Showing papers on "Transition temperature published in 1969"
TL;DR: In this paper, the glass-liquid transition was exhibited thermally by both binary and ternary alloys, and the stability, ease of formation and glass transition temperature, Tg, of the glasses were all increased by the replacement of Pd with small concentrations of the noble metals.
416 citations
TL;DR: In this article, the dependence of the transition temperature and semiconducting resistivity upon uniaxial stress and hydrostatic pressure has been determined, and it was shown that V 2 O 4 has a change in resistivity of a factor of 10 5 at 339°K.
190 citations
TL;DR: In this paper, a study was made of the mechanical properties of vacuum arc-melted tungsten and rhenium-rhenium alloys in the temperature range 77 °-810 °K in order to elucidate the mechanism by which the addition of Rhenium adds lower the ductile-brittle transition temperature of Tungsten.
Abstract: A study was made of the mechanical properties of vacuum arc-melted tungsten and tungsten-rhenium alloys in the temperature range 77 °–810 °K in order to elucidate the mechanism by which rhenium additions lower the ductile-brittle transition temperature of tungsten. The temperature and strain rate dependency of the yield stress of tungsten are reduced by alloying with rhenium, inferring a reduction in the Peierls stress. The reduction in the transition temperature is attributed to the reduced Peierls stress through its effect on the mobility and rate of multiplication of dislocations.
182 citations
TL;DR: In this paper, the temperature of the α-β transition is raised 10.6±0.4°C/kb by uniaxial compression perpendicular and parallel to the optic axis at a confining pressure of 3 kb.
Abstract: Experiments on oriented cores from a single crystal of quartz show that the temperature of the α-β transition is raised 10.6±0.4°C/kb and 5.0±0.4°C/kb by uniaxial compression perpendicular and parallel, respectively, to the optic axis at a confining pressure of 3 kb. Approximately the same results are indicated for confining pressures ranging from 1 to 5 kb. There is no detectable curvature of the phase boundary for uniaxial stresses σ between 0 and 10 kb: |(d2Tα-β/dσ2)| < 0.05°C/kb2. The increase of transition temperature with hydrostatic pressure of 25.8±0.3°C/kb between 1 and 5 kb also determined in these experiments is consistent with previous determinations. These results and others for quartz are analyzed assuming the α-β inversion is either a λ transition or a first-order transition characterized by a small reversible transformation strain. Although both hypotheses are roughly consistent with most of the results, the hysteresis in the transition suggests that the second may be preferable, and a theory is developed that describes the effect of general nonhydrostatic stress on such transitions.
147 citations
TL;DR: The strength of stoiehiometric polycrystalline UO2 has been determined from 20 to 1500 °C for material of two grain sizes as mentioned in this paper, and it is found that the fine grained (~ 8 μm) material is always stronger than the larger grained (approximately 25 μm).
141 citations
IBM1
TL;DR: In this article, a series of A+A22+Nb5O15 compositions with tungsten bronze-related structures are presented, where A+=Na, K, or Rb, and A2+=Sr or Ba.
Abstract: Crystallographic parameters, Curie points, and freezing temperatures are presented for a series of A+A22+Nb5O15 compositions with tungsten bronze-related structures, where A+=Na, K, or Rb, and A2+=Sr or Ba. Results are also reported for bronze solid solutions in the systems KNbO3-PbNb2O6, K(Sr-Ba)2Nb5O15, K(Ba-Pb)2Nb5O15, K(Sr-Pb)2Nb5O15, and (KSr2-K2La)Nb5O15. On the basis of these data, an empirical relation is shown between the ferroelectric transition temperature, Tc, and axial ratio °10 co/a0. The Tc vs °10 c0/a0 curve for compositions with polar axes perpendicular to [00l] has a negative slope, whereas that for compositions with polar axes parallel to [00l] has a positive slope of about the same magnitude. These results are compared with measurements of the temperature dependence of c0/a0 for KSrPbNb5O15, and KBa2Nb5O15; the latter is discussed in terms of the Devonshire free energy theory.
125 citations
112 citations
TL;DR: In this paper, experimental evidence is presented bearing on the low current conduction and on the rapid electrical switching phenomena that have been found in thin films of certain amorphous chalcogenide semiconducting materials.
Abstract: : Experimental evidence is presented bearing on the low current conduction and on the rapid electrical switching phenomena that have been found in thin films of certain amorphous chalcogenide semiconducting materials. The principal findings are that (1) the low current conduction consists of an 'ohmic' region linear with voltage and an exponentially varying nonlinear region, both of which arise from the same conduction process; (2) at voltages just below switching, the equivalent parallel capacitance of the film becomes negative; and (3) a field-influenced dielectric phase transition is implicated in the switching process. The phase transition temperature appears to be related to the glass transition temperature. (Author)
111 citations
TL;DR: In this paper, it was shown that the one-dimensional model postulated by Labbe and Friedel to explain the properties of other high temperature superconductors is inconsistent with these measurements.
