Large Pressure Coefficient Research Articles

Effect of pressure on structural properties and energy band gaps of γ‐InSe

AbstractWe have investigated theoretically the effect of hydrostatic pressure on interatomic bond lengths and energy band gaps of γ‐InSe. Total energy calculations were performed using the linear augmented plane wave (LAPW) method, taking into account scalar relativistic corrections as well as spin‐orbit coupling. Internal structural parameters were optimized for different pressures by adopting as input the unit cell parameters known from experiment. Our theoretical results for the nearest‐neighbor In–Se bond length are in excellent agreement with a recent experimental determination from high‐pressure EXAFS measurements. The covalent In–In bond is found to be more compressible than the partially ionic In–Se bond. We also present the calculated pressure dependence of band gaps and compare to recent high‐pressure experimental studies of optical and transport properties. A large negative pressure coefficient is obtained for the indirect Z–A gap. This leads to a crossover from a direct to an indirect fundamental gap within the stability range of the γ‐polytype of InSe, in qualitative agreement with recent experiments.

Intrinsic tendency of electronic phase separation into two superconducting states inLa2−xSrxCuO4+δ

The effect of hydrostatic pressure up to 2 GPa on the superconductiong transitions in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ is investigated. The ambient- and high-pressure properties of two series of samples with $x=0$ and 0.015 and $0<\ensuremath{\delta}<0.1$ are characterized and compared by ac-susceptibility measurements. At ambient pressure both sets of samples fit into the same phase diagram as a function of the total hole concentration ${n}_{h}.$ For ${n}_{h}<0.085$ there is a single superconducting transition ${(T}_{c}\ensuremath{\approx}30 \mathrm{K})$ with an unusually large pressure coefficient, ${\mathrm{dT}}_{c}^{(30)}/dp\ensuremath{\approx}10 \mathrm{K}/\mathrm{GPa}.$ At a higher hole density ${(n}_{h}>0.085)$ a second superconducting transition ${(T}_{c}\ensuremath{\approx}15 \mathrm{K})$ follows the first transition upon cooling and the pressure shift of this transition is negative, ${\mathrm{dT}}_{c}^{(15)}/dp\ensuremath{\approx}\ensuremath{-}4 \mathrm{K}/\mathrm{GPa}.$ At the boundary as the hole density is close to 0.085 the phase separation can be induced by pressure. The results are explained in terms of a strong correlation of the interstitial oxygen with the hole system in the CuO planes. Pressure, applied at ambient temperature, causes a redistribution of holes. The mobile oxygen dopants follow and enhance ${T}_{c}$ as well as the tendency toward phase separation. If pressure is changed at low temperature $(<100 \mathrm{K})$ the effects on ${T}_{c}$ and phase separations are greatly diminished because the interstitial oxygen becomes immobile at low T. Our results indicate that the dopant effects are important. Dopants and holes should be treated as a single globally correlated state. When thermodynamic euqilibrium is approached in the oxygen-doped samples, we find that there is an intrinsic tendency of electronic phase separation of doped holes into two distinct superconducting states.

Pressure and temperature dependences of the relaxation dynamics of cresolphthalein-dimethylether: Evidence of contributions from thermodynamics and molecular interactions

