Search results

1

X-Ray Diffraction Study of CeT₂Al₁₀ (T = Ru, Os) at Low Temperatures and under Pressures

100%

Kawamura Y., Hayashi J., Takeda K., Sekine C., Tanida H., Sera M., Nakano S., Tomita T., Takahashi H., Nishioka T.

Acta Physica Polonica A

|

2017

|

vol. 131

|

issue 4

988-990

EN

We have carried out a powder X-ray diffraction investigation on antiferromagnetic Kondo semiconductors CeRu₂Al₁₀ and CeOs₂Al₁₀ at low temperatures and under high pressures as well as the structural investigation on single crystal of these compounds. The results of powder X-ray studies of CeRu₂Al₁₀ and CeOs₂Al₁₀ indicate that these compounds do not have structural transition at its antiferromagnetic ordering temperature. The results of single crystal structural refinement indicate that the b-axis of this crystal structure is insensitive not only to pressure but also to temperature and that the effect of cooling to Ce-Ce distance for CeRu₂Al₁₀ is the same as that for CeOs₂Al₁₀.

2

Nanocrystalline and Polycrystalline Phases Present in the Protective Metalloceramic Coatings

63%

Górski L., Pawłowski A.

Acta Physica Polonica A

|

2002

|

vol. 102

|

issue 2

295-299

EN

New data about the structure of high-temperature resistant metalloceramic plasma sprayed coatings in micro and nano areas are presented. Application of the new instrumental methods: transmission electron microscopy combined with selected area electron diffraction made it possible to obtain these data. The first layer in Ni based metallic bondcoat shows nanocrystalline structure. External ceramic layer based on stabilised ZrO_2 is polycrystalline and contains both cubic and tetragonal crystalline phases. Local inhomogeneities in coatings phase composition are determined.

3

Isostructural Transition in RTAl Compounds at High Temperatures

63%

Prchal J., Javorský P., de Boer F., Moleman A.

Acta Physica Polonica A

|

2008

|

vol. 113

|

issue 1

335-338

EN

Based on previously discovered forbidden values of the c/a ratio, we studied anomalies in the temperature evolution of the lattice parameters (a, c) of several hexagonal RTAl compounds at high temperatures (above room temperature). The compound ErNi_{0.45}Cu_{0.55}Al, that seemed to be impossible to be prepared in single-phase form, reaches the single-phase state at temperatures above 493 K (220°C). On the other hand, the compound TbNi_{0.7}Cu_{0.3}Al - that was expected to undergo a first-order structural phase transition at high temperatures - exhibits a second-order type transition when approaching the critical values of the c/a ratio. These results are in agreement with idea of a forbidden range of c/a values in these compounds.

4

X-Ray Diffraction and Electron Microscopy Studies on the Structure of Thermal Barrier Coatings

63%

Górski L., Pawłowski A.

Acta Physica Polonica A

|

2012

|

vol. 122

|

issue 2

405-409

EN

Composites based on Al_2O_3 and ZrO_2 are used. Coatings deposited by plasma spraying technology are studied with the use of X-ray diffraction and electron microscopy combined with electron diffraction methods. Phase transitions and specific coatings layered microstructure with local fluctuations of phase and chemical composition are connected with the conditions of plasma spray process.

5

Austenite Stabilization of Fe-Ni Alloy

63%

Danilchenko V. E., Nedolya A. V.

Acta Physica Polonica A

|

1994

|

vol. 86

|

issue 4

617-620

EN

By X-ray powder diffraction and magnetometric methods we investigated the effect of phase hardening during γ-α-γ transitions. In this case austenite becomes more stable to subsequent γ-α-γ transitions, the dislocation density increases, the grain reduce in fragments and the hardness increases, too. In addition the γ-solid solution in some steels is unstable during ageing. The phase hardening was found to stabilize the γ-solid solution of Fe-Ni alloy to subsequent thermal treatment. This is consistent with an increase in carbon mobility after γ-α-γ transitions. That is why decarbonizations of austenite take place during increase in extent of phase hardening.

6

EPR Study of Ammonium Nitrate Doped with Copper(II) Ions

63%

Wojtowicz W., Więckowski A.

