Search

TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments., Funding Agencies|Knut and Alice Wallenberg Foundation [KAW-2013.0020]; Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Russian Science Foundation [18-12-00492]

TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments., Funding Agencies|Knut and Alice Wallenberg Foundation [KAW-2013.0020]; Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Russian Science Foundation [18-12-00492]

TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments., Funding Agencies|Knut and Alice Wallenberg Foundation [KAW-2013.0020]; Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Russian Science Foundation [18-12-00492]

TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments., Funding Agencies|Knut and Alice Wallenberg Foundation [KAW-2013.0020]; Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Russian Science Foundation [18-12-00492]

TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments., Funding Agencies|Knut and Alice Wallenberg Foundation [KAW-2013.0020]; Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Russian Science Foundation [18-12-00492]

TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments., Funding Agencies|Knut and Alice Wallenberg Foundation [KAW-2013.0020]; Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Russian Science Foundation [18-12-00492]

We investigate the impact of excess PbI2 in the precursor solution on the structural and optical properties of thin films of the model hybrid perovskite methylammonium lead iodide (MAPbI(3)). We find that excess of PbI2 in the precursor solution results in crystalline PbI2 in the final thin film that is located at the grain boundaries. From UPS we find that this crystalline PbI2 phase has no direct impact on the electronic structure of MAPbI(3). In contrast to this, temperature dependent absorption measurements indicate a systematic change in the temperature dependence of the exciton binding energy in the perovskite. We also observe a decrease in the critical temperature and a concomitant smearing out of the tetragonal-orthorhombic phase transition as a function of excess PbI2. Our results thus help to better understand the exact role of PbI2 in the perovskite layer and pave the way for a more tailored design of perovskite solar cells.

We investigate the impact of excess PbI2 in the precursor solution on the structural and optical properties of thin films of the model hybrid perovskite methylammonium lead iodide (MAPbI(3)). We find that excess of PbI2 in the precursor solution results in crystalline PbI2 in the final thin film that is located at the grain boundaries. From UPS we find that this crystalline PbI2 phase has no direct impact on the electronic structure of MAPbI(3). In contrast to this, temperature dependent absorption measurements indicate a systematic change in the temperature dependence of the exciton binding energy in the perovskite. We also observe a decrease in the critical temperature and a concomitant smearing out of the tetragonal-orthorhombic phase transition as a function of excess PbI2. Our results thus help to better understand the exact role of PbI2 in the perovskite layer and pave the way for a more tailored design of perovskite solar cells.

The peculiar bonding situation in gamma boron is characterized on the basis of an experimental electron-density distribution which is obtained by multipole refinement against low-temperature single-crystal x-ray diffraction data. A topological analysis of the electron-density distribution reveals one-electron-two-center bonds connecting neighboring icosahedral B-12 clusters. A unique polar-covalent two-electron-three-center bond between a pair of atoms of an icosahedral cluster and one atom of the interstitial B-2 dumbbell explains the observed charge separation in this high-pressure high-temperature polymorph of boron., Original Publication:Swastik Mondal, Sander van Smaalen, Andreas Schoenleber, Yaroslav Filinchuk, Dmitry Chernyshov, Sergey Simak, Arkady Mikhaylushkin, Igor Abrikosov, Evgeniya Zarechnaya, Leonid Dubrovinsky and Natalia Dubrovinskaia, Electron-Deficient and Polycenter Bonds in the High-Pressure gamma-B-28 Phase of Boron, 2011, PHYSICAL REVIEW LETTERS, (106), 21, 215502.http://dx.doi.org/10.1103/PhysRevLett.106.215502Copyright: American Physical Societyhttp://www.aps.org

The peculiar bonding situation in gamma boron is characterized on the basis of an experimental electron-density distribution which is obtained by multipole refinement against low-temperature single-crystal x-ray diffraction data. A topological analysis of the electron-density distribution reveals one-electron-two-center bonds connecting neighboring icosahedral B-12 clusters. A unique polar-covalent two-electron-three-center bond between a pair of atoms of an icosahedral cluster and one atom of the interstitial B-2 dumbbell explains the observed charge separation in this high-pressure high-temperature polymorph of boron., Original Publication:Swastik Mondal, Sander van Smaalen, Andreas Schoenleber, Yaroslav Filinchuk, Dmitry Chernyshov, Sergey Simak, Arkady Mikhaylushkin, Igor Abrikosov, Evgeniya Zarechnaya, Leonid Dubrovinsky and Natalia Dubrovinskaia, Electron-Deficient and Polycenter Bonds in the High-Pressure gamma-B-28 Phase of Boron, 2011, PHYSICAL REVIEW LETTERS, (106), 21, 215502.http://dx.doi.org/10.1103/PhysRevLett.106.215502Copyright: American Physical Societyhttp://www.aps.org

