共查询到20条相似文献,搜索用时 27 毫秒
1.
V. Kusigerski D. Markovic V. Spasojevic M. Tadic M. Zentkova M. Mihalik 《Journal of nanoparticle research》2010,12(4):1299-1306
Pressure effects on magnetic properties of two La0.7Ca0.3MnO3 nanoparticle samples with different mean particle sizes were investigated. Both the samples were prepared by the glycine-nitrate
method: sample S—as-prepared (10 nm), and sample S900—subsequently annealed at 900 °C for 2 h (50 nm). Magnetization measurements revealed remarkable differences in magnetic properties
with the applied pressure up to 0.75 GPa: (i) for S sample, both transition temperatures, para-to-ferromagnetic T
C = 120 K and spin-glass-like transition T
f = 102 K, decrease with the pressure with the respective pressure coefficients dT
C/dP = −2.9 K/GPa and dT
f/dP = −4.4 K/GPa; (ii) for S900 sample, para-to-ferromagnetic transition temperature T
C = 261 K increases with pressure with the pressure coefficient dT
C/dP = 14.8 K/GPa. At the same time, saturation magnetization M
S recorded at 10 K decreases/increases with pressure for S/S900 sample, respectively. Explanation of these unusual pressure effects on the magnetism of sample S is proposed within the scenario
of the combined contributions of two types of disorders present in the system: surface disorder introduced by the particle
shell, and structural disorder of the particle core caused by the prominent Jahn–Teller distortion. Both disorders tend to
vanish with the annealing of the system (i.e., with the nanoparticle growth), and so the behavior of the sample S900 is similar to that previously observed for the bulk counterpart. 相似文献
2.
P.?A.?Rodny? 《Optics and Spectroscopy》2009,107(2):270-274
The energies of the ground 4f
n
levels of tri- and divalent rare-earth ions with respect to the conduction and valence bands of Gd2O2S crystal has been determined. It is shown that the Pr3+, Tb3+, and Eu3+ ions can be luminescence centers in Gd2O2S. The levels of the Nd3+, Dy3+, Er3+, Tm3+, Sm3+, and Ho3+ ions lie in the valence band; therefore, these ions cannot play the role of activators. The ground 4f level of the Ce3+ ion is near the midgap, due to which Ce3+ effectively captures holes from the valence band and electrons from the conduction band and significantly decreases the afterglow
level of the Gd2O2S:Pr and Gd2O2S:Tb phosphors. 相似文献
3.
V. A. Kravets K. N. Orekhova M. A. Yagovkina E. V. Ivanova M. V. Zamoryanskaya 《Optics and Spectroscopy》2018,125(2):188-194
Spectra of Eu3+ in various dielectric matrices (Gd2O3:Eu3+, Y2O3:Eu3+, Eu2O3, and mSiO2/Gd2O3:Eu3+ mesoporous particles) are studied by local cathodoluminescence. The results allowed identification of the local environment of Er3+ ions in amorphous samples and detection of the monoclinic Eu2O3 phase impurity in samples with yttrium oxide. The cathodoluminescence spectra of chemically pure Y2O3, Eu2O3, and Gd2O3 are recorded. Conclusions about the structural features of the materials are made and confirmed by other methods (XRD and EPMA). 相似文献
4.
D. P. Kozlenko N. T. Dang Z. Jirák S. E. Kichanov E. V. Lukin B. N. Savenko L. S. Dubrovinsky C. Lathe C. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(3):407-411
The crystal and magnetic structures of Pr0.15Sr0.85MnO3
manganite have been studied by means of powder X-ray and neutron diffraction
in the temperature range 10–400 K at high external pressures up to 55 and 4 GPa, respectively. A structural phase transition
from cubic to tetragonal
phase upon compression was observed, with large positive pressure
coefficient of transition temperature dT
ct
/dP = 28(2) K/GPa. The C-type
antiferromagnetic (AFM) ground state is formed below T
N
≈ 260 K
at ambient pressure. While at ambient pressure the structural and magnetic
transition temperatures are close, T
ct
~ T
N
, upon compression
they become decoupled with T
N
≪ T
ct
due to much weaker
T
N
pressure dependence with coefficient dT
N
/dP = 3.8(1) K/GPa. 相似文献
5.
