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The photodielectric effect in lead molybdate (PbMoO4) single crystals grown by the Czochralski method in a direction 30° off the a-axis in the plain (001) was studied. The charge was prepared from MoO3 and PbO α- or β-modifications. The reagents were taken both in a stoichiometric ratio and with excess of 0.5 mol % MoO3. The temperature dependences of the permittivity ε on samples illuminated with UV-light were measured in the temperature range of 290–700 K. Assumptions about the relationship between the magnitude of the photodielectric anomalies and the disorder of the PbMoO4 crystal lattice were made. [ABSTRACT FROM AUTHOR]

Background. At present, much attention is paid to the dielectric engineering of the material of the surrounding matrix and low-dimensional structures, which makes it possible to purposefully change their properties and optimize the characteristics of semiconductor devices. The purpose of this work is a theoretical study of the influence of the pair interacting quantum dots (QDs), as well as their interaction with the surrounding matrix through 2D - dissipative tunneling, on the photodielectric effect (PDE) associated with the excitation of an impurity complex (А+ + е) in a QD system in an external electric field. Materials and methods. Interaction of an electron with a hole in an impurity complex (А+ + е)in a QD has been considered in the adiabatic approximation. The dispersion equations for a hole in an impurity complex (А+ + е) in the presence of an external electric field and 2Ddissipative tunneling for the s- and p-states of an electron in a QD are obtained within the framework of the zero-range potential model in the effective mass approximation. The influence of the electric field on the ground state of an electron in a QD has been taken into account in the second order of the perturbation theory. The probability of 2D - dissipative tunneling is calculated in the one-instanton semiclassical approximation. The relative change in dielectric permittivity has been calculated in the dipole approximation. PDE field dependence curves have been plotted for InSb QDs. Results. It is shown that the PDE field dependence at a certain value of the strength of an external electric field and the parameters of 2D - dissipative tunneling has a characteristic kink associated with the effect of 2D - bifurcation, when under the action of an electric field the double-well oscillatory potential simulating the "QD - surrounding matrix" system is transformed and the tunnel transfer mode changes from synchronous to asynchronous. It has been established that there are irregular oscillations on the PDE curves in the vicinity of the 2D bifurcation point, which are associated with the regime of quantum beats. It is shown that the amplitude of the oscillations increases with increasing phonon mode frequency and temperature, and the break point shifts towards weaker fields. It has been found that an increase in the constant of interaction with the contact medium, as well as with the constant of the pair interaction of QDs, leads to the suppression of the PDE. Conclusions. The theoretically studied PDE at a wavelength of λ=6.2 μm in a QD with an impurity complex (А+ + е) in the presence of interactionwith the surround ng matrix through 2D - dissipative tunneling of a hole localized at the А+- center can be used in photosensor applications, for example, as a sensor, the structural component of which can detect the presence of IR - radiation due to a change in electrical capacitance.

At present, much attention is paid to the dielectric engineering of the material of the surrounding matrix and low-dimensional structures, which makes it possible to purposefully change their properties and optimize the characteristics of semiconductor devices. The aim of this work is a theoretical study of the influence of the pair interaction of quantum dots (QDs), as well as their interaction with the surrounding matrix through 2D dissipative tunneling, on the photodielectric effect (PDE) associated with the excitation of an impurity complex A+ + e in a QD system in an external electric field. Interaction of an electron with a hole in an impurity complex A+ + e in a QD has been considered in the adiabatic approximation. The dispersion equations for a hole in an impurity complex A+ + e in the presence of an external electric field and 2D dissipative tunneling for the s- and p-states of an electron in a QD are obtained within the framework of the zero-range potential model in the effective mass approximation. The influence of the electric field on the ground state of an electron in a QD has been taken into account in the second order of the perturbation theory. The probability of 2D dissipative tunneling is calculated in the one-instanton semiclassical approximation. The relative change in dielectric permittivity has been calculated in the dipole approximation. PDE field-dependence curves have been plotted for InSb QDs. It is shown that the PDE field dependence at a certain value of the strength of an external electric field and the parameters of 2D dissipative tunneling has a characteristic kink associated with the effect of 2D bifurcation, when, under the action of an electric field, the double-well oscillatory potential simulating the "QD–surrounding matrix" system is transformed and the tunnel transfer mode changes from synchronous to asynchronous. It has been established that there are irregular oscillations on the PDE curves in the vicinity of the 2D bifurcation point, which are associated with the regime of quantum beats. It is shown that the amplitude of the oscillations increases with increasing phonon mode frequency and temperature, while the break point shifts towards weaker fields. It has been found that an increase in the constant of interaction with the contact medium, as well as with the constant of the pair interaction of QDs, leads to the suppression of the PDE. [ABSTRACT FROM AUTHOR]

