共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Sahling J. C. Lasjaunias K. Biljakovic P. Monceau 《Journal of Low Temperature Physics》2003,133(3-4):273-289
We have measured under applied magnetic field the heat capacity c
p and heat release
of the quasi-1D conductor (TMTSF)2PF6 in its spin density wave (SDW) ground state. The low-temperature heat capacity (T < 0.5 K) is dominated by a Schottky anomaly contribution. A corresponding term was also found for the heat release. In this T-range both properties are strongly sensitive to moderate magnetic fields (i.e., below 0.5 T): their amplitudes have a sharp maximum for H
c=0.2 T. We show that the corresponding density of two-level states N
S undergoes a sharp maximum at H
c, which rules out an extrinsic origin for the two-level states. Instead we suppose an intrinsic origin, such as defects of commensurability of the SDW, as the (slow) excitations related to the domain walls. This effect is found to be independent on the field orientations H a and H a. 相似文献
2.
A modified chemical deposition process is employed for the preparation of thin-film (CdS)
x
-(PbS)1 −x
composites with 0·2 ≤x ≤ 0·8. Cadmium sulphate, lead acetate and thiourea are used as the basic source materials. The electrical conductivity is
found to decrease with increasing composition parameterx up to 0·5 and increase for further increase inx. The composites are polycrystalline as is revealed from XRD and microscopic observations and show phases of both cubic and
hexagonal CdS, cubic CdO and PbS, and tetragonal PbO and PbO2. Additional peaks of free elemental Cd and S have also been observed. For all the phases no significant variation in lattice
parameters withx has been observed. The optical absorption studies show the presence of four well-defined absorption edges at approximately
0·45 eV, 1·05eV, 1·80 eV and 2·35 eV, at the same energies for allx values. The absorption coefficient is of the order of 104 cm−1 and mode of band-to-band transition is of the direct type. 相似文献
3.
The layer type MoSe
x
Te2−x
(0 ≤x ≤ 2) have been grown in single crystalline form by chemical vapour transport technique using bromine as the transporting
agent. The electrical resistivity and Hall mobility perpendicular to thec-axis of the crystals were measured at room temperature. The variation of the Seeback coefficient with temperature was also
investigated. 相似文献
4.
B. Padlyak R. Vlokh A. Grabar Yu. Vysochanskii I. Dmitruk W. Ryba-Romanowski R. Lisiecki 《Optical Materials》2009,31(12):1831
A large family of Sn2yPb2(1−y)P2S6xSe6(1−x) semiconductor-ferroelectric crystals were obtained by the Bridgman technique. The photoluminescence properties of the Sn2yPb2(1−y)P2S6xSe6(1−x) family crystals strongly depend on their chemical composition, excitation energy and temperature. The influence of the Pb → Sn and S → Se isovalent substitutions on the luminescence properties of a crystal with the Sn2P2Se6 basic composition was investigated. A broad emission band observed in the Sn2P2Se6 crystal with a maximum roughly at 600 nm (at T = 8.6 K) was assigned to a band-to-band electron-hole recombination, whereas broad emission bands, peaked near 785 nm (at T = 8.6 K) and 1025 nm (at T = 44 K) were assigned to an electron-hole recombination from defect levels localised within the bandgap. Possible types of recombination defect centres and specific mechanisms of luminescence in the Sn2P2Se6 semiconductor-ferroelectric crystals were considered and discussed on the basis of the obtained results and the referenced data. 相似文献
5.
A review is given on the theoretical studies of charge correlations in θ-(BEDT-TTF)2X. Various studies show that within a purely electronic model on the θ-type lattice with on-site U and nearest neighbor Vp and Vc interactions, the diagonal stripe, c-axis three-fold, and the vertical stripe charge correlations are favored in the regime Vp<Vc, Vp∼Vc, and Vp>Vc, respectively. In the realistic parameter regime of Vp∼Vc, there is competition between the c-axis three fold state and diagonal stripe state. Since these are different from the experimentally observed a-axis three fold and the horizontal stripe charge correlations, additional effects have to be included in order to understand the experiments. The electron–lattice coupling, which tends to distort the lattice into the θd-type, is found to favor the horizontal stripe state, suggesting that the occurrence of this stripe ordering in the actual materials may not be of purely electronic origin. On the other hand, distant electron–electron interactions have to be considered in order to understand the a-axis three fold correlation, whose wave vector is close to the nesting vector of the Fermi surface. These studies seem to suggest that the minimal model to understand the charge correlation in θ-(BEDT-TTF)2X may be more complicated than expected. Future problems regarding the competition between different types of charge correlations are discussed. 相似文献
6.
