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1.
The manner in which oxygen is incorporated into YBa2Cu3O
x
(YBCO) at 800°C for values ofx close to 6 is shown to be in the form of neutral oxygen interstitials, O
i
x
. The experimental data on which this conclusion is based are obtained from measurements of oxygen partial pressure,P(O2), as a function of compositionx and temperatureT (5.99x 6.35, 825T1120 K). The data are obtained by a solid-state electrochemical method. Other conclusions of this study include: (a) O
i
x
are noninteracting forx 6. (b) The stoichiometric composition of YBCO isx 6.0. (c) The reaction enthalpy of oxidation is 179 kJ/mol O2. (d) The Fermi level changes by –0.2 eV asx increases from 6.05 to 6.35. 相似文献
2.
The zero sound attenuation of normal liquid 3He has been studied over a range of temperatures from slightly above the superfluid transition temperature, T
c, to approximately 10mK at the constant pressures of 1 and 5bar. Using longitudinal LiNbO3 transducers, operating both on and off resonance, the experiment was performed at 15 discrete frequencies located in several broadband frequency windows, including 16–25, 60–70, and 105–111MHz. The results are compared to Landau's prediction for the attenuation of zero sound in the quantum limit, (k
B
Tk
B
T
F), where
0(P,T, )= (P) T
2{1+(/2k
B
T)2}. Calibration of the received zero sound signals was performed by measuring the temperature dependence of the first sound attenuation from 30 to 800mK at those same frequencies and pressures. The data are compared to previous results. 相似文献
3.
Tensile tests at 20° C have been carried out on seventy-three sapphire whiskers and on seventeen silicon nitride whiskers. The sapphire whiskers were of 0001, 1¯120, 10¯10, and 10¯11 orientations, while the silicon nitride whiskers were 0001, 11¯20, and 10¯13. Tensile strengths were in the range 45 to 1500 kg/mm2, and deformation was found to be purely elastic. The tensile strength data have been analysed and fitted to empirical equations describing the effect of size on strength for different orientations. These empirical equations have been used to deduce possible fracture nucleation mechanisms. It is concluded that, in the case of 0001 sapphire whiskers, fracture nucleation may be due to dislocation pile-ups or interactions, while in the other cases a Griffith flaw mechanism is probably applicable. 相似文献
4.
Jeffrey M. Harris K. Krishana N. P. Ong R. Gagnont L. Taillefer 《Journal of Low Temperature Physics》1996,105(3-4):877-886
The washboard frequency of the moving vortex lattice in untwinned YBa2 Cu3 O6.93 may be observed through mode-locking to an externally applied ac current of frequency ext. The interference between and ext results in jumps in the dc current-voltage characteristics when and ext are harmonically related1. The interference effect disappears in the vortex liquid state. The Hall conductivity xy below Tc in YBCO contains contributions2 from a positive quasiparticle (qp) term (H) and a negative vortex term (1/H). The qp term is surprisingly large well below Tc and implies a large gap anisotropy and a long qp mean free path (mfp). The thermal Hall effect3 xy is closely related to the qp xy; xy is produced by asymmetric scattering of qp by pinned vortices. The qp mfp at H = 0, extracted from xy and extended to low T by xy, increases remarkably from 90 Å at Tc to more than 0.5m at 22 K. 相似文献
5.
Experimental data on the lattice parameter, thermoelectric power, and microhardness of PbTeIn crystals and the conversion fromp- to n-type with increasing indium content can be interpreted under the assumption that the indium in PbTeIn has variable valence: 2In2+ In+ + In3+. A crystal-quasi-chemical model is proposed for defect formation in PbTeIn: the incorporation of In+ into octahedral interstices and In3+ into tetrahedral interstices of the close packing of Te atoms, accompanied by In2Te3 precipitation. 相似文献
6.
Coexisting phases in the Ni-Mo-O ternary system at 1373 K have been identified by X-ray diffraction, optical microscopy and scanning electron microscopy. The samples were equilibrated in evacuated quartz capsules. Only one ternary phase, NiMoO4, was found to exist in the system. The reversible e.m.f. values of the following solid-state galvanic cells were measured in the temperature range 900 to 1500 K: (I) Pt, Ni + NiO/(CaO) ZrO2/NiO + MoO2 + NiMoO4, Pt; (II) Pt, Mo + MoO2/(CaO) ZrO2/O2, Pt; and (III) Pt, Mo + MoO2/(CaO) ZrO2/Ni-Mo + MoO2, Pt. The Gibbs energies of formation of NiMoO4 and MoO2 and activities in Ni-Mo alloys were derived from the e.m.f. data. For the reaction NiO + MoO2 + 2(02) NiMoO4 we obtain G
r
0 = -201 195 + 69.70T (±400) J mol–1; for Mo + (02) MoO2 we obtain G
f
0 = –578880 + 168.5T (+500) J mol–1. Based on the information from phase identification studies and thermodynamic stabilities, the isothermal section and oxygen potential diagram for the Ni-Mo-O system at 1373 K have been developed. 相似文献
7.
