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Effect of structural phase transitions on the exciton absorption spectrum of thin CsPbCl3 films (2014)

O. N. Yunakova, V. K. Miloslavsky, E. N. Kovalenko and V. V. Kovalenko

American Institute of Physics (AIP)

In: Low Temperature Physics

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Publication Date: 2014-10-10

Description: The absorption spectrum of thin film CsPbCl 3 in the 2–6 eV range is studied at temperatures of 90–500 K. Sudden changes show up in the temperature dependences of the parameters of the long-wavelength exciton band (spectral position E m ( T ), half width Γ( T ), and oscillator strength f ( T )) at the first order phase transitions at 310 and 320. No phase transitions in E m ( T ), Γ( T ), and f ( T ) are detected at low temperatures. The exciton excitations in CsPbCl 3 are found to have a three-dimensional character.

Print ISSN: 1063-777X

Electronic ISSN: 1090-6517

Topics: Physics

Published by American Institute of Physics (AIP)

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Effect of structural phase transitions on the exciton absorption spectrum of thin CsPbCl3 films (2014)

O. N. Yunakova, V. K. Miloslavsky, E. N. Kovalenko and V. V. Kovalenko

American Institute of Physics (AIP)

In: Low Temperature Physics

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Publication Date: 2014-08-30

Description: The absorption spectrum of thin film CsPbCl 3 in the 2–6 eV range is studied at temperatures of 90–500 K. Sudden changes show up in the temperature dependences of the parameters of the long-wavelength exciton band (spectral position E m ( T ), half width Γ( T ), and oscillator strength f ( T )) at the first order phase transitions at 310 and 320. No phase transitions in E m ( T ), Γ( T ), and f ( T ) are detected at low temperatures. The exciton excitations in CsPbCl 3 are found to have a three-dimensional character.

Print ISSN: 1063-777X

Electronic ISSN: 1090-6517

Topics: Physics

Published by American Institute of Physics (AIP)

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The exciton absorption spectrum of thin CuPb3Br7 superionic conductor films (2016)

O. N. Yunakova, N. N. Yunakov, E. N. Kovalenko and V. V. Kovalenko

American Institute of Physics (AIP)

In: Low Temperature Physics

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Publication Date: 2016-10-08

Description: A study of the absorption spectrum of thin CuPb 2 Br 7 films in the 2–6 eV spectral and 90–500 K temperature ranges. It is shown that the exciton spectrum of the compound is associated with transitions in the lead ion. The temperature dependence of the spectral position and half-width of the low-frequency exciton band contains features associated with phase transitions γ → β ( T c 1 = 159 K) and β → α ( T c 2 = 434 K) and the disordering of the cation sublattice of the compound in the transition to the superionic state.

Print ISSN: 1063-777X

Electronic ISSN: 1090-6517

Topics: Physics

Published by American Institute of Physics (AIP)

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Absorption spectrum of KPb2Cl5 thin films (2015)

O. N. Yunakova, V. K. Miloslavksy, E. N. Kovalenko and V. V. Kovalenko

American Institute of Physics (AIP)

In: Low Temperature Physics

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Publication Date: 2015-09-01

Description: A study of the absorption spectrum of thin KPb 2 Cl 5 films, in the spectral range of 2–6 eV, within the temperature interval 90–520 K. It is found that low-frequency exciton states are localized in the sublattice of the compound containing the Pb 2+ ions, and that they are excitons of intermediate coupling having a two-dimensional nature.

