B. Palosz - Academia.edu (original) (raw)
Papers by B. Palosz
Acta Crystallographica Section A Foundations of Crystallography, 2002
The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-su... more The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-surface layer was examined using the concept of the apparent lattice parameter (alp) determined for different diffraction vectors Q. At low diffraction vectors the peak positions are affected mainly by the structure of the near-surface layer, while at high Qvalues only the interior of the grain contributes to the diffraction pattern. Theoretical alp-Q relations were obtained from diffraction patterns calculated for models of nanocrystals with a strained surface. We studied nanocrystalline SiC and GaN with average crystallite size from 5 to 30 nm. Following the measurements of as synthesized powders we investigated powders annealed at 400°C under vacuum, and same powders wetted with water. A strong dependence of the experimental alp-Q plots on the grain size and purity was found. Evaluation of the strain at the surface shell was made by comparison of experimental alp-Q plots with those computed for the core-shell model. We estimated the thickness of the shell in SiC nanocrystals to be 4-6 Å, with the tensile strain of about 10%. In GaN, the shell thickness is approximately 7Å with the compressive strain in the range 10-15%. Annealing the powders at 400°C under vacuum, as well as wetting them with water leads to a strong change of the measured alp values, Fig.1. We interpret this effect as a reconstruction of the atomic structure of the surface with simultaneous decrease of the surface strain.
The structure of commercial UD96 powder from Microdiamant AG, and the same powder purified by dif... more The structure of commercial UD96 powder from Microdiamant AG, and the same powder purified by different chemical treatment procedures were examined using large-Q neutron diffraction (NPDF at LANSCE). Both real (PDF) and reciprocal (Bragg) space analyses were employed to examine a tentative core-shell model of nanodiamond grains. Elaboration of diffraction data was based on the concept of the "apparent lattice parameters" (alp) calculated for individual interatomic distances determined from experimental PDF results. Experimental alp(r) plots were compared to the theoretical ones calculated for atomic models with multishell structures. It was concluded that the atomic structure of nanodiamond can be best described by a model where the inner core is surrounded by four shells with alternate compressive and tensile strains.
Glass Physics and Chemistry, 2005
Considerable effort is devoted to the synthesis of refractory carbide ceramics as promising mater... more Considerable effort is devoted to the synthesis of refractory carbide ceramics as promising materials for high-temperature applications, such as structural materials for the future generation of nuclear reactors. In this context, nanostructured ceramics are expected to exhibit interesting behavior under irradiation as compared with conventional materials. We report on the synthesis of SiC, TiC, and ZrC nanopowders by laser pyrolysis. The powders were characterized by X-ray diffraction, BET specific surface measurements, scanning electron microscopy, and transmission electron microscopy. SiC nanopowders were obtained from the decomposition of a mixture of silane and acetylene and were composed of grains varying in size from 7.2 to 43.0 nm. Liquid precursors were laser pyrolyzed with ethylene as a sensitizer in order to synthesize Ti-C-O or Zr-C-O powders. Annealing treatments in an argon atmosphere enabled the formation of 45-nm TiC grains or 38-nm ZrC grains through the carburization of the oxide phase by free carbon. Nanocrystalline ceramics were elaborated from SiC or TiC powders by very high pressure (8 GPa) sintering without any sintering additives. The densification reached 94% for SiC and 80% for TiC, without significant grain growth.