The peculiar bonding situation in gamma boron is characterized on the basis of an experimental electron-density distribution which is obtained by multipole refinement against low-temperature single-crystal x-ray diffraction data. A topological analysis of the electron-density distribution reveals one-electron-two-center bonds connecting neighboring icosahedral B-12 clusters. A unique polar-covalent two-electron-three-center bond between a pair of atoms of an icosahedral cluster and one atom of the interstitial B-2 dumbbell explains the observed charge separation in this high-pressure high-temperature polymorph of boron.

info:eu-repo/semantics/published

The peculiar bonding situation in gamma boron is characterized on the basis of an experimental electron-density distribution which is obtained by multipole refinement against low-temperature single-crystal x-ray diffraction data. A topological analysis of the electron-density distribution reveals one-electron-two-center bonds connecting neighboring icosahedral B-12 clusters. A unique polar-covalent two-electron-three-center bond between a pair of atoms of an icosahedral cluster and one atom of the interstitial B-2 dumbbell explains the observed charge separation in this high-pressure high-temperature polymorph of boron., Original Publication:Swastik Mondal, Sander van Smaalen, Andreas Schoenleber, Yaroslav Filinchuk, Dmitry Chernyshov, Sergey Simak, Arkady Mikhaylushkin, Igor Abrikosov, Evgeniya Zarechnaya, Leonid Dubrovinsky and Natalia Dubrovinskaia, Electron-Deficient and Polycenter Bonds in the High-Pressure gamma-B-28 Phase of Boron, 2011, PHYSICAL REVIEW LETTERS, (106), 21, 215502.http://dx.doi.org/10.1103/PhysRevLett.106.215502Copyright: American Physical Societyhttp://www.aps.org

info:eu-repo/semantics/published

The peculiar bonding situation in gamma boron is characterized on the basis of an experimental electron-density distribution which is obtained by multipole refinement against low-temperature single-crystal x-ray diffraction data. A topological analysis of the electron-density distribution reveals one-electron-two-center bonds connecting neighboring icosahedral B-12 clusters. A unique polar-covalent two-electron-three-center bond between a pair of atoms of an icosahedral cluster and one atom of the interstitial B-2 dumbbell explains the observed charge separation in this high-pressure high-temperature polymorph of boron., Original Publication:Swastik Mondal, Sander van Smaalen, Andreas Schoenleber, Yaroslav Filinchuk, Dmitry Chernyshov, Sergey Simak, Arkady Mikhaylushkin, Igor Abrikosov, Evgeniya Zarechnaya, Leonid Dubrovinsky and Natalia Dubrovinskaia, Electron-Deficient and Polycenter Bonds in the High-Pressure gamma-B-28 Phase of Boron, 2011, PHYSICAL REVIEW LETTERS, (106), 21, 215502.http://dx.doi.org/10.1103/PhysRevLett.106.215502Copyright: American Physical Societyhttp://www.aps.org

The peculiar bonding situation in gamma boron is characterized on the basis of an experimental electron-density distribution which is obtained by multipole refinement against low-temperature single-crystal x-ray diffraction data. A topological analysis of the electron-density distribution reveals one-electron-two-center bonds connecting neighboring icosahedral B-12 clusters. A unique polar-covalent two-electron-three-center bond between a pair of atoms of an icosahedral cluster and one atom of the interstitial B-2 dumbbell explains the observed charge separation in this high-pressure high-temperature polymorph of boron., Original Publication:Swastik Mondal, Sander van Smaalen, Andreas Schoenleber, Yaroslav Filinchuk, Dmitry Chernyshov, Sergey Simak, Arkady Mikhaylushkin, Igor Abrikosov, Evgeniya Zarechnaya, Leonid Dubrovinsky and Natalia Dubrovinskaia, Electron-Deficient and Polycenter Bonds in the High-Pressure gamma-B-28 Phase of Boron, 2011, PHYSICAL REVIEW LETTERS, (106), 21, 215502.http://dx.doi.org/10.1103/PhysRevLett.106.215502Copyright: American Physical Societyhttp://www.aps.org

