaxy [1]. The best microwave dielectric properties were discovered in samples with n= 6. Permittivity exhibits huge tuning using electric field and microwave dielectric loss is anomalously low. Unique properties were confirmed using first-principles calculations and by experimental observation of the soft mode behavior in THz region. These films are ideal for components in 5G networks.
Collaborating institutions: Prof. D.G. Schlom from the Cornell University and other American and German institutions.
Figure: Schema of crystal structures of investigated (SrTiO3)n-1(BaTiO3)1SrO films and their view in scanning transmission electron microscope. Yellow octahedra depict TiO6 layers, green and red points mark atoms of Sr and Ba.
[1] N.M. Dawley, E.J.Marksz, A.M. Hagerstrom, G.H. Olsen, M.E. Holtz, V. Goian, C. Kadlec, J. Zhang, X. Lu, J.A. Drisko, R. Uecker, S. Ganschow, C.J. Long, J.C. Booth, S. Kamba, C.J. Fennie, D.A. Muller, N.D. Orloff, D.G. Schlomk, Targeted chemical pressure yields tuneable millimetre-wave dielectric, Nature Mater. 19, 176 (2020).
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Tiling the Silicon for Added Functionality: PLD Growth of Highly Crystalline STO and PZT on Graphene Oxide-Buffered Silicon Surface
ACS Applied Materials and Interfaces 15, 6058 (2023).
Peculiar dynamics of polar states at the morphotropic phase boundary of antiferroelectric Pb(Zr1-xTix)O3
Acta Mater. 258, 119208 (2023).
Ultrafast long-distance electron-hole plasma expansion in GaAs mediated by stimulated emission and reabsorption of photons
Phys. Rev. Lett. 130, 226301 (2023).
Texture, elastic anisotropy and thermal stability of commercially pure titanium prepared by room temperature ECAP
Mater. Des. 226, 111678 (2023).
Charged domain walls in BaTiO3 crystals emerging from superdomain boundaries
Adv. Electron. Mater. 9, 2300005 (2023).
Effect of oxygen defects on microstructure, optical and vibrational properties of ScN films deposited on MgO substrate from experiment and first principles
Appl. Surf. Sci. 615, 156203 (2023).
The correlations between the molecular core structure and mesomorphic behaviour for chiral liquid crystals with several (S)-lactate groups
J. Mol. Liq. 387, 122590 (2023).
Giant permittivity in dimethylamino-terminated ferroelectric nematogens
J. Mol. Liq. 385, 122360 (2023).