28 results on '"pyroelectric current"'
Search Results
2. Dielectric ordering of water molecules in the dipole lattice of potassium hexacyanoferrate(II) trihydrate.
- Author
-
Novik, Olga D., Malyshkina, Inna A., and Gavrilova, Nadezhda D.
- Subjects
- *
POTENTIAL barrier , *DIELECTRICS , *MOLECULES , *MICROWAVE heating , *WATER clusters , *OCTAHEDRA - Abstract
The structure of potassium hexacyanoferrate(II) trihydrate (yellow prussiate) contains layers of water molecules between the layers of potassium and ferrocyanide octahedra. When the temperature drops down to 120 K, the water molecules have a tendency to rearrange. The movement of protons in molecular and individual rings occurs in a coordinated manner. The asymmetry of the ring environment leads to a significant decrease of the double-well potential barrier. The theory of coherent correlated motions of protons allows to explain the discreteness of the observed temperature anomalies of dielectric permittivity ε, thermally stimulated depolarization current j, and pyroelectric coefficient γ. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
3. Photoinduced Persistent Polarization Change in a Spin Transition Crystal.
- Author
-
Su, Sheng‐Qun, Wu, Shu‐Qi, Huang, Yu‐Bo, Xu, Wen‐Huang, Gao, Kai‐Ge, Okazawa, Atsushi, Okajima, Hajime, Sakamoto, Akira, Kanegawa, Shinji, and Sato, Osamu
- Subjects
- *
SPIN crossover , *SPIN polarization , *ELECTRONIC excitation , *CRYSTALS , *INFRARED spectra - Abstract
Using light as a local heat source to induce a temporary pyroelectric current is widely recognized as an effective way to control the polarization of crystalline materials. In contrast, harnessing light directly to modulate the polarization of a crystal via excitation of the electronic bands remains less explored. In this study, we report an FeII spin crossover crystal that exhibits photoinduced macroscopic polarization change upon excitation by green light. When the excited crystal relaxes to the ground state, the corresponding pyroelectric current can be detected. An analysis of the structures, magnetic properties and the Mössbauer and infrared spectra of the complex, supported by calculations, revealed that the polarization change is dictated by the directional relative movement of ions during the spin transition process. The spin transition and polarization change occur simultaneously in response to light stimulus, which demonstrates the enormous potential of polar spin crossover systems in the field of optoelectronic materials. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
4. The magnetoelectric effect in LiFePO4 – revisited
- Author
-
Fogh, Ellen, Klemke, Bastian, Pages, Alexandre, Li, Jiying, Vaknin, David, Rønnow, Henrik M., Christensen, Niels B., Toft-Petersen, Rasmus, Fogh, Ellen, Klemke, Bastian, Pages, Alexandre, Li, Jiying, Vaknin, David, Rønnow, Henrik M., Christensen, Niels B., and Toft-Petersen, Rasmus
- Abstract
We study the magnetoelectric effect in LiFePO4 using the pyrocurrent method to determine the magnetic-field-induced electric polarization as a function of temperature for various applied magnetic field strengths. We discover a diagonal magnetoelectric tensor element not previously reported. This new coupling reflects the emergence of an electric polarization along a induced by a magnetic field along the same direction and is consistent with the symmetry-imposed requirements for the small canting components of the magnetic ground state reported for this compound. Our observation is thus further evidence for a ground state which is not supported by the space group Pnma as originally assigned to LiFePO4.
- Published
- 2023
5. Effect of gadolinium on the dielectric and pyroelectric behavior of Ba(Zr0.52Ti0.48)O3 ceramics.
- Author
-
Sagar, Raghavendra and Raibagkar, R. L.