The relaxation dynamics of a low molecular supercooled liquid, cresolphthalein-dimethylether (KDE), has been investigated in the vicinity of glass transition temperature by dielectric relaxation measurements. Glass transition is approached and studied by the use of isothermal and isobaric paths. Under isobaric condition, the departure of the correlation function of the α-relaxation from exponential decay with time (nonexponentiality) is even less than the intermediate liquids such as glycerol. However, the Tg-scaled temperature dependence of the α-relaxation time, τ, resembles “fragile” glass-formers like orthoterphenyl (OTP). Thus KDE, like propylene carbonate (PC) that has in common a basic chemical structural unit, is an exception to the correlation between “fragility” and nonexponentiality found to hold for most glass formers. The dielectric relaxation measurements with the application of pressure show that KDE has large pressure coefficient of the glass transition temperature, (dTg/dP)P→0, or large activation volume, typically of “fragile” glass-formers. However, unlike “fragile” glass-formers, the change of the scaled activation volume with log τ for KDE is slow, comparable with that of glycerol. The dielectric dispersion of KDE as a function of frequency at different pressure and temperature combinations has an excess high frequency wing but no resolved Johari–Goldstein β-relaxation, resembling that of intermediate liquids. Thus the variable pressure and temperature measurements of the relaxation dynamics show that KDE (and likewise PC) behaves like a “fragile” liquid in some properties and an intermediate liquid in other properties. Previously it has been proposed that there are two distinct factors that determine the molecular dynamics of glass formers, one from thermodynamics and the other from cooperative many-body dynamics. We explain this split character of KDE and PC by the prominence of the thermodynamics factor, possibly due to the unique basic chemical structural unit they have in common. The prominent thermodynamics factor gives rise to properties, such as the Tg-scaled temperature dependence of the α-relaxation time and large (dTg/dP)P→0, that resemble “fragile” liquids. While the cooperative many-body dynamics in KDE and PC is weak as evidenced by low degree of nonexponentiality of the α-relaxation correlation function. Consequently some properties, including the shape of the dielectric dispersion, coincide with that of intermediate liquids. The explanation is supported by the comparison of adiabatic calorimetric data of PC and OTP to show that indeed the thermodynamics factor in PC is like that of a very “fragile” liquid.

High-Pressure Photoluminescence Studies of Pseudomorphic Si1-yCy/Si MQW Structures

We have performed photoluminescence (PL) investigations of pseudomorphic Si 1-y C y /Si (y = 0.45, 1.05, and 1.62%) multiple quantum well (MQW) structures under hydrostatic pressure (0 to 8 GPa) and at low temperatures (10 to 70 K). The main MQW-related emission, at energies below the Si band gap, consists of bound and free exciton no-phonon lines and related Si transverse-optic phonon replicas. All MQW-related PL peaks shift to lower energy with increasing pressure at a rate characteristic for Γ-X indirect transitions in tetrahedral semiconductors. The total band offset and the activation energies for decay of the free and bound exciton emission increase slightly with pressure as a result of the larger negative band gap pressure coefficient of the strained pseudomorphic Si 1 -yCy layers compared to pure silicon. A separation of biaxial strain effects on the conduction and valence band near-gap states in the pseudomorphic Si 1-y C y layers (y < 0.02) on Si indicates a decrease of the intrinsic Si 1-y C y band gap which corresponds to that of pure silicon compressed to the lattice constant of the alloy. From this a type-I band alignment with electrons and light holes localized in the SiC layers is inferred. This assignment is consistent with the dependence of PL-peak intensities and energies on excitation power, temperature and pressure.

Intermolecular Interaction in Carbon Nanotube Ropes

Using Raman spectroscopy we determined the van-der-Waals component of the low-frequency vibration in ropes of single-walled nanotubes at 171 cmy1. While Raman peaks in this frequency range are commonly believed to correspond to the pure radial breathing mode of a single tube, our pressure and temperature-dependent measurements show that van-der-Waals contribution of the peak observed at 514.5 nm excitation is necessary to explain its large pressure coefficient of 9.7 cmy1/GPa. Our results are consistent with the small elastic modulus predicted for nanotube ropes.

Pressure dependence of the external mode spectrum of solid C60

Using inelastic neutron scattering we have investigated the external mode spectrum of solid ${\mathrm{C}}_{60}$ in the orientationally ordered phase. Hydrostatic pressures 1 bar $lPl9$ kbar and temperatures $180 \mathrm{K}lTl335$ K were covered. The entire density of states shows a pronounced pressure dependence. In accordance with theory1 translational phonons have larger pressure coefficients $(d\ensuremath{\Elzxh}\ensuremath{\omega}/dP\ensuremath{\approx}0.2$ meV/kbar) than librons $(d\ensuremath{\Elzxh}\ensuremath{\omega}/dP\ensuremath{\approx}0.06$ meV/kbar). Anharmonic frequency shifts become smaller upon increasing the pressure. It is conjectured that they are related to the orientational disorder in the system arising from competing H and P orientations. A direct link between libron softening and the order-disorder phase transition cannot be established.

