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1.
Measurements of the electrical conductivity were performed in KHSO4 at pressures between 0.5 and 2.5 GPa and in the temperature range 120-350 °C by the use of the impedance spectroscopy. The temperatures of the α-β phase transition (TTr) and of the melting (Tm), determined from the Arrhenius plots ln(σT) vs. 1/T, increase with pressure up to 1.5 GPa having dT/dP∼+45 K/GPa. Above the pressure 1.5 GPa, the pressure dependencies of TTr and Tm are negative dT/dP∼−45 K/GPa. At pressures above 0.5 GPa, the reversible decomposition of KHSO4 into K3H(SO4)2+H2SO4 (and probably into K5H3(SO4)4+H2SO4) affects the electrical conductivity of KHSO4, with the typical values of the protonic electrical conductivity, c. 10−1 S/cm at 2.5 GPa. 相似文献
2.
We report the influence of external high-pressure (P up to 8 GPa) on the temperature (T) dependence of electrical resistivity (ρ) of a Yb-based Kondo lattice, YbPd2Si2, which does not undergo magnetic ordering under ambient pressure condition. There are qualitative changes in the ρ(T) behavior due to the application of external pressure. While ρ is found to vary quadratically below 15 K (down to 45 mK) characteristic of Fermi-liquids, a drop is observed below 0.5 K for P=1 GPa, signaling the onset of magnetic ordering of Yb ions with the application of P. The T at which this fall occurs goes through a peak as a function of P (8 K for P=2 GPa and about 5 K at high pressures), mimicking Doniach's magnetic phase diagram. We infer that this compound is one of the very few Yb-based stoichiometric materials, in which one can traverse from valence fluctuation to magnetic ordering by the application of external pressure. 相似文献
3.
S. Arumugam K. Mydeen N. Manivannan K.U. RamaTulasi Elisa Baggio Saitovitch A.T. Boothroyd 《Solid State Communications》2005,136(5):292-296
We report the temperature dependence of susceptibility for various pressures, magnetic fields and constant magnetic field of 5 T with various pressures on La2−2xSr1+2xMn2O7 single crystal to understand the effectiveness of pressure and magnetic field in altering the magnetic properties. We find that the Curie temperature, Tc, increases under pressure (dTc/dP=10.9 K/GPa) and it indicates the enhancement of ferromagnetic phase under pressure up to 2 GPa. The magnetic field dependence of Tc is about 26 K for 3 T. The combined effect of pressure and constant magnetic field (5 T) shows dTc/dP=11.3 K/GPa and the peak structure is suppressed and broadened. The application of magnetic field of 5 T realizes 3D spin ordered state below Tc at atmospheric pressure. Both peak structure in χc and 3D spin ordered state are suppressed, and changes to 2D-like spin ordered state by increase of pressure. These results reveal that the pressure and the magnetic field are more competitive in altering the magnetic properties of bilayer manganite La1.25Sr1.75Mn2O7 single crystal. 相似文献
4.
S. Kawasaki T. Oka X.F. Wang Guo-qing Zheng 《Journal of Physics and Chemistry of Solids》2011,72(5):501-504
75As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe2As2 under pressure. At P=4.7 and 10.8 kbar, the temperature dependence of nuclear-spin-lattice relaxation rate (1/T1) measured at tetragonal phase show no coherence peak just below Tc and decrease with decreasing temperature. The superconductivity is of gapless at P=4.7 kbar but evolves to multiple gaps at P=10.8 kbar. We find that the superconductivity appears near a quantum critical point. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound. 相似文献
5.