- Subjects
- *
GADOLINIUM , *BARIUM , *CERAMICS , *BARIUM titanate , *CRYSTAL symmetry , *DIELECTRICS , *CURIE temperature - Abstract
The microstructure, dielectric and pyroelectric properties of pure and Gd3+- doped barium zirconium titanate in the form of Ba(Zr0.52Ti0.48)O3 and (Ba1-xGdx)(Zr0.52Ti0.48)O3 (x = 0.1 and 0.2) were studied in this work. These ceramics were synthesized from solid state reaction method at 1050 °C. The patterns obtained from x-ray diffraction revealed the formation of perovskite phase with tetragonal crystal symmetry. As the concentration of Gd-ion increased, the value of temperature dependent dielectric constant varied whereas the Curie temperature of the ceramics shifted towards higher temperature side. The ceramic sample doped with Gd = 0.1 exhibited diffuse phase transition whereas other one showed relaxor like behavior. This result is attributed to unsystematic decrease in average grain size due to doping of Gd-ions. The temperature dependent pyroelectric current was negative at ∼150 °C for pure ceramics and at ∼200 °C for Gd-doped ceramics. This negative pyroelectric current represents the primary pyroelectric effect within that temperature. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
6. Characterisation of Pyroelectric Materials
- Author
-
Whatmore, Roger, Cain, Markys G., Series editor, Tesař, Jiří, Series editor, and van Veghel, Marijn, Series editor
- Published
- 2014
- Full Text
- View/download PDF
7. The magnetoelectric effect in LiFePO4 – revisited
- Author
-
Ellen Fogh, Bastian Klemke, Alexandre Pages, Jiying Li, David Vaknin, Henrik M. Rønnow, Niels B. Christensen, and Rasmus Toft-Petersen
- Subjects
Magnetic symmetry ,Magnetoelectric effect ,Pyroelectric current ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Phase transition - Abstract
We study the magnetoelectric effect in LiFePO4 using the pyrocurrent method to determine the magnetic-field-induced electric polarization as a function of temperature for various applied magnetic field strengths. We discover a diagonal magnetoelectric tensor element not previously reported. This new coupling reflects the emergence of an electric polarization along a induced by a magnetic field along the same direction and is consistent with the symmetry-imposed requirements for the small canting components of the magnetic ground state reported for this compound. Our observation is thus further evidence for a ground state which is not supported by the space group Pnma as originally assigned to LiFePO4.
- Published
- 2023
- Full Text
- View/download PDF
8. Gate-Induced Thermally Stimulated Current on the Ferroelectric-like Dielectric Properties of (BEDT-TTF)(TCNQ) Crystalline Field Effect Transistor
- Author
-
Kazuhiro Kudo, Masakazu Nakamura, Hiroshi Yamauchi, Shigekazu Kuniyoshi, Mitsutoshi Hanada, and Masatoshi Sakai
- Subjects
ferroelectricity ,pyroelectric current ,field effect transistor ,Mott insulator ,charge order ,Crystallography ,QD901-999 - Abstract
A gate-induced thermally stimulated current (TSC) on β′-(BEDT-TTF)(TCNQ) crystalline FET were conducted to elucidate the previously observed ferroelectric-like behaviors. TSC which is symmetric for the polarization of an applied VPG and has a peak at around 285 K was assigned as a pyroelectric current. By integrating the pyroelectric current, temperature dependence of the remnant polarization charge was obtained and the existence of the ferroelectric phase transition at 285 K was clearly demonstrated. We have tentatively concluded that the phase transition between dimer Mott insulator and charge ordered phase occurred at around the interface of organic crystal and substrate.
- Published
- 2012
- Full Text
- View/download PDF
9. Piezoelectric temperature coefficient of transverse resonance mode and thermal depoling investigations on (Pb,Ca)TiO 3 solid solutions.
- Author
-
Estrada, F. R., Milton, F. P., Eiras, J. A., and Garcia, D.
- Subjects
- *
PIEZOELECTRIC materials , *TEMPERATURE coefficient of electric resistance , *ELECTROMECHANICAL effects , *COUPLING constants , *HARMONIC oscillators - Abstract
This work uses the electromechanical resonance technique to investigate the piezoelectric properties of Pb0.55Ca0.45TiO3ceramics as a function of temperature. The elastic compliance coefficient,s11E, and the transverse electromechanical coupling factor,k31, were calculated based on the harmonic oscillator model of piezoelectric vibrating sample. In addition to the analysis of the temperature dependence of the piezoelectric response, the thermal depoling current and the real and imaginary parts of the dielectric permittivity as a function of the temperature were investigated. The thermal stability of the piezoelectric response was determined and the non-accordance of the temperature anomalies ofk31, s11E, dielectric and pyroelectric coefficients were discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
10. Identification of intrinsic deep level defects responsible for electret behavior in TlGaSe2 layered semiconductor.
- Author
-
Seyidov, MirHasan Yu., Mikailzade, Faik A., Uzun, Talip, Odrinsky, Andrei P., Yakar, Emin, Aliyeva, Vafa B., Babayev, Sardar S., and Mammadov, Tofig G.