Hacene Manaa 《Optical and Quantum Electronics》2009,41(10):761-770
The nonlinear optical properties in six Cr3+-doped laser crystals LiCaAlF6, LiSrGaAlF6, Gd3Ga5O12, Gd3Sc2Ga3O12, LaMgAl11O19 and Alexandrite are investigated with the help of the Z-Scan technique at λ = 532 nm in the CW regime. The data reported
here include particularly the excited state absorption cross section and the third-order nonlinear susceptibilities. It is
found that the three first systems only exhibit both refractive and absorptive nonlinear effects, whereas the three others
have only absorptive effects. Gd3Ga5O12 shows the best nonlinear potentialities. The excited state absorption cross section corresponding mainly to the 4T2 → 4T1 transition is found to be ranging between 8.9 × 10−22 cm2 in LiSGaF and 3.1 × 10−20 cm2 in LaMgAl11O19. The calculated ratio of the third order nonlinear susceptibility to the ground state absorption coefficient is found to
be largest in GGG with a value of 146 × 10−6 esu.cm and smallest in Alexandrite (0.6 × 10−6 esu.cm). 相似文献
6.
This paper reports on the spectroscopic properties and energy transfer analysis of Tm3+-doped BaF2-Ga2O3-GeO2-La2O3 glasses with different Tm2O3 doping concentrations (0.2, 0.5, 2.0, 2.5, 3.0, 3.5, 3.5, 4.0 wt%). Mid-IR fluorescence intensities in the range of 1,300 nm−2,200 nm
have been measured when excited under an 808 nm LD for all the samples with the same pump power. Energy level structure and
Judd-Ofelt parameters have been calculated based on the absorption spectra of Tm3+, cross-relaxation rates and multi-phonon relaxation rates have been estimated with different Tm2O3 doping concentrations. The maximum fluorescence intensity at around 1.8 μm has been obtained in Tm2O3-3 wt% sample and the maximum value of calculated stimulated emission cross-section of Tm3+ in this sample is about 0.48 × 10−20 cm2 at 1,793 nm, and there is not any crystallization peak in the DSC curve of this sample, which indicate the potential utility
of Tm3+-doped BaF2-Ga2O3-GeO2- La2O3 glass for 2.0-μm optical fiber laser. 相似文献
7.
O. N. Ivanov E. P. Dan’shina V. V. Sirota I. D. Tarasova 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(9):1257-1259
X-ray structural, X-ray phase, and dilatometric analyses were used to explore specific features of the formation of solid
solutions in the (1 − x)SrTiO3−xBiScO3 system with x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5. It was found that the synthesis of solid solutions from the initial Bi2O3, Sc2O3, TiO2, and SrCO3 components is accompanied by a considerable increase in the linear dimensions of the samples, depending on their composition.
Solid solutions with x > 0.1 are formed through intermediate phases (Sr5Bi6O14 at x = 0.2; Sr0.78Bi2.22O4 at x = 0.3; and Sr2.25Bi6.75O12.38 at x = 0.4 and 0.5). It was shown that the samples with x = 0.2, 0.3, 0.4, and 0.5 have two phases: one with a cubic Pm3m structure and one with a tetragonal I4/mcm structure. 相似文献
8.
