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1.
First-principles calculations using the GGA+U method have been made to investigate the spin transitions of iron in MgSiO3 perovskite up to 120 GPa, with Fe2+ and Fe3+ at the A and B sites involving different substitution mechanisms and various charge compensation configurations. Our results, unlike those from previous local density approximation and generalized gradient approximation calculations, are now consistent with available experimental data for the spin states of Fe3+ in perovskite. In particular, our calculations show that both Fe2+ and Fe3+ at the A site do not exhibit any spin transition at the lower mantle conditions. However, Fe3+ at the B site in both (Mg0.9375Al0.0625)(Si0.9375Fe0.0625)O3 and (Mg0.9375Fe0.0625)(Si0.9375Fe0.0625)O3 undergoes a high-spin to low-spin transition at ~ 35 GPa, and this spin-transition pressure is largely independent on substitution mechanisms and charge compensation configurations. 相似文献
2.
Effects of the high pressure on the emission spectra of Eu3+-activated L-EuBO3 were considered at room temperature up to 100 kbar. The position of five 0–2 lines in the 5D0→7F2 transition region was determined. The pressure does not have the same effect on all these lines. In four of them, high pressure induced a red shift with different shift rates:+0.0022,+0.0035,+0.0034 and+0.0027 nm kbar?1, respectively, whereas in the last one, high pressure induced a blue shift with shift rate?0.0034 nm kbar?1. Possible reasons for the mentioned pressure effects on the line positions were considered. 相似文献
3.
Suleyman Cabuk 《哲学杂志》2020,100(5):601-618
ABSTRACTBased on first principles computations, the structural, mechanical, electronic band structure, and optical properties of SeZnO3 compound have been predicted. The dependence of selected observables of SeZnO3 compound on the effective U (the Hubbard on-site Coulomb repulsion) parameter has been investigated in detail. The elastic constant, Young’s modulus, bulk modulus, shear modulus, Poisson ratio, anisotropic factor, acoustic velocity, and Debye temperature have been computed. The calculated electronic band structure and density of states indicate that SeZnO3 is a semiconductor material and has indirect band gap. The computations of the optical spectra, as a function of the incident photon radiation in 0–35?eV energy range has also been performed and the interband transitions are examined. The results indicate that Hubbard parameter plays a crucial role in explaining mechanical, electronic, and optical properties of SeZnO3. 相似文献
4.
W. -B. Zhang N. Yu W. -Y. Yu B. -Y. Tang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):153-158
Native vacancy defects in typical strongly correlated oxides NiO have been investigated using the GGA+U method. The defect formation energies under different conditions are determined and magnetisms induced by vacancies are studied.
Our results indicate that the predominant defect is Ni vacancy under oxygen-rich condition and the most stable ionization
state varies with different Fermi level. The Ni vacancy forms shallow acceptor, suggesting the native p-type conductivity originates from the cation vacancy. In addition, after introducing a Ni vacancy, a half-metallic antiferromagnet
or half-metallic ferromagnet can form according to different ionization state of cation vacancy. 相似文献
5.
B. Z. Malkin M. V. Vanyunin M. J. Graf J. Lago F. Borsa A. Lascialfari A. M. Tkachuk B. Barbara 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(2):155-163
Temperature and magnetic field dependences of the 19F
nuclear spin-lattice relaxation in a single crystal of LiYF4 doped
with holmium are described by an approach based on a detailed consideration
of the magnetic dipole-dipole interactions between nuclei and impurity
paramagnetic ions and nuclear spin diffusion processes. The observed
non-exponential long time recovery of the nuclear magnetization after
saturation at intermediate temperatures is in agreement with predictions of
the spin-diffusion theory in a case of the diffusion limited relaxation. At
avoided level crossings in the spectrum of electron-nuclear states of Ho3
+ ions, rates of nuclear spin-lattice relaxation increase due to
quasi-resonant energy exchange between nuclei and paramagnetic ions in
contrast to the predominant role played by electronic cross-relaxation
processes in the low-frequency ac-susceptibility. 相似文献
6.