- Subjects
- *
ELECTRETS , *THALLIUM compounds , *PYROELECTRICITY , *POLARITY (Chemistry) , *FERROELECTRIC semiconductors , *ELECTRIC fields - Abstract
Unusual behavior of pyroelectric current signal polarity near the Curie point ( T c ) was observed for TlGaSe 2 a ferroelectric-semiconductor. It has been revealed that the polarity of the spontaneous polarization near T c depends on the sample poling prehistory. In particular, applying an external electric field only in the temperature range of the paraelectric state during cooling regime in darkness brought to the depolarization current at T c with the sign opposite to the external field polarity. Otherwise, if the sample was poled in the temperature interval of the incommensurate phase, pyroelectric current exhibits a peak at T c with the polarity that is the same as for the external poling electric field. These observations indicate that internal electric field is present in the bulk and near-surface layer regions of the electrically poled single crystal TlGaSe 2 . Possible mechanisms and origins responsible for the internal electric fields in TlGaSe 2 are discussed. It is shown that the formation of internal electric fields in TlGaSe 2 is due to charging of intrinsic native defects during the poling process. Characteristics of electrically active intrinsic defects in TlGaSe 2 were investigated by using of Photo-Induced Current Transient Spectroscopy (PICTS) technique. Six deep defect levels in the band gap of TlGaSe 2 were determined, which were localized both in the bulk and on the surface of the sample and could be electrically charged. The correlation between polarization effects and PICTS results has been established. It was shown that native deep defects (A3–A6) localized in the bulk of crystal are responsible for hetero-charge formation and negative sign of the pyroelectric current peak observed around the Curie temperature after poling the sample in the temperature intervals well above T c . It was also shown that the positive sign pyrocurrent observed near the Curie point is attributed to the homo-charge formed by native A2-trapping centers which are localized near the surface region of TlGaSe 2 . Native deep level trap having an activation energy of 0.26 eV and the capture cross section of 2.8×10 −13 cm 2 were established for A2 from PICTS measurements. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
11. Magnetodielectric Effect in Eu0.75Y0.25MnO3.
- Author
-
Gupta, Surbhi, Saha, J., Kaushik, S. D., Patnaik, S., Siruguri, V., and Sathe, V. G.
- Subjects
- *
FERROELECTRICITY , *MAGNETIC properties of rare earth metals , *MAGNETIC transitions , *PERMITTIVITY , *PYROELECTRICITY , *MAGNETIZATION - Abstract
In this work, we have studied the structural, magnetic and ferroelectric properties of Eu1-xYxMnO3 (x=0.25) sample prepared by solid state route. From magnetization measurement, we observed two magnetic transitions at T=47K and 22K. Temperature dependence dielectric constant (ε) shows transition at ~22K but not at higher magnetic ordering temperature, and as a function of field, there occurs a shift of ε at higher temperature. Also in the pyroelectric currrent measurement we observed transitions ~20K which is very close to the magnetic transitions. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
12. Magnetodielectric Effect in Eu0.75Y0.25MnO3.
- Author
-
Gupta, Surbhi, Saha, J., Kaushik, S. D., Patnaik, S., Siruguri, V., and Sathe, V. G.
- Subjects
FERROELECTRICITY ,MAGNETIC properties of rare earth metals ,MAGNETIC transitions ,PERMITTIVITY ,PYROELECTRICITY ,MAGNETIZATION - Abstract
In this work, we have studied the structural, magnetic and ferroelectric properties of Eu
1-x Yx MnO3 (x=0.25) sample prepared by solid state route. From magnetization measurement, we observed two magnetic transitions at T=47K and 22K. Temperature dependence dielectric constant (ε) shows transition at ~22K but not at higher magnetic ordering temperature, and as a function of field, there occurs a shift of ε at higher temperature. Also in the pyroelectric currrent measurement we observed transitions ~20K which is very close to the magnetic transitions. [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
13. The magnetoelectric effect in LiFePO[formula omitted] – revisited.
- Author
-
Fogh, Ellen, Klemke, Bastian, Pages, Alexandre, Li, Jiying, Vaknin, David, Rønnow, Henrik M., Christensen, Niels B., and Toft-Petersen, Rasmus
- Subjects
- *
MAGNETOELECTRIC effect , *POLARIZATION (Electricity) , *MAGNETIC flux density , *CRYSTAL symmetry , *INDUCED polarization , *FERROELECTRICITY - Abstract
We study the magnetoelectric effect in LiFePO 4 using the pyrocurrent method to determine the magnetic-field-induced electric polarization as a function of temperature for various applied magnetic field strengths. We discover a diagonal magnetoelectric tensor element not previously reported. This new coupling reflects the emergence of an electric polarization along a induced by a magnetic field along the same direction and is consistent with the symmetry-imposed requirements for the small canting components of the magnetic ground state reported for this compound. Our observation is thus further evidence for a ground state which is not supported by the space group Pnma as originally assigned to LiFePO 4. • Discovery of new magnetoelectric coupling in LiFePO 4. • The magnetic ground state of LiFePO 4 is non-collinear. • The crystal symmetry of LiFePO 4 is likely lower than the originally proposed orthorhombic symmetry. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
14. Evaluation of the pyroelectric response of embedded piezoelectrics by means of a Nyquist plot.
- Author
-
Suchaneck, G., Eydam, A., Gerlach, G., Gude, M., Weber, T., and Winkler, A.