The effects of substrate temperature (Ts) on the properties of vacuum evaporated p-type Ge thin films have been investigated for 25s<400°C. Increase in the substrate temperature improves the crystallinity and increases the grain size resulting a gradual change from amorphous to polycrystalline structure which was attained above a substrate temperature of 225°C. Low resistive (1×10–2 ohm-cm) and high mobility (280 cm2/V·s) films were obtained at Ts=400°C. It has been observed that the conduction mechanism in polycrystalline films was dominated successively by hopping, tunneling and thermionic emission as the sample temperature was increased from 40 to 400 K. In amorphous samples, conduction was described in terms of different hopping mechanisms. 相似文献
8.
C. Yamagishi K. Tsukamoto J. Hakoshima H. Shimojima Y. Akiyama 《Journal of Materials Science》1992,27(7):1908-1912
-SiAION--SiC composites containing up to 12 wt% -SiC were prepared by pressureless sintering. The strength of composites at room temperature remained relatively unchanged, whereas strength at 1200 °C increased for composites. The fracture toughness (K
IC) for composites was higher than that for -SiAION ceramics. The maximum value was 5.4 MPa m1/2 for 6 wt% -SiC, and this was an improvement of 15% in comparison with -SiAION ceramics. From SEM observations, an improvement inK
IC values was attributed to crack deflections and branching-off of cracks. Intra-granular fractures were frequently observed in -SiAION. From TEM observations, -SiAION crystals were nanocomposites, within which existed the fine crystals in -SiAION crystal. For composite, -SiAION and -SiC crystals were directly in contact. The mismatching zone was observed in -SiC. 相似文献
9.
Sound absorption of3He-B at 0 bar was studied at a frequency of 10 MHz. We performed pulsed experiments with different pulse lengths (4 to 15 s) and pulse powers (0.1 to 160 W) in the temperature range 0.2 < T/TC < 2. For pulse power less than pth 50 W, and in the temperature range 0.4 to 0.8 Tc and zero field, the attenuation coefficient a decreases monotonically at about 0.2 cm–1 per decade of power. Above pth. increases up to values of 3.5 cm–1 and 1.9 cm–1 at highest power for temperatures of 0.8 Tc and 0.4 Tc, respectively. At pulse power around 100 W and at the lowest temperatures, the attenuation changes within the first 200 s after the application of the pulse; also increases with increasing field. In the normal fluid decreases with increasing power. All of our observations are lacking a rigorous theoretical understanding. 相似文献
10.
The study of the direct current electrical conductivity, , of freshly prepared -Fe2O3 and that of a sample stored for seven days in static air suggests that -Fe2O3 adsorbs oxygen and water from the atmosphere. From infra-red spectra it is deduced that the absorbed water in -Fe2O3 is present as the physically adsorbed water and as lattice water. The adsorbed oxygen and physically adsorbed water are removed by heating to 100 C, while the lattice water remains in -Fe2O3 even up to 280 C. The removal of lattice water is associated with a decomposition during which some of the hydrogen formed occupies the vacancy sites. This suggested formation of the hydrogen ferrite phase is based on the kink in the log against T
–1 curve observed at 177 C. This kink is very well resolved for a sample equilibrated at 100 C in normal atmosphere, and the measurements of above 100 C of this sample are done in an N2 atmosphere. The suggestion that the hydrogen ferrite phase is formed has been substantiated by comparison of the X-ray diffraction patterns of -Fe2O3 heated under the different atmospheres. From the log against T
–1 plot for a sample heated under a nitrogen atmosphere the activation energy is small (< 0.05 eV) up to 215 C, and it is comparatively large (0.95 eV) above 215 C. These results suggest a hopping mechanism for the direct current electrical conductivity of -Fe2O3. This suggestion has been substantiated by data of the temperature variation of Seebeck voltage. 相似文献
11.
