Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4821
V. Klimavičius, V. Klimkevicius, L. Dagys, K. Aidas, R. Makuška, V. Balevičius
The solid-state 1H and 13C NMR spectra as well as the 1H–13C cross-polarization upon magic angle spinning (CP MAS) kinetics were studied for poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA), i.e. a smart pH- and thermo-responsive polymer. The stereochemical content of PDMAEMA was determined from the complex shaped 13C MAS signal of CH3 group. The kinetic data were processed using the Hirschinger and Raya spin dynamics model that includes the complete scheme of rotating frame spinlattice relaxation pathways. The general solution was adapted for the spin cluster treatment. The earlier studied experimental CP MAS kinetics data of poly [2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), i.e. one of its quaternized form, were revisited and newly processed applying this model. The spin-lattice relaxation of protons in the rotating frame in PDMAEMA and PMETAC occurs in the same scale from one to tens of milliseconds. Very high anisotropy of spin-diffusion was found for both polymers. However, the local disorder of various spin sites in PDMAEMA is significantly higher than in PMETAC. It is characterized by the order parameters 0.71–0.77 and 0.87–0.91, respectively. The main chain in PDMAEMA is also more disordered and more flexible than in PMETAC.
{"title":"Solid-state NMR study of spin dynamics and local disorder in smart polymers: PDMAEMA","authors":"V. Klimavičius, V. Klimkevicius, L. Dagys, K. Aidas, R. Makuška, V. Balevičius","doi":"10.3952/physics.v62i4.4821","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4821","url":null,"abstract":"The solid-state 1H and 13C NMR spectra as well as the 1H–13C cross-polarization upon magic angle spinning (CP MAS) kinetics were studied for poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA), i.e. a smart pH- and thermo-responsive polymer. The stereochemical content of PDMAEMA was determined from the complex shaped 13C MAS signal of CH3 group. The kinetic data were processed using the Hirschinger and Raya spin dynamics model that includes the complete scheme of rotating frame spinlattice relaxation pathways. The general solution was adapted for the spin cluster treatment. The earlier studied experimental CP MAS kinetics data of poly [2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), i.e. one of its quaternized form, were revisited and newly processed applying this model. The spin-lattice relaxation of protons in the rotating frame in PDMAEMA and PMETAC occurs in the same scale from one to tens of milliseconds. Very high anisotropy of spin-diffusion was found for both polymers. However, the local disorder of various spin sites in PDMAEMA is significantly higher than in PMETAC. It is characterized by the order parameters 0.71–0.77 and 0.87–0.91, respectively. The main chain in PDMAEMA is also more disordered and more flexible than in PMETAC.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46629254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4823
V. Abramova, S. Abramov, V. Lukin, I. Grigelionis, L. Minkevičius, G. Valušis
Due to certain hardware limitations the quality of terahertz images is often lower than desired, which makes it difficult to extract valuable information from them. The goal of this paper is to investigate possibilities to overcome some of these limitations by means of digital image processing. The research is held on a set of images obtained at different distances from the source of terahertz radiation at 0.1 THz frequency. It is shown that the noise in these images is mixed and has a significant level of spatial correlation. For image quality enhancement a fully automatic denoising method based on the use of a discrete cosine transform with a spatially adapted spectrum is proposed. It is shown that despite an initially low spatial resolution of terahertz images and intensive noise, it provides a good noise reduction with a good preservation of edges, which allows one to noticeably improve the quality of these images and make them more convenient for visual analysis carried out by a human operator.
