Sidak V. Relaxation Phenomena and Structural Defects in Sodium Bismuth Titanate Crystals

Українська версія

Thesis for the degree of Candidate of Sciences (CSc)

State registration number

0425U000398

Thesis Registration Form

0425U000398.pdf

Applicant for

Vasyl M. Sidak

Specialization

01.04.07 - Фізика твердого тіла

Date of defense

16-01-2026

Specialized Academic Board

Д 08.051.02

Oles Honchar Dnipro National University

Essay

The performed study addresses the critical need for environmentally benign functional materials. The central focus of the work is to understand the profound impact of proper defects on the material's functional properties. Sodium-bismuth titanate Na0,5Bi0,5TiO3 (NBT) and its solid solutions Na0,5Bi0,5TiO3–BaTiO3 (NBT-BT) are considered as the promising eco-friendly can-didates for replacing lead-based PbZrxTi1−xO3 ceramics in piezo-technics. Study of NBT and NBT-BT electrical and optical properties made it possible to establish the mechanisms of relaxation phenomena and identify the nature of proper lattice de-fects. To achieve this, the temperature-frequency dependences of dielectric permit-tivity, electrical conductivity and impedance, alongside optical absorption and pho-toluminescence spectra were analyzed in NBT and NBT-BT single crystals and ce-ramics. A key methodological approach was the use of heat treatment in both air and vacuum to control the concentration of proper defects and establish a direct link be-tween the defect structure and the observed physical properties. For the first time, it has been demonstrated that the intense dielectric anomaly observed near 700 K in NBT and NBT-BT crystals is related to space-charge polar-ization at the boundaries of polar nanoregions near the transition from the tetragonal paraelectric phase to the rhombohedral ferroelectric one. The pivotal role of oxygen vacancies (VO) in this process was unequivocally proven: the anomaly was signifi-cantly suppressed by annealing in air and substantially enhanced after annealing in vacuum. A novel model was proposed to describe this relaxation anomaly, which, unlike standard models, additionally accounts for the thermal decay of polarizing entities. The model combines the Cole-Cole formalism with a corresponding kinetic equation and allows for a quantitative description of the experimental observations. This approach accurately predicts the dependence of the dielectric permittivity tem-perature and frequency behavior on experimental conditions. The electrical conductivity of NBT crystals was found to be of mixed ion-electron type. In as-grown single crystals, the sample's bulk exhibits mixed conduc-tivity, while in the near-surface layer ionic transport dominates. The latter is at-tributed to the movement of oxygen vacancies, while the electronic component is associated with electron hopping through regular titanium ions (Ti3+). It was demon-strated that the dominant charge transport mechanism can be controlled via thermal treatment. Annealing in air effectively "heals" oxygen vacancies, suppressing the ionic component and transitioning the material to a state with predominantly elec-tronic conductivity. It was established that the optical absorption and photoluminescence in NBT crystal are governed by electronic transitions within Ti3+ ions. Two distinct types of optically active centers were identified: Ti3+ ions within trigonally distorted oxygen octahedra and associated complexes (Ti3+–VO) within tetragonally distorted octahe-dra. A direct correlation between the material's optical response and its dielectric prop-erties was found, confirming their common origin in the defect subsystem. The results obtained in the dissertation deepen the understanding of the intrin-sic defects nature and the mechanisms governing the "defect structure – physical properties" relationship in NBT-based materials. The developed approaches for con-trolling the defect structure via thermal treatment provide a practical pathway to op-timize the key electrical and optical properties of these materials for their application in modern functional devices.