NaSm9(SiO4)6O2 powders were synthesized by mild hydrothermal method at 180 °C for 24 h. The infrared optical properties and structure of the obtained powders were characterized. There existed two narrow and sharp absorptive bands near 943 cm− 1 (10.6 μm). The band at 938 cm− 1 was assigned to the stretching vibrations of SiOSm groups connecting to Q1 species and the band at 989 cm− 1 was attributed to the stretching vibrations of SiOSm groups linking with Q0 species. The reflectivity was lower than 1% from 900 to 1200 nm and reached the minimum of 0.46% at 1073 nm. The prepared powders exhibit potential to act as a new kind of absorptive material for the infrared light of 10.6 μm and 1.06 μm. 相似文献
7.
The structural phase transitions and relaxation processes of Cs2Co(SO4)2·6H2O and Cs2Zn(SO4)2·6H2O single crystals were investigated, with the phase transitions of both crystals being determined from NMR data. The spin–lattice relaxation time, T1, of the 133Cs nucleus in two crystals undergoes a significant change near the phase transition temperature, TC, and these changes coincide with the changes in the splitting of the 133Cs resonance lines. The variations in the temperature dependence for the splitting of the 133Cs resonance lines and T1 near TC are related to changes in the symmetry of surrounding Cs+. In addition, the 133Cs T1 of Cs2Co(SO4)2·6H2O, which contains paramagnetic ions, was found to be shorter than that of Cs2Zn(SO4)2·6H2O. This relaxation time is inversely proportional to the square of the magnetic moment of the paramagnetic ions. The differences between the 133Cs T1 of these compounds are probably due to the differences between the electronic structures of their metal ions. 相似文献
8.
Three new oxycarbonate superconductors recently obtained in our laboratory are described. (1) Sr2CuO2(CO3)1–x
(BO3)
x
(T
c
= 35 K) was synthesized under ambient pressure, providing a new method for carrier doping on the layered copper oxycarbonate system. (2) Ca
n
(Ca, Sr)2Cu
n+1(CO3)O
y
(n = 1, 2, 3) was synthesized under high pressure. Superconductivity was achieved by substituting (BO3)3– for a part of (CO3)2–. (3) A new Hg system HgBa2Sr2Cu2(CO3)O6+
was synthesized.T
c
obtained from the magnetic susceptibility is about 66 K. 相似文献
9.
The Cu4SO4(OH)6 was synthesized by a simple hydrothermal reaction with a yield of ~ 90%. Using Cu4SO4(OH)6 as the starting material, novel fishbone-like Cu(OH)2 was produced by a direct reaction of Cu4SO4(OH)6 with NaOH solution. The Cu(OH)2 consists of many needle-like nanorods parallel to each other and perpendicular to the direction of backbone, forming fishbone-like structure. Using the fishbone-like Cu(OH)2 as the sacrificial precursor, CuO with similar size and morphology was obtained through a simple heat treatment. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, X-ray photoelectron spectroscopy, BET nitrogen adsorption, and UV-Vis absorption spectroscopy were employed to characterize the as-prepared samples. The conversion of the Cu4SO4(OH)6 to the fishbone-like Cu(OH)2 was visualized by time-dependent SEM images. A mechanism was also proposed based on the observed results. 相似文献
10.
The vacuum ultraviolet excited luminescent properties of Eu3+, Tb3+, Dy3+, Sm3+ and Tm3+ in the matrices of Ca4Y6(SiO4)6O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca4Y6(SiO4)6O. For Eu3+-doped samples, the O2− → Eu3+ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb3+-doped samples. For Dy3+-doped and Sm3+-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm3+-doped samples, the O2− → Tm3+ CTB was located at 191 nm. About the color purity and emission intensity, Ca4Y6(SiO4)6O:Tb3+ is an attractive candidate of green light PDP phosphor, and Ca4Y6(SiO4)6O:Dy3+ has potential application in the field of mercury-free lamps. 相似文献
11.
