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1

Structural Basis of Interface Engineering

100%

Świątnicki W.

Acta Physica Polonica A

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1996

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vol. 89

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issue 2

235-249

EN

The paper analyses in a systematic manner these structural factors of interfaces in relation to their properties that constitute the background of "interface engineering". It is shown that the specific properties of interfaces are related to their structure. A brief description of recent structural models of interfaces is therefore presented. A new concept of interface microstructure composed of different kinds of interfacial defects is introduced and their role in determining the interface properties is emphasised. It is shown that interfaces control the processes taking place in the material under external solicitations or during the microstructure formation, mainly through their interaction with other crystal defects. Various examples illustrating the possibility of controlling and improving the material properties by appropriate changes of interface structures are presented in the case of metals, alloys, intermetallics and ceramics.

2

High Temperature Structure and Properties of Grain Boundaries - Insights Obtained from Atomic Level Simulations

63%

Keblinski P.

Acta Physica Polonica A

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2002

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vol. 102

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issue 1

123-134

EN

Molecular-dynamics simulations of grain boundaries in Si and fcc metals reveal that high-energy boundaries are disordered, even at low temperatures, with their local atomic structure very similar to that of bulk amorphous material. By contrast, low energy grain boundaries are crystalline all the way up to the melting point. Upon heating intergranular"confined amorphous" structures of high-energy grain boundaries exhibit reversible transition into universal, highly confined, liquid-like structure. High-temp erature properties, such as the grain boundary diffusion therefore involve liquid-like mechanisms, with activation energies related to the diffusion process in the melt. By contrast to Si and fcc metals, high-energy diamond grain boundaries are more ordered structurally, but contain coordination disorder resulting from ability of carbon to change its hybridization from s p^3 to sp^2 character. Based on the insights obtained from our simulation of individual grain boundaries we were able to design nanocrystalline 3D microstructures, which allow to study grain boundary diffusion creep process by molecular-dynamics simulations. In order to prevent grain growth and thus to enable steady-state diffusion creep to be observed on a time scale accessible to molecular-dynamics simulations (of typically 10^{-9} s), our input microstructures were tailored to (i) have a uniform grain shape and a uniform grain size of nm dimensions and (ii) contain only high-energy grain boundaries that, consistently with our studies of individual, bicrystalline grain boundaries, exhibit rather fast, liquid-like self-diffusion at high temperatures. Our simulations reveal that under relatively high tensile stresses these microstructures, indeed, exhibit steady-state diffusion creep that is homogeneous with a strain rate that agrees quantitatively with that given by the Coble-creep formula.

3

Defects in Detwinned LaGaO_{3} Substrates

63%

Mazur K., Fink-Finowicki J., Berkowski M., Schell N.

Acta Physica Polonica A

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1997

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vol. 92

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issue 1

205-208

EN

Single crystals of lanthanum gallate would be the suitable substrate for YBaCuO films except for the phase transition and the tendency to twinning existing in this material. However, by appropriate choice of growth conditions in the Czochralski method, it is possible to grow single crystal of LaGaO_{3} with low density of twin boundaries. Special stress and temperature treatment can then be applied to such materials to remove majority of existing twins. The substrates were examined by X-ray topography before and after detwinning and the surface was scanned with a profilometer.

4

Orientation States in Rhombic NdGaO_{3}

63%

Savytskii D. I., Ubizskii S. B., Vasylechko L. O., Syvorotka I. M., Matkovskii A. O.

Acta Physica Polonica A

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1997

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vol. 92

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issue 1

231-236

EN

The ferroelastic domain structure of NdGaO_{3} is analyzed by three theories: group symmetry, tensor method and twinning by pseudosymmetry. The theories provide a coherent description of domain pairs and a determination of the position of W and S walls.

5

Cathodoluminescence Profiling of InGaN-Based Quantum Well Structures and Laser Diodes - In-Plane Instabilities of Light Emission

51%

Godlewski M., Ivanov V., Goldys E., Phillips M., Böttcher T., Figge S., Hommel D., Czernecki R., Prystawko P., Leszczynski M., Perlin P., Grzegory I., Porowski S.

Acta Physica Polonica A

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2003

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vol. 103

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issue 6

689-694

EN

Instabilities of light emission and also of stimulated emission in series of GaN epilayers and InGaN quantum well structures, including laser diode structures, are studied. A stimulated emission is observed under electron beam pumping. This enabled us to study light emission properties from laser structures and their relation to microstructure details. We demonstrate large in-plane fluctuations of light emission and that these fluctuations are also present for excitation densities larger than the threshold densities for the stimulated emission.