Thesis supervisor

Mykhailo P. Trubitsyn

Official opponents

Alexander A. Grabar
Nataliia Y. Filonenko

Research papers

1. Kruzina T. V., SIDAK V. M., Trubitsyn M. P., Popov S. A., Suchanicz J. Thermal treatment and dielectric properties of Na0,5Bi0,5TiO3 single crystal // Ferroelectrics. 2014. Vol. 462, no. 1. P. 140–144. DOI: 10.1080/00150193.2014.891411

2. Kruzina T. V., SIDAK V. M., Trubitsyn M. P., Popov S.A., Tuluka A.Yu., Suchanicz J. Impedance spectra of as-grown and heat treated Na0,5Bi0,5TiO3 crystals // Acta Physica Polonica A. 2018. Vol. 133, no. 4. P. 816–818. DOI: 10.12693/APhysPolA.133.816

3. SIDAK V. M., Trubitsyn M. P. Dielectric relaxation and the dipole defects in Na0,5Bi0,5TiO3 single crystal // Applied Nanoscience (Switzerland). 2022. Vol. 12, no. 3. P. 775–780. DOI: 10.1007/s13204-021-01712-y

4. SIDAK V.M., Trubitsyn M.P. Dielectric anomaly and space charge polarization in single crystals of Na0.5Bi0.5TiO3 and Na0.5Bi0.5TiO3 – BaTiO3. // Nanostructured Surfaces, Nanocomposites and Nanomaterials, and Their Applications. / eds. O. Fesenko, L. Yatsenko. Cham: Springer, 2023. (Springer Proceedings in Physics; vol. 296). P. 365–382. DOI: 10.1007/978-3-031-42704-6_26

5. SIDAK V. M., Trubitsyn M. P., Panchenko T. V. Dielectric relaxation induced by oxygen vacancies in Na0,5Bi0,5TiO3 ceramics // Condensed Matter Physics. 2022. Vol. 25, no. 4. Art. 43705. P. 1–10. DOI: 10.5488/CMP.25.43705

6. Panchenko Т. V., SIDAK V. M., Trubitsyn M. P. et al. Heat treatment effect on optical absorption and photoluminescence in Na0,5Bi0,5TiO3 crystals // Ukrainian Journal of Physical Optics. 2025. Vol. 26, iss. 4. Art. 04001. P. 1–12. DOI: 10.3116/16091833/Ukr.J.Phys.Opt.2025.04001

7. Duda V. M., Kruzina T. V., Popov S. O., Rutskyi O. S., SIDAK V. M., Trubitsyn M. P. Impedance relaxation in Na0,5Bi0,5TiO3 ceramics // Вісник Дніпропетровського університету. Серія: Фізика, радіоелектроніка. 2015. Т. 23, № 1. С. 100–103

8. Kruzina T. V., SIDAK V. M., Trubitsyn M. P., Popov S.A., Suchanicz J. Mechanisms of electroconductivity in Na0,5Bi0,5TiO3 single crystals // Вісник Харківського національного університету. Серія: Фізика. 2015. Вип. 23. С. 120–123

9. Kruzina T. V., Panchenko T. V., SIDAK V. M., Popov S. A., Shchetinkin V. S. Electrical and optical properties of heat treated Na0,5Bi0,5TiO3 crystals // Вісник Дніпропетровського університету. Серія: Фізика, радіоелектроніка. 2016. Т. 24, № 1. С. 106–109

10. SIDAK V. M., Tuluk A. Yu., Trubitsyn M. P., Kruzina T. V. Electrical properties of 0.87 Na0,5Bi0,5TiO3-0.13BaTiO3 single crystals // Вісник Харківського національного університету. Серія: Фізика. 2017. Вип. 27. С. 44–48

11. SIDAK V. M., Trubitsyn M. P., Kruzina T. V., Tuluk A. Yu. Impedance spectra of single crystalline 0.87Na0,5Bi0,5TiO3-0.13BaTiO3 solid solutions // Вісник Дніпропетровського університету. Серія: Фізика, радіоелектроніка. 2017. Т. 25, № 1. С. 75–78

12. SIDAK V. M., Trubitsyn M. P. Dipole defect decay and dielectric relaxation in Na₀.₅Bi₀.₅TiO₃ single crystal // Journal of Physics and Electronics. 2020. Vol. 28, no. 2. P. 87–90

13. Kruzina T. V., SIDAK V. M., Trubitsyn M. P., Popov S.A., Suchanicz J. Thermal treatment and dielectric properties of Na0,5Bi0,5TiO3 single crystal // 13th International Meeting on Ferroelectricity (IMF-13) : abstract book, Krakow, Poland, Sept. 2–6, 2013. Krakow, 2013. P. 367