Print ISSN: 1063-777X

Electronic ISSN: 1090-6517

Topics: Physics

Published by American Institute of Physics (AIP)

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Free carrier generation and recombination in PbS quantum dot solar cells (2016)

Jona Kurpiers, Daniel M. Balazs, Andreas Paulke, Steve Albrecht, Ilja Lange, Loredana Protesescu, Maksym V. Kovalenko, Maria Antonietta Loi and Dieter Neher

American Institute of Physics (AIP)

In: Applied Physics Letters

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Publication Date: 2016-03-08

Description: Time Delayed Collection Field and Bias Assisted Charge Extraction (BACE) experiments are used to investigate the charge carrier dynamics in PbS colloidal quantum dot solar cells. We find that the free charge carrier creation is slightly field dependent, thus providing an upper limit to the fill factor. The BACE measurements reveal a rather high effective mobility of 2 × 10 − 3 cm 2 /Vs, meaning that charge extraction is efficient. On the other hand, a rather high steady state non-geminate recombination coefficient of 3 × 10 − 10 cm 3 /s is measured. We, therefore, propose a rapid free charge recombination to constitute the main origin for the limited efficiency of the PbS colloidal quantum dots cells.

Print ISSN: 0003-6951

Electronic ISSN: 1077-3118

Topics: Physics

Published by American Institute of Physics (AIP)

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Thermoelectric properties of semiconductor-metal composites produced by particle blending (2016)

Yu Liu, Doris Cadavid, Maria Ibáñez, Silvia Ortega, Sara Martí-Sánchez, Oleksandr Dobrozhan, Maksym V. Kovalenko, Jordi Arbiol and Andreu Cabot

American Institute of Physics (AIP)

In: APL Materials

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Publication Date: 2016-08-30

Description: In the quest for more efficient thermoelectric material able to convert thermal to electrical energy and vice versa, composites that combine a semiconductor host having a large Seebeck coefficient with metal nanodomains that provide phonon scattering and free charge carriers are particularly appealing. Here, we present our experimental results on the thermal and electrical transport properties of PbS-metal composites produced by a versatile particle blending procedure, and where the metal work function allows injecting electrons to the intrinsic PbS host. We compare the thermoelectric performance of composites with microcrystalline or nanocrystalline structures. The electrical conductivity of the microcrystalline host can be increased several orders of magnitude with the metal inclusion, while relatively high Seebeck coefficient can be simultaneously conserved. On the other hand, in nanostructured materials, the host crystallites are not able to sustain a band bending at its interface with the metal, becoming flooded with electrons. This translates into even higher electrical conductivities than the microcrystalline material, but at the expense of lower Seebeck coefficient values.

Electronic ISSN: 2166-532X

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Published by American Institute of Physics (AIP)

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Magnetic iron oxides in the cementation technology of the boron-containing radioactive waste (2015)

M A Fedotov, O A Gorbunova, O V Fedorova, G E Folmanis and L V Kovalenko

Institute of Physics (IOP)

In: IOP Conference Series: Materials Science and Engineering

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Publication Date: 2015-04-24

Description: Two ways of synthesis of non-detachable dispersed particles of magnetic materials useful for the boron-containing waste cementation process regulation were developed. Powder XRD showed that the method of carbothermic recovery of nanoscale iron hydroxide allows obtaining a mixture of iron oxides with content of the magnetic phase up to 70%. Method of low-temperature hydrogen reduction of the raw materials allows obtaining various compositions of a-iron and iron oxides with the possibility to change the size of the final particles in a wide range. The possibility of using composites of magnetic iron oxides and metal oxide compositions instead of ferromagnetic rods with VEP of boron-containing liquid radioactive waste in the fluidized field was studied. It was shown that the use of fine and nano particles of the iron oxides in the pre-treatment of the boron-containing LRW increases the strength of the final compounds and accelerates the cement setting compounds from 13 to 5-9 days.

