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1
Content available remote

Changes of GaP: N Defect Structure under Hydrostatic Pressure

100%
Bąk-Misiuk J., Domagała J., Kozankiewicz B., Misiuk A., Adamczewska J., Skibska M.
Acta Physica Polonica A
|
1993
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vol. 83
|
issue 1
87-93
EN
The changes of defect structure of GaP:N epitaxial layers subjected to hydrostatic pressures up to 1.8 GPa are investigated by X-ray diffraction and photoluminescence. The observed changes are more pronounced at higher pressures and depend on the nitrogen concentration, c_{N}, and on initial defect structure. Especially complex hydrostatic pressure induced properties are observed for the sample with c_{N} > 10^{20} at. cm^{-3}. The model explaining the hydrostatic pressure induced defect structure changes is proposed.
2
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Transformation of AlGaAs/GaAs Interface under Hydrostatic Pressure

63%
Bąk-Misiuk J., Domagała J., Trela J., Leszczyński M., Misiuk A., Hartwig J., Prieur E.
Acta Physica Polonica A
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1996
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vol. 89
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issue 3
405-409
EN
AlGaAs layers grown by molecular beam epitaxy on GaAs substrates were investigated before and after high hydrostatic pressure (1.2 GPa) at high temperature (770 K) treatment (HP-HT treatment). An influence of HP-HT treatment on the properties of the AlGaAs/GaAs system was studied by lattice parameter measurements using the high resolution diffractometer and by X-ray topography. Observed changes in the lattice parameter of the AlGaAs layers after HP-HT treatment are related to the strain relaxation and explained by the creation of misfit dislocations and other extended defects which are visible on the topographs.
3
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Dilatometric Study of the Phase Transition in (CH_{3}NH_{3})_{5}Bi_{2}Cl_{11}

63%
Pykacz H., Jakubas R.
Acta Physica Polonica A
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1991
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vol. 79
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issue 5
695-697
EN
The paper reports a dilatometric study on (CH_{3}NH_{3})_{5}Bi_{2}Cl_{11} single crystals. It is shown that elongation of the crystal is continuous but linear thermal expansion coefficients are discontinuous at phase transition temperature.
4
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Nonlinear Temperature Dependence of the Band Gap in Hg_{1-x-y}Cd_{x}Mn_{y}Te and Hg_{1-x}Cd_{x}Te Alloys

63%
Dudziak E., Jędral L. Z., Bożym J., Brzeziński J.
Acta Physica Polonica A
|
1991
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vol. 79
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issue 2-3
291-294
EN
The temperature dependence of the band gap for HgCdTe and HgCdMnTe has been experimentally investigated in the temperature range of 7-250 K. The distinct nonlinear dependence has been observed in the low temperature range. It was shown that the lattice dilatation contribution calculated for HgCdTe is a significant part (about 30%) of the total temperature shift of the energy gap.
5
Content available remote

Dilatomelric and Pyroelectric Study of Phase Transition in (CH_{3})_{2}NH_{2}Al(SO_{4})_{2} · 6H_{2}O Ferroelectric Crystal

63%
Pykacz H.
Acta Physica Polonica A
|
1995
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vol. 88
|
issue 6
1097-1101
EN
The results of linear thermal expansion and pyroelectric coefficient are given for crystal of dimethylammoniumaluminium sulphate hexahydrate. Large anomalies of these quantities has been observed around the phase transition temperature at 151 K.
6
Content available remote

Polarity Related Problems in Growth of GaN Homoepitaxial Layers

63%
Leszczyński M., Prystawko P., Śliwinski A., Suski T., Litwin-Staszewska E., Porowski S., Paszkiewicz R., Tłaczała M., Beaumont B., Gibart P., Barski A., Langer R., Knap W., Frayssinet E.
Acta Physica Polonica A
|
1998
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vol. 94
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issue 3
427-430
EN
Homoepitaxial layers of GaN were grown by metalorganic chemical vapour deposition on single crystals obtained by high-pressure, high-temperature technology. For each metalorganic chemical vapour deposition run, four samples were placed, (00.1) and (00.1̲) faces of the Mg-doped insulating and undoped highly-conductive substrates. The layers were examined using X-ray diffraction, photoluminescence and far-infrared reflectivity. It was found that the (00.1̲) easier incorporates donors resulting in higher free-electron concentrations in the layers grown on these sides of the crystals, both, undoped and Mg-doped.
7
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Lattice Constant of Doped Semiconductor

