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1.
Pressure dependence of the Shubnikov-de Haas (SdH)
oscillations spectra of the quasi-two dimensional organic metal
(ET) 8[ Hg 4Cl 12(C 6H 5Br) 2] have been studied up
to 1.1 GPa in pulsed magnetic fields of up to 54 T. According to
band structure calculations, its Fermi surface can be regarded as
a network of compensated orbits. The SdH spectra exhibit many
Fourier components typical of such a network, most of them being
forbidden in the framework of the semiclassical model. Their
amplitude remains large in all the pressure range studied which
likely rules out chemical potential oscillation as a dominant
contribution to their origin, in agreement with recent
calculations relevant to compensated Fermi liquids. In addition to
a strong decrease of the magnetic breakdown field and effective
masses, the latter being likely due to a reduction of the strength
of electron correlations, a sizeable increase of the scattering
rate is observed as the applied pressure increases. This latter
point, which is at variance with data of most charge transfer
salts is discussed in connection with pressure-induced features of
the temperature dependence of the zero-field interlayer
resistance. 相似文献
2.
Temperature-dependent 169Tm Mössbauer measurements are reported for the ternary intermetallic compounds TmT 2Ge 2 (T=Fe, Cu). Based on comparison with results for their TmT 2Si 2 counterparts, it is verified that the T constituent has the more significant influence on the crystal field interaction at the rare-earth site. 相似文献
3.
We have measured the thermal dependence of the f factor and the line shift of the title compounds, in order to determine the (−2) and (+2) moments of the Fe frequency spectrum.
The latter is approximated by a superposition of an acoustic-wave band and an intramolecular optical mode. Our results show
that both frequency bands are well separated, owing to a relatively weak interaction between tetrahedral units. Optical frequencies
thus determined are consistent with Raman data. Debye temperatures were obtained for the low-frequency vibrations of both
crystals. 相似文献
4.
The behavior of magnetoresistance is studied in two samples of the quasi-two-dimensional organic metal (ET) 8Hg 4Cl 12(C 6H 5Cl) 2 having different quality for various magnetic field directions. The interlayer transport in the high-quality sample is shown to be close to a coherent mode, and the interlayer transport in the low-quality sample is closer to an incoherent mode. 相似文献
5.
This paper reports on measurements of the de Haas-van Alfven effect in the quasi-two-dimensional organic conductor (BEDT-TTF) 8Hg 4Cl 12(C 6H 5Cl) 2 performed within the temperature range 0.33–1.44 K in magnetic fields of B≤50 T. An analysis of quantum oscillations together with cyclotron resonance data obtained in the 40–120-GHz frequency range revealed that the complex quantum-oscillation spectrum is formed by the fundamental frequencies α~256 T and β~670–610 T, as well as by combination and multiple frequencies. It is shown that the character of the temperature-induced oscillation-spectrum rearrangement can be interpreted within a model taking into account the existence of a magnetic phase transition at T c~0.9 K and the closeness of the fundamental frequency α with effective mass m*=1.48 m 0 to the spin damping condition. 相似文献
7.
The electrical conductivity of Cu 6PS 5Cl shows purely Arrhenius behavior throughout the temperature range 170–450 K with no evidence of the 241 K thermodynamic phase transition previously reported. Cu 6PS 5Br exhibits two changes in activation energy. The first, at 251 K, apparently coincides with a previously determined thermodynamic transition. The second, at 321 K, is likely associated with a conduction transformation from ionic to electronic. The conductivity of Cu 6PS 5I is characterized by a cusp at a temperature of 194 K, far removed from a previously reported thermodynamic transition at 221 K. In addition, a broad and continuous change in activation energy appears to coincide with another previously reported phase transition at 270 K. 相似文献
8.
ABSTRACTThe complexes of H 2X (X?=?O, S, Se) with hypervalent halogens YF 3 and YF 5 (Y?=?Cl, Br, I) have been studied. The σ-hole on the Y atom participates in a halogen bond with the lone pair on the chalcogen atom. In addition, some secondary interactions coexist with the halogen bond in most complexes. The interaction energy correlates with the nature of both X and Y atoms. In most cases, the complex is more stable for the heavier Y atom and the lighter X atom. Of course, there are some exceptions in H 2X···YF 3. YF 3 forms a more stable complex with H 2X than does YF 5. These complexes are dominated by electrostatic interaction and the halogen bond involving H 2S and H 2Se exhibits some covalent character.Halogen bond plays an important role in chemical reactions and multivalent halogens can regulate chemical reactions by participating in a halogen bond. Thus we compare the effect of the chalcogen electron donor on the strength and nature of halogen bonding involving multivalent halogens. 相似文献
9.