14. Kruzina T. V., SIDAK V. M., Trubitsyn M. P., Popov S.A., Suchanicz J. Low Frequency Dielectric Relaxation in Na0,5Bi0,5TiO3 Single Crystal // 2014 Joint IEEE International Symposium on the Applications of Ferroelectrics (ISAF/PFM) : proceedings, University Park, PA, USA, May 12–16, 2014. University Park : IEEE, 2014

15. Kruzina T. V., SIDAK V. M., Trubitsyn M. P., Popov S. A., Suchanicz J. Electrically and optically active defects in Na0,5Bi0,5TiO3 crystals // Functional Materials and Nanotechnologies (FM&NT-2015) : book of abstracts, Vilnius, Lithuania, Oct. 5–8, 2015. Vilnius, 2015. P. 169

16. SIDAK V. M., Trubitsyn M. P. Structural Defects and Electrical Properties of Na0,5Bi0,5TiO3 Crystal // International Young Scientists Forum on Applied Physics (YSF-2015): proceedings, Dnipropetrovsk, 2015. Dnipropetrovsk IEEE, 2015. DOI: 10.1109/YSF.2015.7334239

17. Крузіна Т. В., Дуда В. М., СІДАК В. М., Трубіцин М.П., Попов С.О., Суханіч Я. Механізми електропровідності монокристалів і кераміки Na0,5Bi0,5TiO3 // Фізичні явища в твердих тілах : матеріали XII Міжнародної конференції, Харків, Україна, 1–4 грудня 2015 р. Харків, 2015. С. 171

18. Крузіна Т. В., Дуда В. М., СІДАК В. М., Трубіцин М.П., Попов С.О., Суханіч Я. Спектри імпедансу монокристалів і кераміки Na0,5Bi0,5TiO3 // VII Українська наукова конференція з фізики напівпровідників : тези доповідей, Дніпро, Україна, 26–30 вересня 2016 р. Дніпро, 2016. С. 443–444

19. Kruzina T. V., SIDAK V. M., Trubitsyn M. P., Popov S. A., Tuluk A. Yu., Suchanicz J. The electric properties of Na0,5Bi0,5TiO3 and 0.87 Na0,5Bi0,5TiO3 - 0.13BaTiO3 single crystals // International Conference on Oxide Materials for Electronic Engineering – fabrication, properties and applications (OMEE-2017) : abstract book, Lviv, Ukraine, May 29–June 2, 2017. Lviv, 2017. P. 62

20. SIDAK V. M., Trubitsyn M. P. Non-Debye dielectric relaxation in Na0,5Bi0,5TiO3 crystal // VIII International Conference “Nanotechnologies and Nanomaterials” (NANO-2020) : book of abstracts, Lviv, Ukraine, Aug. 26–27, 2020. Lviv, 2020. P. 160

21. SIDAK V. M., Trubitsyn M. P. Anomalous dielectric relaxation in Na0,5Bi0,5TiO3 // IX International Conference "Nanotechnology and Nanomaterials" (NANO-2021) : book of abstracts, Lviv, Ukraine, Aug. 25–27, 2021. Lviv, 2021. P. 148

22. СІДАК В. М., Трубіцин М. П., Панченко Т. В., Крузіна Т. В. Na0,5Bi0,5TiO3 crystal dielectric and optical properties induced by the structural defects // X Міжнародний науковий семінар «Властивості сегнетоелектричних і суперіонних систем»: тези доповідей, Ужгород, 26–27 жовтня 2021 р. Ужгород, 2021. С. 45

23. SIDAK V. M., Trubitsyn M. P. Space-charge polarization phenomena in single crystal and ceramics of bismuth sodium titanate // X International Conference "Nanotechnology and Nanomaterials" (NANO-2022): book of abstracts, Lviv, Ukraine, Aug. 25–27, 2022. Lviv, 2022. P. 160

Files

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