John C. Papaioannou George S. Patermarakis 《Journal of Physics and Chemistry of Solids》2005,66(5):839-844
The frequency dependence of the real (?′) and imaginary (?″) parts of the dielectric constant of polycrystalline hematite (α-Fe2O3) has been investigated in the frequency range 0-100 kHz and the temperature range 190-350 K, in order to reveal experimentally the electron hopping mechanism that takes place during the Morin transition of spin-flip process. The dielectric behaviour is described well by the Debye-type relaxation (α-dispersion) in the temperature regions T<233 K and T>338 K. In the intermediate temperature range 233 K<T<338 K a charge carrier mechanism takes place (electron jump from the O2− ion into one of the magnetic ions Fe3+) which gives rise to the low frequency conductivity and to the Ω-dispersion. The temperature dependence of relaxation time (τ) in the −ln τ vs 103/T plot shows two linear regions. In the first, T<238 K, τ increases with increasing T implying a negative activation energy −0.01 eV, and in the second region T>318 K τ decreases as the temperature increases implying a positive activation energy 0.12 eV. The total reorganization energy (0.12-0.01) 0.11 eV is in agreement with the adiabatic activation energy 0.11 eV given by an ab initio model in the literature. The temperature dependence of the phase shift in the frequencies 1, 5, 10 kHz applied shows clearly an average Morin temperature TMo=284±1 K that is higher than the value of 263 K corresponding to a single crystal due to the size and shape of material grains. 相似文献
6.
The La1.32Sr1.68Mn2O7 layered manganite system has been studied by the low temperature electrical resistance and magnetoresistance under hydrostatic pressure up to 25 kbar. We have observe both, a Curie temperature (TC) and a metal-insulator transition (TMI) at 118 K in the ambient pressure. The applied pressure shifts the TMI to higher temperature values and induces a second metal-insulator transition (T2MI) at 90 K, in the temperature dependence of resistivity measurements. Also, the pressure suppresses the peak resistance abruptly at TC. When an external field of 5 T is applied, we have observed a large negative magnetoresistance of 300% at the transition temperature and a 128% at 4.5 K. However, the increased pressure decreases the magnetoresistance ratio gradually. When the pressure reaches its maximum available value of 25 kbar, the magnetoresistance ratio decreases at a rate of 1.3%/kbar. From our experimental results, the decrease of magnetoresistance ratio with pressure is explained by the pressure induced canted spin state which is not favor for the spin polarized intergrain tunneling in layered manganites. 相似文献
7.
V.V. NovikovD.V. Avdashchenko A.V. MatovnikovN.V. Moiseev S.L. Bud'koT. Tanaka 《Physica B: Condensed Matter》2011,406(13):2642-2645
Temperature dependences of heat capacity CP(T) and magnetization M(T) of an icosahedral dysprosium boride (DyB62) single crystal have been experimentally investigated in the temperature range of 2-300 K. The magnetic susceptibility χ(T) of DyB62 follows Curie-Weiss law with a paramagnetic Curie temperature of −3.7 K, which implies that the antiferromagnetic interactions are dominant in this material and suggests the possibility of magnetic ordering at low temperatures. This conjecture is supported by the temperature dependence of heat capacity CP(T), which decreases upon heating from 2 to 7 K. The heat capacity of DyB62 at 2 K is analyzed as a sum of magnetic, Debye, two-level system and soft atomic potential components. 相似文献
8.
We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe2As2, BaFe2As2, and (Ba0.55K0.45)Fe2As2, by means of measurements of electrical resistivity (ρ) in the 1.8-300 K temperature (T) range, pressures up to 20 kbar, and magnetic fields up to 9 T. CaFe2As2 and BaFe2As2 (lightly doped with Sn) display structural phase transitions near 170 and 85 K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba0.55K0.45)Fe2As2 is superconducting for T<30 K. The effect of pressure on BaFe2As2 is to shift the onset of the crystallographic transformation down in temperature at the rate of ~−1.04 K/kbar, while shifting the whole ρ(T) curves downward, whereas its effect on superconducting (Ba0.55K0.45)Fe2As2 is to shift the onset of superconductivity to lower temperatures at the rate of ~−0.21 K/kbar. The effect of pressure on CaFe2As2 is first to suppress the crystallographic transformation and induce superconductivity with onset near 12 K very rapidly, i.e., for P<5 kbar. However, higher pressures bring about another phase transformation characterized by reduced-resistivity, and the suppression of superconductivity, confining superconductivity to a narrow pressure dome centered near 5 kbar. Upper critical field (Hc2) data in (Ba0.55K0.45)Fe2As2 and CaFe2As2 are discussed. 相似文献
9.