63%
Leszczyński M., Litwin-Staszewska E., Suski T., Bąk-Misiuk J., Domagała J.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
837-840
EN
The paper shows an influence of doping on lattice constant of a semiconductor. Three effects are discussed: (i) "size" effect caused by a different ionic radii of dopant and host atoms, (ii) lattice expansion by free electrons proportionally to the deformation potential of the conduction-band minimum occupied by this charge, (iii) different thermal expansion of the undoped and doped samples. The experiments have been performed by using the high resolution X-ray diffraction at 77-770 K on AlGaAs:Te and GaAs:Si.
8
Content available remote

Structural Properties of REM_{2}Sn_{2} (RE=La, Ce and M=Ni, Cu)

63%
Ślebarski A., Kaczmarska K., Pierre J.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
267-270
EN
The lattice parameters a and c of CeM_{2}Sn_{2} show an anomalous temperature dependence compared to the analogous variations for LaM_{2}Sn_{2}. The anomaly Δa of thermal expansion for CeCu_{2}Sn_{2} has a maximum around 90 K, whereas Δc has a maximum near 140 K, near to the maximum of the magnetic resistivity Δρ.
9
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Thermal Expansion of (CH_{3}NH_{3})_{5}Bi_{2}X_{11} (X=Cl, Br) Crystals in the Temperature Range from 80 to 300 K

63%
Jakubas R., Franqois P., Lefebvre J.
Acta Physica Polonica A
|
1994
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vol. 85
|
issue 3
579-583
EN
Thermal expansion studies on (CH_{3}NH_{3})_{5}Bi_{2}Cl_{11} and (CH_{3}NH_{3})_{5}Bi_{2}Br_{11} in the temperature range 80-350 K are reported. The dilatometric measurements revealed a considerable similarity with respect to the anisotropy of dilatations of both isomorphous crystals. A diffused thermal anomaly was found around 170 K in (CH_{3}NH_{3})_{5}Bi_{2}Cl_{11} crystal.
10
Content available remote

Defects of Non-Stoichiometry and Dynamic Stability of SnTe Crystal Lattice

63%
Rogacheva E., Sinelnik N., Nashchekina O., Popov V., Lobkovskaya T.
Acta Physica Polonica A
|
1993
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vol. 84
|
issue 4
733-736
EN
The temperature dependencies of coefficient of linear expansion α in the range of 4.2-300 K were obtained for SnTe samples with various degrees of deviation from stoichiometry. For the sample of stoichiometric composition in the α vs. temperature curves the anomalies connected with ferroelectric phase transition were detected. It was found that within cubic phase existence region α isotherms have a minimum at 50.4 at.% Te. Maximum dynamic stability at indicated composition is believed to be associated with the formation of vacancy superstructure.
11
Content available remote

Magnon and Soliton Excitations in the Carrier-Poor, One-Dimensional S=1/2 Antiferromagnet Yb_{4}As_{3}

51%
Steglich F., Köppen M., Gegenwart P., Cichorek T., Wand B., Lang M., Thalmeier P., Schmidt B., Aoki H., Ochiai A.
Acta Physica Polonica A
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2000
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vol. 97
|
issue 1
91-100
EN
The semimetallic quasi-one-dimensional S=1/2 Heisenberg antiferromagnet Yb_{4}As_{3} was studied by low-temperature measurements of the specific heat C(T,B), thermal expansion α(T,B), and thermal conductivity ĸ(T,B). At finite magnetic fields (B≤12 T) we observed the following distinct anomalies: (1) the magnon contribution to C(T,0), γ T, with large coefficient γ ≈ 200 mJ/(K^{2}mol), becomes strongly reduced with field, and (2) a broad hump in C(T,B=const) is induced at slightly higher temperatures. (3) The latter corresponds to a pronounced peak in α(T,B=const) as well as (4) to a broad minimum in ĸ(T,B= const)/ĸ(T,0). These anomalies are well described by the classical sine-Gordon solution of a one-dimensional Heisenberg antiferromagnet with a weak easy-plane anisotropy. However, the soliton-rest energy deduced from the experimental results depends on the magnetic field like E_{S} ~ B^{ν}, with an exponent ν ≈ 0.66, while the classical sine-Gordon model requires ν=1. Thus, our results suggest an alternative description of soliton excitations in an antiferromagnetic S=1/2 Heisenberg chain in terms of the quantum sine-Gordon model, for which an exponent ν=2/3 is appropriate.
12
Content available remote

X-ray Study of Ferroelectric Phase Transition in (NH(CH_{3})_{3})_{3}Sb_{2}Cl_{9}