102 citations
TL;DR: In this paper, the authors investigated the relationship between superconductivity and the degree of long-range atomic ordering on the crystallographic lattice sites of binary A-15 compounds and found that significant changes in the superconducting transition temperatures and critical fields were produced by quenching from high temperatures followed by low-temperature annealing.
Abstract: Twenty-six different binary A-15 compounds were investigated to determine if superconductivity could be related to the degree of long-range atomic ordering on the crystallographic lattice sites. Significant changes in the superconducting transition temperatures and critical fields were produced by quenching from high temperatures followed by low-temperature annealing. These changes inTcwere accompanied by changes in the degree of long-range ordering as determined using x-ray diffraction methods. The results can be interpreted within the framework of Weger's “linear-chain” model only when the B-element is a nontransition element. When both the A-and B-components are transition elements, however, the superconducting behavior will apparently depend on the nature of “d-electron” interactions between the component atoms. Complete ordering is not always an essential requirement for optimizing the superconducting properties.
97 citations
TL;DR: In this paper, a new high-temperature superconductor, yttrium-thorium sesquicarbide, has been prepared by high-pressure-hightemperature techniques, and the phase, crystallizing in the Pu2C3-type structure, exists over a wide ternary field.
Abstract: A new, high-temperature superconductor, yttrium-thorium sesquicarbide, has been prepared by high-pressure-high-temperature techniques. The phase, crystallizing in the b.c.c., Pu2C3-type structure, exists over a wide ternary field. Lattice parameters are dependent on the Y Th metal and C M t carbon-total metal atomic ratios. The material is superconducting with a variable transition temperature, having a maximum at 17.0 °K. High-temperature ambient-pressure annealing results in the destruction of both the b.c.c. structure and the high-temperature superconductivity. A ternary b.c.t. phase, previously unreported, has been identified in a number of arc-melt preparations. This phase exists over a wide ternary field and is not superconducting down to 4 °K. Elements other than thorium have been incorporated in yttrium sesquicarbide with resultant enhancement of the superconducting temperature.
TL;DR: The transition temperatures of a group of copper compounds of the general formula Cu(CnH2n+1NH3)2Cl4 have been obtained from ac susceptibility data as mentioned in this paper.
Abstract: The transition temperatures of a group of copper compounds of the general formula Cu(CnH2n+1NH3)2Cl4 have been obtained from ac susceptibility data These compounds contain layers of CuCl2, separated by two layers of (CnH2n+1NH3)Cl Also two compounds with the Cl−‐ion replaced by Br− have been investigated In the Cl‐series, n was varied from 1–6, whereby the copper‐copper distance within a layer remains practically constant, the distance between copper ions from adjacent layers increasing from 10 to about 20 A Values for the exchange parameter J have been derived from paramagnetic Curie temperatures and heat‐capacity data at low temperatures Whereas both the interaction between neighboring CuCl2‐layers and the anisotropy clearly vary through the series of compounds, the values of J/kTc we obtained agree rather well to J/kTc=17 This suggests that the transition temperature is indeed characteristic for the layer‐structure
TL;DR: The above room temperature dielectric behavior of the class of BaMF compounds is reported in this article where M = Mg, Zn, Mn, Fe, Co and Ni.
TL;DR: In this paper, it has been known that the transition temperature (Tc) of VO2 is shifted by doping specified elements in VO2 and experiments have been performed with adding various elements.
Abstract: It has been known that the transition temperature (Tc) of VO2 is shifted by doping specified elements in VO2. In order to shift Tc in still wider range, experiments have been performed with adding various elements. As a result, it has become possible to shift the Tc of VO2 either towards a higher temperature or towards a lower temperature. The doping elements which shift Tc towards a higher temperature are Ti and Ge. Those which shift it towards a lower temperature are Fe, Co, Ni, Mo, Nb, and W. In the research conducted, it has been able to vary the Tc within the range of 0–90°C. As for the relationship between the Tc and the lattice constant of the crystals, there exists a correlation with the cr of the tetragonal phase of VO2. Tc is nearly proportional to the quantity or cr: the more the cr, the higher true Tc is; the less the cr, the lower the Tc is.
TL;DR: The phonon spectra for amorphous Bi and Ga superconductors were derived by using McMillan's inversion program on their tunneling data as mentioned in this paper, which indicated an extreme softening of the phonon spectrum from what was found for crystalline supercondors.
