J. Davaasambuu - Academia.edu (original) (raw)
Papers by J. Davaasambuu
Journal of Applied Spectroscopy, 2007
We have used Fourier transform IR spectroscopy to study structural changes in coals of different ... more We have used Fourier transform IR spectroscopy to study structural changes in coals of different degrees of coalification when stored for prolonged periods under normal conditions. As a result of reaction of the surface of the coals with atmospheric oxygen and water vapor, the intensities of characteristic absorption bands were enhanced which, when we considered elemental analysis data for the coals, allowed us to obtain additional information about their structure and impurity composition.
Acta Crystallographica Section A Foundations of Crystallography, 2010
Acta Crystallographica Section A Foundations of Crystallography, 2008
Acta Crystallographica Section A Foundations of Crystallography, 2008
ABSTRACT Poster
Acta Crystallographica Section A Foundations of Crystallography, 2010
Journal of synchrotron radiation, 2004
A general outline of how to perform a light-excited time-resolved diffraction experiment by apply... more A general outline of how to perform a light-excited time-resolved diffraction experiment by applying the optical pump/X-ray probe technique is given. Owing to the difference in penetration depths between the optical light (laser) pump and the X-ray probe, only specific or specially designed crystalline systems can be investigated, so special requirements have to be fulfilled concerning the sample and its compartments. A summary of the experimental conditions of optical pump/X-ray probe experiments is presented, emphasizing why the use of powder diffraction is a useful and necessary X-ray technique for this kind of experiment. The possibilities and bottlenecks of time-resolved X-ray diffraction on the picosecond time scale will be demonstrated in the powder diffraction studies of N,N-dimethylaminobenzonitrile and N,N-diisopropylaminobenzonitrile, where the photo-induced structural changes of these molecular organic systems have been studied as a function of time.
Using a modulation technique and synchrotron radiation, we investigated the charge density variat... more Using a modulation technique and synchrotron radiation, we investigated the charge density variations in cubic ZnSe and trigonal SiO 2 induced by an external high-electric ®eld E applied along the [111] and [11.0] direction, respectively. Selecting particularly weak re¯ections, we observed an almost linear variation of the integrated intensity versus E changing by up to 2% at uEu 3 kV/mm. For both crystals, the displacements of the relative ion positions within the unit cell exceed the piezoelectric induced variation of the unit cell parameters by at least one order of magnitude. The measured intensity variations of ZnSe can be explained by the opposite displacement of the zinc and selenium ions towards the ®eld direction breaking the stiff tetrahedral coordination of the chemical bond. For quartz, the electric ®eld initiates a displacement of those oxygen ions only where the O± Si bond is directed oblique to the ®eld direction. The other oxygen ions and the silicon positions remain nearly unchanged. Thus, the ionic arrangement is described mainly by a change in the O±Si±O bonding angles. q
18th European Frequency and Time Forum (EFTF 2004), 2004
ABSTRACT In order to understand the atomistic origin of the inverse piezoelectric effect in α-SiO... more ABSTRACT In order to understand the atomistic origin of the inverse piezoelectric effect in α-SiO2 and α-GaPO4 we have measured the changes of integrated X-ray intensities of selected Bragg reflection under influence of an external high electric field up to 8 kV/mm. To do this 300 μm thick samples were sandwiched between metallic contacts and the X-ray intensities were recorded with and without the applied field. The difference intensities were evaluated in terms of difference electron density of atoms within the respective crystallographic unit cell. Because the up to now accepted model of the field induced displacement of ionic sublattices against each other fails for the interpretation of experimental data we proposed a new model of the inverse piezoelectric effect, which considers the strong covalent bond between silicon and oxygen and gallium/phosphorous and oxygen, respectively. Here the main effect of screening the external electric field is a change in the Si-O-Si and Ga-O-P bonding angles, i.e. the rotations of nearly rigid MO4 tetrahedra.