- Abstract
In this work, we evaluate the pyroelectric response of PZT plates and rods embedded in epoxy resin, low temperature cofired ceramics and polyamide by measuring the pyroelectric current spectrum originated by temperature oscillations generated by illuminating the sample surface with a square-wave-modulated laser beam. Transfer functions H(iω) describing amplitude attenuation and phase lag at each modulation frequency were analyzed by means of a Nyquist plot. Changes in pyroelectric current amplitude and phase produced by small periodic perturbations around the equilibrium are related to thermal losses governing the return of the system to the equilibrium. This allows evaluating the thermal contact of PZT with the embedding material. [ABSTRACT FROM PUBLISHER]
- Published
- 2013
- Full Text
- View/download PDF
15. The influence “heating-cooling” process rate on temperature hysteresis of ferroelectric capasitor structures.
- Author
-
Dedyk, A. I., Pavlova, Yu. V., Semenov, A. A., Eskov, A., Beliavskiy, P. Yu., Mylnikov, I. L., Pakhomov, O. V., Starkov, A. S., and Starkov, I. A.
- Abstract
We have investigated the influence of the time mode of cooling, electric field and electroconductivity on the thermal hysteresis in capacitor structures based on ceramics Ba0.55Sr0,45TiO3 with 12 wt.% magnesium-containing supplements. Different mechanisms of the appearance of thermal hysteresis are discussed. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
16. The Influence of the “Heating–Cooling” Process Rate on the Temperature Hysteresis of Ferroelectric Capacitor Structures.
- Author
-
Dedyk, A. I., Pavlova, Yu. V., Semenov, A. A., Es’kov, A. V., Beliavskiy, P. Yu., Mylnikov, I. L., Pakhomov, O. V., Starkov, A. S., and Starkov, I. A.
- Subjects
- *
FERROELECTRIC capacitors , *HEATING , *COOLING , *TEMPERATURE effect , *HYSTERESIS , *BARIUM compounds , *CERAMIC metals - Abstract
The influence of the time mode of cooling, electric field and electrical conductivity on the thermal hysteresis loops in capacitor structures based on Ba0.55Sr0,45TiO3(BST) ceramics with 12 wt.% magnesium orthotitanate Mg2TiO4(BSTM) has been studied. The values of pyroelectric coefficients of the BSTM ceramics in the paraelectric phase were found to be between 2–8 · 10–4C / (m2·K). The temperature hysteresis in the absence of an external electric field is caused by the pyroelectric effect. Different mechanisms responsible for the appearance of the thermal hysteresis are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
17. Gate-Induced Thermally Stimulated Current on the Ferroelectric-like Dielectric Properties of (BEDT-TTF)(TCNQ) Crystalline Field Effect Transistor.
- Author
-
Sakai, Masatoshi, Hanada, Mitsutoshi, Kuniyoshi, Shigekazu, Yamauchi, Hiroshi, Nakamura, Masakazu, and Kudo, Kazuhiro
- Subjects
ELECTRIC currents ,FIELD-effect transistors ,PYROELECTRICITY ,POLARIZATION (Electricity) ,DIMERS ,FERROELECTRICITY - Abstract
A gate-induced thermally stimulated current (TSC) on 7beta;1-(BEDT-TTF)(TCNQ) crystalline FET were conducted to elucidate the previously observed ferroelectric-like behaviors. TSC which is symmetric for the polarization of an applied V
G P and has a peak at around 285 K was assigned as a pyroelectric current. By integrating the pyroelectric current, temperature dependence of the remnant polarization charge was obtained and the existence of the ferroelectric phase transition at 285 K was clearly demonstrated. We have tentatively concluded that the phase transition between dimer Mott insulator and charge ordered phase occurred at around the interface of organic crystal and substrate. [ABSTRACT FROM AUTHOR]- Published
- 2012
- Full Text
- View/download PDF
18. Polar properties of nominally pure polarized TGS crystals.
- Author
-
Kushnarev, P., Maslovskaya, A., and Baryshnikov, S.
