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1.
Abstract We have investigated the effect of hydrostatic pressure on zone-boundary and other critical-point phonon frequencies of AlSb by second-order Raman scattering. A softening of the TA(X), TA(L) and (L/T)A([Sgrave]) modes has been observed for pressures up to the first phase transition at 7.7 GPa. The LA(L) as well as the optical TO at X-, L-, and LO at [Sgrave]-, X-points harden with increasing pressure. Mode Griineisen parameters of all the resolved modes were calculated. Reflectivity measurements indicate that the high pressure phase above 7.7 GPa is metallic. 相似文献
2.
H. Olijnyk 《高压研究》2013,33(1-2):461-464
Abstract Measurements of k ≈ 0 optical phonons by Raman scattering are reported for Zn metal and for metallic high pressure phases of Si and Ge up to 50 GPa. Mode Griineisen parameters are determined and the experimental results are compared with theoretical results. 相似文献
3.
To investigate the pressure dependence of the AlN phonon frequencies Raman spectra of single-crystalline bulk AlN under hydrostatic pressure up to 10 GPa were recorded. The Raman peak positions of the A 1 (TO), E 1 (TO), E 2 (high), A 1 (LO) and quasi-longitudinal optical (QLO) phonons were plotted as a function of pressure. The experimental data was fitted using the traditional parabolic fit (M. Kuball et al . (2001) Appl. Phys. Lett., 78, 724 [1]) and fits to physical models, density, volume, etc. The mode Grüneisen parameters of the different phonons were determined for each fit and significant differences are found between the various fits. Results are compared with recent theoretical calculations (J.-M. Wagner et al . (2000) Phys. Rev. B, 62, 4526 [2]). 相似文献
4.
Specific electroresistance and Hall coefficient on oriented ZnAs 2 and CdAs 2 single crystals in the region of room temperatures at hydrostatic pressure up to 9 GPa were measured. In p -ZnAs 2 specific electroresistance falls for one order of magnitude with the increase of pressure, and Hall coefficient falls for two orders in magnitude, and at P =7 GPa specific electroresistance and Hall coefficient come out to a saturation. Under mentioned conditions the phase transition in investigated p -ZnAs 2 samples was not observed, in all probability it occurs under the pressure P >10 GPa. Two groups of n -CdAs 2 samples oriented on [1 0 0] and [0 0 1] directions were investigated. The reversible structural phase transition was observed in investigated n -CdAs 2 samples at P =5.5 GPa from the dependencies of specific electroresistance 𝜌 ( P ) and Hall coefficient R H ( P ). On the basis of the values of concentrations and mobilities before and after phase transition a conclusion was made that semiconductor-semiconductor transition takes place in n -CdAs 2 . Maxima that earlier weren't observed, were detected on dependencies 𝜌 ( P ), R H ( P ) at P =1.8 GPa and at P =3 GPa. 相似文献
5.
Abstract First-order Raman spectra and lattice parameters of BN and SiC were measured simultaneously up to a pressure of 34 and 45 GPa. The bulk moduli, their pressure derivatives and the volume dependence of Gruneisen parameters of LO and TO phonons were obtained. The average Gruneisen parameter for BN does not change much; on the contrary, the same parameter for SiC decreases under pressure. The definite connection between the crystal stability, the pressure behaviour of the optical phonons and the electron structure of the ionic cores is pointed out. 相似文献
6.
The inelastic electron scattering of light and phonons in single crystals of 5d osmium transition metal has been analyzed at pressures up to 60 GPa and temperatures of 10–300 K. An anomalous increase in the intensity of the spectra of the electron scattering of light with the appearance of pronounced continua at ~580 and 350 cm?1 for q ‖ [0001] and q ‖ [10\(\overline 1 \)0], respectively, has been observed in a pressure range of 20–30 GPa at an excitation energy of 2.41 eV. The comparison of the q dependences measured and calculated in the framework of the band theory of the spectra implies the significant renormalization of energies and relaxation of electronic states near the Fermi energy and the dependence of the Fermi energy on the pressure and temperature. 相似文献
7.