The Journal of Physical Chemistry A, 2010
Time-resolved Laue crystallography has been employed to study the structural dynamics of a one-di... more Time-resolved Laue crystallography has been employed to study the structural dynamics of a one-dimensional organic conductor (tetrathiafulvalene-p-chloranil) during photoexcitation in the regime of the neutral to ionic phase transition. Exciting this crystalline system with 800 nm 100 fs long optical pulses leads to ultrafast population of a structural intermediate as early as 50 ps after excitation with a lifetime of at least 10 ns. Starting from the neutral phase, this intermediate has been assigned as a precursor state toward the photoinduced population of the ionic phase. The observed intensity changes are significantly different from comparable equilibrium structures. The interpretation of this structural data is that the potential of this intermediate is being softened during its population in a dynamical process. The depopulation proceeds through thermal processes.
Zeitschrift für Kristallographie, 2001
... [8] Ozolins V.; Zunger A.: Theory of systematic absence of NaCl-Type (b-Sn-Type) high pressur... more ... [8] Ozolins V.; Zunger A.: Theory of systematic absence of NaCl-Type (b-Sn-Type) high pressure phases in covalent (ionic) semi-conductors. ... [20] Willis, BTM: Lattice vibrations and the accurate determina-tion of structure factors for the elastic scattering of X-rays and Neutrons. ...
Journal of Synchrotron Radiation, 2005
In the next decade the scientific community expects a strong impact in physics, chemistry, biolog... more In the next decade the scientific community expects a strong impact in physics, chemistry, biology, material research and life sciences by the availability of highbrilliance X-ray radiation from free-electron laser (FEL) sources. In particular, in the field of ultrafast science these new sources will allow new types of experiments, enabling new phenomena to be discovered. Whereas today ultrafast X-ray diffraction experiments are strongly restricted by the limited X-ray flux of current sources of sub-picosecond X-ray pulses, FELs will provide short pulses of typically 10 12 photons with a duration of the order of 100 fs and monochromaticity of 10 À3 . Here, the feasibility of time-resolved single-shot powder diffraction experiments using these intense pulses, and the requirements of these experiments, are discussed. The detector count rates are estimated for diffraction from a model compound in a wide q-regime under the special consideration of high resolving power. In the case of LCLS radiation parameters, single-shot experiments will be feasible although high-resolution powder diffraction will require a reduction of the intrinsic FEL radiation bandwidth.
Journal of Synchrotron Radiation, 2004
A general outline of how to perform a light-excited time-resolved diffraction experiment by apply... more A general outline of how to perform a light-excited time-resolved diffraction experiment by applying the optical pump/X-ray probe technique is given. Owing to the difference in penetration depths between the optical light (laser) pump and the X-ray probe, only specific or specially designed crystalline systems can be investigated, so special requirements have to be fulfilled concerning the sample and its compartments. A summary of the experimental conditions of optical pump/X-ray probe experiments is presented, emphasizing why the use of powder diffraction is a useful and necessary X-ray technique for this kind of experiment. The possibilities and bottlenecks of time-resolved X-ray diffraction on the picosecond time scale will be demonstrated in the powder diffraction studies of N,Ndimethylaminobenzonitrile and N,N-diisopropylaminobenzonitrile, where the photo-induced structural changes of these molecular organic systems have been studied as a function of time.
Journal of Physics: Condensed Matter, 2012
The dynamics of silver-alkali halide mixed single crystals (Ag(x)Na(1-x)Br, x = 0.23, 0.35, 0.40 ... more The dynamics of silver-alkali halide mixed single crystals (Ag(x)Na(1-x)Br, x = 0.23, 0.35, 0.40 and 0.70) were studied by inelastic neutron scattering during the process of spinodal decomposition. Using the thermal three-axes spectrometer PUMA as well as the time-of-flight spectrometer IN5, the time evolution of phonons was observed in time-resolved, stroboscopic measurements. Complementary to the study of long wavelength acoustic phonons, as studied previously, we extended these investigations to Brillouin-zone boundary modes that are particularly sensitive to variations of the local structure. Starting from the homogeneous mixed phase the behaviour of these modes during demixing is observed in real-time. A simple dynamical model based on local structure variants helps to interpret the results. It is shown that the phonon lifetimes vary strongly during the phase separation and increase drastically during the coarsening process. Up to a critical size of precipitates of about 10 nm, zone-boundary modes are found to be strongly damped, while beyond the line widths are reduced to the experimental resolution. This finding leads to the conclusion that the typical mean free path of these modes is of the order of 10 nm, which corresponds to 20 unit cells.