{"title":"Improvement of terahertz images by adaptive discrete cosine transform (DCT)-based denoising","authors":"V. Abramova, S. Abramov, V. Lukin, I. Grigelionis, L. Minkevičius, G. Valušis","doi":"10.3952/physics.v62i4.4823","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4823","url":null,"abstract":"Due to certain hardware limitations the quality of terahertz images is often lower than desired, which makes it difficult to extract valuable information from them. The goal of this paper is to investigate possibilities to overcome some of these limitations by means of digital image processing. The research is held on a set of images obtained at different distances from the source of terahertz radiation at 0.1 THz frequency. It is shown that the noise in these images is mixed and has a significant level of spatial correlation. For image quality enhancement a fully automatic denoising method based on the use of a discrete cosine transform with a spatially adapted spectrum is proposed. It is shown that despite an initially low spatial resolution of terahertz images and intensive noise, it provides a good noise reduction with a good preservation of edges, which allows one to noticeably improve the quality of these images and make them more convenient for visual analysis carried out by a human operator.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46231546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4817
A. Plyushch, D. Lewin, P. Ažubalis, V. Kalendra, A. Sokal, R. Grigalaitis, V. Shvartsman, S. Salamon, H. Wende, A. Selskis, K. Lapko, D. Lupascu, J. Banys
Multilayered phosphate bonded CoFe2O4–BaTiO3–CoFe2O4 (CBC) and BaTiO3–CoFe2O4 – BaTiO3 (BCB) multiferroic structures were formed by means of uniaxial pressing. The dielectric properties were studied in 20 Hz – 1 GHz frequency and 120–500 K temperature ranges. The complex dielectric permittivity is 15–0.17i for CBC and 22–0.04i for BCB, it is temperature- and frequency-independent below 250 K. At higher temperatures, strong dispersion appeared governed by the Maxwell–Wagner relaxation. Such behaviour is determined by the 2–2 connectivity of the sample. The highest direct magnetoelectric coupling coefficient was found for the BaTiO3–CoFe2O4–BaTiO3 structure of 0.2 mVOe–1cm–1.
{"title":"Phosphate bonded CoFe2O4–BaTiO3 layered structures: Dielectric relaxations and magnetoelectric coupling","authors":"A. Plyushch, D. Lewin, P. Ažubalis, V. Kalendra, A. Sokal, R. Grigalaitis, V. Shvartsman, S. Salamon, H. Wende, A. Selskis, K. Lapko, D. Lupascu, J. Banys","doi":"10.3952/physics.v62i4.4817","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4817","url":null,"abstract":"Multilayered phosphate bonded CoFe2O4–BaTiO3–CoFe2O4 (CBC) and BaTiO3–CoFe2O4 – BaTiO3 (BCB) multiferroic structures were formed by means of uniaxial pressing. The dielectric properties were studied in 20 Hz – 1 GHz frequency and 120–500 K temperature ranges. The complex dielectric permittivity is 15–0.17i for CBC and 22–0.04i for BCB, it is temperature- and frequency-independent below 250 K. At higher temperatures, strong dispersion appeared governed by the Maxwell–Wagner relaxation. Such behaviour is determined by the 2–2 connectivity of the sample. The highest direct magnetoelectric coupling coefficient was found for the BaTiO3–CoFe2O4–BaTiO3 structure of 0.2 mVOe–1cm–1.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44982026","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4813
Lithuanian Journal of Physics,
This year, on 30 December, is the 60th anniversary of the outstanding physicist, Vilnius University professor, academician, president of the Lithuanian Academy of Sciences Jūras Banys. J. Banys graduated with honours from the Faculty of Physics of Vilnius University in 1985, defended his doctoral thesis in 1990. In 1989–1990, he worked at a professor Mike Glazer’s laboratory at the University of Oxford (UK), studying the structural properties of ferroelectric crystals using X-ray diffraction methods. In 1993–1995, after receiving Alexander von Humboldt scholarship, he worked at the University of Leipzig, where he studied the local dynamics of phase transitions using electron paramagnetic spectroscopy. After returning to his Alma Mater, J. Banys took charge of the Laboratory of Microwave Spectroscopy, turning it into a modern centre for the study of the dielectric properties of ferroelectric materials. Over the years, he assembled here a group of highly qualified scientists who perform scientific experiments using unique materials developed in well-known foreign and Lithuanian laboratories. In 2000, J. Banys successfully defended his habilitation thesis, and in 2003 the title of Vilnius University professor was awarded to him.