The photodielectric effects of rare earth elements Er, Eu, and Ho doped Na 1/2 Bi 1/2 TiO 3 (NBT) ceramics are investigated. The dependence of light intensity and irradiation time on the photodielectric effects were clarified, and the thermal-induced and photo-induced changes in permittivity are distinguished. At 1 kHz, the Δε r /ε dark (Δε r = ε photo -ε dark) of NBT-Er/Eu and NBT-Er/Ho are 2.57 % and 2.08 %, respectively. Furthermore, poling and quenching treatments are employed to improve the photodielectric effect of NBT-Er/Ho ceramics. At 1 kHz, the Δε r /ε dark of poled and quenched NBT-Er/Ho increase to 5.22 % and 2.71 %, respectively. The increase of Δε r /ε dark of poled sample is resulted from the lattice distortion of the ceramics while the increase of Δε r /ε dark of quenched sample is due to the increase in oxygen vacancies. This work is conducive to understand the unconventional optical and dielectric effects in ferroelectric ceramics. [ABSTRACT FROM AUTHOR]

The photodielectric effect is demonstrated in Mott-insulator BaCoSiO4 with a stuffed-tridymite-type structure under irradiation of visible light at 365 nm. The real part of dielectric permittivity is enhanced by ~300% with little increase of tan δ in a low-frequency region. Results of diffuse reflectance spectroscopy, first-principles calculations and dielectric measurements suggest that the photodielectric effect stems from a response of photo-excited electrons in an unoccupied upper-Hubbard band for 3d-orbitals of cobalt, which have significantly small mobility due to the unique configuration of Co ions in the stuffed-tridymite-type structure. [ABSTRACT FROM AUTHOR]

The investigation results of clathrate properties GaSeβ-cyclodextrinFeSO4 of the hierarchical architecture with the fourfold expansion at different degrees of a guest cavitations loading have been presented. Based on the frequency dependence of the specific complex impedance, the changes of the impurity energy spectrum expanded matrix parameters as a result of forming the supramolecular ensembles on its basis are clarified. For some architecture, impedance, photo and magneto responses showed the extraordinary behavior of the magnetoimpedance and photoconductivity and also the giant negative photodielectric and the colossal magnetocapacitance effects at room temperature, which open new possibilities of their practical application.

In this work, solid solutions of (0.88–x)Bi 0.5 Na 0.5 TiO 3 –0.12BaTiO 3 – xBa(Ti 0.5 Ni 0.5 )O 3–δ were designed and prepared. These compositions exhibit ferroelectricity at room temperature, with the tetragonal symmetry. The c/a values are varied from ∼1.0067 (x = 0.1) to ∼1.0208 (x = 0.04). A transition from the high–temperature relaxor state to the low–temperature ferroelectric state is demonstrated by the temperature dependence of dielectric data and Raman spectrum. The direct bandgap decreases from 3.40 eV for x = 0 to 3.16 eV for x = 0.1. The Ba(Ti 0.5 Ni 0.5 )O 3–δ addition leads an additional optical absorption peak in the visible range. The obvious photodielectric effect was discovered. In particular, the relative permittivity of the x = 0.1 composition rises from ∼756 to ∼807 under light illumination. [ABSTRACT FROM AUTHOR]

The results of studies of the effect of illumination on the frequency dependence of the electrical parameters of bismuth silicate Bi12SiO20 single crystals are presented. Illumination in the visible spectral region induces a change in the dielectric parameters (the photodielectric effect) and the manifestation of photoconductivity in the low-frequency region under study. The hopping character of conduction in the dark and upon excitation with light is established. The possible mechanisms of the photodielectric effect and charge transport in the crystals are discussed. [ABSTRACT FROM AUTHOR]