- Subjects
- *
TRIGLYCINE sulfate , *FERROELECTRIC crystals , *POLARIZATION (Electricity) , *ELECTRIC fields , *FREDHOLM equations - Abstract
Using the method of dynamic pyroeffect, polar properties of surface layers of nominally pure triglycinesulfate (TGS) crystals prepolarized in an electrostatic field are experimentally investigated. The results on the pyrocoefficient distribution over the crystal thickness modeled using the experimental dependences are reported. The model relies on the solution to the first-order integral Fredholm equation by the method of Tikhonov's regularization. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
19. Effect of Polarization State on Photovoltaic Properties of Ferroelectric Semiconductor Sn2P2S6 Films.
- Author
-
Bogomolov, A. A., Solnyshkin, A. V., Troshkin, A. S., Raevsky, I. P., Sandjiev, D. N., and Shonov, V. Yu.
- Subjects
- *
PYROELECTRICITY , *PHOTOVOLTAIC effect , *SEMICONDUCTOR films , *ELECTRIC fields , *FERROELECTRIC crystals - Abstract
In this work, the experimental results of pyroelectric and photovoltaic responses of semiconductor-ferroelectric Sn2P2S6 films are presented for both preliminary polarized samples and films under external electric field. The measurements were carried out in short-circuit conditions under illumination of the Al/Sn2P2S6/Al structure by modulated laser light with λ = 6328 Å. It is shown that varying the intensity of monochromatic laser irradiation by focusing enables to separate the pyroelectric and photovoltaic responses of ferroelectric semiconductors. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
20. A Large-Area PVDF Pyroelectric Sensor for CO 2 Laser Beam Alignment.
- Author
-
Mazzoni, M.., Capineri, L.., and Masotti, L..
- Abstract
We present the design of a large-area (50 mm times 50 mm) polyvynilidene fluoride (PVDF) pyroelectric sensor array for industrial CO2 (lambda = 10.6 mum) laser beam positioning. The array dimensions were chosen to match the area typically monitored in the alignment procedure of external optics (beam steering moving arm system, for example) used to redirect the laser beam from the laser output window to a remote working station. The instrument is provided with a tilted, high reflection, ZnSe plate which partially transmits the laser beam onto the sensor array. From positioning simulations with a Gaussian laser intensity profile with a sigma = 3.2 mm standard deviation (equivalent spot size 3sigma cong 20 mm), the positional accuracy along the two orthogonal array dimensions was found to be better than 0.02 mm for an 8 times 8 array and one order of magnitude higher for a 16 times 16 array. The centroid position of a CO2 industrial laser beam was evaluated by integrating the pyroelectric current for a time comparable to the time duration (100-200 ms) of the laser pulses used in the alignment procedure. [ABSTRACT FROM PUBLISHER]
- Published
- 2007
- Full Text
- View/download PDF
21. Lattice Dynamics and Negative Search for Pyroelectricity in Sr(1-1.5X) LaxTiO3 Ceramics.
- Author
-
Almeida, A., Chaves, M. R., Gregora, I., Muga, N. J., Vilarinho, P. M., Kholkin, A. L., and Costa, A. M.
- Subjects
- *
PYROELECTRICITY , *LATTICE dynamics , *CRYSTALLOGRAPHY , *CRYSTAL lattices , *CERAMICS , *TITANIUM dioxide - Abstract
Lattice dynamics and polar properties in lanthanum doped SrTiO3 (STO) ceramics, with general formulae Sr(1-1.5x)LaxTiO3 were studied in the temperature range between to K and room temperature. Despite the similarities of the low frequency Raman spectra, for differently (x = 0.0533, 0.080 and 0.133) La-doped ceramics, and the spectra of the undoped ceramics, the TO1 polar soft mode could not he detected in those systems, which confirms the non-existence of a ferroelectric phase at low temperatures. Raman spectra analysis provides evidence for drastic effects determined by La3+ impurity in the critical temperature shift of the para-antiferrodistortive phase transition of STO, accompanied with a continuing change of the lattice dynamics by increasing lanthanum concentration. The absence of a pyroelectric current confirms the non-existence of a polar character in the low temperature range. The existence of semiconducting like behaviour at high temperatures was disclosed. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
22. Pyroelectric current spectroscopy: example of application on Nb doped Pb(Zr0.92Ti0.08)O3 ceramics for infrared detection
- Author
-
Pintilie, L., Pereira, M., Gomes, M.J.M., and Boerasu, I.