The Cr3+:KAl(MoO4)2 single crystal was grown by top seeding solution growth method (TSSG). Based on the absorption and emission spectra, the crystal field strength Dq, the Racah parameters B and C, the effective phonon energy ?ω and the Huang-Rhys factor S were calculated: Dq = 1494.8 cm− 1, B = 585.5 cm− 1 and C = 3049 cm− 1, ?ω = 373.8 cm− 1 and the Huang-Rhys factor S = 3.74, respectively. The value Dq/B = 2.55 indicates that Cr3+ ion occupies the strong crystal field site in KAl(MoO4)2 crystal. A comparison of crystal field parameters for Cr3+:KAl(MoO4)2 with other Cr3+-doped crystals was presented. The results of spectral measurement show that Cr3+:KAl(MoO4)2 may be a potential candidate for broadband laser applications. 相似文献
12.
C.H. Cheng X.H. GongY.F. Lin Z.D. LuoY.J. Chen J.H. HuangY.D. Huang 《Optical Materials》2011,33(6):763-767
A Ho3+-doped NaLa(MoO4)2 single crystal was grown by the Czochralski method. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of the crystal were measured at room temperature. The spontaneous emission probabilities, radiative lifetimes, and fluorescence branching ratios of the typical fluorescence multiplets of Ho3+ ions were calculated. The polarized stimulated emission and gain cross-sections of the 5I7 → 5I8 transition were obtained. The results show that the Ho3+:NaLa(MoO4)2 crystal is a promising gain medium for tunable and ultrashort pulse lasers operating around 2.0 μm. 相似文献
13.
A high optical quality Er3+-doped NaGd(WO4)2 single crystal with dimensions of ∅18 × 50 mm3 has been grown using the Czochralski method. The structure of the grown crystal was proved by X-ray powder diffraction. The accurate concentration of Er3+ ion in the crystal was measured. The absorption spectra, fluorescence spectra and fluorescence lifetime of the crystal were measured at room temperature. Green up-conversion luminescence has been observed when the crystal is excited at 965 nm. 相似文献
14.
K. M. Pansuria D. G. Kuberkar G. J. Baldha R. G. Kulkarni 《Journal of Superconductivity and Novel Magnetism》1997,10(1):59-62
The structural and superconducting properties of (Er1-xCax)Ba2-ySry(Cu2.76Co0.24)Oz are investigated using X-ray diffraction, resistivity, ac susceptibility, and oxygen content measurements. Increasing the
Sr content in (Er0.76Ca0.24)Ba2-ySry(Cu2.76Co0.24)Oz lowers the oxygen content and decreases theT
c, which is attributed to the rearrangement of oxygen atoms in the basal plane. This suppression ofT
c aty =0.6 cannot be improved by appropriate hole doping with Ca in (Er1-xCax)Ba1.4Sr0.6(Cu2.76Co0.24)Oz forx = 0.24-0.48. 相似文献
15.
Dynamic strength and failure behavior of titanium alloy Ti-6Al-4V for a variation of heat treatments
Lothar W. Meyer Lutz Krüger Kristin Sommer Thorsten Halle Matthias Hockauf 《Mechanics of Time-Dependent Materials》2008,12(3):237-247
In our study, samples of Ti-6Al-4V were subjected to modifications of an aging treatment where temperatures for solution annealing
and final aging as well as the cooling rate were varied. The titanium alloy was annealed above and below the β-transus temperature followed by cooling in a vacuum furnace or by water quenching. Additionally, the final annealing temperature
was varied. Compression tests under quasistatic and dynamic loading rates were performed to determine the flow stress and
strain hardening behavior. Furthermore, instrumented Charpy impact tests on U-notch specimen were performed at room temperature
to monitor the load-time response of deformation and fracturing. The obtained high rate mechanical properties are discussed
and correlated with the present microstructure. Our results reveal a very strong effect of the microstructure on the material
behavior and will assist to choose the appropriate heat treatment technology, especially if impact loaded or safety structures
have to be considered. 相似文献
16.