Copyright of Radio Electronics, Computer Science, Control is the property of Zaporizhzhia National Technical University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The investigation results of clathrate properties GaSe(β-cyclodextrin> of the hierarchical architecture with the fourfold expansion at different degrees of a guest cavitations loading have been presented. Based on the frequency dependence of the specific complex impedance, the changes of the impurity energy spectrum expanded matrix parameters as a result of forming the supramolecular ensembles on its basis are clarified. For some architecture, impedance, photo and magneto responses showed the extraordinary behavior of the magnetoimpedance and photoconductivity and also the giant negative photodielectric and the colossal magnetocapacitance effects at room temperature, which open new possibilities of their practical application. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Nano- & Electronic Physics is the property of Sumy State University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A photo-dielectric effect (i.e., a change in dielectric permittivity due to photo-irradiation) has been demonstrated in LaAl0.99Zn0.01O3-δ. Photo-irradiation with an incident energy of 3.4 eV was found to enhance the dielectric permittivity in LaAl0.99Zn0.01O3-δ over a wide frequency range from 100Hz to 1MHz. The change in dielectric permittivity in the high-frequency region hardly depended on frequency and was not accompanied by an increase in dielectric loss, indicating an intrinsic photo-dielectric effect in LaAl0.99Zn0.01O3-δ that is not due to photo-conduction. The dependence of the photo-dielectric effect on incident energy suggests the existence of deep in-gap states introduced by Zn substitution. The mechanism of the photo-dielectric effect in LaAl0.99Zn0.01O3-δ relates to the dielectric response of the photo-excited electrons trapped in the deep in-gap states, which work as effective polar displacements under an applied electric field. These findings are expected to contribute to the development of photo-capacitors that enable the remote control of the dielectric response via photo-irradiation. [ABSTRACT FROM AUTHOR]

A photo-dielectric effect (i.e., a change in dielectric permittivity due to photo-irradiation) has been demonstrated in LaAl0.99Zn0.01O3-δ. Photo-irradiation with an incident energy of 3.4 eV was found to enhance the dielectric permittivity in LaAl0.99Zn0.01O3-δ over a wide frequency range from 100Hz to 1MHz. The change in dielectric permittivity in the high-frequency region hardly depended on frequency and was not accompanied by an increase in dielectric loss, indicating an intrinsic photo-dielectric effect in LaAl0.99Zn0.01O3-δ that is not due to photo-conduction. The dependence of the photo-dielectric effect on incident energy suggests the existence of deep in-gap states introduced by Zn substitution. The mechanism of the photo-dielectric effect in LaAl0.99Zn0.01O3-δ relates to the dielectric response of the photo-excited electrons trapped in the deep in-gap states, which work as effective polar displacements under an applied electric field. These findings are expected to contribute to the development of photo-capacitors that enable the remote control of the dielectric response via photo-irradiation. [ABSTRACT FROM AUTHOR]

0.4(BaCa)LaTiO-0.6Bi(MgTi)O ( x = 0.00, 0.15, 0.30) ceramics were prepared by a conventional mixed oxide route. Crystal structure of the ceramics was determined using XRD. Dielectric constant of the samples decreases with the increase of La content, however, the temperature stability of dielectric constant was improved. For x = 0.3, a near-plateau dielectric constant 700 ± 80, extended across the temperature range, 30-550 °C (at 1 kHz) was obtained. The corresponding loss tangent, tan δ, was ≤0.025 in the temperature range from 93 to 353 °C. All samples show a relaxor behavior and measurement frequency and the temperature ( T ) corresponding to the maximum of dielectric constant follow the Vogel-Fulcher relationship. Compared the dielectric properties of the samples with other materials, the former has highly attractive for developing capacitors over a wide working temperature range. [ABSTRACT FROM AUTHOR]

New photosensitive polymeric film composites based on oligomer containing ferrocenyl and carbazolyl fragments doped with symmetric polymethine dye are synthesized. Their photoelectric properties are investigated. Photovoltaic properties of these composites are detected. The mechanisms and peculiarities of the photovoltaic and photodielectric effects are discussed. [ABSTRACT FROM AUTHOR]