S.W.H. Eijt R. Currat J.E. Lorenzo P. Saint-Grégoire B. Hennion Y.M. Vysochanskii 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):169-178
The low frequency lattice dynamics and its relationship to the second order paraelectric-to-ferroelectric transition in Sn2P2S6 is studied. The dispersion branches of the acoustic and lowest lying optical phonons in the a*-c* plane have been obtained in the ferroelectric phase, for x-polarized phonons. Close to the phase transition a considerable softening is found for the lowest optical mode (Px), comparable to the behaviour observed in previous Raman investigations. As found previously in Sn2P2Se6, a strong coupling between the TO(Px) and TA(uxz) phonons is observed, although, apparently, not strong enough to lead to an incommensurate phase. The soft TO(Px) mode at the zone center is observed. The temperature dependence of its frequency and damping shows that the transition is
not entirely displacive. At low temperatures an unusual apparent negative LO-TO splitting is observed which is shown to arise
from the coupling of the x-polarized soft mode to the nearby z-polarized optical phonon. For comparison, the soft TO(Px) dispersion in the a*-b* plane is measured in both the paraelectric and ferroelectric phases. Consistent frequency changes and LO-TO splitting are
observed, revealing a significant interaction between the TA(uyx) and LA(uxx) acoustics branches and the TO and LO soft optic branches, respectively. In contrast, the nearby y-polarized optic branch shows almost no temperature dependence. Finally, the influence of piezoelectric effects on the limiting
acoustic slopes in the ferroelectric phase is discussed.
Received: 11 May 1998 / Revised and Accepted: 15 June 1998 相似文献
8.
K. Parlinski Y. Kawazoe 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):49-58
Using the local-density approximation, calculating the Hellmann-Feynman forces, applying the direct method and deriving the
phonon dispersion relations, the stability of the perovskite-like structures of MgSiO3 at T
=0 have been studied. The cubic Pmm phase shows a dispersion-less soft phonon branch spreading from the R to M points of the cubic Brillouin zone. This soft
branch persists up to high pressures of 150 GPa. The low-symmetry phases I4/mcm and Imma, P4/mbm can be considered as a result
of the soft mode condensation at the M and R points, respectively. These phases prove to be unstable at T
=0. The experimentally observed Pmnb phase is a consequence of the intersection of Imma and P4/mbm space groups. Thus, it can
be regarded as a simultaneous condensation of two soft modes: one at the M and a second at the R high-symmetry points of the
cubic Brillouin zone. The phonon dispersion relations of Pmnb show that this phase is stable and its optical phonons appear
above 4.0 THz only.
Received 15 October 1999 and Received in final form 14 January 2000 相似文献
9.
Abstract PbSe/SnSe superlattice, phase transition, high pressure, SR x-ray diffraction) Synchrotron x-ray diffraction experiments have revealed successive phase transitions in epitaxially-grown PbSe/SnSe superlattices. The transition pressures from the low-pressre cubic B1- to the high-pressure orthorhombic B16-type structures are observed to vary systematically depending upon thickness of the PbSe layer. For example, a [PbSe(36A)/SnSe(12A)]19, with the B1 structure in both layers stabilized in its asgrown state, undergoes the [B1/B1]-to-[B1/B16] and [B1/B16]-to-[B16/B16] structural transitions at 1.9 and 3.8GPa, respectively. This result is in contrast to their bulk data that the B1-to-B16 transition takes place at 5.3GPa in PbSe while the B16 phase is stable in SnSe at atmospheric pressure. 相似文献
10.
Additive contributions to the Seebeck and Peltier coefficients made by nonequilibrium longitudinal optical phonons have been
calculated. The results obtained are valid for any temperature and applicable to polar nondegenerate semiconductors with low
carrier concentrations. The calculated components of the thermoelectric coefficients are exponentially small in the low-temperature
domain and reach a maximum at k
BT∼ħω
0. In materials with a large carrier mass and strong electron-phonon coupling the contribution of optical phonons to the Seebeck
coefficient can exceed 1 mV/K.
Fiz. Tverd. Tela (St. Petersburg) 40, 1209–1215 (July 1998) 相似文献
11.
