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  1. 31 Acta Physica Polonica A

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  1. 3 2018

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  1. 3 Gierałtowska S.

  2. 3 Kaczkowski J.

  3. 3 Przyslupski P.

  4. 3 Sawicki M.

  5. 3 Wachnicki Ł.

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1
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Raman Imaging Approach to the Study of Ferroelectric Domains and Raman Spectra of Multiferroic Boracites

100%
Iliev M., Hadjiev V., Íñiguez J., Pascual J.
Acta Physica Polonica A
|
2009
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vol. 116
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issue 1
19-24
EN
The boracites with general formula M_3B_7O_{13}X (M = divalent metal, X = Cl, Br, I), shortly denoted as M-X, are among the first known multiferroic materials. They exhibit a sequence of transitions from the high temperature paraelectric cubic phase to ferroelectric orthorhombic, monoclinic, trigonal phases, and finally to a monoclinic phase at low temperatures, where both ferroelectric and magnetic orders coexist. The lattice dynamics of boracites has been scarcely studied with the Raman spectroscopy, the main problem with non-cubic phases being the coexistence of twin variants with different crystallographic and polarization orientation. In this work, on the example of Co_3B_7O_{13}Cl (Co-Cl), Co_3B_7O_{13}Br (Co-Br) and Ni_3B_7O_{13}Br (Ni-Br) we demonstrate that using the Raman microscopy imaging one can visualize the twin variants, follow their transformation through the crystallographic transitions, obtain Raman spectra from untwinned domains in exact scattering configurations, determine the Raman mode symmetries, and assign Raman lines to definite atomic motions. The effects of structural transitions and elemental substitution are discussed in close comparison with results of ab initio calculations of the phonon structure of the cubic phase.
2
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Effect of Uniaxial Pressure on the Ferroelectric Phase Transition in Pb_5Ge_3O_{11}:Ba Crystals

100%
Molak A., Koralewski M., Saunders G., Juszczyk W.
Acta Physica Polonica A
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2005
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vol. 108
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issue 3
513-520
EN
The effect of uniaxial pressure up to 1 kbar applied perpendicular and parallel to c-axis, on the Curie temperature and electric permittivityε_c of Ba-doped Pb_5Ge_3O_{11} single crystals was investigated. The Curie temperature decreases with uniaxial pressure and the coefficientγ_i (γ_i ≡ δ T_{c}/δ X_i) is determined as -7 and -11 K kbar^{-1} for the b- and c-axes, respectively. It was found that uniaxial pressure increases the phase transition diffuseness and the tricritical point cannot be achieved for this pyroelectric and ferroelectric single crystal.
3
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XRD Study of Eu₂O₃-ZrO₂ Feedstock Powders and Sintered Materials

80%
Jucha S., Moskal G., Mikuśkiewicz M., Stopyra M.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
866-868
EN
Presented article described synthesis process of nonstoichiometric europium zirconate by solid state reaction between weight-equal mixture of ZrO₂ and Eu₂O₃ feedstock powders. To final material synthesis high temperature vacuum press was used as well as a free standing process of sintering. As a result europium zirconates were obtained. X-ray diffraction characterization revealed that relatively homogeneous materials were synthesised but scanning electron microscopy analysis showed many areas with nonhomogeneous composition. On the base of X-ray diffraction patterns, characterization of crystallite size as well as a lattice strain were calculated. The Williamson-Hall, Halder-Wagner and Cauchy-Gauss methods were used to make the calculations. Obtained data showed that there was no significant differences between crystallite size with zirconate materials obtained by solid state reaction at temperature 1350°C in vacuum press and by free standing process. The short heating at higher temperature (1450°C/5 h) has no influence on crystallite size as well, but 24 h of additional heating strongly increases the crystallite size.
4
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Signature of the Spin Triplet Phase in La_{0.7}Sr_{0.3}MnO_3/Yba_2Cu_3O_7/La_{0.7}Sr_{0.3}MnO_3 Trilayers

80%
Przyslupski P., Dybko K., Werner-Malento K., Aleshkevych P., Wojcik M., Sawicki M.
Acta Physica Polonica A
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2010
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vol. 118
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issue 2
313-315
EN
Differential dynamical subgap transport measurements were performed on LSMO/YBCO/LSMO trilayers to probe local evolution of the Andreev bound states which are manifested as the zero bias conductance peak. Dynamical conductivity dI/dV vs. magnetic field measured in current in plane and current perpendicular to plane geometries show nonmonotonic behavior with maximum at about 500 Oe. The shape of the zero bias conductance peak measured in current in plane geometry is sharp, whereas zero bias conductance peak measured in current perpendicular to plane geometry demonstrates V shape. These shapes of the zero bias conductance peak were predicted theoretically for unconventional p-wave spin triplet phase superconductor and superconductor with d-wave symmetry of the order parameter, respectively.
5
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The Influence of Partial Isomorphic Substitution on Electronic and Optical Parameters of ABSO₄ Group Crystals