Acta Physica Polonica A

|

2005

|

vol. 108

|

issue 2

395-401

EN

This work is devoted to a study of the structural changes in a single crystal of ammonium nitrate, NH_4NO_3, doped with copper(II) cations by electron paramagnetic resonance. Ammonium nitrate crystallizes at atmospheric pressure in several polymorphic forms, phase VII → V → IV → III → II → I → melt, with transition temperatures of 103 K, 255 K, 305 K, 357 K, 398 K, and 443 K, respectively. The aim of our work was to study the temperature phase transition V → IV at about 255 K using electron paramagnetic resonance technique. The electron paramagnetic resonance spectra were performed using an X-band spectrometer with microwave frequency of 9.4 GHz and magnetic modulation of 100 kHz in the temperature range of 153-296 K. For a single crystal the angular dependence of the copper(II) electron paramagnetic resonance spectra was measured at 293 K and 168 K. The anisotropic behaviour measured at 293 K points to the existence of one kind of two equivalent copper(II) complexes with inverse g and A tensors. A second pair of equivalent complexes also with inverse g and A tensors was observed. The minimal values of g-factors correspond to the maximum values of A. The angular dependence taken at 168 K shows the existence of two types of non-equivalent copper complexes which differ in comparison with the complexes observed at room temperature. The temperature dependence of the intensities of hyperfine structure lines for all copper(II) complexes observed shows a phase transition V → IV occurring in the temperature range of 237-246 K with a hysteresis. One of the hyperfine structure lines of a copper(II) complex measured at low temperatures shows a superhyperfine structure with line intensities 1:2:3:2:1 originating from the interaction of the copper ^{63,65}Cu (I=3/2) nucleus with two ^{14}N (I = 1) nuclei of two ammonia, NH_3, ligand molecules.

7

Thermal Resistance and Phase Transitions Studies for Some composite Materials Based on Al_{2}O_{3}

63%

Górski L.

Acta Physica Polonica A

|

1999

|

vol. 96

|

issue 2

275-281

EN

In this paper the studies of phase transitions in some material compositions based on Al_{2}O_{3} caused by high-temperature processes are presented. These material compositions may be used to high-temperature resistant plasma sprayed coatings. The occurring phase transitions are studied by X-ray diffraction methods. Phase transitions and thermal resistance for studied oxide systems are different. In the coatings from the materials belonging to Al_{2}O_{3}-NiO and Al_{2}O_{3}- ZrO_{2} systems complex phase transitions were observed. More resistant to the conditions of thermal fatigue are coatings containing aluminum titanate Al_{2}TiO_{5} and mullite 3 Al_{2}O_{3}-2 SiO_{2}.

8

Phase and Structural Behaviour of the PrAlO_{3}-SmAlO_{3} System

51%

Basyuk T., Vasylechko L., Fadeev S., Berezovets V., Trots D., Niewa R.

Acta Physica Polonica A

|

2010

|

vol. 117

|

issue 1

98-103

EN

High resolution in situ X-ray powder diffraction applying synchrotron radiation and differential thermal analysis/scanning calorimetry methods have been used to examine the pseudo-binary system PrAlO_3-SmAlO_3. Two kinds of solid solutions with rhombohedral and orthorhombic structure exist at room temperature. At elevated temperatures, a continuous phase transition Pm3m ↔ R3c and a first-order transformation R3c ↔ Pbmn occur in the two respective phases. A sequence of low-temperature phase transformations R3c ↔ Imma ↔ C2/m has been detected in Pr_{1-x}Sm_xAlO_3 samples with x < 0.35. Based on in situ powder diffraction and differential thermal analysis/scanning calorimetry data, the phase diagram of the pseudo-binary system PrAlO_3-SmAlO_3 has been constructed.

9

Connection between Reorientational Motions of NH_{3} Groups and Phase Transitions in [Ni(NH_{3})_{6}](NO_{3})_{2} and [Mg(NH_{3})_{6}](NO_{3})_{2} Compounds

51%

Migdał-Mikuli A., Mikuli E.