- Subjects
- *
SPECTRUM analysis , *ELECTRON microscopes , *CONSTRUCTION materials , *DETECTORS , *IRON metallurgy - Abstract
Pyroelectric current spectroscopy (PCS) was used to investigate the homogeneity of the Nb doped lead zirconate–titanate Pb(Zr0.92Ti0.08)O3, (PZT) ceramics intended to be used in the infrared (IR) pyroelectric detectors manufacturing. The non-homogeneous composition in the ceramic volume is reflected by the occurrence of several peaks in the PCS spectra, suggesting the presence of PZT phases with different Zr/Ti ratio, thus having different transition temperatures. The non-homogeneity was confirmed by compositional analysis performed using an Energy Dispersive X-ray Spectrometer (EDAX) attached to a Scanning Electron Microscope (SEM). PCS can be a useful tool in optimizing the calcination and sintering parameters (temperature and time) during ceramic preparation. [Copyright &y& Elsevier]
- Published
- 2004
- Full Text
- View/download PDF
23. Functional and Responsive Polymers via Controlled Radical Polymerization
- Author
-
Wang, Jian and Klok, Harm-Anton
- Subjects
Surface interaction ,Bioadhesion ,Solvent effects ,Polyelectrolyte brushes ,Polymer brushes ,Pyroelectric current ,Controlled radical polymerization ,Ester hydrolysis ,Mechanochemistry - Abstract
This Thesis is built around 4 topics, which share in common that they all take advantage of the assets of controlled radical polymerization to either (i) prepare well-defined model systems to address fundamental research questions with regard to the sensitivity of chemical bonds towards mechanical forces or (ii) to synthesize ultrathin, surface-grafted polymer brush films that can serve as light-activatable bioadhesives or which possess non-centrosymmetric materials properties. Chapter 2 demonstrates the use of SI-ATRP to prepare PtBMA brush films that are used as a model system to better understand the effect of weak mechanical forces on the hydrolysis of ester/amide and siloxane bond. The motivation originates from previous reports that describe the degrafting of hydrophilic polymer brushes in aqueous media. The fundamental question is that decoupling the effect of swelling and the water contribution to the rate of the hydrolysis is not possible. Using the hydrophobic brushes here, it has been possible for the first time to unambiguously decouple swelling and bond hydrolysis. Comparison of reaction rate constants measured in solvents of different quality suggested that degrafting correlates with brush swelling, demonstrating the mechanochemical nature of this process In Chapter 3, the sensitivity of ester bond hydrolysis towards external mechanical forces is investigated, focusing on ester bond hydrolysis. ATRP is used to construct a series of polystyrene polymers that contain two central ester bonds. Solution ultrasonication experiments, which were performed in THF and THF water mixture with different molecular weights and under different power densities provided evidences for an increase in the apparent rate constants for ester hydrolysis with increasing mechanical force generated via mild ultrasonication. Chapter 4 and Chapter 5 present the use of SI-ATRP to produce thin, functional polymer films. Chapter 4 focuses on the development of thin polymer films that allow to control adhesion between synthetic materials and tissue. PHEMA brushes have been prepared that can be transformed, on-demand using UV light from a non-fouling surface coating into a bioadhesive interface. Two synthetic approaches towards such films are discussed. A first strategy involves direct irradiation of a PHEMA brush film with UV-light. The second strategy uses PHEMA brushes that have been post-modified to introduce photo-reactive diazirine moieties. Chapter 5 attempts to understand the pyroelectric behavior of thin PE brushes prepared via SI-ATRP. This chapter builds upon the serendipitous discovery that was made when a substrate modified with a PE brush was connected to an open circuit and subjected to an alternating sequence of temperature changes. Surprisingly, a clear current change was detected in the circuit upon the temperature change. We hypothesize that the pyroelectric current which is generated upon applying an alternating sequence of temperature changes because of a permanent dipole moment in the materials. This permanent dipole moment is believed to be the consequence of a non-neutral net charge within the polymer brush film.
- Published
- 2020
- Full Text
- View/download PDF
24. Raman Spectroscopy and Pyroelectric Studies of SrTiO 3 Ceramics Doped with Different Concentrations of Bismuth.
- Author
-
Almeida, A., Teles, Pedro, Chaves, M. R., Vilarinho, P. M., and Baptista, J. L.
- Subjects
- *
RAMAN spectroscopy , *PYROELECTRICITY , *BISMUTH , *FERROELECTRIC devices - Abstract
Raman spectra and pyroelectric studies in bismuth doped SrTiO 3 ceramics, with general formulae Sr (1 - 1.5x) Bi x TiO 3 , were undertaken. For x = 0.0053, the low frequency Raman spectra exhibit striking similarities with the spectra of the undoped ceramics also revealing the existence of a polar soft-mode TO 1 , that obeys the classical Cochran softening law. The sample with x = 0.133 presents a very different dynamics, and its Raman spectra give evidence for the inexistence of an anti-ferrodistorsive phase transition, that occurs in the undoped ceramics at 104 K. Pyroelectric measurements disclose the existence of small electrical dipoles probably due to polar grain boundaries, off-centre positions of Bi 3+ and Ti 4+ ions, and Sr vacancies, that strongly influence the behaviour of these systems with temperature variation. There is a strong evidence for the existence of a relaxor state in the x = 0.133 ceramic at low temperatures. [ABSTRACT FROM AUTHOR]
- Published
- 2003
- Full Text
- View/download PDF
25. A Study of Evolution of Structural Parameters of PZT-Based Ferrosoft Ceramics in the Vicinity of Transition to a Paraelectric Phase.