P Ganguly 《Bulletin of Materials Science》1981,3(3):255-260
The low-temperature preparation of some La2MM′O6 compounds (M,M′=Cr, Mn, Fe, Co, Ni, M≠M′) by the decomposition of coprecipitated basic carbonates is described. Single phase
compounds are formed. The stability of physical properties of these phases towards further heating depends on the M and M′
ions. The results are interpreted in terms of the stability of the M-M′ oxidation states.
Communication No. 122 from the Solid State and Structural Chemistry Unit 相似文献
17.
Yoshiya Akagi Hiroyuki Sasakura Satoru Noguchi Shigeki Tsukui Takashi Oka Motoaki Adachi 《Journal of Superconductivity》2004,17(3):449-453
The Ru-1232 compounds have been synthesized in the (Ru1–xNb
x
)Sr2(GdCe1.8Sr0.2)Cu2O
z
system, and effects of Nb substitution for Ru on superconductivity and ferromagnetism of the Ru-1232 compounds have been investigated. First, X-ray powder diffraction study shows that nearly the single 1232 phase samples can be obtained in the x composition range from 0.0 to 0.3. Then, from the electrical resistivity study, it is found that each of the samples shows resistivity dropping phenomenon at two temperatures of T
c
l and T
c
h, which originates from superconductivity of the Ru-1232 phase and the Ru-1222 one, respectively. Both of the starting temperatures are lowering with increasing Nb content x. Lastly, from the magnetic susceptibility study, it is found that superconducting transition temperature T
c is 20 K for the Ru-1232 sample with x = 0.0 and the ferromagnetic transition temperature T
m is about 90 K. This study also shows that both of the values of T
c and T
m become low with increasing x from 0.0 to 0.3. 相似文献
18.
Shan Xu Xinyang Huang Bingxuan Li Yong Wei Chenghui Huang Fengjiang Zhuang 《Journal of Modern Optics》2013,60(11):920-924
The crystal characteristics of a disordered Nd:LiLa(MoO4)2 laser crystal were investigated in detail, including its structure, absorption, emission and Raman scattering spectra. Laser operation, end-pumped by an 808?nm diode laser, has been demonstrated in both a concave-plano and plane-parallel resonator cavity. A broad-spectral dual-peak laser emission at 1061?nm and 1060?nm with a full width at half maximum of 2?nm was obtained in the experiment. A maximum output power of 267?mW was obtained in the concave-plano cavity. However, in the plane-parallel cavity, laser output of 381?mW was obtained, giving a slope efficiency of 14.5%. The results lay the groundwork for Raman, mode-locked and tunable laser applications generated by a Nd:LiLa(MoO4)2 laser crystal. 相似文献
19.
New iridium complexes, [Ir(dpq)2(acac), Ir(PF-dpq)2(acac) and Ir(PF-dpq-5F)2(acac)] (dpq = 2,4-diphenylquinoline, dpq-5F = 2-(3′-fluorophenyl)-4-phenylquinoline), PF-dpq-5F = 2-(3-fluoro-phenyl)-6-pentafluorophenyl-4-phenylquinoline and acac = acetylacetonate) have been synthesized and characterized for efficient red organic light-emitting diodes (OLEDs). In order to improve the luminescence efficiency by preventing self-quenching and to tune photoluminescence (PL) and electroluminescence (EL) spectra to a longer wavelength, dpq ligand was fluorinated by -PF and -F moieties. However, the iridium complex of PF-dpq-5F underwent a weak MLCT transition because of the weak coupling between the 5d orbital of the iridium atom and HOMO of the substituted ligand. Thus, the maximum luminous efficiencies of the device using Ir(dpq)2(acac), Ir(PF-dpq)2(acac) and Ir(PF-dpq-5F)2(acac) are 4.36 cd/A, 6.04 cd/A and 4.35 cd/A, respectively. 相似文献
20.
Nanocrystalline Nd2(Zr1 − xSnx)2O7 series solid solutions were prepared by a convenient salt-assisted combustion process using glycine as fuel. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The results showed the Zr ion can be partially replaced by Sn ion. The partial substituted products were still single-phase solid solutions and the crystal form remained unchanged. TEM images reveal that the products are composed of well-dispersed square-shaped nanocrystals. The method provides a convenient and low-cost route for the synthesis of nanostructures of oxide materials. 相似文献