Journal of Nanoparticle Research, 2017
AbstractThe results of molecular dynamics (MD) simulations of CdSe crystals terminated by low-ind... more AbstractThe results of molecular dynamics (MD) simulations of CdSe crystals terminated by low-index atomic planes, (100), (110) and (111), are presented. The effect of the crystal termination on the atomic arrangement (interatomic distances) at the surface and underneath the surface is examined. It is shown that the crystal lattice is distorted in lateral and normal directions to the depth of up to about 2 nm from the surface. The exact characteristic of the changes of interatomic distances is specific to the type of the atomic plane terminating the crystal lattice. At some surfaces, the very last monoatomic layer loses the long-range ordering and becomes quasi amorphous. The atoms group into randomly distributed pairs or short linear groups. Graphical abstract
hard with soft materials in nanoscale under high-pressure high-
Journal of Physics: Condensed Matter, 1990
PbI 2 polytype 2H cristallise dans P3m1 avec a=4,5580, c=6,986 A, Z=1; affinement jusqu'a R=0... more PbI 2 polytype 2H cristallise dans P3m1 avec a=4,5580, c=6,986 A, Z=1; affinement jusqu'a R=0,021. PbI 2 polytype 4H cristallise dans P3m1 avec a=4,554, c=13,962 A, Z=2; affinement jusqu'a R=0,049. Une forte modulation de l'occupation des couches Pb et I (pour 2H, les occupations sont de 0,8 dans les deux couches) le long de c est observee pour 4H. Les occupations varient entre 0,7 et 0,9
Journal of Physics: Condensed Matter, 1990
High resolution x-ray diffraction peaks of diamond nanosize powders of nominal sizes ranging from... more High resolution x-ray diffraction peaks of diamond nanosize powders of nominal sizes ranging from 5 to 250 nm were analyzed and provided information on grain structure, average size of crystallites, and concentration of dislocations. Selected samples were heat treated at 1670 K at pressures 2.0 and 5.5 GPa or had surface modified by outgassing, heat treatment at vacuum conditions, and by controlled adsorption of gases. The apparent lattice parameter method was applied to characterize the structure of a shell-core model of nanosize particles. The multiple whole profile fitting provided information on crystallite sizes and density of dislocations. Population of dislocations increased with applied pressure, while strain and interplanar distances in the surface layers decreased. Adsorption of foreign gases on the grain surface modified the structure of the surface layers but did not affect dislocations near the center of the grains. © 2005 American Institute of Physics. DOI: 10.1063/1.1...
Acta Crystallographica Section A Foundations of Crystallography
Solid State Phenomena, 2005
SiC-Zn nanocomposites with about 20% volume fraction of metal were fabricated by infiltration pro... more SiC-Zn nanocomposites with about 20% volume fraction of metal were fabricated by infiltration process under the pressure of 2-8 GPa and at the temperature of 400_1000oC. SiC nanopowders used in the experiments formed loosely agglomerated chains of single crystal nanoparticles. The dimension of the agglomerates was in the micrometer range, the mean grain size was up to tens of nanometers. Microstructural investigations of the nanocomposites were performed at a different resolution levels using scanning, transmission electron microscopy and atomic force microscopy techniques (SEM, TEM, AFM, respectively). SEM observations indicate a presence of nano-dispersed, uniform (on the micrometer scale) mixture of two phases. TEM observations show that distribution of SiC and Zn nanocrystallites is uniform on the nanometer scale. High-resolution TEM images demonstrate an existence of thin (on the order of tens of Angstroms) Zn layers separating SiC grains. AFM images of the mechanically polishe...
Zeitschrift für Kristallographie Supplements, 2006
Thermal atomic motions of nanocrystalline SiC were characterized by two temperature atomic factor... more Thermal atomic motions of nanocrystalline SiC were characterized by two temperature atomic factors B core and B shell. With the use of wide angle neutron diffraction data it was shown that at the diffraction vector of above 15 Å-1 the Wilson plot gives directly the temperature factor of the grain interior (B core). At lower Q values the slope of the plot provides information on the relative amplitudes of vibrations of the core and shell atoms.