- Author
-
Akbaeva, G. M., Zakharchenko, I. N., Borodin, V. Z., and Sitalo, E. G.
- Subjects
- *
DIELECTRICS , *PYROELECTRICITY , *PHASE transitions , *ELECTRIC fields , *PIEZOELECTRICITY , *FERROELECTRICITY - Abstract
The peculiarities of structural changes of the material were investigated in the temperature range from 20 to 280°C. Electroelastic parameters: the frequency constant of radial vibrations N r and the piezoelectric modulus d 31 of the preposed sample and the poled sample being in a 1 kV/cm dc electric field were studied. It has been established that the electric field increases a temperature stability of structure of ferroelectric domains. [ABSTRACT FROM AUTHOR]
- Published
- 2003
- Full Text
- View/download PDF
26. Transient processes in a pyroelectric detector
- Subjects
pyroelectric current ,simulator of a pyroelectric detector ,выходное напряжение ,тепловой поток ,pyroelectric output voltage ,симулятор пироэлектрического преобразователя ,heat flow ,пироэлектрический ток - Abstract
В работе рассматриваются динамические характеристики пироэлектрических детекторов, а именно переходные процессы при их реакции на импульсное тепловое воздействие. Отмечены особенности переходных характеристик как при нагревании, так и при охлаждении детектора. Полученные зависимости использованы при разработке симулятора пироэлектрического преобразователя, с помощью которого возможен анализ и визуализация характеристик как существующих детекторов, так и вновь разрабатываемых. Указаны примеры использования пиродетекторов, для которых переходные характеристики наиболее важны. Разработанный симулятор может быть использован и в учебных целях. In this paper, we consider the transient characteristics of a standard single-chip pyroelectric detector. Output voltage transients are easy to measure. Direct measurement of the pyroelectric current presents some difficulties, associated primarily with a sharp jump in the initial crystal current and the input capacitance of the measuring device. Direct measurement of the crystal temperature is impossible, so it can be obtained either by modeling based on known processes, or by mathematical transformations of the results of measuring the thermal time constant with respect to the pyroelectric current. Dynamic characteristics in the time domain, particularly, transient responses are considered. Specificities of transient responses when the detector is heated and cooled, are noted. Results obtained applied to a simulator of a pyroelectric detector. The simulator plots the transient responses. It allows to change a number of parameters to receive new results. The latter is important for not only modeling or analysis existing devices, but also designing new ones. Some applications of pyroelectric detectors are pointed. The simulator is free and can be used in labs at the Universities, or anywhere in the world. Identification of differences between the movement of a person and, for example, the movement of ascending heated air currents or cold drafts in motion sensors occurs precisely in the transient response of the detector output voltage, decomposition of which into Fourier series, in this case, is unacceptable. Thus, for a number of applications of pyroelectric detectors, the problem of research and transient characteristics is relevant. Identification of differences between the movement of a person and, for example, the movement of ascending heated air currents or cold drafts in motion sensors occurs precisely in the transient response of the detector output voltage, decomposition of which into Fourier series, in this case, is unacceptable. Thus, for a number of applications of pyroelectric detectors, the problem of research and transient ch aracteristics is relevant.
- Published
- 2018
27. Gate-Induced Thermally Stimulated Current on the Ferroelectric-like Dielectric Properties of (BEDT-TTF)(TCNQ) Crystalline Field Effect Transistor
- Author
-
Hiroshi Yamauchi, Masatoshi Sakai, Kazuhiro Kudo, Shigekazu Kuniyoshi, Masakazu Nakamura, and Mitsutoshi Hanada
- Subjects
Phase transition ,Materials science ,ferroelectricity ,pyroelectric current ,field effect transistor ,Mott insulator ,charge order ,Condensed matter physics ,General Chemical Engineering ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Pyroelectricity ,Inorganic Chemistry ,Phase (matter) ,lcsh:QD901-999 ,General Materials Science ,Field-effect transistor ,lcsh:Crystallography ,Polarization (electrochemistry) - Abstract
A gate-induced thermally stimulated current (TSC) on β′-(BEDT-TTF)(TCNQ) crystalline FET were conducted to elucidate the previously observed ferroelectric-like behaviors. TSC which is symmetric for the polarization of an applied VPG and has a peak at around 285 K was assigned as a pyroelectric current. By integrating the pyroelectric current, temperature dependence of the remnant polarization charge was obtained and the existence of the ferroelectric phase transition at 285 K was clearly demonstrated. We have tentatively concluded that the phase transition between dimer Mott insulator and charge ordered phase occurred at around the interface of organic crystal and substrate.