Acta Physica Polonica A

|

1995

|

vol. 88

|

issue 3

527-532

EN

Quasielastic neutron scattering data for [Νi(ΝH_{3})_{6}](ΝO_{3})_{2} and [Mg(ΝH_{3})_{6}](NO_{3})_{2} were subjected to a new analysis. On the basis of the excess of intensity of elastic component observed in these spectra in comparison to the intensity of this component resulting from the applied reorientational model this analysis determined temperature dependence of the new "R" parameter. This parameter gives us information concerning the number of these NH_{3} groups which in the [Me(NΗ_{3})_{6}]^{2+} cation reorientate with the correlation time of order of 10^{-12} s. It has been ascertained that in phases I and II of both substances under study all NH_{3} groups reorientate fast (R = 6ΝH_{3} groups), whereas in phases III and IV only part of these groups reorientate fast (R = 3ΝΗ_{3} groups - in the case of [Νi(ΝΗ_{3})_{6}](ΝO_{3})_{2} and R = 2ΝΗ_{3} groups - in the case of [Mg(ΝΗ_{3})_{6}](NO_{3})_{2}). Moreover, the temperature dependence of reorientational correlation time τ for these fast reorienting ΝH_{3} groups were also determined. The remaining NH_{3} groups reorientate on a much slower time scale. Both temperature dependencies: R vs. Τ and τ vs. Τ register a deep thermal hysteresis of the phase transition: phase II - phase III (Τ^{h}_{C2} - T^{c}_{C2} ≈ 95 K and ≈ 35 K respectively for [Ni(ΝΗ_{3})_{6}](ΝO_{3})_{2} and [Mg(ΝΗ_{3})_{6}](NO_{3})_{2}).

10

High-Pressure Study of Gd_2(MoO_4)_3 by Raman Scattering and Ab Initio Calculations

51%

Lucazeau G., Bouvier P., Pasturel A., Le Bacq O., Pagnier T.

Acta Physica Polonica A

|

2009

|

vol. 116

|

issue 1

25-31

EN

High-pressure induced phase transitions in a single crystal of gadolinium molybdate, Gd_2(MoO_4)_3 were studied by the Raman spectroscopy and ab initio calculations. The amorphization of the sample takes place at about 6 GPa in a mixture of alcohol as a pressure transmitting medium and begins as soon as 3 GPa in argon. In both media, the amorphization is irreversible in the 0-9 GPa investigated pressure range. The joint ab initio and Raman results allowed us to conclude that rotations of MoO_4 tetrahedra are the primary structural changes involved in the first phase transition (at about 2 GPa) explaining the softening of the low frequency modes at about 50 cm^{-1}. In addition, a progressive distortion of tetrahedra followed by a coordination change (IV-VI) of Mo atoms is observed through the five structural transitions including amorphization. This mechanism based on the steric hindrance of polyhedra is believed to be the most relevant for explaining the amorphization of Gd_2(MoO_4)_3.

11

Physics of Neutral-to-Ionic Phase Transition in Organic Charge Transfer Semiconducting Compounds

51%

Cailleau H., Lemée-Cailleau M. H., Le Cointe M., Luty T.

Acta Physica Polonica A

|

1997

|

vol. 92

|

issue 4

597-608

EN

An uncommon excitonic instability takes place in some exotic semiconducting compounds. Indeed, the equilibrium neutral-to-ionic (N-I) phase transition, as well as the non-equilibrium photo-induced phase transformation, observed in some organic charge-transfer complexes, originate from intra- and inter-chain cooperative effects between structurally relaxed charge-transfer excitations. This electronic-structural phase transition manifests itself by a change of the degree of charge-transfer and a dimerization distortion with the formation of donor-acceptor pairs along the stacking axis in the I phase. Thermal charge-transfer excitations associated with the formation of I strings along N chains are at the heart of the mechanism of this phase transition. These relaxed electronic excitations, which are an intrinsic feature of low-dimensional systems with strong electron-phonon coupling, can be described in terms of self-trapping and self-multiplication of charge-transfer excitons. Precise structural studies on the prototype compound, tetrathiafulvalene-p-chloranil allow to highlight the respective role taken by the ionicity and the dimerization. Symmetry and thermodynamics analysis of the N-I transition, based on recent determination of the pressure-temperature phase diagram, make possible to present a consistent picture of this phase transition. Supported by theoretical considerations taking into account the interplay between quantum and thermal effects, the experimental observations show that the N-I transition results from the condensation and the ordering (crystallization) of charge-transfer excitations, following a phase diagram analogous to the solid-liquid-gas one.

12

Some Elastic Properties and Phase Transitions in Some Alkali Halides Using Interatomic Potential Model

51%

Yazar H.