80%
Shchepanskyi P., Gaba V., Stadnyk V., Rudysh M., Brezvin R., Piasecki M.
Acta Physica Polonica A
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2018
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vol. 133
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issue 4
819-823
EN
First principles calculations of band energy, density of states and dielectric function of K_{1.75}(NH₄)_{0.25}SO₄ single crystals in Pnma structure is performed in the framework of density functional theory. In order to describe the exchange-correlation interaction the general gradient approximation and local density approximation are used. Character and genesis of main energy bands of the crystal are discussed and comparison with data set for K₂SO₄ isomorphic crystal performed. The influence of partial isomorphic substitution K→ NH₄ found itself mainly in altering the bottom of conduction band and decrease of band gap value. From the dielectric functions dependences, the refractive indices dispersion and absorption coefficient spectra are deduced. Obtained refractive indices satisfactorily agree with experimental data in the visible spectrum region.
6
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Electronic Structure of the Cubic Perovskites BiMO_3 (M = Al, Ga, In, Sc)

80%
Kaczkowski J., Jezierski A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
852-854
EN
The electronic structure of four cubic perovskites were calculated by using density functional theory. For electronic structure calculations standard generalized gradient approximation and semilocal Tran-Blaha modified Becke-Johnson potential were used. Nonlocal hybrid Heyd-Scuseria-Ernzerhof functional was used to obtain lattice constants and bulk moduli. Standard generalized gradient approximation results are in good agreement with previous calculations but the band gap calculated within TB-mBJ are significally larger for all compounds. For BiAlO_3 this values are: 1.49 eV (GGA) and 2.47 eV (TB-mBJ), BiGaO_3: 1.23 eV (GGA) and 2.12 (TB-mBJ), BiInO_3: 0.06 eV (GGA) and 0.83 eV (TB-mBJ), BiScO_3: 0.70 eV (GGA) and 1.38 eV (TB-mBJ).
7
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Magnetic Ordering in Boron-Rich Borides TbB_{66} and GdB_{66}

80%
Flachbart K., Gabani S., Mori T., Siemensmeyer K.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
875-876
EN
Magnetic ordering in TbB_{66} and GdB_{66} was investigated at very low temperatures. Measurements of ac susceptibility have shown rather clear features of magnetic ordering below 1 K, at 0.34 K for TbB_{66} and at 0.20 K for GdB_{66}. However, no clear evidence of long range magnetic order was found by neutron scattering experiments. Reasons leading to these observations are discussed.
8
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Optical Characterization of ZnO Nanorods Grown by the Ultra-Fast and Low Temperature Hydrothermal Process

80%
Witkowski B., Ivanov V., Wachnicki Ł., Gierałtowska S., Godlewski M.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1199-1201
EN
The results of photoluminescence investigations of zinc oxide nanorods are reported. These nanorods grown on undoped silicon substrates were obtained by low temperature and ultra-fast version of a microwave-assisted hydrothermal method. The photoluminescence investigations show very high quality of the obtained material. From photoluminescence studies we conclude the lack of carrier localization effects. The photoluminescence is dominated by band gap edge emission of bound excitonic (donor bound excitons) origin. Thus, the photoluminescence quenching observed at increased temperatures is associated with thermal ionization of shallow donors. From photoluminescence analysis (changes of photoluminescence line width) a strength of exciton-acoustic phonon coupling is evaluated.
9
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Conduction Mechanism of 4-Aminoantipyrine as a New Organic Semiconductor

80%
Yahia I.
Acta Physica Polonica A
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2014
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vol. 125
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issue 5
1167-1171
EN
X-ray diffraction pattern of 4-aminoantipyrine was studied and it is a single phase with a polycrystalline structure. 4-aminoantipyrine has hexagonal structure with space group P6/mcc. The electrical properties of 4-aminoantipyrine were studied in the temperature range (303-373 K) below the melting point of the studied compound and in the frequency range (100 Hz-100 kHz). The obtained results of dc conductivity showed a positive temperature coefficient at the lower temperatures and a negative temperature coefficient at the higher temperatures. The ac conductivity obeys the power law. Ac conductivity can be reasonably interpreted in terms of overlapping-large polaron tunneling model and the correlated barrier hopping model. 4-aminoantipyrine is a good candidate for electronic device due to its electrical conductivity and capacitance.
10
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Compositional Dependence of Optical Modes Frequencies in TlGa_xIn_{1-x}S_2 Layered Mixed Crystals (0 ≤ x ≤1)

