共查询到20条相似文献,搜索用时 15 毫秒
1.
S. V. Trukhanov I. O. Troyanchuk A. V. Trukhanov I. M. Fita A. N. Vasil’ev A. Maignan H. Szymczak 《JETP Letters》2006,83(1):33-36
The magnetic properties of La0.70Sr0.30MnO2.85 anion-deficient manganite are studied experimentally under hydrostatic pressure. The results show that, in the whole pressure range under investigation (0–1 GPa), the sample is a spin glass with a smeared phase transition to the paramagnetic state. It is found that the spin glass state arises from the frustration of the exchange coupling of the ferromagnetic clusters embedded in the antiferromagnetic matrix. The fraction of the sample volume occupied by the ferromagnetic phase is found to be V fer ~ 13%. Under hydrostatic pressure, the freezing temperature T f of the magnetic moments of the ferromagnetic clusters increases at a rate of 4.30 K/GPa and the magnetic ordering temperature T MO increases at a rate of 12.90 K/GPa. In addition, the ferromagnetic part of the sample increases by ΔV fer ~ 5%. The enhancement of the ferromagnetic properties of La0.70Sr0.30MnO2.85 anion-deficient manganite under hydrostatic pressure is explained by the redistribution of oxygen vacancies and a decrease in the unit-cell parameters. 相似文献
2.
We report the temperature dependence of electrical resistance (R) and thermopower (S) of clathrate Cs8Sn44 under high pressure up to 1.2 GPa. We observe a reversible gap widening, prominent relaxation effect of R, irreversible increase of |S| under high pressure. We also find that the power factor S2σ (σ: electrical conductivity) reaches a maximum at pressure of 0.3 GPa. Comparison of the experimental results with band structure calculations suggests that the intrinsic vacancy in the clathrate structure of Cs8Sn44 plays an important role in transport properties under high pressure. Measurements on Cs8Zn4Sn42, a clathrate which has defects other than vacancies, are compared with Cs8Sn44. The results indicate that replacing Sn by Zn has similar effect as the intrinsic vacancy on S. 相似文献
3.
First principles calculations, by means of the full-potential linearized augmented plane wave method within the local density approximation, were carried out for the effect of pressure on the electronic and optical properties of the filled tetrahedral compounds LiMgN, LiMgP and LiMgAs. The bandgap pressure coefficient trend in the ternaries is found to be similar to the one encountered in the zinc-blende-like AlX. The first order bandgap pressure coefficient aΓ-Γ in LiMgN is larger than the corresponding one in AlN, while it is smaller in LiMgP and LiMgAs compared to the one in AlP and AlAs. The predicted values of the dielectric constants for LiMgN, LiMgP and LiMgAs are close to those of the binary compounds AlN, AlP and AlAs. 相似文献
4.
《Superlattices and Microstructures》2002,32(1):25-34
We have determined the pressure dependence of the direct bandgap, ionicity, transverse effective charge and refractive index for CdTe. The study is performed using the sp3s * semi-empirical tight-binding method with the scaling law and Murnaghan`s equation of state. All these properties were found to have a sublinearity behaviour with the pressure. The results are compared with other works. 相似文献
5.
We have investigated the formation and the normal- and superconducting properties of TaCxNy. By analogy to NbCN the superconducting transition temperature of the nitrogen-rich samples increases with pressure and decreases for carbon-rich samples. This is correlated with a different resistivity vs temperature behaviour. 相似文献
6.
The effect of hydrostatic pressure on the crystal structure, electronic and optical properties of distorted rare-earth manganite TbMnO3 has been studied on the basis of first-principle calculations. The results reveal that the band gaps reduce quadratically with increasing pressure. The optical properties of TbMnO3 predict that the peaks in the dielectric function shift to higher photon energy due to the transformation of inner electronic states with increasing pressure. Otherwise, the peaks in the reflectivity spectra and loss function were also found to move to higher photon energy with pressure increasing and the relationships between the positions of these peaks and pressure can be fitted by third order polynomial expressions. 相似文献
7.