{"title":"Dedication to Professor Jūras Banys","authors":"Lithuanian Journal of Physics,","doi":"10.3952/physics.v62i4.4813","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4813","url":null,"abstract":"This year, on 30 December, is the 60th anniversary of the outstanding physicist, Vilnius University professor, academician, president of the Lithuanian Academy of Sciences Jūras Banys. J. Banys graduated with honours from the Faculty of Physics of Vilnius University in 1985, defended his doctoral thesis in 1990. In 1989–1990, he worked at a professor Mike Glazer’s laboratory at the University of Oxford (UK), studying the structural properties of ferroelectric crystals using X-ray diffraction methods. In 1993–1995, after receiving Alexander von Humboldt scholarship, he worked at the University of Leipzig, where he studied the local dynamics of phase transitions using electron paramagnetic spectroscopy. After returning to his Alma Mater, J. Banys took charge of the Laboratory of Microwave Spectroscopy, turning it into a modern centre for the study of the dielectric properties of ferroelectric materials. Over the years, he assembled here a group of highly qualified scientists who perform scientific experiments using unique materials developed in well-known foreign and Lithuanian laboratories. In 2000, J. Banys successfully defended his habilitation thesis, and in 2003 the title of Vilnius University professor was awarded to him.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"1 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41657333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4824
S. Rudys, S. Balčiu̅nas, C. Vollinger, J. Banys, V. Kalendra
Ferrites are usually used in accelerators for tuning radiofrequency (RF) cavities and in nonreciprocal devices controlling the power flow in RF accelerating systems. The conventional parallel‐biased Ni Zn ferrites employed for varying the frequency of accelerating cavities have the disadvantage of high saturation magnetization (4πMs). Application of the transversely biased yttrium iron garnet (YIG) material in RF tuners promises a significant reduction of power loss compared with systems that use the longitudinal bias. To inject the beam and extract the beam out of the CERN accelerator rings the fast kicker magnets made from ferrite materials must be used. Power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. Investigation of the ferrite electromagnetic properties of materials up to the GHz frequency range is essential for a correct impedance evaluation. This report summarizes an approach for deriving electromagnetic properties as a function of both frequency and temperature of the AL-800 garnet material. This information will be useful for simulating ferrite behaviour under realistic operating conditions.
{"title":"Investigation of dielectric and magnetic properties of AL-800 ferrite","authors":"S. Rudys, S. Balčiu̅nas, C. Vollinger, J. Banys, V. Kalendra","doi":"10.3952/physics.v62i4.4824","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4824","url":null,"abstract":"Ferrites are usually used in accelerators for tuning radiofrequency (RF) cavities and in nonreciprocal devices controlling the power flow in RF accelerating systems. The conventional parallel‐biased Ni Zn ferrites employed for varying the frequency of accelerating cavities have the disadvantage of high saturation magnetization (4πMs). Application of the transversely biased yttrium iron garnet (YIG) material in RF tuners promises a significant reduction of power loss compared with systems that use the longitudinal bias. To inject the beam and extract the beam out of the CERN accelerator rings the fast kicker magnets made from ferrite materials must be used. Power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. Investigation of the ferrite electromagnetic properties of materials up to the GHz frequency range is essential for a correct impedance evaluation. This report summarizes an approach for deriving electromagnetic properties as a function of both frequency and temperature of the AL-800 garnet material. This information will be useful for simulating ferrite behaviour under realistic operating conditions.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47219286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4814
P. Peksa, A. Sieradzki
The metal–organic frameworks (MOFs) crystallizing in a perovskite-like architecture became extremely interesting for scientists due to a variety of applications including memory devices, energy conversion and drug delivery. These compounds are constructed from a metal–oxygen or metal–nitrogen octahedral coordinated by organic ligands. They exhibit various interesting properties due to their hybrid organic–inorganic nature. However, ferroelectric MOFs still remain scarce and the topic of ferroelectricity raises a lot of controversies. In this article, we will discuss the actual state of knowledge of these specific compounds with a focus on ferroelectric properties. We will try to create an order out of the current confusion that followed attributing ferroelectric properties to metal–formate frameworks without a direct proof.
{"title":"Controversy on the ferroelectricity in metal–formate frameworks","authors":"P. Peksa, A. Sieradzki","doi":"10.3952/physics.v62i4.4814","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4814","url":null,"abstract":"The metal–organic frameworks (MOFs) crystallizing in a perovskite-like architecture became extremely interesting for scientists due to a variety of applications including memory devices, energy conversion and drug delivery. These compounds are constructed from a metal–oxygen or metal–nitrogen octahedral coordinated by organic ligands. They exhibit various interesting properties due to their hybrid organic–inorganic nature. However, ferroelectric MOFs still remain scarce and the topic of ferroelectricity raises a lot of controversies. In this article, we will discuss the actual state of knowledge of these specific compounds with a focus on ferroelectric properties. We will try to create an order out of the current confusion that followed attributing ferroelectric properties to metal–formate frameworks without a direct proof.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44139660","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4825
R. Grigalaitis, R. Šalaševičius, J. Banys, M. V. Vijatović Petrović, A. Dzunuzovic, M. Zaghete, G. F. Teixeira, B. Stojanović
Flexible multiferroic composite films are perspective materials for sensors, actuators and similar components of wearable and stretchable devices. Here we present the study of functional properties of flexible composites prepared by embedding nickel zinc ferrite and barium titanate powder into polyvinylidene fluoride (PVDF) polymer optimizing the ratio of polymer and fillers to get the best flexibility and functionality. ATR-FTIR analysis revealed that hot pressing of the flexible films caused a transformation of about 38% of the electro-inactive PVDF α phase into electrically active β and γ phases. Broadband dielectric spectroscopy revealed two relaxation processes responsible for PVDF and space charge relaxations. Activation energies of both processes and the freezing temperature of PVDF to the glass phase were estimated for all films. Ferroelectric measurements have shown unsaturated hysteresis loops for all samples, although the clear dependence of the amount of the electrically active phase on polarization values of composites is visible.