Abstract: The phonon spectra for amorphous Bi and Ga are derived by using McMillan's inversion program on our tunneling data. The results indicate an extreme "softening of the phonon spectrum" from what is found for crystalline superconductors. Parameters derived from our phonon spectra are used to test recent theories of the transition temperature of amorphous and strong-coupling superconductors, and also to test the McMillan equation for the maximum possible transition temperature in the limit of extremely strong coupling.
TL;DR: In this paper, a theory of the superconducting transition temperature using a simple model for the electron-phonon interaction has been used to calculate the pressure dependence of the transition temperature for nontransition metals.
Abstract: A theory of the superconducting transition temperature using a simple model for the electron-phonon interaction has been used to calculate the pressure dependence of the transition temperature for nontransition metals. The pressure dependence of the Debye temperature and phonon frequencies is included by using a Gr\"uneisen model. The theory is compared to experiment for aluminum, lead, zinc, cadmium, indium, and tin, and the agreement is generally quite good. The results have been used to predict the critical pressures at which ${T}_{c}=0$; and for the cases of zinc, cadmium, and possibly aluminum, it should be possible to carry out experiments where ${T}_{c}$ is pushed below presently measurable temperatures. The empirical ${T}_{c}=f(P)$ relations published in the literature are discussed and compared with the present results.
TL;DR: Grain size reduction depresses α-La and enhances bcc Mo. Consistency with phonon-mediated electron pairing requires a grain size dependence of the quantity N (0) 〈 I 2 〉 as mentioned in this paper.
Patent•
12 Jun 1969
TL;DR: In this article, the METAL ALLOYS of the TINIXCO1-X, TICOXFE 1-X are worked and treated to effect a reversion back to an original configuration as the result of the MARTENSITIC TRANSITION of the alloys.
Abstract: METAL ALLOYS OF THE FORMULA TINIXCO1-X, TICOXFE1-X, WHEREIN X IS AN INTEGER FROM 0 TO 1 UNDERGO MARTENSITIC TRANSITIONS OVER A VERY WIDE TEMPERATURE RANGE FROM LESS THAN 4*K. TO 1000*K. THE METAL ALLOYS ARE WORKED AND HEAT TREATED TO EFFECT A REVERSION BACK TO AN ORIGINAL CONFIGURATION AS THE RESULT OF THE MARTENSITIC TRANSITION OF THE ALLOYS DUE TO THE HEAT TREATMENT.
TL;DR: In this article, the fracture stress at the ductile-brittle transition temperature of polycrystalline molybdenum was found to be constant, 64± 2 kg mm−2, as the strain rate was raised from 5 × 10−6 to 5× 10−2sec−1.
TL;DR: In this article, the authors measured the frequency of hypersonic sound waves in the range of 1010 Hz in PMMA as a function of temperature through the glass-transition region.
Abstract: Brillouin scattering of laser light has been used to measure the frequency of hypersonic sound waves in the range of 1010 Hz in PMMA as a function of temperature through the glass‐transition region. A discontinuity in the temperature coefficient of sound velocity is observed at the glass‐transition temperature; this is explained as a consequence of a corresponding discontinuity in the temperature coefficient of the specific volume (thermal expansion coefficient). The ratio of the light scattered by isothermal density fluctuations to that scattered by adiabatic density fluctuations was also measured. This ratio was large and did not change appreciably near the glass‐transition temperature. The value of the Landau‐Placzek ratio is approximately what one would expect from previously observed ultrasonic‐velocity‐dispersion data as a function of temperature well above the glass‐transition temperature. Both the velocity and intensity ratio data indicate that no velocity‐dispersion effects are present for the hypersonic sound waves up to temperatures 35° above the glass‐transition temperature. These results also indicate that the glass transition is not a classical second‐order phase transition.
Patent•
27 May 1969
TL;DR: In this article, a method and an apparatus for stabilizing and employing temperature sensitive material exhibiting martensitic transitions for use in control and work performing devices is presented, which includes subjecting the material to a greater unit stress than the material would be required to work against in its application to thereby stretch the material beyond its expected deflection, and subsequently completing a number of temperature cycles while the material is in such overstressed condition.
Abstract: A method and apparatus for stabilizing and employing temperature sensitive material exhibiting martensitic transitions for use in control and work performing devices. The method includes subjecting the martensitic-transition material to a greater unit stress than the material would be required to work against in its application to thereby stretch the material beyond its expected deflection, and subsequently completing a number of temperature cycles while the material is in such overstressed condition, through which it is heated to a point above its transition temperature and cooled back to its annealed temperature. After treatment the material operates through complete work cycles with no loss of dimension stability. In one embodiment, the apparatus defines a temperature sensitive switch including a load to apply an increased stress to the material during the initial stabilization temperature-cycling period and a reduced work-load stress during periods of in-service operation.