It was found that the photophysical characteristics of film composites based on poly(vinyl butyral) with additions of particles of the hetero-polyoxometalate complex (NH){[Cu(en)][PMoVO]}·9HO have an unusual dependence on the duration of illumination with visible light, which is expressed as change in the sign of the photocurrent during long-term illumination. It is suggested that the negative photoconductivity is due to the formation of significant volume charge in the volume of the composite film. It was concluded from analysis of the photovoltaic characteristics that the volume charge is formed by non-equilibrium negative electric charges. A phenomenological model that describes the observed effect is proposed. [ABSTRACT FROM AUTHOR]

Photosensitive polymer fi lm composites based on non-photoconductive polyvinyl butyral with an added heterometallic Cu/Ca complex were prepared and investigated. It was found that such composites had photovoltaic properties and exhibited a photodielectric effect when irradiated in the complex absorption band. The mechanism and characteristics of the photovoltaic and photodielectric effects in the studied fi lm composites were discussed. [ABSTRACT FROM AUTHOR]

Two known methods of research of electric properties were applied on semiconducting materials and their methodology was significantly improved to obtain quantitative data on elementary reactions of charge carriers. The resonator method of microwave photoconductivity included the measurements of the frequency dependences of photoresponse. The modified frequency- and time-resolved microwave photoconductivity method gives the opportunity to separate contributions to a photoresponse of the free electrons which did not experience capture by acceptors and structural defects, and the electrons which are again released in a free state from traps. The use of a light source (λ = 350 ÷ 2500 nm) together with a broadband dielectric spectrometer provides an effective tool (the broadband photodielectric spectroscopy--BPDS) for research of relaxation processes in semiconductors caused by excess current carriers. Examples of investigation of the photoelectric properties of CdS, CdTe, and Cu(In,Ga)Se2 received with modified methods are presented. [ABSTRACT FROM AUTHOR]

We report a method to optically control the effective permittivity of a composite dielectric in which the active inclusions are fabricated from pulverized semi-insulating GaAs. The electric dipoles from the inclusions are controlled by photo-generation of charge carriers using infrared light. An infrared transparent binder provides the matrix material. Our primary purpose is to develop a low-cost pigment-based ink, or paint, for optically tuning electromagnetic devices including metamaterials, frequency-selective surfaces, filters, phase delays, and antennas. In bulk form, applications of the optically controllable dielectric are imagined including a gradient index lens in which inhomogeneous light intensity can provide a dynamic response for focusing or steering of beams. An important feature is that the effective permittivity is linear with electric field intensity over a usable parameter space. We present experimental results as well as a simple model to describe the behavior qualitatively. [ABSTRACT FROM PUBLISHER]

Time and spectral dependences of the dielectric permittivity of the LiYLuF ( x = 0, 0.5, and 1) crystals doped with Ce and co-doped with Yb ions under UV laser excitation were studied by the 8-mm microwave resonant technique at room temperature. The obtained photoconductivity spectrum in 240-310 nm spectral range was interpreted as a stepwise photoionization spectrum of the Ce ions due to sequential 4 f-5 d and 5 d-6 s transitions. Average lifetimes of free and defect trapped (color centers) charge carriers were estimated. [ABSTRACT FROM AUTHOR]

The room temperature, dark and photo-dielectric properties of the novel crystals TlGaSeS are investigated in the frequency, intensity and biasing voltage having ranges of ~ 1-120 MHz, 14-40 klux and 0-1 V, respectively. The crystals are observed to exhibit a dark high frequency effective dielectric constant value of ~ 10·65 × 10 with a quality factor of ~ 8·84 × 10 at ~ 120 MHz. The dielectric spectra showed sharp resonance- antiresonance peaks in the frequency range of ~ 25-250 kHz. When photoexcited, pronounced increase in the dielectric constant and in the quality factor values with increasing illumination intensity are observed. Signal amplification up to ~ 33% with improved signal quality up to ~ 29% is attainable via photoexcitation. On the other hand, the illuminated capacitance-voltage characteristics of the crystals reflected a downward shift in the voltage biasing and in the built-in voltage of the device that is associated with increase in the uncompensated carrier density. The increase in the dielectric constant with increasing illumination intensity is ascribed to the decrease in the crystal's resistance as a result of increased free carrier density. The light sensitivity of the crystals, the improved dielectric properties and the lower biasing voltage obtained via photoexcitation and the well-enhanced signal quality factor of the crystals make them promising candidates for optical communication systems. [ABSTRACT FROM AUTHOR]