K. P. Meletov 《Physics of the Solid State》2013,55(3):581-588
The Raman spectra of a naphthalene crystal have been measured at room temperature in the pressure range up to 20 GPa. The pressure shift and Grüneisen parameters for intermolecular and intramolecular phonons have been determined. The maximum rate of the pressure shift for intermolecular phonons is 44 cm?1/GPa, and the rate of the pressure shift for intramolecular phonons lies in the range from 1 to 11 cm?1/GPa for different modes. The pressure dependence of the phonon frequencies for direct and inverse pressure variations has a hysteresis in the pressure range from 2.5 to 16.5 GPa. It has been shown that the linear dependence of the intermolecular phonon frequency on the crystal density has a peculiarity, which indicates a possible phase transition at a pressure of 3.5 GPa. The pressure dependence of intramolecular phonons related to the stretching vibrations of hydrogen atoms exhibits features that are characteristic of intermolecular phonons, which is associated with the influence of shortened distances between the hydrogen atoms of the neighboring molecules on the intermolecular interaction potential. 相似文献
12.
AbstractIn this study, the elastic, electronic, optical and thermoelectric properties of CaTiO3 perovskite oxide have been investigated using first-principles calculations. The generalised gradient approximation (GGA) has been employed for evaluating structural and elastic properties, while the modified Becke Johnson functional is used for studying the optical response of this compound. In addition to ground state physical properties, we also investigate the effects of pressure (0, 30, 60, 90 and 120 GPa) on the electronic structure of CaTiO3. The application of pressure from 0 to 90 GPa shows that the indirect band gap (Γ-M) of CaTiO3 increases with increasing pressure and at 120 GPa it spontaneously decreases transforming cubic CaTiO3 to a direct (Γ-Γ) band gap material. The complex dielectric function and some optical parameters are also investigated under the application of pressures. All the calculated optical properties have been found to exhibit a shift to the higher energies with the increase of applied pressure suggesting potential optoelectronic device applications of CaTiO3. The thermoelectric properties of CaTiO3 have been computed at 0 GPa in terms of electrical conductivity, thermal conductivity and Seebeck coefficient. 相似文献
13.
A.?A.?Kvasov Yu.?F.?Markov E.?M.?Roginski? M.?B.?Smirnov 《Physics of the Solid State》2009,51(7):1426-1430
Thefrequency dispersion curve of acoustic and optical phonons are calculated and constructed, and the density of states of the phonon spectrum is obtained for Hg2Cl2 crystals. The influence of the hydrostatic pressure on the frequencies of acoustic and optical phonons and their dispersion is analyzed theoretically. It is revealed that an increase in the pressure leads to a considerable softening of the slowest acoustic TA branch (soft mode) at the X point of the Brillouin zone boundary. This behavior is consistent with the phenomenological Landau theory and correlate with experiments. 相似文献
14.
Abstract A synchrotron X-ray diffraction study on hexagonal graphite-like boron nitride (h-BN) was performed under high pressures and temperatures. From the measured P-V-Trelation for h-BN (with a three-dimensional ordering parameter P3 = 0.9) in the temperature range from 298 to 1273 K and up to 6.7 GPa, the thermoelastic parameters are derived by fitting a modified high temperature Birch-Murnaghan equation of state. The results are: bulk modulus B0[GPa] = 27.6-0.0081(T[K]-298) and its pressure derivative B1 = 10.5 + 0.0016(T [K] - 298). These values are for samples with P3 = 0.9 and are quite different for samples with different values of the order parameter. This parameter is shown to have a leading role in the determination of the thermoelastic properties of h-BN, which explains and reconciles the differences between previous results. 相似文献
15.
A. Milekhin Yu. Pusep Yu. Yanovskii V. Preobrazhenskii B. Semyagin 《Physics of the Solid State》1998,40(3):507-509
A study is reported of optical vibrational modes in [311]-grown GaAs/AlAs superlattices. An analysis of the TO and LO localized modes observed in IR reflectance spectra showed that the difference between the TO and LO mode frequencies in superlattices grown on (311)A and (311)B surfaces is due to the different localization lengths of these modes. The dispersion of transverse optical phonons in GaAs
derived from IR reflectance spectra is in a good agreement with Raman scattering data.