80%
Isik M., Gasanly N., Korkmaz F.
Acta Physica Polonica A
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2014
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vol. 126
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issue 3
747-751
EN
The infrared transmittance and Raman scattering spectra in TlGa_xIn_{1-x}S_2 (0 ≤ x ≤1) layered mixed crystals grown by the Bridgman method were studied in the frequency ranges of 400-2000 and 250-400 cm^{-1}, respectively. The bands observed at room temperature in IR transmittance spectra of TlGa_xIn_{1-x}S_2 were interpreted in terms of multiphonon absorption processes. The dependences of the frequencies of IR- and Raman-active modes on the composition of TlGa_xIn_{1-x}S_2 mixed crystals were also established. The structural characterization of the mixed crystals was investigated by means of X-ray diffraction measurements and compositional dependence of lattice parameters was revealed.
11
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Investigation of Crystal and Magnetic Structure of BiFeO_{3} Using Neutron Diffraction

80%
Sosnowska I., Przeniosło R., Fischer P., Murashov V. A.
Acta Physica Polonica A
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1994
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vol. 86
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issue 4
629-631
EN
Polycrystalline material obtained from the ground single crystal of BiFeO_{3} reported as not having the superstructure, shows the superstructure reflections in neutron diffraction pattern. The determined magnetic moment of antiferromagnetically ordered Fe^{3+} ions is μ_{Fe} = (3.70±0.03)μ_{B} at 293 K.
12
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Properties and Characterization of ALD Grown Dielectric Oxides for MIS Structures

80%
Gierałtowska S., Sztenkiel D., Guziewicz E., Godlewski M., Łuka G., Witkowski B., Wachnicki Ł., Łusakowska E., Dietl T., Sawicki M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
692-695
EN
We report on an extensive structural and electrical characterization of undergate dielectric oxide insulators Al_2O_3 and HfO_2 grown by atomic layer deposition. We elaborate the atomic layer deposition growth window for these oxides, finding that the 40-100 nm thick layers of both oxides exhibit fine surface flatness and required amorphous structure. These layers constitute a base for further metallic gate evaporation to complete the metal-insulator-semiconductor structure. Our best devices survive energizing up to ≈ 3 MV/cm at 77 K with the leakage current staying below the state-of-the-art level of 1 nA. At these conditions the displaced charge corresponds to a change of the sheet carrier density of 3 × 10^{13} cm^{-2}, which promises an effective modulation of the micromagnetic properties in diluted ferromagnetic semiconductors.
13
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Content available

Surface Concentration of Defects at Grain Boundaries in Sintered Alumina Determined by Positron Annihilation Lifetime Spectroscopy

80%
Kansy J., Si Ahmed A., Liebault J., Moya G.
Acta Physica Polonica A
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2001
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vol. 100
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issue 5
737-742
EN
Sintered alumina samples of grain diameters spanning from 1.2 to 4.5μm have been investigated by positron annihilation lifetime spectroscopy. One series of samples was produced from material containing about 150 ppm impurities (mainly SiO_2). The second one was made from material having about 2700 ppm of various elements (SiO_2, MgO, CaO). Two models of positron trapping at grain boundaries are compared: The first one relates to the diffusion-limited regime; and the other one - to the transition-limited regime of trapping. As a result the relative change of surface concentration of defects at grain boundaries is determined. Additionally, the positron diffusion constant in bulk alumina at room temperature, D_+=0.36±10 cm^2/s, is estimated.
14
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Orthorhombic Phase of La_{0.5}Bi_{0.5}NiO₃ Studied by First Principles

80%
Kaczkowski J., Pugaczowa-Michalska M., Jezierski A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
408-410
EN
The aim of presented first principles study of La_{0.5}Bi_{0.5}NiO₃ is to investigate electronic structure of orthorhombic phase Pbnm. The calculations show that metallicity and magnetism of the system are strongly related with hybridization between Ni 3d and O 2p. To improve the quality of the electronic structure description of the system, especially the treatment of correlation for the Ni 3d, we employ GGA, LDA, and GGA+U, LDA+U. The LSDA results give good agreement with experiment. Thus, the screening effects originating from the hybridized Ni 3d and O 2p electrons are sufficiently strong that they reduce the electronic correlations in the La_{0.5}Bi_{0.5}NiO₃, making it a weakly correlated metal.
15
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Dielectric and AC Conductivity οf Potassium Perchlorate, KCLO_{4}