M. Krupski 《高压研究》2013,33(1-6):466-468
Abstract The pressure coefficient of the phase transition temperature Tc, dTc/dp = -(11+-1) K/GPa, has been determined for Ni (NH3)6Cl2 using a new high pressure and low temperature probe. The relations between Tc and dTc/dp were determined for antifluorite K2MCl6 compounds and hexammines applying the rigid-sphere model. 相似文献
7.
A. S. Krylov S. V. Goryainov A. N. Vtyurin S. N. Krylova S. N. Sofronova N. M. Laptash T. B. Emelina V. N. Voronov S. V. Babushkin 《Journal of Raman spectroscopy : JRS》2012,43(4):577-582
Raman spectra of Rb2KTiOF5 crystal were obtained and analyzed in the temperature range from 77 to 297 K and under hydrostatic pressure up to 4.2 GPa (at T = 295 K). The experimental results were compared with quantum‐chemical simulation of TiOF5 pseudo‐octahedron. To interpret effects of lattice ordering, phonon spectra of several ordered phases of Rb2KTiOF5 were calculated within ab initio generalized Gordon–Kim model, and ordering of TiOF5 molecular groups were simulated within Monte Carlo approach. The spectra exhibited orientation disordering in the cubic phase under ambient conditions. Cooling below the phase transition temperature (215 K) leads to partial ordering of the structure. The isotropic perovskite‐like phase was found to undergo first‐order transition into a low‐symmetry anisotropic phase at about 1 GPa. Further compression up to 4.1 GPa did not show any effects associated with phase transitions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Low‐density lipoproteins (LDL) are natural lipid transporter in human plasma whose chemically modified forms contribute to the progression of atherosclerosis and cardiovascular diseases accounting for a vast majority of deaths in westernized civilizations. For the development of new treatment strategies, it is important to have a detailed picture of LDL nanoparticles on a molecular basis. Through the combination of X‐ray and neutron small‐angle scattering (SAS) techniques with high hydrostatic pressure (HHP) this study describes structural features of normolipidemic, triglyceride‐rich and oxidized forms of LDL. Due to the different scattering contrasts for X‐rays and neutrons, information on the effects of HHP on the internal structure determined by lipid rearrangements and changes in particle shape becomes accessible. Independent pressure and temperature variations provoke a phase transition in the lipid core domain. With increasing pressure an interrelated anisotropic deformation and flattening of the particle are induced. All LDL nanoparticles maintain their structural integrity even at 3000 bar and show a reversible response toward pressure variations. The present work depicts the complementarity of pressure and temperature as independent thermodynamic parameters and introduces HHP as a tool to study molecular assembling and interaction processes in distinct lipoprotein particles in a nondestructive manner. 相似文献
9.
基于密度泛函理论的第一性原理方法,系统研究了Ga和Sb纳米线的电子能带结构和声子结构以及电子-声子耦合(EPC)作用.通过对声子的完整Brillouin区分析来研究纳米线的结构稳定性.结果表明,所考察的纳米线显示出不稳定性,不稳定声子波矢远离Brillouin区中心.与通常的Peierls变形机理相比,不稳定的横向声子模会导致一种无开口带隙的相变.Sb比Ga纳米线的EPC要强很多,并且横向变形导致的锯齿形结构使纳米线中的电子-声子相互作用增加了几个数量级. 相似文献
10.
REN QingBao ZHU WeiTing HONG Bo & ZHANG YuHeng Department of Physics Lishui University Lishui China National High Magnetic Field Laboratory University of Science Technology of China Hefei China 《中国科学G辑(英文版)》2007,(3)
Magnetic properties of Nd_(0.5)Sr_(0.5)Mn_(1-x)(Ga_x, Ti_x)O_3 system (0.04≤x≤0.4) were inves- tigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melt- ing of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-T curves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region. 相似文献
11.