The effect of temperature and strain-rate on the fracture behaviour during high strain-rate ( 103 sec–1) impact of two highly filled polymeric composite propellants (containing segmented polyurethanes based on hydroxy-term inated polybutadiene (HTPB) or glycidyl azide polymer (GAP) filled with ammonium perchlorate (AP) particles) and a plasticized thermoplastic (cast double base (CDB) nitrocellulose-nitroglycerine) propellant have been examined over a wide temperature range encompassing the ittle-ductile transition. In the elastic region of the loaddisplacement curve, the yield stress and fracture toughness is highest for GAP/AP and lowest for HTPB/AP. In the elastic and post-yield ductile regions CDB is more fracture-resistant than GAP/AP and HTPB/AP over the temperature range –20 to 50° C, but below –40° C, where both CDB and GAP/AP are brittle, GAP/AP is more fracture-resistant than CDB (as observed in the elastic region). Although all the propellants are known to develop small cracks in the elastic and post-yield ductile regions of the load-displacement curve, the overall fracture behaviour is largely governed by viscoelastic properties (because the cracks close up in compression). The good mechanical properties of CDB, above the brittle-ductile transition temperature, can be attributed to the presence of a large-transition loss peak. In the composites, the fracture behaviour is also influenced to a lesser extent by the degree of filler-binder interactions. Dynamic mechanical analysis indicates that GAP/AP has a slightly higher degree of filler-binder interactions than HTPB/AP. A temperature-strain rate reduction has been obtained for the yield stress and the composite curve can be expressed by the equation y =K
1 +K
2 log (ea
T
) whereK
1 andK
2 are constants anda
T
is a shift factor.K
2 is a material constant which reflects the temperature and strain-rate sensitivity. 相似文献
12.
An Al-6061 metal matrix composite, reinforced with 10 vol % Al2O3 particulates, was subjected to equal-channel angular (ECA) pressing at room temperature to a total strain of 5. It is shown that the intense plastic straining introduced by ECA pressing reduces the grain size from 35 m to 1 m and this leads to an increase in the microhardness measured at room temperature. Inspection revealed some limit cracking of the larger Al2O3 particulates as a consequence of the ECA pressing. Tensile testing after ECA pressing gave a maximum ductility of 235% at a temperature of 853 K when testing at strain rates from 10–4 to 10–3 s–1. It is suggested that high strain rate superplasticity is not achieved in this material after ECA pressing due to the presence of relatively large Al2O3 particulates. 相似文献
13.
V. A. Naumov 《Journal of Engineering Physics and Thermophysics》1995,68(5):683-686
The article is concerned with the study of the effect of E. S. Asmolov's corrections to Saffman's lift force for the wall vicinity and a nonzero ratio of Reynolds numbers. It is shown in what way these corrections change the particle paths in a Couette layer and the conditions of deposition.Notation
x=X/D, y=Y/D
dimensionless longitudinal and transverse coordinates
-
u=U
p
/U
, =V
p
/U
dimensionless projections of particle velocity on the longitudinal and transverse axes
- =tU
/D
dimensionless time
-
U
2/(18D)
Stokes number
- =
g
/
p
,
coefficient of the gas kinematic viscosity
-
particle diameter
-
/D
-
g
,
p
densities of the gas and particle material
-
du/d
-
dv/d
-
P
s
Saffman's force
-
C
coefficient in the formula for Saffman's force
-
yRe
d
1/2
-
A
v
r
Re
d
1/2
-
3.08
- Re
V
r
/
- Re
k
2/)U
g
/Y
-
A
Re/Re
k
1/2
- Re
d
U
D/
-
V
r
((U
g
–U
p
)2+V
p
2
)1/2
Indices
g
refers to gas parameters
-
p
refers to the parameters of particles
- 0
at the time momentt=0
-
S
Saffman's force
-
k
Reynolds number based on the velocity gradient
-
based on velocity
-
r
relative velocity
-
x
projection on thex axis 相似文献
14.
J. Freudenberger V. N. Narozhnyi V.N. Kochetkov K. A. Nenkov G. Fuchs A. Handstein K.-H. Müller L. Schultz 《Journal of Low Temperature Physics》1999,117(5-6):1605-1609
It was shown that the Hall resistivity
xy
for LuNi
2
B
2
C and YNi
2
B
2
C is negative in the normal and mixed states and has no sign reversal below T
c
. In the mixed state the scaling relation xy
xx
(xx
is the longitudinal resistivity) was found for both compounds with 2.0. In the normal state a distinct nonlinearity in the
xy(H) dependence, accompanied by a large magnetoresistance, was found below 40 K only for LuNi
2
B
2
C. The difference in the behaviour of Lu- and Y-based borocarbides seems to be connected with the difference in the Fermi surfaces of these compounds. 相似文献
15.
Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with (B2)- (A1)/(L12), - or - microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of -Cr, which can supplant the -phase during ageing of three-phase -/ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from -/ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L10 type martensite and interdendritic /. Extensive intra- and interdendritic -Cr precipitation was also observed. The stability during ageing of the interdendritic / microstructure is also considered and transformation of the L10 martensite is examined. 相似文献
16.