Acta Physica Polonica A

|

2006

|

vol. 109

|

issue 6

743-751

EN

We have predicted the phase transition pressure in some alkali halides using an interatomic potential approach based on rigid ion model. This potential form represents the composite form of the inverse power dependence and exponential dependence of the repulsive energy on interionic distance. Some thermoelastic properties such as second order elastic constants have been calculated using the same potential. The phase transition pressures (28.69 and 2.4 GPa) obtained by us for two alkali halides (NaCl and KCl) are in closer agreement with their corresponding experimental data (29.0 and 2.0 GPa). This approach is promising with respect to prediction of the phase transition pressure of other alkali halides as well.

13

Evolution of Disordering in SiC upon Sintering; Phase Analysis of SiC by Rietveld Method with Application of Neutron and X-Ray Diffraction

51%

Pałosz B., Boysen H., Schneider J., Schulz H.

Acta Physica Polonica A

|

1993

|

vol. 83

|

issue 1

95-106

EN

Neutron and X-ray diffraction patterns of α and β powders as well as of sintered SiC were analysed by a multiphase Rietveld method. It is shown that structural models combined of large period polytypes can be used to approximate the disordering of these polytype structures. The hexagonality of the samples could be terminated with reproducibility 1-2% using different combinations of large-period polytypes. It follows that the usual classification into α and β SiC is an oversimplification. The polytype behaviour of SiC powders and the role of twinning of cubic layer stackings is discussed. Distribution functions of stacking sequences of different length in α and β phases are derived.

14

Annealing Effect of Equiatomic Co/Pt Alloy Films

51%

Gontarz R., Luciński T., Uba L., Uba S., Kudryavtsev Y.

Acta Physica Polonica A

|

1994

|

vol. 85

|

issue 2

427-431

EN

Polycrystalline as-sputtered CoPt alloy films near the equiatomic composition were characterized as consisting of a disordered fcc phase with preferred texture along [111] orientation perpendicular to the film plane. The film annealing at 600°C/16 h induces the disorder-order phase transition confirmed by X-ray diffraction. As a result of the transition an appearance of the ordered tetragonal (fct) phase of AuCuI type with c/a = 0.974 is observed. The c-axis is the easy axis of magnetization. Both longitudinal and polar Kerr hysteresis loops reveal a dramatic increase in the coercivity from 0.1 to 4.5 kOe in annealed CoPt alloy films due to ordering.

15

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.

16

High Quality (100) and (001) Oriented Substrates Prepared from Czochralski Grown SrLaGaO_{4} and SrLaAlO_{4} Single Crystals

51%

Berkowski M., Fink-Finowicki J., Sass J., Mazur K.

Acta Physica Polonica A

|

1997

|

vol. 92

|

issue 1

201-204

EN

The growth of SrLaGaO_{4} and SrLaAlO_{4} crystals on ⟨100⟩ and ⟨001⟩ oriented seeds was investigated. Various defects, which appeared in crystals grown on these two orientations, were observed in polarized light and by X-ray diffraction topography. It was found that to obtain a substrate of the best quality, the crystal should be cut along the growth directions. Therefore, crystals pulled along ⟨100⟩ direction are utilized for preparation of (001) substrates, whereas (100) substrates are better to cut from crystals grown on ⟨001⟩ seed. The quality of the prepared substrates was determined by high resolution X-ray diffraction study in terms of rocking curve and mean mosaic angle.

17

Mesoscopic Ordering Effects in Single-Crystalline Thin Films of Lanthanum Manganites

51%

Samoilenko Z., Okunev V., Pushenko E., Abal'oshev A., Baran M., Gierłowski P., Lewandowski S., Szymczak R.

Acta Physica Polonica A

|

2004

|

vol. 105

|

issue 1-2

93-98

EN

We have investigated thin films of lanthanum manganites epitaxially grown by pulsed laser deposition on single-crystalline substrates. X-ray diffraction studies show that the characteristic feature of the investigated films is a superposition of fractions with long range atomic order in the basic single-crystalline matrix, and mesoscopic order in the clusterized structure encompassing the Mn-O layers. A detailed analysis of diffusive scattering shows that the size of metallic clusters and their volume concentration in the dielectric matrix varies. In the case of a small size and concentration, the metallic clusters in low temperature behave as quantum dots and their presence leads to a tunneling mechanism of conductivity with characteristic R(T)= const. In the case of large cluster size, the discrete energy levels become smeared. It appears also that the optical, transport, and magnetic properties of the investigated films depend critically on the distribution of Mn^{2+}, Mn^{3+}, and Mn^{4+} ions in the clusters.