Journal of Physics and Chemistry of Solids, 2001
Using a modulation technique and synchrotron radiation, we investigated the charge density variat... more Using a modulation technique and synchrotron radiation, we investigated the charge density variations in cubic ZnSe and trigonal SiO 2 induced by an external high-electric ®eld E applied along the [111] and [11.0] direction, respectively. Selecting particularly weak re¯ections, we observed an almost linear variation of the integrated intensity versus E changing by up to 2% at uEu 3 kV/mm. For both crystals, the displacements of the relative ion positions within the unit cell exceed the piezoelectric induced variation of the unit cell parameters by at least one order of magnitude. The measured intensity variations of ZnSe can be explained by the opposite displacement of the zinc and selenium ions towards the ®eld direction breaking the stiff tetrahedral coordination of the chemical bond. For quartz, the electric ®eld initiates a displacement of those oxygen ions only where the O± Si bond is directed oblique to the ®eld direction. The other oxygen ions and the silicon positions remain nearly unchanged. Thus, the ionic arrangement is described mainly by a change in the O±Si±O bonding angles. q
Journal of Physics and Chemistry of Solids, 2001
The valence charge density distribution (VCD) of cubic ZnSe was studied by means of theoretical a... more The valence charge density distribution (VCD) of cubic ZnSe was studied by means of theoretical and experimental methods. The theoretical VCDs were calculated in terms of the Hartree±Fock (HF), density functional (DF) and pseudopotential (PP) approach provided by the CRYSTAL95 program package. The experimental VCD was calculated via inverse Fourier transformation of X-ray structure factors. To avoid the extinction problem, we only measured a few low-indexed weak re¯ections (h 1 k 1 l 4n 1 2) in high precision, which are most sensitive for the chemical bond. The measured structure factors were analysed in terms of a bond charge model including charge transfer. The experimental data set was completed by re¯ections with h 1 k 1 l ± 4n 1 2 calculated in terms of the spherical atom model, but corrected by the parameters which received from the weak re¯ections. All structure factors were extrapolated to zero temperature using experimental temperature factors including anharmonicity. Despite the approximation made, the experimental VCD con®rms the ab initio calculations qualitatively. The experimental and theoretical VCDs of ZnSe are characterised by almost spherical charge densities around the ions carrying an effective charge of about 10.7 electrons. A bond charge was found to be located inside the electron cloud around the Se nucleus. Comparing the VCDs of the isoelectronic series Ge, GaAs and ZnSe the bond charge decreases in amount and shifts closer to the anion, increasing the charge transfer between the ions. q
Europhysics Letters (EPL), 2003
... A, 27 (1972) 469. [8] Calamiotou M., Psicharis V., Filippakis SE and Anastassakis E., J. Phys... more ... A, 27 (1972) 469. [8] Calamiotou M., Psicharis V., Filippakis SE and Anastassakis E., J. Phys. C, 20 (1987) 5641. ... [17] Le Page Y., Calvert LD and Gabe EJ, J. Phys. Chem. Sol., 41 (1980) 721. [18] Lager GA, Jorgensen JD and Rotella FJ, J. Appl. Phys., 53 (1982) 6751. ...
The Journal of Physical Chemistry A, 2006
Photoinduced structural variations in single crystals of 2,4-dichloro-trans-cinnamic acid (C9H6Cl... more Photoinduced structural variations in single crystals of 2,4-dichloro-trans-cinnamic acid (C9H6Cl2O2, DiClCA) have been investigated using X-ray diffraction (photocrystallography) and optical spectroscopic methods. During UV irradiation, which initiates the irreversible dimerization reaction, a loss of the long-range order of the reactant single crystal was found, i.e., that the dimerization is a heterogeneous one. This unexpected result emphasizes the still-existing problem of predicting changes or of remaining periodicity during chemical reactions in the solid state. On the basis of the experimental results, we propose a qualitative kinetic reaction scheme for DiClCA heterogeneous dimerization reaction.
