Showing papers on "Transition temperature published in 1982"
TL;DR: In this article, a theory of the tetramethyltetraselenafulvalene (TMTSF) salts and their sulfur analogs is developed, which accounts for differences between the sulfur and selenium series, and the absence of Peierls' transitions.
Abstract: A theory of the tetramethyltetraselenafulvalene (TMTSF) salts and their sulfur analogs is developed. It is shown that the phase diagram is controlled by electron-electron umklapp scattering. The theory accounts for differences between the sulfur and selenium series, and the absence of Peierls' transitions. Predictions of the pressure dependence of the spin-density-wave critical temperature and correlations of the dimerization of the organic stacks with critical pressures and temperatures are verified experimentally.
210 citations
TL;DR: In this paper, the authors studied the volume dependence of the first-order transition temperature TC' by using the expansion of the free energy up to the M6 term, and showed that large experimental values of d ln TC'/d ln V for DyCo2, HoCo2 and ErCo2 can be explained by this model.
Abstract: The magnetic free energy in the so-called s-d model where the itinerant d electrons and localised spins coexist is expanded in a power series of the total magnetisation M. The first-order transition observed for DyCo2, HoCo2 and ErCo2 is explained from the negative values of the coefficient of the M4 term at TC where the paramagnetic susceptibility diverges in the expansion of the free energy. Volume dependence of the first-order transition temperature TC' is studied by using the expansion of the free energy up to the M6 term. It is shown that large experimental values of d ln TC'/d ln V for DyCo2, HoCo2 and ErCo2 can be explained by this model.
169 citations
TL;DR: In this article, a completely dehydrated dipalmitoylphosphatidylcholine (DPPC) was prepared with dehydration under high vacuum and at a temperature above its main transition temperature.
107 citations
TL;DR: The structure and thermotropic properties of a homologous series of diacylphosphatidylserines (PS) in the anhydrous and hydrated states have been examined with low-angle X-ray diffraction and differential scanning calorimetry.
Abstract: The structure and thermotropic properties of a homologous series of diacylphosphatidylserines (PS) in the anhydrous and hydrated states have been examined with low-angle X-ray diffraction and differential scanning calorimetry. In the anhydrous state at low temperatures both acidic PS and its NH4+ salts exhibit lamellar bilayer crystal forms that transform to liquid-crystalline hexagonal (type II) structures at higher temperatures. The crystal leads to liquid-crystal transition temperature increases with increasing chain length, the transition temperature of an NH4+-PS being higher than that of its corresponding acidic form. In contrast, the transition enthalpies of the acidic PS are higher than those of the NH4+ salt forms. Hydrated cyclic PS and NH4+-PS exhibit reversible lamellar gel leads to liquid-crystal transitions. In this case the acidic form undergoes this chain length dependent transition at a higher temperature, but with a lower enthalpy change, than the NH4+-PS. Both below and above the hydrocarbon chain melting transition, hydrated lamellar bilayer structures are present. The temperature-composition phase diagram of the NH4+-dimyristoyl-PS/H2O system has been studied in detail. The chain melting transition decreases with increasing hydration, reaching a limiting value of 39 degrees C. X-ray diffraction shows that both the bilayer gel structure and the bilayer liquid-crystal form take up water continuously (i.e., no hydration limit), a characteristic of lipid bilayers with a net charge. Electron-density profiles a NH4+-dimyristoyl-PS at different hydration levels permit detailed analysis of the structural parameters of the PS bilayer.
90 citations
TL;DR: In this paper, the authors report detailed measurements of the magnetization of Cu/Ni composition modulated foils as a function of temperature, magnetic field, composition wavelength, and composition amplitude.
Abstract: We report detailed measurements of the magnetization of Cu/Ni composition modulated foils as a function of temperature, magnetic field, composition wavelength, and composition amplitude. We find a Curie temperature that initially increases rapidly with wavelength but quickly saturates. We also find that the Curie temperature is independent of composition amplitude which we ascribe to the existence of disk‐like Ni clusters.