18

Atomic Order and the Interaction of Electronic and Magnetic Subsystems in Epitaxial LaSr(Ca)MnO Films

51%

Okunev V., Samoilenko Z., D'yachenko T., Abal'oshev A., Baran M., Gierłowski P., Lewandowski S., Szewczyk A., Szymczak R.

Acta Physica Polonica A

|

2004

|

vol. 105

|

issue 1-2

121-126

EN

We have investigated the structure, and electric, optical, and magnetic properties of LaSr(Ca)MnO films containing atomic clusters of various types coherently built into the basic crystallographic matrix. Below the transition to the metallic state, the electrical conductivity of the films is determined by tunneling of charge carriers between metallic clusters. We have found that for each sample there exists a threshold value of magnetic ordering, above which the magnetic subsystem starts to affect actively the film conductivity. The observed increase of conductivity with decreasing temperature is caused by the fact that in the process of magnetic ordering of the samples the cluster size and concentration of metallic phase increase. Experimental results are in agreement with theoretical calculations.

19

Studies of the Magnetic Axis Switching in Magnetite

51%

Król G., Kusz J., Tarnawski Z., Kąkol Z., Tabiś W., Kozłowski A.

Acta Physica Polonica A

|

2006

|

vol. 109

|

issue 4-5

601-605

EN

The influence of the external magnetic field on magnetic and crystallographic structure of magnetite was studied. We have confirmed, by means of vibrating sample magnetometer measurements, that external magnetic field can switch the easy magnetic axis to the new crystallographic direction. We have also proved by the direct observation of the crystalline structure that this phenomenon is strictly related to the crystallographic structure relaxation.

20

Influence of Isomorphic Atom Substitution on Lattice Anisotropy of Thallium Dichalcogenide Layered Mixed Crystals

51%

Gasanly N.

Acta Physica Polonica A

|

2006

|

vol. 110

|

issue 4

471-477

EN

Compositional variation of the lattice parameters of TlBX_2-type (B = Ga or In and X = S or Se) mixed crystals with monoclinic structure were studied by X-ray diffraction technique. The lattice anisotropy (c/b) of these mixed crystals changes linearly with substitution of the atoms located both at the centers and the vertices of the corresponding BX_4 tetrahedra. A brief survey of the important features of the effect of isomorphic atom substitution on the lattice anisotropy and the unit cell volume of TlBX_2-type mixed crystals with layered structure was presented.

Refine search results

X-Ray Diffraction Study of CeT₂Al₁₀ (T = Ru, Os) at Low Temperatures and under Pressures

Nanocrystalline and Polycrystalline Phases Present in the Protective Metalloceramic Coatings

Isostructural Transition in RTAl Compounds at High Temperatures

X-Ray Diffraction and Electron Microscopy Studies on the Structure of Thermal Barrier Coatings

Austenite Stabilization of Fe-Ni Alloy

EPR Study of Ammonium Nitrate Doped with Copper(II) Ions

Thermal Resistance and Phase Transitions Studies for Some composite Materials Based on Al_{2}O_{3}

Phase and Structural Behaviour of the PrAlO_{3}-SmAlO_{3} System

Connection between Reorientational Motions of NH_{3} Groups and Phase Transitions in [Ni(NH_{3})_{6}](NO_{3})_{2} and [Mg(NH_{3})_{6}](NO_{3})_{2} Compounds

High-Pressure Study of Gd_2(MoO_4)_3 by Raman Scattering and Ab Initio Calculations

Physics of Neutral-to-Ionic Phase Transition in Organic Charge Transfer Semiconducting Compounds

Some Elastic Properties and Phase Transitions in Some Alkali Halides Using Interatomic Potential Model

Evolution of Disordering in SiC upon Sintering; Phase Analysis of SiC by Rietveld Method with Application of Neutron and X-Ray Diffraction

Annealing Effect of Equiatomic Co/Pt Alloy Films

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

High Quality (100) and (001) Oriented Substrates Prepared from Czochralski Grown SrLaGaO_{4} and SrLaAlO_{4} Single Crystals

Mesoscopic Ordering Effects in Single-Crystalline Thin Films of Lanthanum Manganites

Atomic Order and the Interaction of Electronic and Magnetic Subsystems in Epitaxial LaSr(Ca)MnO Films

Studies of the Magnetic Axis Switching in Magnetite

Influence of Isomorphic Atom Substitution on Lattice Anisotropy of Thallium Dichalcogenide Layered Mixed Crystals