J. H. Merkin 《Journal of Engineering Mathematics》1985,19(3):189-201
Summary The similarity solutions for free convection on a vertical plate when the (non-dimensional) plate temperature is x
and when the (non-dimensional) surface heat flux is –x
are considered. Solutions valid for 1 and 1 are obtained. Further, for the first problem it is shown that there is a value 0, dependent on the Prandtl number, such that solutions of the similarity equations are possible only for >0, and for the second problem that solutions are possible only for >–1 (for all Prandtl numbers). In both cases the solutions becomes singular as 0 and as –1, and the natures of these singularities are discussed. 相似文献
17.
Supercarrier effective mass isotope effect (exponent ) is investigated using a two-band model with interband pair scattering. The corresponding repulsive interaction incorporates besides the dominating electronic (Coulomb) part an electron-phonon contribution inversely proportional to the ionic mass factor. Calculations illustrating the behaviour of T
c
, its isotope exponent , and with doping in La
2–x
Sr
x
CuO
4
type underdoped system reflect the observed tendencies.
2
Both and diminish with doping, the sign of is opposite to . A typical estimation gives || 0.2. 相似文献
18.
V. Ya. Chekhovskoi R. A. Belyaev Yu. V. Vavilov 《Journal of Engineering Physics and Thermophysics》1972,22(6):728-731
An apparatus is described for measuring the thermal conductivity and diffusivity on small specimens of solid materials; also the results are shown which have been obtained for refractive high-alumina concrete by such measurements.Notation
thermal conductivity at the mean temperature of specimens, W/m· °C
- Q
power of the central heater, W
- F
cross section area of a specimen, m2
- t1,2
temperature drop across the specimens, °C
-
1,
2
difference in heights between the thermocouple beads, center-to-center, in the first and in the second specimen respectively, m
- t
temperature, °C
-
time coordinate, min
- d1= (d1u+d1l
)/2
mean distance between specimen contact plane and nearest thermocouple beads, for the upper and lower specimen, m
- d2= (d2u+d2l
)/2
mean distance between specimen contact plane and farthest thermocouple beads, for the upper and lower specimen, m
- dt(d1,)/d
rate of temperature rise at section d1 of the specimen at time, °C/h
- t=t1+t2
sum of temperature drops in the specimens at time, °C
- m
heating rate, h–1
-
a
thermal diffusivity of specimens, referred to their mean temperature, m2/h
-
=m/a, m–1 b=¦(tu–tl)/tu¦
heating nonuniformity factor
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1049–1054, June, 1972. 相似文献
19.
Experimental data of a high degree of accuracy are presented on the temperature-density parameters of Freon-13 on the saturation line in the density range of (0.08246–1.6061)·10 kg/m3.Notation T
absolute temperature of phase transition from two-phase to one-phase state (or vice versa)
- Tc
critical temperature
- ,
densities of liquid and vapor, respectively, on saturation line
- c
density at critical points
-
average density
- =(Tc–T)/2
reduced temperature
-
parameter of order, equal to ' – c – b for the liquid phase and c + b – "for the vapor phase
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 830–834, November, 1979. 相似文献
20.
V. Voegelé B. Liu P. Cordier Z. Wang H. Takei P. Pan S. Karato 《Journal of Materials Science》1999,34(19):4783-4791
High temperature plastic deformation in a single crystal of a 2-3-4 garnet, Ca3Ga2Ge3O12, was investigated. A Czochralski-grown single crystal of Ca3Ga2Ge3O12 was deformed in compression in air along 100 or 110 at temperatures of 1472 to 1573 K (T/Tm = 0.90–0.96). The samples show higher resistance to creep than other 3-3 garnets, namely the flow stress at the strain-rate of 4 × 10– 6 s– 1 is 200–400 MPa in this temperature range. The TEM observations of dislocation microstructures show little evidence of climb and plastic deformation in this garnet appears to occur exclusively by dislocation glide, using mostly the 1/2111{110} slip systems. Dislocations with b = 100 are frequently observed but they are interpreted as products of dislocation reactions among 1/2111. The single crystal used contained a number of precipitates that grew during annealing and also during deformation. These precipitates act as sources for dislocations but no evidence for their significant effects on creep strength is observed. The normalized flow law of Ca3Ga2Ge3O12 is similar to other 3-3 oxide garnets (e.g., YAG, GGG), but in contrast to 3-3 garnets, the more stable and hence less mobile dislocations have a large edge component. 相似文献