6

Anelastic Phenomena in Mg-Al Alloys

51%

Nagarajan D., Caceres C., Griffiths J.

Acta Physica Polonica A

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2012

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vol. 122

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issue 3

501-504

EN

Cyclic loading-unloading in tension and compression has been used to quantify the anelastic behaviour, in the form of hysteresis loops, of pure Mg and three Mg-Al alloys (0.5, 2, and 9 at.% Al). The effect reached a maximum at a plastic strain of ≈ 0.02 for all of the materials, and decreased at higher strains. The amount of anelasticity at any given strain was smaller for the dilute alloys in comparison with the pure Mg whereas it increased above that of pure Mg for the most concentrated alloy. Possible reasons for this behaviour are discussed in terms of reversible twinning, solid solution softening, and hardening and short range order.

7

Some Recent Results on the 3C-SiC Structural Defects

51%

Mantzari A., Andreadou A., Marinova M., Polychroniadis E.

Acta Physica Polonica A

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2012

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vol. 121

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issue 1

187-189

EN

This work presents some recent results on the 3C-SiC structural defects, studied by transmission electron microscopy. The samples were grown in several laboratories, using different methods. There has always been special attention to the region close to the interface between the seed and the overgrown material. This is due to the fact that this region is very important to the evolution of defects during growth. The main defects in SiC are micropipes, double position boundaries, stacking faults and dislocations. The defects that are most frequently observed in 3C-SiC and more difficult to eliminate are inclusions of other polytypes, twins and microtwins and mainly stacking faults.

8

Phase Field Modeling of the Zn_{1-x}Cd_xO Solid Solutions

51%

Shtepliuk I., Podolskaia N., Lashkarev G.

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vol. 126

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issue 5

1079-1082

EN

The analysis of spinodal decomposition in the Zn_{1-x}Cd_xO ternary alloy was carried out by means of the nonlinear Cahn-Hilliard equation. Interaction parameter as a function of composition x was provided by valence force field simulations and was used in this analysis. The morphological patterns for the ternary alloys with different Cd content (x=5, 10, 50%) were experimentally obtained using the semi-implicit Fourier-spectral method. The simulated microstructure evolution Zn_{0.95}Cd_{0.05}O demonstrates that the microstructure having a form of bicontinuous worm-like network is evolved with the progress of aging. An effect of the phase-field mobility and the gradient energy on the microstructure evolution of the Zn_{1-x}Cd_xO alloys is discussed. It was found that the higher driving force for the decomposition in the higher Cd content film results in a higher decomposition rate revealed by the simulations. The temporal evolution of the simulated Zn_{0.95}Cd_{0.05}O microstructure is in good agreement with experimental results, which have been obtained for this solid solution.

9

Image Force Effect on the Separation of Partial Dislocations in Bicrystals of Hexagonal Structure Zn-Tl and Zn-Be

51%

Ayadi A., Khalfallah O.

Acta Physica Polonica A

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2013

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vol. 123

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issue 2

302-303

EN

We study the elastic interaction between a pair of partial dislocations, resulting from the dissociation of a perfect dislocation, and a bimetallic interface. The forces that act on two partials dislocations are the forces due to elastic interaction between the partial and image forces due to interactions of partial dislocations with interface. We are interested in the effect of image force on width of the stacking fault ribbon between two Schockley partials. We show that the separation of two partials dislocations is modified compared to that in the single crystal. It depends on the ratio of shear modulus and the distance between the interface and the dislocation.

10

The Effect of Reversed Loading Conditions on the Mechanical Behaviour of Extruded Magnesium Alloy AZ31

51%

Bohlen J., Dobron P., Nascimento L., Parfenenko K., Chmelik F., Letzig D.

Acta Physica Polonica A

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2012

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vol. 122

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issue 3

444-449

EN

An indirectly extruded round bar of magnesium alloy AZ31 has been subjected to a cyclic test consisting of preloading in compression to different values of maximum stress followed by a single tensile test segment. Concurrent acoustic emission measurements were used to determine the active deformation mechanisms during plastic flow and work hardening. Electron backscattering diffraction was applied to obtain local orientation images in order to reveal twins and twinned fractions of the microstructure. Twins form preferentially in larger grains during the compression test segment and only with increasing stress do smaller grains show twinning. Some grains are completely re-oriented as a result of twinning. During the tensile test segment, untwinning is the most significant deformation mechanism although in some re-oriented grains new twins also nucleate. The acoustic emission count rates confirm that this is only the case after compression to higher stress levels.

11

Evolution of Matrix-Twin Interfaces of (101̅2) Twin in Magnesium

51%

Ostapovets A., Serra A.