We investigate the influence of high hydrostatic pressure on the electrical resistance in the ab-plane in HoBa2Cu3O7– δ single crystals with oxygen deficiency. It is determined that the high-pressure-induced redistribution of labile oxygen enhances phase separation, which is accompanied by structural relaxation and ascending diffusion within the volume of the sample. This results in a significant displacement of the temperature intervals that correspond to metal-to-dielectric-type transitions. It is determined that the formation of the low-temperature phase can occur at the twin boundaries. 相似文献
12.
A magnetic-parameter measurement system for study of ferromagnetic materials under high pressure using a diamondanvil cell is built. The factors affecting the measurement sensitivity are analyzed and the possibility of improving the sensitivity is mentioned. Based on the system, the magnetization curves of iron as a function of pressure are obtained. The start point and end point of pressure-induced magnetic transition of iron are observed at room temperature. 相似文献
13.
A. S. Krylov A. N. Vtyurin A. S. Oreshonkov V. N. Voronov S. N. Krylova 《Journal of Raman spectroscopy : JRS》2013,44(5):763-769
This paper reports Raman spectroscopy investigation of phase transitions in Rb2NaYF6 crystal. The experimental spectra were compared with the calculated one. The spectra were obtained in temperature range from 8 to 300 K. The Raman spectra shows anomalous temperature‐dependent behavior at T1 = 154 and T2 = 122 K. Soft mode restoration has been found, which allows us to attribute first transition at 154 K to displacive type. Detailed analysis temperature dependencies of the line positions and widths have been performed. We found no effects of possible lattice disorder anywhere, except narrow (about 20 K) range above the T1 temperature. The Raman spectra of Rb2NaYF6 crystal have been obtained and analyzed under hydrostatic pressure up to 4.33 GPa (at T = 295 K). The high pressure experiment up to 4.33 GPa did not disclose any effects associated with phase transitions. The lattice vibration spectra were calculated up to 10 GPa. The calculation has been demonstrated that the Rb2NaYF6 does not undergo high pressure phase transition. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
14.
Gurpreet Singh R. Prasad S. Auluck Anjan Sil 《Journal of Physics and Chemistry of Solids》2009,70(8):1200-644
The effect of doping spinel LiMn2O4 with chromium and magnesium has been studied using the first-principles spin density functional theory (DFT) within generalized gradient approximation (GGA ) and GGA+U. We find that GGA and GGA+U give different ground states for pristine LiMn2O4 and same ground state for doped systems. For LiMn2O4, the body-centered tetragonal phase was found to be the ground-state structure using GGA and face-centered orthorhombic using GGA+U, while for LiM0.5Mn1.5O4 (MCr or Mg) it was base-centered monoclinic and for LiMMnO4 (MCr or Mg) it was body-centered orthorhombic in both GGA and GGA+U. We find that GGA predicts the pristine LiMn2O4 to be metallic while GGA+U predicts it to be insulating, which is in accordance with the experimental observations. For doped spinels, GGA predicts the ground state to be half metallic while GGA+U predicts it to be insulating or metallic depending on the doping concentration. GGA+U predicts insulator-metal-insulator transition as a function of doping in case of Cr and in case of Mg the ground state is found to go from insulating to a half metallic state as a function of doping. Analysis of the charge density and the density of states (DOS) suggest a charge transfer from the dopants to the neighboring oxygen atoms and manganese atoms. We have calculated the Jahn-Teller active mode displacement Q3 for doped compounds using GGA and GGA+U. The bond lengths calculated from GGA+U are found to be in better agreement with experimental bond lengths. Based on the bond lengths of metal and oxygen, we have also estimated the average oxidation states of the dopants. 相似文献
15.
Ferromagnetic half metallicity with a high spin polarization of 100% was predicted in the bulk Ni0.5Cu0.5O using density-functional theory method. The band gap of majority spin is 3.45 eV for Ni0.5Cu0.5O. The density of states of minority spin at the Fermi level are mainly from Cu 3d and O 2p in the Ni0.5Cu0.5O. The magnetic moments are from Ni 3d states. Ni0.5Zn0.5O and Ni0.5Cd0.5O systems are ferromagnetic insulators, but the magnetic moment of Ni2+ ions is enhanced by the Zn and Cd incorporation. Therefore, Ni0.5Cu0.5O is the potential candidate for spintronics devices because of the predicted high spin polarization. 相似文献
16.