Carlo Cavallotti Marco Derudi Renato Rota 《Proceedings of the Combustion Institute》2009,32(1):115-121
The C7H7 potential energy surface was studied from first principles to determine the benzyl radical decomposition mechanism. The investigated high temperature reaction pathway involves 15 accessible energy wells connected by 25 transition states. The analysis of the potential energy surface, performed determining kinetic constants of each elementary reaction using conventional transition state theory, evidenced that the reaction mechanism has as rate determining step the isomerization of the 1,3-cyclopentadiene, 5-vinyl radical to the 2-cyclopentene,5-ethenylidene radical and that the fastest reaction channel is dissociation to fulvenallene and hydrogen. This is in agreement with the literature evidences reporting that benzyl decomposes to hydrogen and a C7H6 species. The benzyl high-pressure decomposition rate constant estimated assuming equilibrium between the rate determining step transition state and benzyl is k1(T) = 1.44 × 1013T0.453exp(−38400/T) s−1, in good agreement with the literature data. As fulvenallene reactivity is mostly unknown, we investigated its reaction with hydrogen, which has been proposed in the literature as a possible decomposition route. The reaction proceeds fast both backward to form again benzyl and, if hydrogen adds to allene, forward toward the decomposition into the cyclopentadienyl radical and acetylene with high-pressure kinetic constants k2(T) = 8.82 × 108T1.20exp(1016/T) and k3(T) = 1.06 × 108T1.35exp(1716/T) cm3/mol/s, respectively. The computed rate constants were then inserted in a detailed kinetic mechanism and used to simulate shock tube literature experiments. 相似文献
10.
Matthew A. Oehlschlaeger Ronald K. Hanson 《Proceedings of the Combustion Institute》2007,31(1):211-219
The two-channel thermal decomposition of toluene, C6H5CH3 → C6H5CH2 + H (1) and C6H5CH3 → C6H5 + CH3 (2), was investigated in shock tube experiments over the temperature range of 1400-1780 K at a pressure of 1.5 (±0.1) bar. Rate coefficients for reactions (1) and (2) were determined by monitoring benzyl radical (C6H5CH2) absorption at 266 nm during the decomposition of toluene diluted in argon and modeling the temporal behavior of the benzyl concentration with a kinetic model. The first-order rate coefficients determined at a pressure of 1.5 bar are expressed by k1(T) = 2.09 × 1015 exp (−87510 [cal/mol]/RT) [s−1] and k2(T) = 2.66 × 1016 exp (−97880 [cal/mol]/RT) [s−1]. The resulting branching ratio, k1/(k1 + k2), ranges from 0.8 at 1350 K to 0.6 at 1800 K. 相似文献
11.
Xiaosheng Huang William Mickelson B.Christopher Regan Alex Zettl 《Solid State Communications》2005,136(5):278-282
We have measured the temperature dependence of the upper critical field, Hc2(T), of carbon-doped MgB2. Hc2(T) does not follow the well-known Werthamer-Helfand-Hohenberg (WHH) result for a one-gap dirty superconductor but can be described well by the result of a recent theoretical calculation for a two-gap dirty superconductor. Hc2(0) of the carbon-doped material is determined to be between 29 and 38 T, substantially higher than that of pure MgB2 (15-23 T). 相似文献
12.
Thin films of tungsten trioxide (WO3) are prepared by reactive pulsed laser deposition (PLD) technique on glass substrates at three different substrate temperatures (Ts). The structural, morphological and optical properties of the deposited films are systematically studied using X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), micro-Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-VIS spectrophotometry techniques. X-ray diffraction analysis reveals that crystalline WO3 films can grow effectively even at 300 K at an oxygen pressure of 0.12 mbar. All the films deposited at various Ts exhibit mixed oxide phase consisting of orthorhombic and triclinic phase of tungsten oxide with a preferred orientation along (0 0 1) lattice plane reflection. Micro-Raman results are consistent with X-ray diffraction findings. The SEM analysis shows that deposited films are porous and crystalline grains are of nano-metric dimension. The effect of Ts on mean surface roughness studied by AFM analysis reveals that mean surface roughness decreases with increase in Ts. The optical response of WO3 layers measured using UV-VIS spectrophotometry is used to extract the optical constants such as refractive index (n), extinction coefficient (k) and optical band gap (Eg), following the method of Swanepoel. 相似文献
13.