{"title":"Functional properties of PVDF-based NZF-BT flexible films","authors":"R. Grigalaitis, R. Šalaševičius, J. Banys, M. V. Vijatović Petrović, A. Dzunuzovic, M. Zaghete, G. F. Teixeira, B. Stojanović","doi":"10.3952/physics.v62i4.4825","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4825","url":null,"abstract":"Flexible multiferroic composite films are perspective materials for sensors, actuators and similar components of wearable and stretchable devices. Here we present the study of functional properties of flexible composites prepared by embedding nickel zinc ferrite and barium titanate powder into polyvinylidene fluoride (PVDF) polymer optimizing the ratio of polymer and fillers to get the best flexibility and functionality. ATR-FTIR analysis revealed that hot pressing of the flexible films caused a transformation of about 38% of the electro-inactive PVDF α phase into electrically active β and γ phases. Broadband dielectric spectroscopy revealed two relaxation processes responsible for PVDF and space charge relaxations. Activation energies of both processes and the freezing temperature of PVDF to the glass phase were estimated for all films. Ferroelectric measurements have shown unsaturated hysteresis loops for all samples, although the clear dependence of the amount of the electrically active phase on polarization values of composites is visible.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45753581","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4826
E. Kazakevičius, A. Žalga, V. Kavaliukė, S. Daugėla, T. Šalkus, A. Kežionis
Li0.4La0.56TiO3 (LLTO) lithium-ion conducting solid electrolyte has been synthesized by aqueous sol-gel synthesis method. The free standing and alumina substrate supported thick films have been prepared from the obtained powder by tape casting. The films and bulk ceramics were studied by impedance spectroscopy in the frequency range from 10 Hz to 10 GHz. The equivalent circuit modelling was implemented in order to determine the electrical parameters of LLTO films and ceramics. The free standing LLTO films grain conductivity was found to be similar to the one of ceramic sample, while the grain boundary conductivity of the free standing film was slightly higher compared to LLTO ceramics.
{"title":"Electrical properties of LLTO thick films","authors":"E. Kazakevičius, A. Žalga, V. Kavaliukė, S. Daugėla, T. Šalkus, A. Kežionis","doi":"10.3952/physics.v62i4.4826","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4826","url":null,"abstract":"Li0.4La0.56TiO3 (LLTO) lithium-ion conducting solid electrolyte has been synthesized by aqueous sol-gel synthesis method. The free standing and alumina substrate supported thick films have been prepared from the obtained powder by tape casting. The films and bulk ceramics were studied by impedance spectroscopy in the frequency range from 10 Hz to 10 GHz. The equivalent circuit modelling was implemented in order to determine the electrical parameters of LLTO films and ceramics. The free standing LLTO films grain conductivity was found to be similar to the one of ceramic sample, while the grain boundary conductivity of the free standing film was slightly higher compared to LLTO ceramics.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41709976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4816
S. Svirskas, T. Kudrevičius, E. Birks, M. Dunce, A. Sternbergs, C. Huang, J. Banys
In this paper, we present the dielectric and piezoelectric properties of tetragonal 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 modified with NaNbO3 ((1-x)[0.8Na0.5Bi0.5TiO3-0.2BaTiO3]-xNaNbO3). Our experimental study has revealed that the ferroelectric phase in these compositions is suppressed with the increase of sodium niobate concentration. A broad anomaly, resembling relaxor ferroelectrics, appears in the 325–450 K temperature interval. The investigation of the electric field dependence of polarization has indicated that the double hysteresis loop behaviour is characteristic of the modified compositions, which is associated with the 1st order phase transition under the applied electric field. The experiments below room temperature have revealed that the range of stability of the ferroelectric phase is shifted to lower temperatures upon the increase of sodium niobate concentration. The electromechanical displacement in the modified compositions shows a similar maximum displacement in the whole concentration range. The electromechanical response in 0.8Na0.5B0.5TiO3-0.2BaTiO3 solid solutions is due to the piezoelectric effect, while, in the mixed compositions, it is related to the jump-like change of the lattice constants in the vicinity of electric fieldinduced 1st order phase transition.