Alkylperoxyl spin adducts of pyrroline‐N‐oxide spin traps: Experimental and theoretical CASSCF study of the unimolecular decomposition in organic solvent,potential applications in water
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Sergiu Lescic Hakim Karoui Micaël Hardy Laurence Charles Paul Tordo Olivier Ouari Anouk Gaudel‐Siri Didier Siri 《Journal of Physical Organic Chemistry》2017,30(10)
Spin trapping coupled with electron paramagnetic resonance spectroscopy is the most direct method for detection of very low concentrations of free radicals, and it has been intensively used to detect superoxide or alkylperoxyl radicals in biological systems, using cyclic nitrones as spin traps. The half‐life time of the ensuing spin adducts depends dramatically on the spin trap structure; however, their mechanism of decay has never been definitely established. We investigated at the MRMP2/CASSCF (MultiReference second‐order Møller‐Plesset perturbation theory/Complete Active Set Self Consistent Field) level of theory the mechanism of decay of methylperoxyl and tert‐butylperoxyl spin adducts formed with various cyclic nitrones. We showed that no transition state can be located for the O─O homolytic cleavage, which yields an intermediate biradical with the following sequence ?O─N─C─O?. Then, homolytic cleavage of the N─C bond yields a nitrosoaldehyde, through an early transition state with a very low activation energy. For each nitrone used as spin trap, electrospray ionization mass spectrometry analysis of the spin trapping mixture allowed to detect the presence of the expected nitrosoaldehyde. We generated tert‐butylperoxyl spin adducts in toluene, and we found a good correlation between their half‐life time and the bond dissociation energy of their peroxidic O─O bond. The theoretical method was then extended to hydroperoxyl spin adducts in water and provided promising results. 相似文献
17.
Magnetic properties of Nd0.5Sr0.5Mn1-x(Gax,Tix)O3 system (0.04≤x≤0.4) were investigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melting of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-Tcurves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region. 相似文献
18.
《Ultrasonics sonochemistry》2014,21(5):1858-1865
One of the uses of ultrasound in dentistry is in the field of endodontics (i.e. root canal treatment) in order to enhance cleaning efficiency during the treatment. The acoustic pressures generated by the oscillation of files in narrow channels has been calculated using the COMSOL simulation package. Acoustic pressures in excess of the cavitation threshold can be generated and higher values were found in narrower channels. This parallels experimental observations of sonochemiluminescence. The effect of varying the channel width and length and the dimensions and shape of the file are reported. As well as explaining experimental observations, the work provides a basis for the further development and optimisation of the design of endosonic files. 相似文献
19.
Using density-functional calculations within the generalized gradient approximation (GGA)+U framework,we investigate the structural,electronic,and magnetic properties of the ground states of SrFeOn (n = 2 and 2.5).The magnetism calculations show that the ground states of both SrFeO2 and SrFeO2.5 have G type antiferromagnetic ordering,with indirect band gaps of 0.89 and 0.79 eV,respectively.The electronic structure calculations demonstrate that Fe cations are in the high-spin state of (dz2 )2(dxz,dyz)2(dxy)1(dx2 y2 )1(S = 2),unlike the previous prediction of (dxz,dyz)3(dxy)1(dz2 )1(dx2 y2 )1(S = 2) for SrFeO2,and in the high-spin state of (dxy,dxz,dyz,dx2 y2 ,dz2 )5(S = 5/2) for SrFeO2.5. 相似文献
20.
M. Picco F. Ricci-Tersenghi F. Ritort 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):211-217
We present a detailed study of the scaling behavior of correlations functions and AC susceptibility relaxations in the aging
regime in three-dimensional spin glasses. The agreement between simulations and experiments is excellent confirming the validity
of the full aging scenario with weak sub-aging effects.
Received 21 December 2000 and Received in final form 22 February 2001 相似文献