Yositaka Yosida 《Physica C: Superconductivity and its Applications》2009,469(14):795-797
Isothermal magnetization near a fishtail peak in nanocrystalline B1 NbCy encapsulated in multiwall carbon nanocages is studied within the time window of 100 < t < 4000 s. The current density J exhibits a linear logarithmic time decay. The effective activation energy Ueff increases linearly with temperature T and is independent of applied magnetic field H. The results of J(t) and Ueff (T, H) are consistent with the Anderson–Kim flux–creep model for thermally activated motion of uncorrelated vortices or vortex bundles over a net potential barrier Ueff. Ueff at a fishtail peak field Hfp evolves quickly above a fishtail peak temperature Tfp, but slowly below that temperature. The result suggests that a decrease of flux viscosity coefficient above Tfp at Hfp is the origin of the fishtail peak in nanocrystalline B1 NbCy encapsulated in multiwall carbon nanocages. 相似文献
14.
The dielectric properties of the [4-NH2C5H4NH] SbCl4 (abbreviated as 4-APCA) crystal were investigated under hydrostatic pressure up to 300 Mpa. The pressure-temperature phase diagram was given. The paraelectric-ferroelectric phase transition (II→III) temperature (Tc) increases linearly with increasing pressure with a slope dTc/dp=21×10−2 K/MPa. The pressure dependence of Curie-Weiss constants has been evaluated also. In the paraelectric phase (II) the Curie constant (C+) was pressure dependent whereas the C− constant over the ferroelectric phase (III) was almost constant. The results are interpreted in terms of improper and displacive type phase transition model with a soft phonon at a zone boundary. 相似文献
15.
Stephen J. Klippenstein Lawrence B. Harding 《Proceedings of the Combustion Institute》2007,31(1):221-229
The kinetics of reactions on the C7H8 surface were studied with state-of-the-art ab initio transition state theory (TST) and master equation methodologies. A priori predictions of the capture rate for C6H5 + CH3 and for C7H7 + H are obtained from direct variable reaction coordinate TST simulations. These simulations employ small basis set CASPT2 interaction energies coupled with one-dimensional reaction path corrections based on higher level simulations for related reactions. For the C7H7 + H reaction, predictions are obtained for both the total rate and for the branching between toluene, o-isotoluene and p-isotoluene. A mapping of the low energy pathways for isomerization from these three C7H8 isomers identifies a number of processes with barriers at or below the dissociation threshold. Nevertheless, at combustion temperatures the dissociation rates are predicted to exceed the isomerization rates, and it is reasonable to treat the kinetics of each isomer as a simple single well association/dissociation equilibrium. Master equation simulations yield predictions for the temperature and pressure dependence of each of the recombination and dissociation processes, as well as for the C7H7 + H → C6H5 + CH3 bimolecular reaction. These simulations implement collisional energy transfer probabilities based on the work of Luther and co-workers. The theoretical predictions are found to be in satisfactory agreement with the available experimental data for the photodissociation of toluene, the temperature and pressure dependent dissociation of toluene, and the reaction of benzyl radical with H. For the C6H5 + CH3 recombination, the theoretical predictions exceed the experimental measurements of Lin and coworkers by a factor of 2 or more for all temperatures. 相似文献
16.