72 citations
TL;DR: In this article, the mixing state of the polymer/liquid crystal composite membrane was investigated on the basis of differential scanning calorimetry, x-ray, density, sorption isotherm and sorption-desorption studies and also by electron microscopic observations.
65 citations
TL;DR: In this article, the authors examined the thermal behavior of the synthesized higher n-alkanes from n-C32H66 to N-C80H162 by means of DSC, small-and wide-angle X-ray scattering and optical microscopy.
Abstract: The general principle for synthesizing higher n-alkanes of the highest purity is described briefly. Thermal behavior of the synthesized n-alkanes from n-C32H66 to n-C80H162 were examined by means of DSC, small- and wide-angle X-ray scattering and optical microscopy. All the crystalline n-alkanes except for n-C80H162, when crystallized from solution, showed transitions to high-temperature monoclinic modifications (Mh01, h=1 or 2) before the rotator transition or the melting, irrespective of the number of carbon atoms (n) being odd or even and the difference in room-temperature modifications of even n-alkane. One feature of the transition was its irreversibility. The odd n-alkanes of n-C33H68, n-C37H76, and n-C45H92 showed also another type of solid-solid transition below the transition mentioned above. Both types of the transitions were thermally proved to be of the first-order. Although no simple functional forms were generally given to the relationships between the transition temperature and n, the temperatures for the transition of orthorhombic higher n-alkanes to the Mh01 phase increased with n, reaching about 90°C for n-C69H140. The transition to Mh01 was accompanied by a morphological change on the crystal surface, in the form of characteristic striations parallel to the bs subcell axis. This suggests that the solid-solid transition proceeds successively from a nucleating site with a staggering of molecules in the chain direction. If the slow rate of the process and complicated behavior of the Mh01 phase are taken into account, the kinetical view point of the phase transition leads to the working hypothesis that the molecular motion of the long chains in the n-alkane crystals, which consists of rotational and longitudinal motions or a flip-flop motion, takes place only in this transformation process.
64 citations
TL;DR: In this article, the electrical conductivity of metallic amorphous Si 1− x Au x films was measured down to 10 mK and superconducting transition was observed in a certain range of Au content.
59 citations
TL;DR: In this paper, the angle-dependent pair interactions are assumed to be of second-rank form, and a simple theory of rod/plate liquid-crystal mixtures is presented.
Abstract: We present a simple theory of rod/plate liquid-crystal mixtures in which the angle-dependent pair interactions are assumed to be of second-rank form. Calculations are reported for varying relative anisotropies of the “rods” and “plates”. Temperature vs. mole-fraction phase diagrams show successive isotropic (I) → uniaxial ( U) and U → biaxial ( B) transitions which are first- and second-order, respectively. For each pair of species there exists a special composition ( x rod*) for which cooling of the isotropic phase leads directly (and continuously) to a biaxial liquid. As X rod approaches X rod* from either side, the first-orderness of the I → U transition (i.e. discontinuities in volume, order parameter, etc.) becomes vanishingly small. Furthermore the transition temperature of the rod-(plate-) solvent is found to be depressed when “doped” by not-too-anisotropic plates (rods) and elevated when doped by sufficiently anisotropic plates (rods). These behaviors are explained in terms of simple excl...
55 citations
TL;DR: In this paper, solid solutions of the formula La2−xLnxCuO4 (Ln = Pr, Nd) possess the orthorhombic structure of La2NiO4 for small values of x and transform to the tetragonal Nd2NiF4 structure at a critical value of x.
53 citations
TL;DR: In this article, the structural phase transition of the layer compound RbAlF4 is shown to undergo structural phase transitions at 553K and 282K under investigation by DSC and X-ray powder diffraction.