{"title":"Dielectric and piezoelectric properties of 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 modified with sodium niobate","authors":"S. Svirskas, T. Kudrevičius, E. Birks, M. Dunce, A. Sternbergs, C. Huang, J. Banys","doi":"10.3952/physics.v62i4.4816","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4816","url":null,"abstract":"In this paper, we present the dielectric and piezoelectric properties of tetragonal 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 modified with NaNbO3 ((1-x)[0.8Na0.5Bi0.5TiO3-0.2BaTiO3]-xNaNbO3). Our experimental study has revealed that the ferroelectric phase in these compositions is suppressed with the increase of sodium niobate concentration. A broad anomaly, resembling relaxor ferroelectrics, appears in the 325–450 K temperature interval. The investigation of the electric field dependence of polarization has indicated that the double hysteresis loop behaviour is characteristic of the modified compositions, which is associated with the 1st order phase transition under the applied electric field. The experiments below room temperature have revealed that the range of stability of the ferroelectric phase is shifted to lower temperatures upon the increase of sodium niobate concentration. The electromechanical displacement in the modified compositions shows a similar maximum displacement in the whole concentration range. The electromechanical response in 0.8Na0.5B0.5TiO3-0.2BaTiO3 solid solutions is due to the piezoelectric effect, while, in the mixed compositions, it is related to the jump-like change of the lattice constants in the vicinity of electric fieldinduced 1st order phase transition.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42763842","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-10DOI: 10.3952/physics.v62i4.4822
D. Vizbaras, K. Ikamas, S. Pralgauskaitė, J. Matukas, A. Generalov, A. Lisauskas
This contribution presents the results of investigations performed on monolayer graphene field effect transistor- based (GFET-based) terahertz detectors. We have implemented three different types of planar antennae: a bowtie, a bow-tie with transmission lines and a slot-disc, allowing us to realize different conditions for high-frequency impedance matching. We present a semi-empirical model which uses physical parameters derived from electrical characterization results of devices and electrodynamic characteristics of antennae, allowing us to predict THz responsivity. Model predictions have been compared with the responsivity measurements performed at room temperature in a frequency range from 50 to 1250 GHz. Good agreement between the model predictions and experimental results implies the eligibility of a distributed resistive mixing approximation for GFET. In addition, the device stability, the temperature dependence and the origin of noise in the transistor channel have been investigated. Finally, to the best of our knowledge, we demonstrate the record performance values for room temperature graphene-based terahertz detectors: 80V/W optical responsivity without the normalization to the antenna effective area and a noise equivalent power of 111 pW/√ — Hz at 336 GHz.
{"title":"Optimization of terahertz detectors based on graphene field effect transistors by high impedance antennae","authors":"D. Vizbaras, K. Ikamas, S. Pralgauskaitė, J. Matukas, A. Generalov, A. Lisauskas","doi":"10.3952/physics.v62i4.4822","DOIUrl":"https://doi.org/10.3952/physics.v62i4.4822","url":null,"abstract":"This contribution presents the results of investigations performed on monolayer graphene field effect transistor- based (GFET-based) terahertz detectors. We have implemented three different types of planar antennae: a bowtie, a bow-tie with transmission lines and a slot-disc, allowing us to realize different conditions for high-frequency impedance matching. We present a semi-empirical model which uses physical parameters derived from electrical characterization results of devices and electrodynamic characteristics of antennae, allowing us to predict THz responsivity. Model predictions have been compared with the responsivity measurements performed at room temperature in a frequency range from 50 to 1250 GHz. Good agreement between the model predictions and experimental results implies the eligibility of a distributed resistive mixing approximation for GFET. In addition, the device stability, the temperature dependence and the origin of noise in the transistor channel have been investigated. Finally, to the best of our knowledge, we demonstrate the record performance values for room temperature graphene-based terahertz detectors: 80V/W optical responsivity without the normalization to the antenna effective area and a noise equivalent power of 111 pW/√ — Hz at 336 GHz.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49160862","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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