Materials Science Forum, 2001
Zeitschrift Fur Kristallographie, 1995
Disordering in SiC is analyzed both theoretically and experimentally. Classification of the stack... more Disordering in SiC is analyzed both theoretically and experimentally. Classification of the stacking faults into (i) intrinsic, (ii) twin-like and (iii) extrinsic faults is proposed. This classification correlates well with distinct diffraction effects, characteristic for specific faults. Based on proposed classification, the disordering in SiC
Solid State Ionics, 2008
Rigid, mechanically reinforced, composite Ag+-ion conductors based on xAgI·(100-x) (0.67Ag2O·0.33... more Rigid, mechanically reinforced, composite Ag+-ion conductors based on xAgI·(100-x) (0.67Ag2O·0.33B2O3), 40≤x≤60, glasses and hard insulating powders of α-Al2O3 (2 µm) or ZrO2 (1 µm) were prepared by a high-pressure method. Microstructure of the composites, depended on the content of AgI in the glasses and the temperature of the high-pressure stage of the synthesis. In all cases, however, it consisted of the evenly distributed phases (conductive and insulating), which did not interpenetrate at a nanometer length scale. It was found that the high electrical conductivity of the composites, though somewhat lower than that of the glasses, generally followed the temperature- and composition dependencies of the latter. An important advantage of the composites over the corresponding glasses was their higher microhardness and non-brittleness, which, contrary to the glasses, enabled their post-synthesis machining, cutting or polishing.
MRS Proceedings, 1998
Compacts of composites SiC-diamond were made by infiltration of Si into nanocrystalline diamond p... more Compacts of composites SiC-diamond were made by infiltration of Si into nanocrystalline diamond powders in a toroid-type press under the pressure of 7.7 GPa at 1300 °C. In-situ high pressure diffraction studies of these processes were performed in MAX80 cubic anvil press at a pressure of 8.5 GPa in temperatures up to 1800°C in HASYLAB at DESY, Hamburg, Germany. Sintering was performed for (i) pure nanocrystalline diamond powders, (ii) a mixture of nanocrystalline powders of diamond and nanocrystalline SiC, (iii) a mixture of nanocrystalline diamond with microcrystalline Si powders and (iv) compacts of nanocrystalline diamond infiltrated by Si. The SiC-diamond composites obtained by infiltration of Si have best physical properties: hardness similar to conventional diamond compacts (approximately 50 GPa), highest density 3.35 g cm-3 and uniform nanocrystalline microstructure.
Acta Crystallographica Section A Foundations of Crystallography, 2002
The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-su... more The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-surface layer was examined using the concept of the apparent lattice parameter (alp) determined for different diffraction vectors Q. At low diffraction vectors the peak positions are affected mainly by the structure of the near-surface layer, while at high Qvalues only the interior of the grain contributes to the diffraction pattern. Theoretical alp-Q relations were obtained from diffraction patterns calculated for models of nanocrystals with a strained surface. We studied nanocrystalline SiC and GaN with average crystallite size from 5 to 30 nm. Following the measurements of as synthesized powders we investigated powders annealed at 400°C under vacuum, and same powders wetted with water. A strong dependence of the experimental alp-Q plots on the grain size and purity was found. Evaluation of the strain at the surface shell was made by comparison of experimental alp-Q plots with those computed for the core-shell model. We estimated the thickness of the shell in SiC nanocrystals to be 4-6 Å, with the tensile strain of about 10%. In GaN, the shell thickness is approximately 7Å with the compressive strain in the range 10-15%. Annealing the powders at 400°C under vacuum, as well as wetting them with water leads to a strong change of the measured alp values, Fig.1. We interpret this effect as a reconstruction of the atomic structure of the surface with simultaneous decrease of the surface strain.
The structure of commercial UD96 powder from Microdiamant AG, and the same powder purified by dif... more The structure of commercial UD96 powder from Microdiamant AG, and the same powder purified by different chemical treatment procedures were examined using large-Q neutron diffraction (NPDF at LANSCE). Both real (PDF) and reciprocal (Bragg) space analyses were employed to examine a tentative core-shell model of nanodiamond grains. Elaboration of diffraction data was based on the concept of the "apparent lattice parameters" (alp) calculated for individual interatomic distances determined from experimental PDF results. Experimental alp(r) plots were compared to the theoretical ones calculated for atomic models with multishell structures. It was concluded that the atomic structure of nanodiamond can be best described by a model where the inner core is surrounded by four shells with alternate compressive and tensile strains.