51%
Tomaszewski P. E.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 3
631-634
EN
The lattice parameters of a title crystal, TMACA, were measured from a room temperature to 405 K by the X-ray single-crystal Bond method. The high-temperature paraelectric phase should have the monoclinic symmetry (space group P2/c). Some peculiarities on dielectric behaviour of the crystal were explained. The hypotheses on incommensurability of the paraelectric phase as well as on the parent normal (trigonal) phase were presented.
13
Content available remote

The Anisotropy of the Electrical Resistivity and Thermal Expansion of Single Crystal DyNi_{5}

51%
Kačmarčiková E., Reiffers M., Mihálik M., Kováč J., Menovsky A., Garcia Soldevilla J., Señas Pariente A., Goméz Sal J.
Acta Physica Polonica A
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2000
|
vol. 97
|
issue 5
811-814
EN
The results of the measurements of temperature dependence of the electrical resistivity ρ(T), thermal expansion L(T) and susceptibility χ(T) on single crystal DyNi_{5} in the temperature range 4.2-300 K are reported. The maximum in ρ(T) at T_{N}=12.2 K was observed which corresponds to the transition to antiferromagnetically ordered state. Taking into account the Bloch-Grüneisen formula for electron-phonon contribution ρ_{ph}(T) to ρ(T) the anisotropic magnetic contribution ρ_{mag}(T) was determined. We also observed the anisotropic behaviour of L(T) at low temperatures.
14
Content available remote

High Pressure - High Temperature Diffraction Study of MnTe Using Synchrotron Radiation

51%
Paszkowicz W., Dynowska E., Peun T.
Acta Physica Polonica A
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1997
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vol. 91
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issue 5
939-944
EN
High pressure - high temperature experiments for MnTe of NiAs type were performed using a synchrotron radiation as X-ray source and a cubic anvil X-ray diffraction press to produce nonambient sample environment. In the investigated range of pressure (0-67.5 kbar) on uploading and with following temperature rise from 296 to 1273 K (at 67.5 kbar), the structure type of MnTe is conserved. An earlier reported nonlinear behaviour of lattice-parameter c_{0} is not found in the present study. Possible reasons of this discrepancy are discussed. The value of bulk modulus and its pressure derivative were calculated from the pressure-volume dependence by fitting the Birch-Murnaghan equation.
15
Content available remote

Epitaxial Layers Versus Bulk Single Crystals of GaN. Temperature Studies of Lattice Parameters and Energy Gap

51%
Teisseyre H., Perlin P., Leszczyński M., Suski T., Dmowski L., Grzegory I., Porowski S., Jun J., Moustakas T.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 2
403-406
EN
Gallium nitride epitaxial layer grown by molecular beam epitaxy and bulk crystal grown at high pressure were examined by using X-ray diffrac­tion methods, and by optical absorption at a wide temperature range. The free electron concentration was 6 × 10^{17} cm^{-3} for the layer and about 5 × 10^{19} cm^{-3} for the bulk crystal. The experiments revealed a different po­sition of the absorption edge and its temperature dependence for these two kinds of samples. The structural examinations proved a significantly higher crystallographic quality of the bulk sample. However, the lattice constants of the samples were nearly the same. This indicated that a rather different electron concentration was responsible for the different optical properties via Burstein-Moss effect.
16
Content available remote

Relations Between Hole Volume and Macroscopic Volume in Various Polymers

51%
Dlubek G., Alam M., Saarinen K., Stejny J., Fretwell H.
Acta Physica Polonica A
|
1999
|
vol. 95
|
issue 4
521-526
EN
Different definitions of the free volumes are discussed and related to the total specific volume and to the local free (hole) volume. Positron lifetime measurements are reported for polyethylene, polytetrafluoroethylene, and CR39-copolymers. Two long-lived components appear in polyethylene and polytetrafluoroethylene, which were attributed to o-Ps annihilations in crystalline regions and in holes of the amorphous phase. From a relation between the coefficients of the thermal expansion of macroscopic and hole volume, the fractional hole volume h and from this the number of holes, N, is estimated. Values of T_{g}=195 K, h_{g}=4.5% (polyethylene) and 5.7% (polytetrafluoroethylene) and N_{g}=0.73 nm^{-3} (polyethylene) and 0.36 nm^{-3} (polytetrafluoroethylene) were obtained. In semicrystalline polymers these values agree with estimates obtained from the densities of the crystalline and amorphous phases. The effect of cross-linking on the free-volume properties of CR39-copolymer networks was studied. The comparison of the hole volume with the specific volume allowed us to estimate the number density of holes to ≈1 nm^{-3}.
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