Print ISSN: 1757-8981

Electronic ISSN: 1757-899X

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Published by Institute of Physics (IOP)

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Broadband transient absorption spectroscopy with 1- and 2-photon excitations: Relaxation paths and cross sections of a triphenylamine dye in solution (2015)

J. Moreno, A. L. Dobryakov, I. N. Ioffe, A. A. Granovsky, S. Hecht and S. A. Kovalenko

American Institute of Physics (AIP)

In: Journal of Chemical Physics

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Publication Date: 2015-07-11

Description: 1-photon (382 nm) and 2-photon (752 nm) excitations to the S 1 state are applied to record and compare transient absorption spectra of a push-pull triphenylamine (TrP) dye in solution. After 1-photon excitation, ultrafast vibrational and structural molecular relaxations are detected on a 0.1 ps time scale in nonpolar hexane, while in polar acetonitrile, the spectral evolution is dominated by dipolar solvation. Upon 2-photon excitation, transient spectra in hexane reveal an unexpected growth of stimulated emission (SE) and excited-state absorption (ESA) bands. The behavior is explained by strong population transfer S 1 → S n due to resonant absorption of a third pump photon. Subsequent S n → S 1 internal conversion (with τ 1 = 1 ps) prepares a very hot S 1 state which cools down with τ 2 = 13 ps. The pump pulse energy dependence proves the 2-photon origin of the bleach signal. At the same time, SE and ESA are strongly affected by higher-order pump absorptions that should be taken into account in nonlinear fluorescence applications. The 2-photon excitation cross sections σ (2) = 32 ⋅ 10 −50 cm 4 s at 752 nm are evaluated from the bleach signal.

Print ISSN: 0021-9606

Electronic ISSN: 1089-7690

Topics: Chemistry and Pharmacology , Physics

Published by American Institute of Physics (AIP)

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Materials, Vol. 4, Pages 651-702: Magnetoelectric Interactions in Lead-Based and Lead-Free Composites (2011)

Mirza Bichurin; Vladimir Petrov; Anatoly Zakharov; Denis Kovalenko; Su Chul Yang; Deepam Maurya; Vishwas Bedekar; Shashank Priya

MDPI Publishing

In: Materials

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Publication Date: 2011-07-21

Description: Magnetoelectric (ME) composites that simultaneously exhibit ferroelectricity and ferromagnetism have recently gained significant attention as evident by the increasing number of publications. These research activities are direct results of the fact that multiferroic magnetoelectrics offer significant technological promise for multiple devices. Appropriate choice of phases with co-firing capability, magnetostriction and piezoelectric coefficient, such as Ni-PZT and NZFO-PZT, has resulted in fabrication of prototype components that promise transition. In this manuscript, we report the properties of Ni-PZT and NZFO-PZT composites in terms of ME voltage coefficients as a function of frequency and magnetic DC bias. In order to overcome the problem of toxicity of lead, we have conducted experiments with Pb-free piezoelectric compositions. Results are presented on the magnetoelectric performance of Ni-NKN, Ni-NBTBT and NZFO-NKN, NZFO-NBTBT systems illustrating their importance as an environmentally friendly alternative.

Electronic ISSN: 1996-1944

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Published by MDPI Publishing

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Predictive Multiscale Modeling of Nanocellulose Based Materials and Systems (2014)

Andriy Kovalenko

Institute of Physics (IOP)

In: IOP Conference Series: Materials Science and Engineering

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Publication Date: 2014-08-23

Description: Cellulose Nanocrysals (CNC) is a renewable biodegradable biopolymer with outstanding mechanical properties made from highly abundant natural source, and therefore is very attractive as reinforcing additive to replace petroleum-based plastics in biocomposite materials, foams, and gels. Large-scale applications of CNC are currently limited due to its low solubility in non-polar organic solvents used in existing polymerization technologies. The solvation properties of CNC can be improved by chemical modification of its surface. Development of effective surface modifications has been rather slow because extensive chemical modifications destabilize the hydrogen bonding network of cellulose and deteriorate the mechanical properties of CNC. We employ predictive multiscale theory, modeling, and simulation to gain a fundamental insight into the effect of CNC surface modifications on hydrogen bonding, CNC crystallinity, solvation thermodynamics, and CNC compatibilization with the existing...

Print ISSN: 1757-8981

Electronic ISSN: 1757-899X

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Published by Institute of Physics (IOP)

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