Fiz. Tverd. Tela (St. Petersburg) 40, 550–552 (March 1998) 相似文献
16.
Abstract Measurements of steady-state photoconductivity for hydrogenated amorphous silicon (a-Si:H) have been carried out at pressures up to 14 GPa and at room temperature. The ratio of photoconductivity to darkconductivity [sgrave]p/[sgrave]D decreases with increasing pressure. The activation energy for photoconductivity Ep, which is 0.25 eV at ambient pressure, decreases with increasing pressure at the rate -7 meV/GPa. These resultls are discussed with change in density of states. 相似文献
17.
A II B 2 III C 4 VI compounds have been prepared with A II =Zn, Cd, Mn, B III =In, and C VI =S, Se. These atomic substitutions induce modifications in the structure and frequency for some of the phonons. These compounds have been studied by Raman spectroscopy at ambient conditions and under hydrostatic pressures. All phonons appear in the spectral region below 400 cm m 1 . High-pressure measurements have shown the existence of soft modes. New modes seem to appear at high pressures due to the phonon splitting. All low frequency phonons of the Zn 0.6 Mn 0.4 In 2 S 4 compound show a sudden modification in the frequency dependence on pressure above ~2 GPa. Based on the Raman results we propose an assignment for the modes and try to extract information about the structure and the possible phase transitions. 相似文献
18.
Abstract The Raman spectra of monoclinic ZnWO4 (c4 2h-space group) are reported over wide ranges of pressure (0-24GPa) and temperature (13-970 K). All 18 Raman active pho-nons are observed throughout these ranges. Combining the pressure and temperature Raman data, an identification scheme is suggested which makes possible to distinguish the internal modes (vibrations in the octahedral WO6 units) from the external ones (pure lattice modes). All phonons harden with pressure, thus showing normal positive dω/dP slopes, and soften with temperature in the region 250 - 970 K (normal negative dω/dT slopes). However, two phonons show a change of slope sign below 300 K, resulting in small positive slopes at low temperatures. Since the pressure dependence of these two phonons is normal and linear, it is concluded that their anomalous, non-linear dependence with temperature is due to anharmonic (temperature induced) phonon interactions rather that volume expansion. It is found that ZnWO4 remains stable throughout the pressure and temperature ranges. 相似文献
19.
We have investigated the pressure-induced phase transition behavior (~3.0 GPa) of aqueous 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) solutions with N-methylacetamide (NMA), which is a simple protein model compound, using Raman spectroscopy. From Raman spectral changes and optical observation in the sequence of elevated pressure, we found that the aqueous [bmim][Cl] solution with NMA in the water-rich condition induces the high pressure crystallization at 2.6 GPa. On the other hand, in the [bmim][Cl]-rich condition, high pressure crystalline phase was not observed even up to 3.0 GPa. Our results show that the aqueous [bmim][Cl] solution in the ionic liquid-rich condition along with the use of pressure has a potential for protein-preserving solvent. 相似文献
20.
Tariq Mahmood Chuanbao Cao Waheed S. KhanZahid Usman Faheem K. ButtSajad Hussain 《Physica B: Condensed Matter》2012,407(6):958-965
The electronic, elastic constants and optical properties of rutile TiO2 have been investigated using first principle pseudopotential method within generalized gradient approximation (GGA) proposed by Perdew-Burke-Ernzerhof (PBE). The calculated volume, bulk modulus and pressure derivative of bulk modulus are in good agreement with previous experimental and computational results. An underestimated band gap (1.970 eV) along with the higher density of states and expanded energy bands around the fermi level is obtained. Calculated elastic constants satisfying the Born stability criteria suggest that rutile TiO2 is mechanically stable under higher hydrostatic pressure. The acoustic wave speeds in [1 0 0], [0 1 0], [0 0 1], [1 1 0] and [45° to [1 0 0] and [0 0 1]] directions are predicted using the investigated elastic constants. The dielectric constant is identified with respect to electronic band structure and is utilized to derive the other optical properties like refractive index, energy loss function, reflectivity and absorption. The effect of hydrostatic pressure (0-70 GPa) is described for listed properties. Our investigated results are in good accord with the existing theoretical and experimental results. 相似文献