M. ErdemÖ. Özturk E. YucelS.P. Altintas A. VarilciC. Terzio?lu I. Belenli 《Physica B: Condensed Matter》2011,406(3):705-709
We have investigated the effect of addition of Gd in Bi1.8Pb0.35Sr1.9Ca2.1Cu3GdxOy superconductor with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared using the standard solid-state reaction method. The activation energies, irreversibility fields (Hirr), upper critical fields (Hc2) and coherence lengths at 0 K (ξ(0)) were calculated from the resistivity versus temperature (R-T) curves under DC magnetic fields up to 7 T. The superconducting transition temperature, Tc, and activation energy, U0, were found to decrease with increase in Gd concentration and with increase in applied magnetic field. The offset transition temperature of the pure (Gd00) sample without applied magnetic field is 108 K, whereas for Gd05 sample, the offset transition temperature drops to 5 K with 7 T applied magnetic field. The activation energy of the Gd00 sample without applied magnetic field is 34,980 K, and for Gd05 sample with 7 T applied field it is 98 K. Hirr and Hc2 values also decrease with increase in Gd addition. The possible reasons for the observed degradation in microstructural and superconducting properties due to Gd addition were discussed. 相似文献
17.
K. Praveena 《Journal of magnetism and magnetic materials》2009,321(16):2433-2437
Microwave-Hydrothermal (M-H) method has been successfully used for the synthesis of nanocrystalline Mn-Zn ferrites which are used for high-frequency applications. As synthesized powders were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The nanopowders were annealed at 600 °C/20 min using the microwave sintering method. The frequency dependence of dielectric constant (ε′) was measured in the range of 10 Hz-1.3 GHz and initial permeability (μi) was measured in the range of 10 Hz-1 MHz. The total power loss (Pt) was measured on the annealed samples at 100 kHz and 200 mT condition. Conductor-embedded-ferrite transformers were fabricated and output power (Po), efficiency (η) and temperature rise (ΔT) were measured at sinusoidal voltage of 25 V at 1 MHz. The transformer efficiency (η) was found to be high and surface rise of temperature (ΔT) is very low. 相似文献
18.
Molecular dynamics (MD) simulations have been performed to investigate the effects of pressure and temperature on the isothermal bulk modulus of CaO using pair-wise interactions that include polarization effects through the shell model (SM). The dependence of isothermal bulk modulus BT of CaO on the compression ratio V/V0 and pressure P have been obtained from MD runs at T=300 K, and compared with the available experimental data and other theoretical results. A good agreement between theory and experiment is obtained. Meanwhile, BT dependence on temperature T at zero pressure is investigated. At extended pressure and temperature ranges, SM-MD method has also been carried out for predicting the P-V-T equation of state and isothermal bulk modulus at different temperatures along the isotherms 0, 1000, 2000, 3000, and 4000 K, and at different pressures along the isobars 5, 15, 30, 40, and 50 GPa for CaO, respectively. 相似文献
19.
Fumiaki Tomioka Masato Hedo Yoshiya Uwatoko Yusuke Okuda Yoshichika ōnuki 《Journal of Physics and Chemistry of Solids》2008,69(12):3199-3201
We measured the heat capacity of CeIrSi3 (100 mK<T<6 K) under high pressure up to P=1.38 GPa. The measurements have been used a quasiadiabatic method utilizing a CuBe piston-cylinder pressure cell in a dilution refrigerator. At 0 GPa, a sharp anomaly which indicates the antiferromagnetically transition is observed at TN=5 K. TN decreases monotonically with increasing pressure up to P=1.38 GPa. The magnetic entropy is released below TN only 19% of R ln 2 at 0 GPa. And the magnetic entropy decreases with increasing pressure up to 1.38 GPa, 64% compared to that at 0 GPa. 相似文献
20.
We have investigated the pressure-induced structural phase transition in ReO3 by neutron diffraction on a single crystal. We collected neutron diffraction intensities from the ambient and high pressure phases at P=7 kbar and refined the crystal structures. We have determined the stability of the high pressure phase as a function temperature down to T=2 K and have constructed the (P-T) phase diagram. The critical pressure is Pc=5.2 kbar at T=300 K and decreases almost linearly with decreasing temperature to become Pc=2.5 kbar at T=50 K. The phase transition is driven by the softening of the M3 phonon mode. The high pressure phase is formed by the rigid rotation of almost undistorted ReO6 octahedra and the Re-O-Re angle deviates from 180°. We do not see any evidence for the existence of the tetragonal (P4/mbm) intermediate pressure phase reported earlier. 相似文献