Based on a molecular mechanics coupled with atomistic-based continuum theory, a closed-form formula is presented to examine the elastic properties of single- and double-walled carbon nanotubes subjected to hydrostatic pressure. Following the present model, the effects of the armchair and zigzag CNT structures on the pressure behavior are theoretically investigated. The computational result indicates that the bulk modulus is less sensitive to the chiral structures except for very small tube diameters. Moreover, closed-end nanotubes under hydrostatic pressure exhibit a larger bulking modulus than open ended nanotubes. The cap of the zigzag tubes has a larger effect on the bulk modulus when compared to the armchair tubes, especially in small diameter nanotubes. The predicted strain and the bulk modulus are in good agreement with existing theoretical results. PACS 61.46.+w; 62.20.Dc; 62.20.-x; 62.25.+g 相似文献
8.
Photoluminescence measurements on GaSb samples were carried out at low temperatures (2 – 5 K) and high pressures (0 – 9 kbar). The energy shift of the direct gap was determined: . At pressures above 8 kbar the spectra showed additional structure from the indirect L-conduction band minima. The energy shift of the L-conduction bands were determined: From these data the critical pressure for the inversion of the two conduction bands was calculated: . 相似文献
9.
Transport properties of topological nodal-line semimetal candidate CaAs_3 under hydrostatic pressure
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《中国物理 B》2019,(4)
We report the transport properties of the CaAs_3 single crystal, which has been predicted to be a candidate for topological nodal-line semimetals. At ambient pressure, CaAs_3 exhibits semiconducting behavior with a small gap, while in some crystals containing tiny defects or impurities, a large "hump" in the resistivity is observed around 230 K. By applying hydrostatic pressure, the samples appear to a tendency towards metallic behavior, but not fully metallized up to 2 GPa.Further high pressure studies are needed to explore the topological characteristics for CaAs_3. 相似文献
10.
Photoluminescence spectra of Sm2+-doped BaBr2 have been measured under hydrostatic pressures up to 17 GPa at room temperature. In the low pressure range a red-shift of the broad 5d-4f transition of −145 cm−1/GPa is observed. From 5 to 8 GPa a phase mixture of the initial orthorhombic phase and the high-pressure monoclinic phase gives rise to two 5d-4f bands, which are strongly overlapping. Above 8 GPa the crystal is completely transformed to its high-pressure phase where two different Sm2+ sites exist, but only one broad 5d-4f transition is detected. It exhibits a red-shift of −36 cm−1/GPa. In addition, the line shifts of the 5D0→7FJ (J=0, 1, 2) transitions are investigated. Linear shifts of −19 cm−1/GPa for J=0, 2 and of −13 cm−1/GPa for J=1 are observed in the pressure range from 0 to 5 GPa. 相似文献
11.
Pressure effects on the Curie temperature and the crystallographic phase transition temperature of CeAg were determined from an electrical resistivity measurement from 4.2 to 300 K at hydrostatic pressures up to 5 kb. Results correspond to the alloying effect in Ce(Ag,In). 相似文献
12.
Al-Douri Y. Reshak Ali Hussain 《Applied Physics A: Materials Science & Processing》2011,104(4):1159-1167
The hydrostatic pressure dependence of the principal energy gaps and of the optical properties of GaX (X = P, As and Sb) has been calculated using the full potential-linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) for the exchange and correlation potential is applied. Also, we have used the Engel–Vosko GGA formalism, which optimizes the corresponding potential for band-structure and the optical properties calculations. Structural properties such as equilibrium lattice constants, the bulk modulus, and its pressure derivatives were calculated for GaP, GaAs, and GaSb in the zinc-blende structure (ZB). We have found that the results of the structural properties calculations are in agreement with those of ab initio and experimental data. In general, the pressure dependence of the principal energy gaps is compared to other values. The same is for the pressure coefficient. However, for the same structure, the comparison of our results with those of experimental and theoretical calculations shows good agreement. On the other hand, the effect of the applied pressure is clearly seen in the optical properties especially near the energy transition regions. 相似文献
13.