TL;DR: In this article, a linear dependence of the superconducting transition temperature on the reciprocal of sample thickness is reported for amorphous Bi and Ga films having thicknesses from 150 up to several thousand Angstroms.
TL;DR: The tunneling paraconductivity of tunneling junctions has been shown to have a strong temperature dependence, tending to infinity at the transition as mentioned in this paper, and the numerical magnitude of this property is sufficiently large to be observable for junctions of very low normal resistance.
Abstract: When one metallic film of a tunneling junction is in the superconducting state but the other is above its transition temperature, fluctuations in the pair field of the second film cause instantaneous Josephson currents to flow. Application of the Kubo formula to these current fluctuations yields a conductivity with a strong temperature dependence, tending to infinity at the transition. The numerical magnitude of this "paraconductivity" is sufficiently large to be observable for junctions of very low normal resistance (and may possibly be compared with some recent measurements of Lipsonet al.). High-frequency studies would determine directly the pair relaxation rate. An experimental advantage of tunneling paraconductivity is that it is not sensitive to the electron mean free path and therefore does not require amorphous films.
TL;DR: In this article, a quasi-chemical treatment is applied to a face-centered cubic lattice system containing N0 holes (or solute molecules) and Nx interacting rods of length-to-breadth ratio x.
Abstract: A quasi-chemical treatment is applied to a face-centered cubic lattice system containing N0 holes (or “solute molecules”) and Nx interacting rods of length-to-breadth ratio x. The resulting partition function is then maximized with respect to the numbers of rods in each of the six allowed directions on the lattice. Two stable “phases” are obtained: a completely aligned “phase”, more stable at lower volume fractions of holes ν0, and an isotropic “phase”, more stable at higher ν0's. When alignment is not favored energetically, the relative stabilities of these two “phases” are temperature independent, but when alignment is favored, this is no longer the case and a first-order aligned → isotropic transition is observed. When the dependencies of the transition temperature and enthalpy of transition on the segment interaction energies of the system, on ν0, and on x are determined, it is found that our simple model is able to predict a number of important aspects of the behavior of nematogenic substanc...
TL;DR: In this article, it was shown that supercritical heat flow in He II is consistent with a mutal friction constant which diverges near the critical heat flux near the boundary of He II.
Abstract: Measurements of supercritical heat flow in He II are consistent with a mutal friction constant which diverges near ${T}_{\ensuremath{\lambda}}$. They also explain the apparent depression of ${T}_{\ensuremath{\lambda}}$ observed by Erben and Pobell, and the "critical heat flux" near ${T}_{\ensuremath{\lambda}}$ reported by Bhagat and Winer.
TL;DR: In this article, the low frequency dielectric constant of thiourea was measured along the b-direction in the temperature region from 25°C to -120°C at various hydrostatic pressure up to 7 kbar.
Abstract: The low frequency dielectric constant of thiourea was measured along the b -direction in the temperature region from 25°C to -120°C at various hydrostatic pressure up to 7 kbar. The pressure-temperature phase diagram was obtained. The initial pressure coefficients for the V-IV transition temperature (-72.0°C), the IV-III transition temperature (-94.0°C), the III-II transition temperature (-96.8°C) and for the II-I transition temperature (-103.0°C) are -19±2°C kbar -1 , -34±1°C kbar -1 , -31±1°C kbar -1 and -26±1°C kbar, respectively. the V-VI transition pressure, which is 3.3 kbar at room temperature, decreases with lowering temperature. The phase VI is not identical with any of low temperature ferroelectric phases.
TL;DR: In this paper, a simple low-temperature D.T.A. set-up, designed for measurements in the temperature region 120°K -600°K, is described.
TL;DR: The magnetic susceptibilities for neodymium, gadolinium and dysprosium germanides and silicides were measured between about 60° to about 700°K as mentioned in this paper.
Abstract: The magnetic susceptibilities for neodymium, gadolinium and dysprosium germanides and silicides were measured between about 60° to about 700°K. Plots of 1/χ vs T show a Curie‐Weiss behavior, but deviations from it are observed below room temperature. The deviations become smaller with decreasing temperature and in most instances tend to approach the asymptote just above the transition temperature. These compounds have the D88 structure and a ferromagnetic spin ordering for rare earth atoms in the crystallographic 6(g) sites, and an antiferromagnetic ordering in the 4(d) sites is consistent with the observed behavior.