Abstract: The layer compound RbAlF4 is shown to undergo structural phase transitions at 553K and 282K under investigation by DSC and X-ray powder diffraction. The structures of the three phases are determined by neutron powder profile refinement. The high-temperature phase has the ideal TlAlF4 structure P4/mmm which corresponds to the tilt system a0a0c0. The intermediate room-temperature phase is confirmed as P4/mbm, the tilt system is a0a0c+. The low-temperature phase is consistent with the space group Pmmn which corresponds to both ap+b0c+ (near the transition temperature) and ap+bp+c+ (at very low temperature). The 553K phase transition is a non-ferroic phase transition while the 282K transition is ferroelastic. According to Aizu the low-temperature phase is a 4/mmmFmmm species. The temperature behaviour of the structural parameters is discussed, particularly in the framework of ferroelasticity.
TL;DR: In this article, the structural relaxation of amorphous metal alloys with different Mo content was studied through electrical resistivity measurements between the room temperature and the glass transition temperature Tg, and a simple relation between the variation of α after annealing, and the reduction of the alloys free volume was derived and discussed.
Abstract: The structural relaxation of Fe‐Ni‐Mo‐B alloys with different Mo content is studied through electrical resistivity measurements between the room temperature and the glass transition temperature Tg. The observed behavior of the resistivity during isothermal annealing treatments gives evidence for the presence of competing processes of compositional and topological short‐range ordering, whose nature and role are discussed. The variation of the temperature coefficient of resistivity, α, observed after annealing of ribbons, is related to the variation of the degree of topological short‐range order, and interpreted on the basis of the theories describing the electrical resistivity and the structural relaxation of amorphous metals. A simple relation between the variation of α after annealing, and the reduction of the alloys’s free volume, is derived and discussed.
TL;DR: In this article, the effect of the order-disorder transformation on electron transport in transition metal carbides was investigated, with special attention to ordering effects in substoichiometric specimens and to the influence of hydrogen doping.
Abstract: Electron transport in transition metal carbides was investigated, with special attention to ordering effects in substoichiometric specimens and to the influence of hydrogen doping. Hydrided carbides specimens showed reduced resistivity values, a result attributed to the reduction of defect scattering as the carbon vacancies were filled with substitutional hydrogen ions. The effect of the order‐disorder transformation NbC0.83 = Nb6C5 at 1030 °C was also to reduce defect scattering as the carbon vacancies became incorporated into the periodic potential of the ordered phase. As another illustration of vacancy scattering, the resistivities of non‐stoichiometric HFCx and stiochiometric WC were compared. The superconducting transition temperatures of partially ordered Nb6C5 and hydrided NbCx decreased from those of the original specimens, disordered NbC0.83 and NbCx, respectively. The normal state resistivity of Nb6C5 displayed the bulge in its temperature dependence characteristic of high Tc superconducters....
TL;DR: In this paper, the existence of superconductors with high transition temperatures is analyzed for both the ordinary electron-phonon interaction and nonphonons superconductivity mechanisms, and it is shown that negative values of the static dielectric permittivity are possible in the case of strong local-field effects.
Abstract: The possible existence of superconductors with high transition temperatures is analyzed for both the ordinary electron-phonon interaction and nonphonon superconductivity mechanisms. The existence of such systems depends on a negative static dielectric permittivity. The possible occurrence of this situation for an electron-ion system is analyzed. It is shown that negative values of the static dielectric permittivity are possible in the case of strong local-field effects, i. e., in the case of exchange-correlation interactions in the electron subsystem or the localization of point ions for an electron-phonon system. Equations for the transition temperature of strong-coupling superconductors are analyzed. Restrictions imposed on the transition temperature by the equations themselves and by the conditions for stability of the material are examined.
TL;DR: Amorphous Nb-19 at% Si alloy, prepared by rapid quenching from the molten state, was annealed while being subjected to a pressure of 10 GPA as mentioned in this paper.