Carrier-induced dynamic strain effects in semiconductor nanocrystals

In this paper, we reveal, for the first time, the basic nature of electron–phonon interaction in semiconductor nanocrystals. On the basis of the experimental results on GaAs, GaP, Si nanocrystals, and porous silicon, we further prove that the carrier-induced dynamic strain effect (CIDSE) is a common feature in solids, which plays an extremely important role on the electronic and optical properties of semiconductor nanocrystals. The optical transitions in semiconductor nanocrystals are dominated by multiphonon-assisted electronic transition processes. Nanocrystals with direct-gap and a large pressure coefficient for the band gap (as GaAs) no longer show band-edge emission due to the intrinsic strong electron – long wavelength anharmonic acoustic phonon coupling. Nanocrystals with an indirect-gap show a carrier-induced dynamic Jahn–Teller effect and two fairly strong intrinsic emission bands. Most of the open questions in the semiconductor nanocrystal field, including porous silicon, can be consistently explained by the carrier-induced dynamic strained quantum dot model. © 1998 Kluwer Academic Publishers

Revival of the spin-Peierls transition inCu1−xZnxGeO3under pressure

Pressure and temperature dependent susceptibility and Raman scattering experiments on single crystalline Cu_xZn_(1-x)GeO_3 have shown an unusually strong increase of the spin-Peierls phase transition temperature upon applying hydrostatic pressure. The large positive pressure coefficient (7.5 K/GPa) - almost twice as large as for the pure compound (4.5 K/GPa) - is interpreted as arising due to an increasing magnetic frustration which decreases the spin-spin correlation length, and thereby weakens the influence of the non-magnetic Zn-substitution.

Pressure Effects on Structure and Tc in Superconducting PrBa2Cu3Ox.

The pressure dependence of Tc of superconducting PrBa2Cu3Ox was studied by electrical resistance measurements under hydrostatic pressure up to 10 GPa. A large positive pressure coefficient of Tc, dTc/dP, with a maximum of 7. 3K/GPa, was observed. The coefficient was found to vary with the oxygen content of the compounds, in a similar manner as the isostructural YBa2Cu3Ox compound behaves. The present research revealed an opposite pressure effect on Tc with those reported for the Pr-substituted Y-Ba-Cu-O compounds with high Pr concentration.

Excess molar enthalpies and excess molar volumes for (pronane + propan-1-ol) at a temperature of 348.15 K and at pressures of 5, 10, and 15) MPa

Excess molar enthalpies H m Eand excess molar volumes V m Ehave been determined for (propane + propan-l-ol) at a temperature T= 348.15 K and pressures p= (5, 10, and 15) MPa. Large and positive H m Ewith a large positive temperature coefficient (excess molar heat capacity) C p,m Eare explained in terms of hydrogen bonds being broken when the propan-1-ol is diluted with the propane. V m Eis negative with a large positive pressure coefficient, suggesting that the propane fits into cavities in the hydrogen-bonded structure of the propan-1-ol, with the number of cavities decreasing with increasing pressure. The V m Efor (propane + propan-1-ol) is intermediate between the values obtained for (ethane + propan-1-ol) and (butane + propan-1-ol). The relative magnitudes of V m Efor these three systems are explained in terms of the relationship of the temperature of measurement to the critical temperature of the alkanes.

High pressure studies of the acridine/fluorene photoreaction: Vibration assisted tunneling

We report a multifaceted investigation of the hydrogen transfer photoreaction in acridine-doped fluorene crystals at higher temperature. The purpose is to elucidate the role of vibrationally assisted tunneling in this reaction system. Raman experiments were conducted at various pressures and 77 K to document the change of vibrational frequency for the promoting mode(s). Upon compression, a line with a large pressure coefficient emerges from under the strong phonon mode at 96.5 cm−1. Through polarization studies under pressure, we have identified it as a molecular butterfly mode of B1 symmetry. We have measured the reaction rate at 150 K in order to examine the effect of a suggested promoting mode at ∼440 cm−1. The reaction rate again increases exponentially with pressure, but with a significantly higher pressure coefficient than that at 1.4 and 77 K. Mode patterns based on a recently published [J. Phys. Chem. 98, 12 223 (1994)] normal coordinate analysis of fluorene are used to help establish the promoting modes for this reaction. This consideration suggests that the 95 and 238 cm−1 modes are likely promoting modes in addition to the 125 cm−1 libration. A computation of the Franck–Condon factor for the H-transfer process indicates that a small population of a high overtone of a promoting mode may make a disproportionally large contribution to the reaction rate. This calculation fails to account for the greater pressure coefficient of the reaction rate at higher temperature. Instead, such an increase may come partly from a greater compressibility at higher temperature.