Journal of Applied Spectroscopy, 2007
We have used Fourier transform IR spectroscopy to study structural changes in coals of different ... more We have used Fourier transform IR spectroscopy to study structural changes in coals of different degrees of coalification when stored for prolonged periods under normal conditions. As a result of reaction of the surface of the coals with atmospheric oxygen and water vapor, the intensities of characteristic absorption bands were enhanced which, when we considered elemental analysis data for the coals, allowed us to obtain additional information about their structure and impurity composition.
Acta Crystallographica Section A Foundations of Crystallography, 2010
Acta Crystallographica Section A Foundations of Crystallography, 2008
Acta Crystallographica Section A Foundations of Crystallography, 2008
ABSTRACT Poster
Acta Crystallographica Section A Foundations of Crystallography, 2010
Journal of synchrotron radiation, 2004
A general outline of how to perform a light-excited time-resolved diffraction experiment by apply... more A general outline of how to perform a light-excited time-resolved diffraction experiment by applying the optical pump/X-ray probe technique is given. Owing to the difference in penetration depths between the optical light (laser) pump and the X-ray probe, only specific or specially designed crystalline systems can be investigated, so special requirements have to be fulfilled concerning the sample and its compartments. A summary of the experimental conditions of optical pump/X-ray probe experiments is presented, emphasizing why the use of powder diffraction is a useful and necessary X-ray technique for this kind of experiment. The possibilities and bottlenecks of time-resolved X-ray diffraction on the picosecond time scale will be demonstrated in the powder diffraction studies of N,N-dimethylaminobenzonitrile and N,N-diisopropylaminobenzonitrile, where the photo-induced structural changes of these molecular organic systems have been studied as a function of time.
Using a modulation technique and synchrotron radiation, we investigated the charge density variat... more Using a modulation technique and synchrotron radiation, we investigated the charge density variations in cubic ZnSe and trigonal SiO 2 induced by an external high-electric ®eld E applied along the [111] and [11.0] direction, respectively. Selecting particularly weak re¯ections, we observed an almost linear variation of the integrated intensity versus E changing by up to 2% at uEu 3 kV/mm. For both crystals, the displacements of the relative ion positions within the unit cell exceed the piezoelectric induced variation of the unit cell parameters by at least one order of magnitude. The measured intensity variations of ZnSe can be explained by the opposite displacement of the zinc and selenium ions towards the ®eld direction breaking the stiff tetrahedral coordination of the chemical bond. For quartz, the electric ®eld initiates a displacement of those oxygen ions only where the O± Si bond is directed oblique to the ®eld direction. The other oxygen ions and the silicon positions remain nearly unchanged. Thus, the ionic arrangement is described mainly by a change in the O±Si±O bonding angles. q
18th European Frequency and Time Forum (EFTF 2004), 2004
ABSTRACT In order to understand the atomistic origin of the inverse piezoelectric effect in α-SiO... more ABSTRACT In order to understand the atomistic origin of the inverse piezoelectric effect in α-SiO2 and α-GaPO4 we have measured the changes of integrated X-ray intensities of selected Bragg reflection under influence of an external high electric field up to 8 kV/mm. To do this 300 μm thick samples were sandwiched between metallic contacts and the X-ray intensities were recorded with and without the applied field. The difference intensities were evaluated in terms of difference electron density of atoms within the respective crystallographic unit cell. Because the up to now accepted model of the field induced displacement of ionic sublattices against each other fails for the interpretation of experimental data we proposed a new model of the inverse piezoelectric effect, which considers the strong covalent bond between silicon and oxygen and gallium/phosphorous and oxygen, respectively. Here the main effect of screening the external electric field is a change in the Si-O-Si and Ga-O-P bonding angles, i.e. the rotations of nearly rigid MO4 tetrahedra.