Abstract: Amorphous Nb-19 at% Si alloy, prepared by rapid quenching from the molten state, was annealed while being subjected to a pressure of 10 GPA. X-ray diffraction investigations on the alloy specimens quenched to ambient conditions have shown that pressure greatly alters the crystallization characteristics and the cubic A15 (Nb3Si)-phase forms in preference to the tetragonal Nb3Si-phase at temperatures in the range from 710° C to 800° C. Up to 680° C, the component atoms do not show any tendency towards ordering upon crystallization and the body-centred tetragonal solid solution forms; while, at 830° C, niobium atoms diffuse to form the body-centred cubic Nb precipitates. Superconducting properties have been measured for the single-phase A15 structure with the lattice parametera=0.5155 nm with the results that the transition temperature,TC, is 3.4 K and the temperature coefficient of the upper critical field,HC2, is 1.2 MA m−1 K−1 (15 kOe K−1).
TL;DR: In this article, the Hall coefficient and conductivity of TiS2 have been measured and it has been shown that the strong temperature dependence of the conductivity is matched by a strong pressure dependence that is consistent with electron-phonon scattering.
Abstract: Measurements of the pressure dependence of the Hall coefficient and conductivity of TiS2 indicate that TiS2 is an extrinsic semiconductor. The strong temperature dependence of the conductivity is matched by a strong pressure dependence that is consistent with electron-phonon scattering. In contrast, TiSe2 is a semimetal, with a strongly pressure dependent p-d band overlap. The transition temperature of the structural phase transition in TiSe2 falls at -1.2K kbar-1.
TL;DR: In this article, it was shown that the resistivity of an infinitely thick film with the same structure as a thin film can be determined from the graph of ϱd versus d (where ϱ is the resistivities and d the film thickness).
TL;DR: In this paper, the X-ray precession method using diamond-anvil pressure cells was used to observe the VII-VIII phase transition in a diamond anvil pressure cell.
Abstract: The ice VII-VIII phase transition was observed by the X-ray precession method using diamond-anvil pressure cells. Single crystals of ice VII–cubic, a=3.350±0.005 A (sample A) and a=3.360±0.005 A (sample B)–transformed into twin-mosaic crystals of ice VIII–tetragonal, a=4.68±0.01 A and c=6.81±0.01 A (sample A) and a=4.70±0.01 A and c=6.84±0.01 A (sample B)–. The formation of the twin mosaics caused some misorientation and distortion in the crystal. These disappeared during the VIII→VII transition. Thermal hysteresis of the transition temperature was observed.
TL;DR: The dielectric constants of orthorhombic Li 2 Ge 7 O 15 and their dependence on hydrostatic and uniaxial pressure as well as temperature have been determined above and below the transition temperature at 284.3 K.
TL;DR: In this article, the elastic stiffness constants have been determined at room temperature using Brillouin spectroscopy, and the spectral width of the corresponding spectral width has been shown to show important variations around the transition temperature (Ti = -143°C) between prototypic and incommensurate phases.
Abstract: All elastic stiffness constants have been determined at room temperature using Brillouin spectroscopy. Some of them and the spectral width of the corresponding Brillouin peaks show important variations around the transition temperature (Ti = -143°C) between prototypic and incommensurate phases. Below Ti, the anomalies associated with the acoustic phonons propagating in the (001) direction are explained assuming a linear coupling between deformations and an overdamped mode. This mode is equivalent to a Debye relaxation process characterized by a relaxation time τ0 = 2.6 10-12 s.K.
TL;DR: The elastic instability in the ferroelastic phase transition of BiVO 4 was investigated by the observation of the Brillouin scattering spectra as a function of temperature around the transition temperature.
Abstract: The elastic instability in the ferroelastic phase transition of BiVO 4 was investigated by the observation of the Brillouin scattering spectra as a function of temperature around the transition temperature. From the temperature dependence of the observed spectra in two different scattering geometries it turns out clear that the softening of elastic stifiness constant c 11 - c 12 , not of c 66 , causes the ferroelastic transition. The elastic softening is discussed in connection with the domain structure.
TL;DR: In this paper, conductivity measurements along the most conductive a-axis in magnetic fields applied along three different principal crystallographic axes were studied by conductivity measurement along the a-, b-, and c*-axes.