Excess enthalpies for (ethane + ethene) at the temperatures (273.15, 298.15, 323.15, 348.15, and 363.15) K and the pressures (5, 7.5, 10, 12.5, and 15) MPa

Excess molar enthalpies H E mfor { xC 2H 6+ (1 − x)C 2H 4} have been measured over the entire composition range at the temperatures T= (273.15, 298.15, 323.15, 348.15, and 363.15) K and the pressures p= (5, 7.5, 10, 12.5, and 15) MPa. Thus, measurements were made at a temperature where both components are liquid ( T= 273.15 K), at a temperature where one component (C 2H 6) is a liquid while the other (C 2H 4) is a supercritical fluid ( T= 298.15 K), and at three temperatures where both components are supercritical fluids { T= (323.15, 348.15, and 363.15) K}. At T= 273.15 K, a temperature near the critical temperature of ethene, H E m( x) is positive with a large positive pressure coefficient. At T= 298.15 K and p= 5 MPa, a temperature and pressure near, but below, the critical locus, H E m( x) is S shaped, changing from large positive values at low xto negative values at high x. At each of the three higher temperatures, maxima and minima in H E mare obtained at intermediate pressures. A corresponding-states method correctly predicts the pressure and temperature effects on H E min both the subcritical and supercritical ( p, T) regions. At high pressures, H E m( x= 0.5) converges at all the temperatures to a value of approximately 100 J mol −1. A (quadrupole + quadrupole) interaction is probably a major contribution to H E mfor this system, since ethane and ethene have quadrupole moments of opposite sign.

The effect of pressure on the luminescence of CdTe/CdMnTe quantum wells

We have studied photoluminescence in two CdTe/ Cd 1− x Mn x Te multiple quantum-well samples with well thicknesses from 9.7 Å to 100 Å and with barrier compositions x = 0.5 and x = 0.68. The following effects have been observed after hydrostatic pressure up to 3 GPa was applied: (i) decrease of the luminescence intensity from wider wells, which can be related to the stress-induced deterioration of initially strained CdTe layers; (ii) transfer of photoexcited electrons from thinner wells into the barriers where Mn-related recombination occurs; (iii) large negative pressure coefficient (≈ −80 meV/GPa) of the Mn-related photoluminescence; (iv) positive pressure coefficients for CdTe well luminescence, which do not practically depend on the well thickness, while their magnitude decreases with increasing Mn concentration in the barriers (75 meV/GPa for Cd 0.50Mn 0.50Te and 60 meV/GPa for Cd 0.32Mn 0.68Te).

Γ-X Mixing studied by electroluminescence spectroscopy under hydrostatic pressure in a GaAs/AlAs p-i-n superlattice resonant tunnelling device

Electroluminescence measurements under hydrostatic pressure have been performed to study the Γ-X mixing in GaAs AlAs p-i-n double barrier resonant tunnelling structures incorporating superlattice energy filters in the emitter and collector regions. For a sample with a 5 nm quantum well, an anti-crossing with the lowest confined X-states in the AlAs barriers is observed under hydrostatic pressure. The observed anti-crossing agrees well with the expected position and pressure coefficient of the confined X-states. A sample with a narrower 3.1 nm quantum well exhibits a recombination which is higher in energy than the lowest confined X-states in the AlAs barrier and decreases with an anomalously large pressure coefficient.

Large increase of the low-frequency dielectric constant of gallium sulfide under hydrostatic pressure.

The pressure dependence of the low-frequency dielectric constant of layered gallium sulfide, parallel to the c axis, is investigated through capacitance measurements. The measured pressure coefficient \ensuremath{\Delta}(ln${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{\ensuremath{\parallel}}}$)/\ensuremath{\Delta}P is found to be (80\ifmmode\pm\else\textpm\fi{}5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{GPa}}^{\mathrm{\ensuremath{-}}1}$. This large and positive pressure coefficient is shown to be coherent with models of charge transfer from the Ga-Ga intralayer bond to the interlayer space under pressure.