Acta Physica Polonica A

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2015

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vol. 128

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issue 4

661-663

EN

Recently, the presence of basal-prismatic interfaces in hexagonal close packed metals became subject of intensive investigation. We model the {101̅2} twin in magnesium bounded by two types of boundaries, i.e. {101̅2} interface and basal-prismatic facets. The migration of all boundary types is mediated by the motion of interfacial disconnections. It was shown that basal-prismatic interfaces play an important role in twin growth. The lengths of basal-prismatic facets remain constant during migration independently of the applied strain. In contrast, the {101̅2} interfaces increase their lengths during growth.

12

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

51%

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.

13

Relationship between Sample Morphology and Carrier Diffusion Length in GaN Thin Films

51%

Godlewski M., Goldys E., Phillips M., Böttcher T., Figge S., Hommel D., Czernecki R., Prystawko P., Leszczynski M., Perlin P., Wisniewski P., Suski T., Bockowski M., Grzegory I., Porowski S.

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issue 4-5

627-632

EN

Scanning and spot-mode cathodoluminescence investigations of homo- and hetero-epitaxial GaN films indicate a surprisingly small influence of their microstructure on overall intensity of a light emission. This we explain by a correlation between structural quality of these films and diffusion length of free carriers and excitons. Diffusion length increases with improving structural quality of the samples, which, in turn, enhances the rate of nonradiative recombination on structural defects, such as dislocations.

14

Alpha Variant Selection Determined from Grain Misorientations in Ti-6Al-7Nb Alloy with a Duplex Microstructure

51%

Harcuba P., Václavová K., Čapek J., Stráský J., Janeček M., Janovská M.

Acta Physica Polonica A

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2015

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vol. 128

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issue 4

570-573

EN

Titanium occurs in two structures; a high temperature body-centered cubic structure which is known as β phase and an ambient temperature α phase which has the hexagonal closed-packed structure. In the present study a biomedical Ti-6Al-7Nb alloy was investigated. The so-called duplex structure consisting of α lamellae and equiaxed primary α-grains was prepared by a thermal treatment. The α lamellae are created during cooling from a β-field according to the Burgers relation. This relation allows the formation of the α lamellae with different crystallographic orientations - so-called variants. The preferential misorientation between α lamellae was studied by a detailed electron backscattered diffraction analysis. The misorientation of grains in the duplex structure was modelled by a sum of random Mackenzie distribution and Gaussian peaks related to the preferred misorientations according to the Burgers relation. The preferred misorientations based on the Burgers relationship were identified in the biomedical Ti-6Al-7Nb alloy with duplex structure. It is confirmed that the variant selection of α lamellae is not random.

15

Calculation of Free Volume in Computer Generated Grain Boundaries

51%

Van Petegem S., Kuriplach J.

Acta Physica Polonica A

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2005

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vol. 107

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issue 5

769-775

EN

We investigate the positron lifetime distribution in grain boundaries originating from computer generated nanocrystalline configurations. We give a brief overview of the computational methods and we discuss the influence of thermal vibrations and grain size on the obtained positron lifetime distributions.

16

Identification of the Domain Walls Configuration in the Ferroelastic Nanosize Material La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x}

51%

Savytskii D., Paulmann C., Bismayer U., Berkowski M.

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issue 1

62-73

EN

This paper deals with the identification of multidomain configuration in ferroelastic phases of La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x} using polychromatic synchrotron X-ray radiation (Laue method). A nondestructive approach for the determination of domain misorientations, orientation of domain walls and their configuration in the nanosize ferroelastic domain structure was developed. The proposed approach can be used to study the nanosize ferroelastic domain structure in small crystals of submillimeter sizes at different external fields, including temperature. The ferroelastic domain structure in the orthorhombic as well as in the rhombohedral phases of La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x} crystals has been identified. The intersection of walls leads to the formation of a chevron-like pattern. The observed reversibility of domain patterns during temperature cycles is probably caused by the interaction of domain boundaries with point defects, most likely oxygen vacancies.

17

Symmetry Pattern and Domain Wall Structure in GdFeO_{3} Perovskite Type

51%

Savytskii D., Tataryn T., Bismayer U.