- Published
- 2012
- Full Text
- View/download PDF
28. Effet de l'ancrage sur les propriétés d'un cristal liquide Antiferroélectrique confiné en cellule mince
- Author
-
Da Sylva, Julien, Laboratoire de Physique de la Matière Condensée - UR UPJV 2081 (LPMC), Université de Picardie Jules Verne (UPJV), Université de Picardie Jules Verne, and Pavel Jiri(jiry.pavel@sc.u-picardie.fr)
- Subjects
courant de dépolarisation ,electro-optical scanning ,paraélectrique ,[PHYS.PHYS]Physics [physics]/Physics [physics] ,Liquid crystals ,ferroélectrique ,switching current ,paraelectric ,antiferroélectrique ,spectroscopie électro-optique de balayage ,anchoring ,pyroelectric current ,Cristaux liquides ,courant pyroélectrique ,phase transition ,confinement ,ancrage ,ions ,ferroelectric ,antiferroelectric ,transition de phase - Abstract
MM. Buisine Jean-Marc Professeur, U.S.T.L. PrésidentLegrand Christian Professeur, Université du Littoral RapporteurJoly Gilles Professeur, U.S.T.L. RapporteurNeyts Kristiaan Professeur, Université de GentCluzeau Philippe Maître de Conférence, CRPPPavel Jiri Maître de Conférence, UPJVLorman Vladimir Professeur, Université Montpellier II; The influence of boundary conditions on macroscopic properties of antiferroelectric liquid crystal cells were studied in 2µm thick planar samples of MHPOBC. The special attention was paid to the transition ferro-antiferroelectric phase. A theoretical analysis shows that in the antiferroelectric phase, ferroelectric (FE) and antiferroelectric (AF) anchorings can be realized (at the same temperature) on the glass plate surface, while in the ferroelectric phase only ferroelectric anchoring is allowed. It means, that we can obtain in some temperature interval in the antiferroelectric phase four different structures (states) combining anchorings on both upper-lower glasses : 1) FE-FE, 2) AF-AF, 3) AF-FE, 4) FE-AF. Two later structures are called mixed structures (states) and are obtained from both homogeneous states by applying an electric impulsion. In the thesis three experimental methods were used to proof the existence of the mixed state. Namely 1) electro-optical spectroscopy with rotating sample (scanning electro-optical spectroscopy), 2) switching current measurements at extremely low frequencies (from 20mHz) and 3) pyroelectric measurements. The results obtained by these tree methods are complementary and clearly confirm the existents of mixed states. In the switching experiment the influence of ionic current is important. Therefore one part of the thesis is devoted to the study of ions. The results of pyroelectric measurements confirm so cooled “surface electroclinic effect” which is observable in the SmA phase close to the transition to the ferroelectric phase. This effect is also an example of the influence of boundary conditions on the sample properties in thin cells.; L'influence du confinement sur les propriétés macroscopiques d'un cristal liquide antiferroélectrique (MHPOBC) a été étudiée sur une cellule planaire de 2µm d'épaisseur. Une attention toute particulière a été apportée à la transition de phase ferroélectrique-antiferroélectrique.Une analyse théorique a montré que deux ancrages distincts, ferroélectrique (FE) et antiferroélectrique (AF), peuvent exister dans la phase antiferroélectrique. La combinaison des ces ancrages (FE) et (AF) avec les surfaces supérieures et inférieures de la cellule autorise quatre structures différentes : 1) FE-FE, 2) AF-AF, 3) AF-FE, 4) FE-AF. Les états 3) et 4) sont appelés états mixtes. Ils peuvent être obtenus par application d'une impulsion électrique sur la cellule.Trois méthodes expérimentales ont été développées durant cette thèse afin de prouver l'existence des ces états mixtes : 1) spectroscopie électro-optique de balayage, 2) courant de dépolarisation à très basse fréquence (de l'ordre de 20 mHz), 3) mesures de courant pyroélectrique. Les résultats obtenus sont complémentaires et confirment clairement l'existence de ces états. Une étude complémentaire a montré une très forte influence des ions dans les mesures de courant de dépolarisation.Les mesures de courant pyroélectrique menées à la transition para-ferro ont également confirmé de précédentes études portant sur l'effet électroclinique de surface. Cet effet est un exemple typique de l'influence des conditions aux limites sur les propriétés générales des échantillons confinés en cellules minces.
- Published
- 2005
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.