We have examined the HeI photoelectron spectra of the oxalyl halides (COX) 2, (X = F, Cl, and Br). We assume the presence of the trans-isomer onWe have used semi-empirical calculations (SCF MO), and Koopmans' Theorem, as aids in assigning the spectral bands. 相似文献
11.
The polarized reflectivity and optical conductivity spectra of microcrystals of the new organic conductor (BEDO-TTF) 5[CsHg(SCN) 4] 2 based on the donor molecule bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) have been studied in the spectral ranges 600–6500 and 9000–40000 cm ?1 at 300 K for three principal lattice directions. The optical evidence for the quasi-two-dimensional character of the conducting electronic system is obtained. The conclusion is made that the studied crystal is the quasi-two-dimensional semimetal with overlapping electron energy bands. The basic parameters of the electronic system of the crystal are determined in the framework of the Drude model. It is found that the allowed electron energy bands of the crystal are somewhat narrower than those of the previously studied structurally allied superconductor based on the same molecule. The features of vibrational structure are identified in the σ(ω) spectra for the specified three polarizations. 相似文献
12.
The IR and Raman spectra of the oxyapatite Ca 8La 2(VO 4) 6O 2 has been measured and discussed in comparison with those of related species. Data for Ca 8La 2(PO 4) 6O 2 and for a solid solution of composition Ca 8La 2(PO 4) 6O 2 are also reported. 相似文献
13.
In this paper, the formulae of optical spectral levels and electron paramagnetic resonance (EPR) spectra in trigonal symmetry of 3d 8 ions are established on the basis of strong field mechanism and a two spin-coupling (SO) parameters model. Unlike the classical crystal-field approach which has only taken the SO coupling of the central metal ions into account, the contribution of the SO coupling of the ligand ions to the optical and EPR spectra has been included in these formulae. When the optical and EPR spectra of the strong covalent crystals are calculated, the reasonable results can be obtained if the two SO parameters model has been put into action. As an application, the optical and EPR spectra of the (NiX 6) 4− clusters in CsMgX 3:Ni 2+ (X=Cl, Br, I) crystals have been studied by the complete diagonalization (of energy matrix) method (CDM). The calculated results agree well with experimental findings. From the investigations, a more valid method to calculate the optical and EPR spectra for 3d 8 ions clusters is provided. 相似文献
14.
Research has been undertaken to develop polymer electrolytes based on biodegradable natural polymers such as cellulose acetate, starch, gelatin, and chitosan, which are being used as polymer hosts for obtaining new polymer electrolytes for their applications in various electrochemical devices such as batteries, sensors, and electrochromic windows. Pectin is a naturally available material which is extracted from the skin of citrus fruits. Pectins, also known as pectic polysaccharides, are rich in galacturonic acid. The present study focuses on the proton-conducting polymer electrolytes based on the biopolymer pectin doped with ammonium chloride (NH4Cl) and ammonium bromide (NH4Br) prepared by solution casting technique. The prepared membranes are characterized using XRD, FTIR, and AC impedance techniques to study their complexation behavior, amorphous nature, and electrical properties. The conductivity of pure pectin membrane has been found to be 9.41 × 10−7 S cm−1. The polymer systems with 30 mol% NH4Cl-doped pectin and 40 mol% NH4Br-doped pectin have been found to have maximum ionic conductivity of 4.52 × 10−4 and 1.07 × 10−3 S cm−1, respectively. The conductivity value has increased by three orders of magnitude compared to pure pectin membrane. The dielectric behavior of both the systems has been explained using dielectric permittivity and electric modulus spectra. 相似文献
15.
Optics and Spectroscopy - The spectral-luminescent properties of complex compounds of tellurium(IV) halides with pyridine of the composition (C5H5NH)2TeHal6 (Hal = Cl, Br) are studied. In the case... 相似文献
16.