High-pressure transport phenomena in polycrystalline (Pb(1+x)/2Cu(1-x)/2) Sr2(Y1-xCax)Cu2O7+ delta.

The effect of pressure on ${\mathit{T}}_{\mathit{c}}$ for polycrystalline ``Pb 1:2:1:2''-phase material is investigated up to 2 GPa using a piston-cylinder apparatus. The pressure coefficient of ${\mathit{T}}_{\mathit{c}}$ is positive and depends strongly on the ambient-pressure ${\mathit{T}}_{\mathit{c}}$. We discuss the relation between d ln${\mathit{T}}_{\mathit{c}}$/dp and ${\mathit{T}}_{\mathit{c}}$. The general trend that d ln${\mathit{T}}_{\mathit{c}}$/dp increases with decreasing ${\mathit{T}}_{\mathit{c}}$ can be explained by two phenomenological assumptions: a parabolic relation between ${\mathit{T}}_{\mathit{c}}$ and the carrier concentration n in the ${\mathrm{CuO}}_{2}$ planes and a linear increase of n with increasing pressure. An unusually large logarithmic pressure coefficient of ${\mathit{T}}_{\mathit{c}}$ is reported (d ln${\mathit{T}}_{\mathit{c}}$/dp=0.65 ${\mathrm{GPa}}^{\mathrm{\ensuremath{-}}1}$, ${\mathit{T}}_{\mathit{c}}$=16.8 K at ambient pressure). This result suggests that there is another mechanism for the increase in the carrier concentration with an increase in pressure, besides that due to charge transfer. We propose that this large d ln${\mathit{T}}_{\mathit{c}}$/dp is correlated with the pressure-induced delocalization of holes.

High-Pressure transport phenomena in [formula omitted

Pressure effect on T c for “Pb-1212” phase is investigated up to 2GPa using a piston- cylinder apparatus. Unusually large pressure coefficient of T c is observed ( dln T c dp =0.65 GPa −1 , T c =16.8K at latm.). Pressure induced-delocalization of holes is discussed.

Photoluminescence at high pressures from highly strained MOVPE grown GaAs/GaSb/GaAs heterostructures

The authors report photoluminescence measurements made on highly strained nominally GaAs/GaSb/GaAs heterostructures (grown by MOVPE) at pressures up to 5.5 GPa in a diamond anvil cell. Two samples have been studied, a single 15 AA GaSb layer, and a five 15 AA GaSb layer heterostructure. In both cases the 1.3 eV strained layer luminescence increased in energy with pressure with a large pressure coefficient. This identifies the transition as one involving a Gamma state in the conduction band. It is suggested that lower energy luminescence, observed only from the five-layer sample, involves a defect. A theoretical model predicts that the bands line up in a type-II configuration, and the observed behaviour at pressures beyond the GaAs Gamma -X crossover confirms this. The possibility of incorporation of As atoms in the thin nominally GaSb layer is considered.

An automated falling-cylinder high pressure laser-Doppler viscometer

A microcomputer-controlled optical viscometer for the measurement of the viscosity of liquids under pressure is reported The viscometer is of the falling-cylinder type with a measurement range greater than six decades making it well suited for viscosity measurements of liquids with very large viscosity pressure coefficients. Results are presented for a range of alkanes and polypropylene glycol derivatives.

鉱石運搬船の船首底衝撃による過渡振動曲げモーメントと波浪曲げモーメントから見た可航限界について

The theoretical study on the critical navigation of a ore carrier (L_<pp>=247m, C_b=0.824) has been carried out from the viewpoint of structural seaworthiness in longitudinal strength. The navigable wave conditions were obtained by the same procedure for the single screw container ship, previously reported. From the results, it is shown that whipping of full ship due to slamming grows rapidly at lower ship speed in head sea condition because of large impact pressure coefficient and flat fore bottom. And, wave bending moment in following sea condition is larger than in head sea condition, so that the operations of full ship in heavy seaways should be dicided with attentions not only to slamming but also to wave bending moment. From the comparison of navigable wave condition between the present ore carrier and the previous container ship, it is found that the difference of structural seaworthiness in longitudinal strength between them is not significant in seaway of longer average wave period.