14.
Abstract Deep Level Transient Spectroscopy (DLTS) was applied to nitrogen related deep electron trap 0.4 eV in green emitting diodes of GaP under hydrostatic pressure. The pressure coefficient of the level energy is determinated as equal -31 meV/kbar with respect to the valence band edge. 相似文献
15.
The effect hydrostatic pressure of up to 9 GPa has on the electrical behavior of polymer composites based on multiwalled carbon nanotubes (MWCNT) is investigated at room temperature. The ratio R 9GPa/R 0 ≈ 7 for samples with resistance in the kilo-ohm range is higher than for samples in the ohm range. Pressure-induced MWCNT features at P ≈ 1.5 GPa are associated with the deformation of the circular form of nanotube walls, in agreement with theoretical predictions. Measurements of direct and reverse resistance and current voltage characteristics under pressure demonstrate the reversibility of electrophysical properties, which could find practical application in creating pressure sensors. 相似文献
16.
S.N. Mustafaeva Sh.G. Gasymov E.M. Kerimova M.M. Asadov 《Journal of Physics and Chemistry of Solids》2011,72(6):657-660
The effect of hydrostatic pressure (up to 0.82 GPa) on the electric properties of chain TlGaTe2 single crystals has been investigated in the temperature range 77-296 K. It has been shown that pressure leads to a considerable increase of conductivity (σ⊥) across the chains of TlGaTe2 single crystals. Parameters of localized states in the band gap of TlGaTe2 single crystal according to the low-temperature electrical measurements were obtained at various pressures. 相似文献
17.
Photoluminescence measurements on CdSe and CdTe samples have been made under hydrostatic pressure up to the phase transition. Transition pressure values are reported. Nonlinear pressure dependence of the direct gap is observed for both materials. Pressure coefficients are in good agreement with values calculated from the dielectric theory of the chemical Bond. 相似文献
18.
《Infrared physics》1993,34(4):345-350
We report on n-InSb photoconductive detectors, which are either mounted on different substrates (metals and synthetic materials) or embedded in a special glue. If these detectors are cooled to 4.2 K, the different coefficients of expansion provide either a uniaxial or a hydrostatic pressure. This pressure causes a shift of the resonances (for the mounted detectors up to 5.5%, for the embedded detector 5.8% at 2.3 T) and a freeze out of electrons, which results in a decrease of the cyclotron resonance (CR) signal in comparison to the impurity cyclotron resonance (ICR) signal for the embedded detector. 相似文献
19.
From the electroreflectance spectra measured under hydrostatic pressure to 7 kbar we have determined the pressure coefficients for germanium (dE1/dP = 7.8 ± 0.4−6eV/bar, dP = 1.4 ± 0.8 10−6eV/bar), for Si (dE′o/dP = 1 ± 1 10−6eV/bar, dE1dP = 6.2 ± 0.4 10−6eV/bar) and for GeSi alloys in the entire composition region. For the composition 80–100% of Si which is widely discussed in the literature, we could distinguish two maxima with substantially different pressure coefficients. The absolute experimental values of dE/dP agree rather well with theoretical values which, together with composition shift of electroreflectance peaks, enable us to connect the peak E1 predominantly with λ and L and E′o with Г and Δ transitions in the entire composition region. 相似文献
20.
K.R. Allahverdiev S.S. Babaev E.Yu. Salaev M.M. Tagyev E.A. Vinogradov A.F. Goncharov N.N. Melnick S.I. Subbotin V.V. Panfilov 《Solid State Communications》1980,35(9):705-708
Raman-active lattice vibrational modes of GaTe have been investigated at 300 K in the range 15–300 cm?1 in equilibrium conditions under different hydrostatic pressures up to 11.25 kbar. The spectra of the Bridgman grown crystals were excited with the 1.06 μm line of the continuously operated YAG:Nd3+ laser. The mode-Grüneisen parameters were determined for all fourteen Raman bands observed. It is shown that there is no low frequency rigid-layer modes or Davydov pairs in Raman spectra of GaTe crystals. 相似文献