The specific heats of the compounds MnX 2L 2 with X = Cl or Br and L = N2C3H4 (pyrazole) or NC 5H 5 (pyridine), have been measured in the 1.3–80 K temperature range. The well-resolved broad maxima in the magnetic specific heat curves of all the compounds can be interpreted in terms of linear chain exchange interactions. The measured specific heats are compared with the isotropic antiferromagnetic Heisenberg linear chain model, but a model assuming, in addition, a moderately large single-ion anisotropy gives a much better agreement with experiment. The values obtained for the intrachain exchange parameter are in the range 0.5 K < | J/ k| < 1 K, and for the uniaxial single-ion anisotropy parameter, 0.2 K < | D/ k| < 0.5 K.The lambda-like anomalies observed in MnBr 2.2pz, MnCl 2.2py and MnBr 2.2py at T = 1.930 K, 1.380 K and 2.055 K, respectively, are attributed to long-range ordering due to the influence of weak interchain interactions. The strength of the interchain interactions has been estimated as about 1% of the intrachain interactions. The compound MnCl 2.2pz does not exhibit a transition to a long-range ordered state down to 1.3 K, which suggests that the interactions between the chains are very weak. 相似文献
17.
The reflection spectra and optical conductivity spectra of the new organic conductor ϰ-(ET) 2[Hg(SCN) 2Cl] with a metal-insulator transition in the spectral regions 700–5500 and 9000–40 000 cm −1 have been studied in polarized light at 300 K. A comparisonis made between the spectra obtained and the corresponding spectra
of related isostructural conductors based on the ET molecule, and also the properties of the crystal structure of the investigated
compounds. An electronic transition between the ET molecules of the dimer (ET)
2
+
in the spectral region 700–5500 cm −1 has been identified, as have the features of the electronic-vibrational structure arising as a consequence of the interaction
of this transition with the completely symmetric intramolecular vibrations of the ET molecule. It is found that the conductor
with the stronger dimer interaction between the ET molecules has the higher the transition temperature.
Fiz. Tverd. Tela (St. Petersburg) 39, 1313–1319 (August 1997) 相似文献
18.
The high-resolution N.M.R. spectra of a series of bicyclo [2.2.1] heptanols are discussed. Three unusual features are observed: ( a) relatively large 4 J's; ( b) unequal J endo-endo's and J exo-exo's; and ( c) unusual magnetic shieldings. These are presented as empirical phenomena and only little attempt is made to discuss their implications. 相似文献
19.
The crystal structure of [C(NH 2) 3] 2HgBr 4 has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH 2) 3] + and distorted tetrahedral [HgBr 4] 2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr 4] 2? ion. In accordance with the crystal structure, two 81Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH 2) 3] 2HgI 4 yielded four 127I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The 1H NMR T 1 measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C 3 reorientations of the planar [C(NH 2) 3] + ions gave the activation energies of 29.8 kJ mol ?1 for the bromide, and 30.2 and 40.0 kJ mol ?1 for the iodide. 相似文献
20.
Specific-heat data on CuL 6(ClO 4) 2 and CuL 6(BF 4) 2 in the temperature range 0.05 < T < 20 K are presented (L ≡ C 5H 5NO). The magnetic contributions are found to have the form of broad maxima, occurring near 1 K. Small χ-type anomalies are observed at Tc = 0.62 ± 0.01 K and 0.142 ± 0.002 K for CuL 6(BF 4) 2 and CuL 6(ClO 4) 2, respectively. The analyses show the magnetic structure to be an assembly of weakly coupled antiferromagnetic chains or layers for CuL 6(ClO 4) 2 and CuL 6(BF 4) 2, respectively. For CuL 6(ClO 4) 2 the intrachain exchange constant is J/ K = -1.02 ± 0.02 K, for CuL 6(BF 4) 2 the intralayer exchange constant is J/ K = -1.10 ± 0.02 K. Additional evidence for the lower-dimensional magnetic structures is obtained from the temperature dependences of the antiferromagnetic susceptibilities. The data on CuL 6(BF 4) 2 clearly indicate the absence of a divergence in the specific heat for the quadratic-layer Heisenberg antiferromagnet, and provide an estimate for the specific heat for this model. A comparison is made with the corresponding result for the ferromagnetic Heisenberg layer. 相似文献
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