Glass Physics and Chemistry, 2005
Considerable effort is devoted to the synthesis of refractory carbide ceramics as promising mater... more Considerable effort is devoted to the synthesis of refractory carbide ceramics as promising materials for high-temperature applications, such as structural materials for the future generation of nuclear reactors. In this context, nanostructured ceramics are expected to exhibit interesting behavior under irradiation as compared with conventional materials. We report on the synthesis of SiC, TiC, and ZrC nanopowders by laser pyrolysis. The powders were characterized by X-ray diffraction, BET specific surface measurements, scanning electron microscopy, and transmission electron microscopy. SiC nanopowders were obtained from the decomposition of a mixture of silane and acetylene and were composed of grains varying in size from 7.2 to 43.0 nm. Liquid precursors were laser pyrolyzed with ethylene as a sensitizer in order to synthesize Ti-C-O or Zr-C-O powders. Annealing treatments in an argon atmosphere enabled the formation of 45-nm TiC grains or 38-nm ZrC grains through the carburization of the oxide phase by free carbon. Nanocrystalline ceramics were elaborated from SiC or TiC powders by very high pressure (8 GPa) sintering without any sintering additives. The densification reached 94% for SiC and 80% for TiC, without significant grain growth.
Journal of Nanoparticle Research, 2017
AbstractThe results of molecular dynamics (MD) simulations of CdSe crystals terminated by low-ind... more AbstractThe results of molecular dynamics (MD) simulations of CdSe crystals terminated by low-index atomic planes, (100), (110) and (111), are presented. The effect of the crystal termination on the atomic arrangement (interatomic distances) at the surface and underneath the surface is examined. It is shown that the crystal lattice is distorted in lateral and normal directions to the depth of up to about 2 nm from the surface. The exact characteristic of the changes of interatomic distances is specific to the type of the atomic plane terminating the crystal lattice. At some surfaces, the very last monoatomic layer loses the long-range ordering and becomes quasi amorphous. The atoms group into randomly distributed pairs or short linear groups. Graphical abstract
hard with soft materials in nanoscale under high-pressure high-
Journal of Physics: Condensed Matter, 1990
PbI 2 polytype 2H cristallise dans P3m1 avec a=4,5580, c=6,986 A, Z=1; affinement jusqu'a R=0... more PbI 2 polytype 2H cristallise dans P3m1 avec a=4,5580, c=6,986 A, Z=1; affinement jusqu'a R=0,021. PbI 2 polytype 4H cristallise dans P3m1 avec a=4,554, c=13,962 A, Z=2; affinement jusqu'a R=0,049. Une forte modulation de l'occupation des couches Pb et I (pour 2H, les occupations sont de 0,8 dans les deux couches) le long de c est observee pour 4H. Les occupations varient entre 0,7 et 0,9
Journal of Physics: Condensed Matter, 1990
High resolution x-ray diffraction peaks of diamond nanosize powders of nominal sizes ranging from... more High resolution x-ray diffraction peaks of diamond nanosize powders of nominal sizes ranging from 5 to 250 nm were analyzed and provided information on grain structure, average size of crystallites, and concentration of dislocations. Selected samples were heat treated at 1670 K at pressures 2.0 and 5.5 GPa or had surface modified by outgassing, heat treatment at vacuum conditions, and by controlled adsorption of gases. The apparent lattice parameter method was applied to characterize the structure of a shell-core model of nanosize particles. The multiple whole profile fitting provided information on crystallite sizes and density of dislocations. Population of dislocations increased with applied pressure, while strain and interplanar distances in the surface layers decreased. Adsorption of foreign gases on the grain surface modified the structure of the surface layers but did not affect dislocations near the center of the grains. © 2005 American Institute of Physics. DOI: 10.1063/1.1...