V. V. Osipov K. E. Luk’yashina V. I. Solomonov V. A. Shitov A. N. Orlov V. V. Platonov A. V. Spirin 《Bulletin of the Lebedev Physics Institute》2009,36(12):347-349
The possibility of synthesis and characteristics of highly transparent Y2O3 ceramics doped with Nd3+ and Yb3+ were studied. The ceramics crystal structure was disordered for the first time by simultaneously substituting Y3+ cations by Lu3+ or Sc3+ isovalent ions and Zr4+ heterovalent ions. The developed technique allowed synthesis of highly transparent Nd3+:Y2O3, Nd3+: Y2O3 + 6 mol % ZrO2, Nd3+: (Lu0.25Y0.75)2O3 + 6 mol % ZrO2, Nd3+:(Sc0.25Y0.75)2O3 + 6 mol % ZrO2, and Yb3+:(Sc0.25Y0.75)2O3 + 6 mol % ZrO2 ceramics with transmittance to 82.2%. It was shown that introduction of iso- and heterovalent additives Sc2O3, Lu2O3, and ZrO2 into Nd3+:Y2O3 decreases average crystallite sizes to ∼1 μm and reduces the pore content, thus making it possible to produce pore-free ceramics.
These additives broaden the spectral band of the 4
F
3/2 → 4
I
11/2 transition of the neodymium ion to 40 nm. 相似文献
9.
The results of the ab initio FLAPW-GGA computations of the band structure of the recently synthesized layered tetragonal (space group I4/mmm) arsenide (Sr3Sc2O5)Fe2As2 as a possible basis phase of a new group of FeAs superconductors are presented. For (Sr3Sc2O5)Fe2As2, the energy bands, electron state density distributions, Fermi surface topology, low-temperature electron specific heat, molar Pauli paramagnetic susceptibility, and effective atomic charges have been determined. These results are discussed compared to similar data for the layered tetragonal crystals LaFeAsO, SrFeAsF, SrFe2As2, and LiFeAs that are the basis phases of the recently discovered high-temperature (T C ~ 26–56 K) 《1111》, 《122》, and 《111》 FeAs superconductors. 相似文献
10.
First principle FLAPW-GGA calculations have been performed with the purpose to understand the effect of Ti-doping on the electronic
properties for the newly discovered tetragonal iron arsenide-oxide Sr4Sc2Fe2As2O6 (abbreviated as FeAs42226) as the possible parent phase for the new FeAs superconductors. Our results show that the insertion
of Ti into Sc sublattice of this five-component iron arsenide-oxide phase leads to the resolute change of electronic structure
of FeAs42226. Namely, the insulating oxygen-containing [Sr4Sc2O6] blocks in Ti-doped FeAs42226 became conducting, and this differs essentially from the known picture for all others FeAs
superconductors where the conducting [Fe2As2] blocks are alternated with insulating blocks. Moreover in sharp contrast with FeAs-based superconductors with Fe 3d bands
near the Fermi level, for Ti-doped FeAs42226 in this region the Ti 3d states are dominated, whereas the Fe 3d states are suppressed. 相似文献
11.
(Y1-xGdx)2O3:Eu phosphor particles with dense morphology were prepared by flame spray pyrolysis and the effect of LiCl flux on the crystallinity, morphology, and photoluminescence characteristics of the particles was investigated. All as-prepared particles had monoclinic phase regardless of flux and had different luminescence characteristics from those of commercial Y2O3:Eu particles of cubic phase. The addition of LiCl flux reduced the post-treatment temperature by 300 °C for phase transformation from the monoclinic phase to the cubic phase. The post-treatment temperature of (Y0.75Gd0.25)2O3:Eu particles for phase transformation decreased from 1100 °C to 700 °C when LiCl flux was used. The morphology of the particles was also influenced by the Y/Gd ratio and the LiCl flux. The as-prepared particles had spherical shape and non-aggregation characteristics regardless of Y/Gd ratio and flux. The sphericity of the as-prepared particles prepared without flux was maintained after post-treatment for phase transformation in all Y/Gd ratios. However, LiCl addition promoted the aggregation between product particles. The prepared particles had high photoluminescence intensities comparable to that of the commercial product. PACS 64.70.Kb; 78.55.-m; 81.20.Rg; 75.50.Tt 相似文献
12.