The Journal of Physical Chemistry A, 2010
Time-resolved Laue crystallography has been employed to study the structural dynamics of a one-di... more Time-resolved Laue crystallography has been employed to study the structural dynamics of a one-dimensional organic conductor (tetrathiafulvalene-p-chloranil) during photoexcitation in the regime of the neutral to ionic phase transition. Exciting this crystalline system with 800 nm 100 fs long optical pulses leads to ultrafast population of a structural intermediate as early as 50 ps after excitation with a lifetime of at least 10 ns. Starting from the neutral phase, this intermediate has been assigned as a precursor state toward the photoinduced population of the ionic phase. The observed intensity changes are significantly different from comparable equilibrium structures. The interpretation of this structural data is that the potential of this intermediate is being softened during its population in a dynamical process. The depopulation proceeds through thermal processes.
Zeitschrift für Kristallographie, 2001
... [8] Ozolins V.; Zunger A.: Theory of systematic absence of NaCl-Type (b-Sn-Type) high pressur... more ... [8] Ozolins V.; Zunger A.: Theory of systematic absence of NaCl-Type (b-Sn-Type) high pressure phases in covalent (ionic) semi-conductors. ... [20] Willis, BTM: Lattice vibrations and the accurate determina-tion of structure factors for the elastic scattering of X-rays and Neutrons. ...
Journal of Synchrotron Radiation, 2005
In the next decade the scientific community expects a strong impact in physics, chemistry, biolog... more In the next decade the scientific community expects a strong impact in physics, chemistry, biology, material research and life sciences by the availability of highbrilliance X-ray radiation from free-electron laser (FEL) sources. In particular, in the field of ultrafast science these new sources will allow new types of experiments, enabling new phenomena to be discovered. Whereas today ultrafast X-ray diffraction experiments are strongly restricted by the limited X-ray flux of current sources of sub-picosecond X-ray pulses, FELs will provide short pulses of typically 10 12 photons with a duration of the order of 100 fs and monochromaticity of 10 À3 . Here, the feasibility of time-resolved single-shot powder diffraction experiments using these intense pulses, and the requirements of these experiments, are discussed. The detector count rates are estimated for diffraction from a model compound in a wide q-regime under the special consideration of high resolving power. In the case of LCLS radiation parameters, single-shot experiments will be feasible although high-resolution powder diffraction will require a reduction of the intrinsic FEL radiation bandwidth.
Journal of Synchrotron Radiation, 2004
A general outline of how to perform a light-excited time-resolved diffraction experiment by apply... more A general outline of how to perform a light-excited time-resolved diffraction experiment by applying the optical pump/X-ray probe technique is given. Owing to the difference in penetration depths between the optical light (laser) pump and the X-ray probe, only specific or specially designed crystalline systems can be investigated, so special requirements have to be fulfilled concerning the sample and its compartments. A summary of the experimental conditions of optical pump/X-ray probe experiments is presented, emphasizing why the use of powder diffraction is a useful and necessary X-ray technique for this kind of experiment. The possibilities and bottlenecks of time-resolved X-ray diffraction on the picosecond time scale will be demonstrated in the powder diffraction studies of N,Ndimethylaminobenzonitrile and N,N-diisopropylaminobenzonitrile, where the photo-induced structural changes of these molecular organic systems have been studied as a function of time.
Journal of Physics: Condensed Matter, 2012
The dynamics of silver-alkali halide mixed single crystals (Ag(x)Na(1-x)Br, x = 0.23, 0.35, 0.40 ... more The dynamics of silver-alkali halide mixed single crystals (Ag(x)Na(1-x)Br, x = 0.23, 0.35, 0.40 and 0.70) were studied by inelastic neutron scattering during the process of spinodal decomposition. Using the thermal three-axes spectrometer PUMA as well as the time-of-flight spectrometer IN5, the time evolution of phonons was observed in time-resolved, stroboscopic measurements. Complementary to the study of long wavelength acoustic phonons, as studied previously, we extended these investigations to Brillouin-zone boundary modes that are particularly sensitive to variations of the local structure. Starting from the homogeneous mixed phase the behaviour of these modes during demixing is observed in real-time. A simple dynamical model based on local structure variants helps to interpret the results. It is shown that the phonon lifetimes vary strongly during the phase separation and increase drastically during the coarsening process. Up to a critical size of precipitates of about 10 nm, zone-boundary modes are found to be strongly damped, while beyond the line widths are reduced to the experimental resolution. This finding leads to the conclusion that the typical mean free path of these modes is of the order of 10 nm, which corresponds to 20 unit cells.