Statistical copolymers of indigo (1a) and N-acetylindigo (1b) building blocks with defined structures were studied. They belong to the class of polymeric colorants. The polymers consist of 5,5′-connected indigo units with keto structure and N-acetylindigo units with uncommon tautomeric indoxyl/indolone (=1H-indol-3-ol/3H-indol-3-one) structure (see 2a and 2b in Fig. 1). They formed amorphous salts of elongated monomer lengths as compared to monomeric indigo. The polymers were studied by various spectroscopic and physico-chemical methods in solid state and in solution. As shown by small-angle-neutron scattering (SANS) and transmission-electron microscopy (TEM), disk-like polymeric aggregates were present in concentrated solutions (DMSO and aq. NaOH soln.). Their thickness and radii were determined to be ca. 0.4 and ca. 80 nm, respectively. From the disk volumes and by a Guinier analysis, the molecular masses of the aggregates were calculated, which were in good agreement with each other. Defined structural changes of the polymer chains were observed during several-weeks storage in concentrated DMSO solutions. The original keto structure of the unsubstituted indigo building blocks reverted to the more flexible indoxyl/indolone structure. The new polymers were simultaneously stabilized by intermolecular H-bonds to give aggregates, preferentially dimers. Both aggregation and tautomerization were reversible upon dissolution. The polymers were synthesized by repeated oxidative coupling of 1,1′-diacetyl-3,3′-dihydroxybis-indoles 5 (from 1,1′-diacetyl-3,3′-bis(acetyloxy)bis-indoles 6) followed by gradual hydrolysis of the primarily formed poly(N,N′-diacetylindigos) 7 (Scheme). N,N′-Diacetylbis-anthranilic acids 9 were isolated as by-products.

A crystalline sample of TiOBr is probed at room temperature by a combination of electron spectroscopies and the results are compared to theoretical embedded-cluster calculations. Resonant photoemission of the valence band confirms that the lowest binding energy feature arises from the singly occupied Ti 3d orbital. The polarization dependence of this orbital in nonresonant photoemission is consistent with the expected dominant d(y)(2)-z(2) character. The analysis of the Ti L-2,L-3 x-ray absorption spectra confirms the complete splitting of the Ti 3d shell. X-ray absorption and resonant photoemission at the O 1s edge provide direct evidence for hybridization between the transition metal orbitals and the O 2p levels, which leads to superexchange interactions between the Ti ions. The existence of a mixing of O and Ti states and of strong superexchange interactions is supported by calculations of the ground-state electronic and magnetic properties. The calculated superexchange interchain interaction is one fifth in strength of the total magnetic coupling along the chain, and is antiferromagnetic in character. This O-mediated interchain interaction is frustrated in the room temperature phase of TiOBr and thus couples strongly to distortions of the soft lattice. The competition between the interchain magnetoelastic coupling and the spin-Peierls interaction might be at the origin of the complex TiOX phase diagram.

A semiclassical study presented here indicates that a sufficiently short and intense pulse can be much more effective in inducing a collisional radiative transition than cw radiation or a long pulse, although the intensity must not be too high because the Rabi oscillation can bring down the probability. For the situation of a molecule physisorbed on a crystalline surface and irradiated by a laser, a master equation approach, used to describe the time evolution of the population of the vibrational adbond levels, shows that for high intensities laser-induced vibrational excitation is the same for pulsed and cw lasers. Keywords: Molecular dynamics, Laser induced, Short pulses, Molecular collisions, Electronic transitions, Desorption.

A system of a phonon-damped adbond, coherently excited by a laser, is considered. The effect of a series of laser pulses is compared with effect of a continuous-wave laser. Consider an adsorbed atom in a vibrational bond, driven by a laser, and damped due to the lattice vibrations of the substrate. We approximate the vibrating adatom by a one-dimensional oscillator, for the motion perpendicular to the surface. The interaction between the adatom and the substrate is given by the potential between the atom and the nearest surface atom.

The irradiation by infrared laser light of an atom adsorbed on the surface of a harmonic crystal is considered. The dynamic coupling between the atom (its motion) and the substrate degrees of freedom (phonon field) in the presence of a confining potential well (van der Waals bond between atom and crystal) gives rise to thermal relaxation of this adbond configuration. Both the atom and the substrate are assumed to be transparent, but the bond is allowed to have non-vanishing dipole-moment matrix elements, which couple the external field to the adsorbate. The equation of motion for the reduced adbond density operator is obtained with reservoir theory, and the relaxation constants are expressed in properties of the crystal. With a similar method, the spectral profile for absorption of weak radiation is derived. Subsequently, the illumination by a strong finite-linewidth laser field which is in close resonance with a single transition of the adbond is examined. The optical Bloch equations in operator form are derived and applied to study the process of laser heating of the crystal. It is pointed out how this mechanism can be understood as resulting from (multi)photon-phonon conversion reactions which are mediated by the adbond. Keywords: Kinetic Phonon Coupling; Thermal Relaxation; Line Shape; Dressed States; Laser Heating; Photon Phonon Conversion.