W. J. Nellis 《The European physical journal. Special topics》2011,196(1):121-130
Dynamic compression has been used to synthesize liquid metallic hydrogen at 140 GPa (1.4 million bar) and experimental data
and theory predict Al2O3 might be a metallic glass at ∼ 300 GPa. The mechanism of metallization in both cases is probably a Mott-like transition.
The strength of sapphire causes shock dissipation to be split differently in the strong solid and soft fluid. Once the 4.5-eV
H-H and Al-O bonds are broken at sufficiently high pressures in liquid H2 and in sapphire (single-crystal Al2O3), electrons are delocalized, which leads to formation of energy bands in fluid H and probably in amorphous Al2O3. The high strength of sapphire causes shock dissipation to be absorbed primarily in entropy up to ∼400 GPa, which also causes
the 300-K isotherm and Hugoniot to be virtually coincident in this pressure range. Above ∼400 GPa shock dissipation must go
primarily into temperature, which is observed experimentally as a rapid increase in shock pressure above ∼400 GPa. The metallization
of glassy Al2O3, if verified, is expected to be general in strong oxide insulators. Implications for Super Earths are discussed. 相似文献
13.
A. Akrap R. Gaal L. Forró 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):287-291
We investigate the pressure and temperature behavior of current-dependent resistivity of β-SrV6O15. We observe a switching between states of different resistivities in the insulating state of β-SrV6O15. In the low pressure phase, the resistive switching appears at temperatures below the semiconductor-insulator transition.
In the high pressure phase, under ~1.6 GPa, the switching appears in the temperature range of the phase transition. The existence
of switching may imply an important role of strontium off-stoichiometry for the electrical transport in β-SrV6O15. No electric-field-induced enhancement of the conductivity is observed. However, the conduction is significantly nonlinear
under ~1.6 GPa, indicating that the charge order pattern in the high pressure phase is considerably different from that of
the low pressure phase. 相似文献
14.
It is demonstrated that 50% substitution of vanadium for molybdenum in the pyrochlore lattice of the complex oxide Y2(V x Mo1 ? x )2O7 results in a transition from the spin-glass ground state (at x = 0) to the ferromagnetic state in Y2VMoO7 (a = 10.1645(2) Å, T C = 55 K). The Gd2V0.67Mo1.33O7 compound (a = 10.2862(3) Å) is a ferromagnet with T C (84 K) exceeding that of undoped Gd2MnO2O7. 相似文献
15.
The α-Zn2P2O7 compound was obtained by conventional solid-state reaction. The sample was characterized by X-ray powder diffraction, solid
state 31P NMR MAS, and electrical impedance spectroscopy. The solid state 31P MAS NMR, performed at 121.49 MHz, shows three isotropic resonances at −21.1, −18.8, and −15.8 ppm, confirming the non-equivalency
of the three PO4 groups in the α-Zn2P2O7 form. They are characterized by different chemical shift tensor parameters with the local geometrical features of the tetrahedra.
Electrical impedance measurements of β-Zn2P2O7, form stable for temperature greater than 403 K, were performed as a function of both temperature and frequency. The electrical
conduction and dielectric relaxation have been studied. The AC conductivity obeys the universal power law. The approximation
type correlated barrier hopping model explains the universal behavior of the n exponent. The impedance plane plot shows semicircle arcs at different temperatures, and an electrical equivalent circuit
has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance R
p and constant phase elements CPE. The simulated spectra show a good correlation with the experimental data. 相似文献
16.
J.-E.?J?rgensen T. C.?Hansen 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(4):411-415
The crystal structure of BaFe2As2 was studied
by high-pressure neutron powder diffraction in the pressure range from
ambient to 6.5 GPa as well as in the temperature range from 12 K to 293 K at
4.4 GPa and no pressure or temperature induced phase changes were observed.
The compression mechanism of BaFe2As2 was found to be anisotropic
as the a- and c-axes are reduced by 2.49 and 3.66%, respectively at 6.5
GPa. Within the FeAs layers the Fe-As and Fe-Fe bonds decrease by 2.49 and
3.66%, respectively. The Ba-As distance decreases by 3.70% while the
As-As inter-atomic distance along the c-axis exhibits a complex pressure
dependence. The bulk modulus B
0 and its pressure derivative B
0' were
determined to be B
0 = 59(2) GPa and B
0' = 6.1(7) at ambient
temperature. 相似文献
17.