Journal of Physics and Chemistry of Solids, 2001
Using a modulation technique and synchrotron radiation, we investigated the charge density variat... more Using a modulation technique and synchrotron radiation, we investigated the charge density variations in cubic ZnSe and trigonal SiO 2 induced by an external high-electric ®eld E applied along the [111] and [11.0] direction, respectively. Selecting particularly weak re¯ections, we observed an almost linear variation of the integrated intensity versus E changing by up to 2% at uEu 3 kV/mm. For both crystals, the displacements of the relative ion positions within the unit cell exceed the piezoelectric induced variation of the unit cell parameters by at least one order of magnitude. The measured intensity variations of ZnSe can be explained by the opposite displacement of the zinc and selenium ions towards the ®eld direction breaking the stiff tetrahedral coordination of the chemical bond. For quartz, the electric ®eld initiates a displacement of those oxygen ions only where the O± Si bond is directed oblique to the ®eld direction. The other oxygen ions and the silicon positions remain nearly unchanged. Thus, the ionic arrangement is described mainly by a change in the O±Si±O bonding angles. q
Journal of Physics and Chemistry of Solids, 2001
The valence charge density distribution (VCD) of cubic ZnSe was studied by means of theoretical a... more The valence charge density distribution (VCD) of cubic ZnSe was studied by means of theoretical and experimental methods. The theoretical VCDs were calculated in terms of the Hartree±Fock (HF), density functional (DF) and pseudopotential (PP) approach provided by the CRYSTAL95 program package. The experimental VCD was calculated via inverse Fourier transformation of X-ray structure factors. To avoid the extinction problem, we only measured a few low-indexed weak re¯ections (h 1 k 1 l 4n 1 2) in high precision, which are most sensitive for the chemical bond. The measured structure factors were analysed in terms of a bond charge model including charge transfer. The experimental data set was completed by re¯ections with h 1 k 1 l ± 4n 1 2 calculated in terms of the spherical atom model, but corrected by the parameters which received from the weak re¯ections. All structure factors were extrapolated to zero temperature using experimental temperature factors including anharmonicity. Despite the approximation made, the experimental VCD con®rms the ab initio calculations qualitatively. The experimental and theoretical VCDs of ZnSe are characterised by almost spherical charge densities around the ions carrying an effective charge of about 10.7 electrons. A bond charge was found to be located inside the electron cloud around the Se nucleus. Comparing the VCDs of the isoelectronic series Ge, GaAs and ZnSe the bond charge decreases in amount and shifts closer to the anion, increasing the charge transfer between the ions. q
Europhysics Letters (EPL), 2003
... A, 27 (1972) 469. [8] Calamiotou M., Psicharis V., Filippakis SE and Anastassakis E., J. Phys... more ... A, 27 (1972) 469. [8] Calamiotou M., Psicharis V., Filippakis SE and Anastassakis E., J. Phys. C, 20 (1987) 5641. ... [17] Le Page Y., Calvert LD and Gabe EJ, J. Phys. Chem. Sol., 41 (1980) 721. [18] Lager GA, Jorgensen JD and Rotella FJ, J. Appl. Phys., 53 (1982) 6751. ...
The Journal of Physical Chemistry A, 2006
Photoinduced structural variations in single crystals of 2,4-dichloro-trans-cinnamic acid (C9H6Cl... more Photoinduced structural variations in single crystals of 2,4-dichloro-trans-cinnamic acid (C9H6Cl2O2, DiClCA) have been investigated using X-ray diffraction (photocrystallography) and optical spectroscopic methods. During UV irradiation, which initiates the irreversible dimerization reaction, a loss of the long-range order of the reactant single crystal was found, i.e., that the dimerization is a heterogeneous one. This unexpected result emphasizes the still-existing problem of predicting changes or of remaining periodicity during chemical reactions in the solid state. On the basis of the experimental results, we propose a qualitative kinetic reaction scheme for DiClCA heterogeneous dimerization reaction.