The dynamics of an adsorbed atom irradiated by an IR laser in resonance with a single pair of states of the vibrational adbond is studied. Using a non-perturbative treatment for the laser adbond interaction, a master equation is derived, which governs the time evolution of the populations of the laser dressed states of the adbond. The effect of resonant heating and laser induced desorpton, as an example of a possible laser induced surface process, is discussed. A master equation for the time evolution of the populations of the laser dressed states of the reduced density matrix of the adbond is derived. The transitions between the states can be interpreted as phonon transitions between the dressed levels of the adbond. Stimulated radiative transitions are incorporated in the transformation to dressed states. The phonon transitions between the adbond states give rise to an energy flow from the laser into the substrate. Even in the steady state (where the level populations are time independent) the energy flow assumes a non-zero value., Presented at the International Conference on Chemistry by IR Lasers, 29 Sep - 3 Oct 86, Liblice (Czechoslovakia).

The modulated structure of alpha-Uranium is analyzed using the neutron scattering data. The results of the refinements are given for all the superspace groups compatible with the neutron diffraction pattern. Fits to the experimental data of equal quality are obtained for different structure models (different symmetries), thus prohibiting the determination of the structure from neutron scattering alone. Together with the recently reported results of electron microscopy, the refinements lead to an unique assignment of a superspace group to the incommensurately modulated structure of alpha-uranium below T = 37 K, with the tentative symbol P2/m11(beta)(gamma). The values of the structural parameters, as follow from the refinements, are also reported.

A coated surface of a crystal is irradiated by intense infrared light. The optically active atomic bonds absorb photons from the laser field, and the subsequent spontaneous decay goes together with emissions of phonons into the crystal. This photon phonon conversion results in an energy flux into the crystal. An equation for this flux is derived from the master equation for the level populations of the dressed atomic states. The saturation limit is discussed, and the general theory is illustrated with two examples. Furthermore, it is outlined with qualitative arguments that quantum yield of photodesorption is not sensitive to the laser power. Keywords: Laser heating; Transparent crystal; VIA Adsorbed atoms; Photon phonon conversion; Master equation; photodesorption.

Adsorbed atoms irradiated by an infrared laser in resonance with one pair of vibrational levels of the adbond are studied. A pulsed laser is considered which has pulse duration short compared to the relaxation times of the system. The equations governing the time evolution of the adbond under a series of pi-pulses are derived. Two criteria are defined to compare the effects of a series of pi-pulses and of a continuous-wave laser. They are: (1) equal average energy in both lasers and (2) equal average resonant heating due to both lasers. These criteria are used to compare the effects of al pulsed laser and a continuous wave laser on laser induced resonant desorption. It is shwon that a pulsed laser does not lead to a dramatic increase of the desorption. In the high-intensity limit, resonance heating and desorption reach the same saturation limit for a pulsed laser as for a continuous-wave laser.

A theoretical study of the vibrational relaxation of the adbond between a physisorbed molecule and a crystalline substrate is presented. The bond between the admolecule and substrate is described as a one-dimensional Morse-oscillator. Using standard perturbation theory, expressions for the relaxation of the vibrational adbond due to its interaction with the substrate lattice vibrations are derived. Both energy relaxation and pure dephasing are considered. A numerical evaluation of the resulting expressions for the relaxation constants is given for a Debye spectrum for the phonons and for a surface phonon spectrum. The relative importance of pure dephasing and energy relaxation in determining the absorption linewidth is derived as a function of the fundamental frequency of the active mode.

The phonon relaxation of the vibrational adbond of an adsorbed molecule and a phonon-damped adbond irradiated by a laser are studied. Approximations are made within the Zwanzig projection operator formalism in order to arrive at a master equation for the reduced density operator of a small subsystem (the adbond) in contact with a reservoir (the phonons). The conditions of validity for the Born and Markov approximations are derived. It is shown that the master equation is only valid for times t tau sub c, where tau sub c is the characteristic time of the reservoir. These results are then applied to the phonon relaxation of the vibrational adbond of physisorbed molecules. It is shown that for Carbon Monoxide adsorbed on Nickel or Copper (a strongly-bound physisorbed system), the Born and Markov approximations are not justified. For the weakly-bound system Arogon on Tungesten numerical results show that these approximations can be made. Finally, an adbond interacting with both laser radiation and lattice vibrations is considered. This system can be regarded as a subsystem (the adbond) in contact with two reservoirs, where the conditions for validity of the Markov approximation is then seen to be more severe than when each reservoir is considered independently. For the phonons, these conditions can never be matched. However, for an initial state given by an adbond in equilibrium with the lattice vibrations, the conditions for validity of the approximation prove to be the same as for the phonons and the laser considered independently.