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issue 1

78-85

EN

Symmetry relations between the domain states in GdFeO_{3} type crystals have been obtained using group-theoretical analysis for prototype and ferroelastic space groups. Models for possible domain pairs are developed. The ion locations on the domain boundary were estimated as intermediate positions between the sites in crystal structure of neighboring domain states. It is shown that the crystalline structure of the boundary approaches to the prototype phase structure - the ideal ABO_{3} perovskite-type structure, however certain deformations remain. In addition to the shifts of the all ions the tilts of oxygen octahedra of the some type and related displacements of A ions should take place during the switching of orientation states. The tilts of octahedra and displacements of A ions are sufficient to form translation states (antiphase domains). Antiphase domains can have boundaries between themselves basically along the three faces of the orthorhombic cell.

18

Theoretical Study of the Ferroelastic Domain Structure in La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x}

51%

Savytskii D., Tataryn T., Martynyuk N., Bismayer U.

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issue 1

48-61

EN

Theoretical analysis of the ferro-elastic domain structure of a La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{2.925} crystal in three different crystallographic phases is presented. Parameters of these configurations are obtained using group theoretical approach, the method of spontaneous deformation as well as theoretical interpretation of twinning resulting from mechanical deformation (mechanical twinning theory). In the three phases of La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{2.95} - trigonal, orthorhombic and monoclinic - the parameters of ferro-elastic domain structures are determined; namely the quantity of orientation states, symmetry elements of connection between states, orientations and types of domain walls, tensors of spontaneous deformations of the perovskite-type cells for every orientation state, elements of twin shifts, which are needed for the reorientation of some orientation states to others. By using the found parameters of bidomain configurations a mechanism is proposed, which causes chevron-like domain configurations in compounds with martensitic phase transitions.

19

High Pulsed Magnetic Field Sensor Based on La-Ca-Mn-O Thin Polycrystalline Films

51%

Balevičius S., Žurauskienė N., Stankevič V., Keršulis S., Novickij J., Altgilbers L., Clarke F.

Acta Physica Polonica A

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2005

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vol. 107

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issue 1

207-210

EN

It is demonstrated that polycrystalline La_{0.33}Ca_{0.67}MnO_3 thin film sensors can be used to measure pulsed strong magnetic fields with microsecond duration rise and decay times. The response characteristics of these sensors were investigated using 0.7-1.0 ms duration bell-shaped magnetic field pulses of 10-20 T amplitudes and by using special waveform magnetic field pulses with amplitudes of 40 T and decay times of 50μs. The response of these magnetic field sensors was compared with those of conventional loop sensors and Faraday rotation sensors using Bi_{12}SiO_{20} single crystals as a known standard.

20

Comparison of Grain Boundary Structure in Metals and Semiconductors as Probed by Positrons

51%

Kuriplach J.

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vol. 125

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issue 3

722-725

EN

Vacancy behavior and positron trapping at selected grain boundaries in iron, nickel, and zirconia are investigated theoretically. It is found that the grain boundary vacancy loses its free volume in metals at moderate temperatures whereas it is kept up to very high temperatures in zirconia. The consequences of these findings for positron annihilation studies of nanocrystalline materials are discussed.

Refine search results

Structural Basis of Interface Engineering

High Temperature Structure and Properties of Grain Boundaries - Insights Obtained from Atomic Level Simulations

Defects in Detwinned LaGaO_{3} Substrates

Orientation States in Rhombic NdGaO_{3}

Cathodoluminescence Profiling of InGaN-Based Quantum Well Structures and Laser Diodes - In-Plane Instabilities of Light Emission

Anelastic Phenomena in Mg-Al Alloys

Some Recent Results on the 3C-SiC Structural Defects

Phase Field Modeling of the Zn_{1-x}Cd_xO Solid Solutions

Image Force Effect on the Separation of Partial Dislocations in Bicrystals of Hexagonal Structure Zn-Tl and Zn-Be

The Effect of Reversed Loading Conditions on the Mechanical Behaviour of Extruded Magnesium Alloy AZ31

Evolution of Matrix-Twin Interfaces of (101̅2) Twin in Magnesium

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

Relationship between Sample Morphology and Carrier Diffusion Length in GaN Thin Films

Alpha Variant Selection Determined from Grain Misorientations in Ti-6Al-7Nb Alloy with a Duplex Microstructure

Calculation of Free Volume in Computer Generated Grain Boundaries

Identification of the Domain Walls Configuration in the Ferroelastic Nanosize Material La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x}

Symmetry Pattern and Domain Wall Structure in GdFeO_{3} Perovskite Type

Theoretical Study of the Ferroelastic Domain Structure in La_{0.95}Sr_{0.05}Ga_{0.9}Mg_{0.1}O_{3-x}

High Pulsed Magnetic Field Sensor Based on La-Ca-Mn-O Thin Polycrystalline Films

Comparison of Grain Boundary Structure in Metals and Semiconductors as Probed by Positrons