Acta Crystallographica Section A Foundations of Crystallography
Solid State Phenomena, 2005
SiC-Zn nanocomposites with about 20% volume fraction of metal were fabricated by infiltration pro... more SiC-Zn nanocomposites with about 20% volume fraction of metal were fabricated by infiltration process under the pressure of 2-8 GPa and at the temperature of 400_1000oC. SiC nanopowders used in the experiments formed loosely agglomerated chains of single crystal nanoparticles. The dimension of the agglomerates was in the micrometer range, the mean grain size was up to tens of nanometers. Microstructural investigations of the nanocomposites were performed at a different resolution levels using scanning, transmission electron microscopy and atomic force microscopy techniques (SEM, TEM, AFM, respectively). SEM observations indicate a presence of nano-dispersed, uniform (on the micrometer scale) mixture of two phases. TEM observations show that distribution of SiC and Zn nanocrystallites is uniform on the nanometer scale. High-resolution TEM images demonstrate an existence of thin (on the order of tens of Angstroms) Zn layers separating SiC grains. AFM images of the mechanically polishe...
Zeitschrift für Kristallographie Supplements, 2006
Thermal atomic motions of nanocrystalline SiC were characterized by two temperature atomic factor... more Thermal atomic motions of nanocrystalline SiC were characterized by two temperature atomic factors B core and B shell. With the use of wide angle neutron diffraction data it was shown that at the diffraction vector of above 15 Å-1 the Wilson plot gives directly the temperature factor of the grain interior (B core). At lower Q values the slope of the plot provides information on the relative amplitudes of vibrations of the core and shell atoms.
Materials Science Forum, 2001
Zeitschrift Fur Kristallographie, 1995
Disordering in SiC is analyzed both theoretically and experimentally. Classification of the stack... more Disordering in SiC is analyzed both theoretically and experimentally. Classification of the stacking faults into (i) intrinsic, (ii) twin-like and (iii) extrinsic faults is proposed. This classification correlates well with distinct diffraction effects, characteristic for specific faults. Based on proposed classification, the disordering in SiC
Solid State Ionics, 2008
Rigid, mechanically reinforced, composite Ag+-ion conductors based on xAgI·(100-x) (0.67Ag2O·0.33... more Rigid, mechanically reinforced, composite Ag+-ion conductors based on xAgI·(100-x) (0.67Ag2O·0.33B2O3), 40≤x≤60, glasses and hard insulating powders of α-Al2O3 (2 µm) or ZrO2 (1 µm) were prepared by a high-pressure method. Microstructure of the composites, depended on the content of AgI in the glasses and the temperature of the high-pressure stage of the synthesis. In all cases, however, it consisted of the evenly distributed phases (conductive and insulating), which did not interpenetrate at a nanometer length scale. It was found that the high electrical conductivity of the composites, though somewhat lower than that of the glasses, generally followed the temperature- and composition dependencies of the latter. An important advantage of the composites over the corresponding glasses was their higher microhardness and non-brittleness, which, contrary to the glasses, enabled their post-synthesis machining, cutting or polishing.
MRS Proceedings, 1998
Compacts of composites SiC-diamond were made by infiltration of Si into nanocrystalline diamond p... more Compacts of composites SiC-diamond were made by infiltration of Si into nanocrystalline diamond powders in a toroid-type press under the pressure of 7.7 GPa at 1300 °C. In-situ high pressure diffraction studies of these processes were performed in MAX80 cubic anvil press at a pressure of 8.5 GPa in temperatures up to 1800°C in HASYLAB at DESY, Hamburg, Germany. Sintering was performed for (i) pure nanocrystalline diamond powders, (ii) a mixture of nanocrystalline powders of diamond and nanocrystalline SiC, (iii) a mixture of nanocrystalline diamond with microcrystalline Si powders and (iv) compacts of nanocrystalline diamond infiltrated by Si. The SiC-diamond composites obtained by infiltration of Si have best physical properties: hardness similar to conventional diamond compacts (approximately 50 GPa), highest density 3.35 g cm-3 and uniform nanocrystalline microstructure.