V. D. Fokina I. N. Flerov M. V. Gorev E. V. Bogdanov A. F. Bovina N. M. Laptash 《Physics of the Solid State》2007,49(8):1548-1553
The thermophysical properties of oxyfluoride (NH4)3NbOF6 were studied in detail over wide ranges of temperatures and pressures. At atmospheric pressure, a sequence of four structural phase transitions was established with the following changes in entropy: ΔS 1 = Rln 2.7, δS 2 = Rln38.3, ΔS 3 = 0.08R, and ΔS 4 = 0.17R. An external hydrostatic pressure was found to narrow the region of existence of the initial cubic phase. A triple point was detected in the p-T diagram; at a pressure above 0.07 GPa, the transition between the tetragonal and monoclinic phases occurs through a distorted high-pressure phase. 相似文献
18.
Specific features of the magnetic properties and magnetic dynamics of isolated phase separation domains in GdMn2O5 and Gd0.8Ce0.2Mn2O5 have been investigated. These domains represent 1D superlattices consisting of dielectric and conducting layers with the ferromagnetic orientation of their spins. A set of ferromagnetic resonances of separate superlattice layers has been studied. The properties of the 1D superlattices in GdMn2O5 and Gd0.8Ce0.2Mn2O5 are compared with the properties of the previously investigated RMn2O5 (R = Eu, Tb, Er, and Bi) series. The similarity of the properties for all the RMn2O5 compounds with different R ion types is established. Based on the concepts of the magnetic dynamics of ferromagnetic multilayers and properties of semiconductor superlattices, a 1D model of the superlattices in RMn2O5 is built. 相似文献
19.
A simple and sensitive chemiluminescence (CL) method coupled with flow-injection technique is proposed to determine naproxen
(NAP). The method is based upon the enhancement of the weak CL signal arising from the reaction of Ce(IV) and Na2S2O4 with Eu3+ to form the Eu3+-Ce(IV)-Na2S2O4 system. The CL intensity was significantly increased by the introduction of NAP into this system in the presence of silver
nanoparticles (Ag NPs). Examination of the recorded UV–vis spectra and fluorescence spectra indicated that the energy of the
intermediate SO2*, which originated from the redox reaction of Ce(IV) and Na2S2O4, was transferred to Eu3+ via NAP and that the process was accelerated by Ag NPs due to their catalytic activity. Under the optimum conditions, the
CL intensity was increased with increasing NAP concentration and the correlation was linear (r = 0.9992) over the NAP concentration range of 1–420 ng mL−1. The limit of detection (LOD) was 0.11 ng mL−1 with a relative standard deviation (RSD) of 1.15% for 5 replicate determinations of 200 ng mL−1 NAP. The method was successfully applied to determine NAP in pharmaceutical and biological samples. 相似文献
20.
AlF3-coating is attempted to improve the performance of LiNi0.5Mn1.5O4 cathode materials for Li-ion batteries. The prepared powders are characterized by scanning electron microscope, powder X-ray
diffraction, charge/discharge, and impedance. The coated LiNi0.5Mn1.5O4 samples show higher discharge capacity, better rate capability, and higher capacity retention than the uncoated samples.
Among the coated samples, 1.0 mol% AlF3-coated sample shows highest capacity after charge–discharged at 30 mA/g for 3 cycles, but 4.0 mol% coated sample exhibits
the highest capacity and cycling stability when cycled at high rate of 150 and 300 mA/g. The 40th cycle discharge capacity
at 300 mA/g current still remains 114.8 mAh/g for 4.0 mol% AlF3-coated LiNi0.5Mn1.5O4, while only 84.3 mAh/g for the uncoated sample. 相似文献