80%
Abdelmoneim H.
Acta Physica Polonica A
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2010
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vol. 117
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issue 6
936-940
EN
The AC conductivity σ (ω) and the complex dielectric permittivity ε*(ω) were studied as function of temperature 300 K < T < 600 K and at some selected frequencies (1-20 kHz) for polycrystalline sample of KClO_4. The differential thermal analysis (DTA) thermograph was also performed. The combined data support each other and indicate the existence of a structural phase transition at ≈ 575 K. Moreover, the temperature dependence of the ac conductivity behaves in accordance with Arrhenius relation, whereas the frequency dependent conductivity obeys the power law σ(ω) = Aω^{s(T)}. The behavior of s with temperature suggests that the hopping over the barrier model prevails. No evidence for the existence of a ferroelectric phase transition at the transition temperature.
16
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BiFeO_3 Crystal Structure at Low Temperatures

80%
Palewicz A., Sosnowska I., Przeniosło R., Hewat A.
Acta Physica Polonica A
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2010
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vol. 117
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issue 2
296-301
EN
The crystal and magnetic structure of BiFeO_3 have been studied with the use of high resolution neutron diffraction between 5 K and 300 K. The atomic coordinates in BiFeO_3 are almost unchanged between 5 K and 300 K.
17
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Electronic Properties of Stacked ZrO₂ Films Fabricated by Atomic Layer Deposition on 4H-SiC

80%
Król K., Kwietniewski N., Gierałtowska S., Wachnicki Ł., Sochacki M.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
329-331
EN
The electronic properties of ZrO₂/SiO₂ stacked dielectric layers are reported as a function for temperature of the atomic layer deposition process. A dielectric layer has been characterized by C-V and I-V measurements of MIS structures. A strong dependence of κ value of ZrO₂ layer has been observed as a function of deposition temperature T. The values within the range of κ≈16-26 have been obtained. All measured stacked dielectric layers show an increase in dielectric breakdown voltage compared to simple SiO₂ dielectric by average factor of 1.7 and factor of 2 (21 MV/cm) for high-κ oxides deposited at low temperature (85°C).
18
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Ion Beam Surface Modification of GaN Films for High Efficient Light Emitting Diodes

80%
Wu G., Lin Y., Tu K.
Acta Physica Polonica A
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2013
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vol. 123
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issue 5
884-887
EN
Focused gallium (Ga) ion beam technology has been proposed to modify the surface of GaN thin films. Due to the significant advancement in nitride semiconductors, the solid-state light emitting diodes will gradually replace fluorescent lamps in the next decade. However, further improvements in light extraction and power efficiency are still highly desired. GaN is limited by its high refractive index, with low light escape cone angle at about 24.6°. The external quantum efficiency is low due to the unwanted reflection and absorption. As the patterning technology scales down to the nanometer level, photonic crystal lattice in the visible light wavelength range can be achieved. Therefore, we improved the external efficiency by the new design of hexagonal photonic crystal lattice with air hole arrays in the diameter of 150 nm and the depth of 120 nm. The Ga beam was accelerated at 30 kV and the ion current was 100 pA. The plane wave expansion method along with the finite difference time domain was useful to investigate the quantum confinement. The nanopatterning by the focused ion beam could save time and processing step. In addition, we have successfully prepared blue InGaN/GaN samples with hexagonal period of 200 nm. The device micro-photoluminescence results have demonstrated that the peak illumination intensity was improved by 30%.
19
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Bonding Analysis of BiFeO₃ Substituted by Gd³⁺

80%
Pugaczowa-Michalska M., Kaczkowski J.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
362-364
EN
We present results of first-principles calculations for Bi₅GdFe₆O₁₈ compound in idealized the rhombohedral R3c structure for a variety of magnetic ordering. Within DFT+U approach it is found that the insulating ground state with the G-type antiferromagnetic arrangement of Fe sublattice gives a minimal total energy for BiFeO₃ substituted by magnetically active Gd³⁺. The Bi₅GdFe₆O₁₈ compound has nonzero total magnetic moment, which arises from antiparallel spin moments on Fe sites and reduced spin moment on Gd. Chemical bonding of the studied compound is analyzed using partial density of states, electron localization function and charge density distribution.
20
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Structure and Magnetic Characterization οf BiFeO_3/YBa_2Cu_3O_7 Bilayers

80%
Werner-Malento K., Tsarou A., Dluzewski P., Paszkowicz W., Minikayev R., Sawicki M., van der Beek K., Konczykowski M., Przyslupski P.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
95-97
EN
Bilayered epitaxial BiFeO_3/YBa_2Cu_3O_7 films were fabricated on (100) [(LaAlO_3)_{0.3}(Sr_2TaAlO_6)_{0.7}] substrates by sputtering method. For structural comparison the bilayered BiFeO_3/La_{0.67}Sr_{0.33}MnO_3 films were also deposited on (100) SrTiO_3 substrates. A weak ferromagnetic moment is observed in BiFeO_3/YBa_2Cu_3O_7 films. The mechanism responsible for weak ferromagnetic moment arises presumably from the epitaxy strain induced canted antiferromagnetic structure.
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