Abstract: Superconducting transition of (TMTSF)2ClO4 was studied by conductivity measurements along the most conductive a-axis in magnetic fields applied along three different principal crystallographic axes. The GL coherence lengths at OK along the a-, b-, and c*-axes, ϵa(0)≈ 600A, ϵ(0) ≈ 540A, and ϵc*(0) ≈ 60A were obtained from the measurements of the temperature dependence of the upper critical field HC2 near the transition temperature. The anisotropy is discussed in terms of the dimensionality arising from the crystal structure and of the conductivity anisotropy in the normal state.
TL;DR: In this article, the lattice energy of the triclinic phase of ferrocene has been analyzed at 130 K and 15 K and it has been shown that it has two possible molecular packings, quite energetically similar, of face-centred or P 1 symmetry.
TL;DR: In this article, the authors measured the electrical resistivity from 1.3 to 320 K and the critical magnetic field for superconductivity in single crystals of Nb 3 Se 4, where the resistivity along the Nb-chain direction is represented as a sum of a temperature independent and an intrinsic temperature dependent term.
TL;DR: In this paper, the magnetoresistance, Hall effect and nonlinear conductivity characteristics in pure and radiation damaged TMTSF>2PF6 were measured and the material below the metal-insulator transition temperature was best described as quasi-two-dimensional with a very high mobility.
Abstract: We have measured the magnetoresistance, Hall effect and the nonlinear conductivity characteristics in pure and radiation damaged (TMTSF>2PF6. We find that the material below the metal-insulator transition temperature is best described as quasi-two-dimensional with a very high mobility (105 cm2/volt-sec). The nonlinear conductivity is suppressed by the application of a magnetic field and by radiation damage. The magnetoresistance, metal-insulator transition temperature and the superconducting transition temperature are also reduced by radiation damage of order 1000 ppm for the latter and 100 ppm for the former.
TL;DR: In this paper, the specific heat in an incommensurate phase of the K 2 SeO 4 -type crystals was calculated on the basis of the Landau-type thermodynamic potential functional, which was solved within the phase modulation only approximation.
Abstract: The specific heat in an incommensurate phase of the K 2 SeO 4 -type crystals was calculated on the basis of the Landau-type thermodynamic potential functional, which was solved within the phase modulation-only approximation. It was found that the calculated specific heat decreases first with decreasing temperature and shows a small anomaly just above the incommensurate-commensurate transition temperature. The observed data of K 2 SeO 4 and Rb 2 ZnCl 4 seem to be well reproduced by adjusting parameters.
TL;DR: In this article, the incommensurate-commensurate phase transition of CrMn single crystals is shown to be of first order and the observed relative length changes and latent heat effects at the transition correlate well with the known pressure dependence of the transition temperature.
Abstract: The incommensurate-commensurate phase transition of CrMn single crystals is shown to be of first order. Coexistence of the two phases reported in the past is shown conclusively to be due to inhomogeneities in the Mn concentration of large samples. The observed relative length changes and latent heat effects at the transition correlate well with the known pressure dependence of the transition temperature. At this temperature very small resistivity anomalies are present as a result of a different temperature dependence of the resistivity of the incommensurate and commensurate phases.
TL;DR: The irradiation of yttrium iron garnet films with 181 −MeV xenon ions (1.4 MeV per nucleon) creates paramagnetic cylinders around the path of the ion with a radius of about 7.5 nm as mentioned in this paper.
Abstract: The irradiation of yttrium iron garnet films with 181‐MeV xenon ions (1.4 MeV per nucleon) creates paramagnetic cylinders around the path of the ion with a radius of about 7.5 nm. These nuclear tracks consist of needle shaped regions of high crystalline defect density reaching 10 μm deep into the garnet material. The saturation magnetization decreases exponentially with dose. However, its temperature dependence remains unchanged by the irradiation except for small deviations near the Curie temperature. Owing to the creation of paramagnetic volumes, the Faraday rotation is also reduced, but contrary to the behavior of the saturation magnetization, the temperature dependence is changed. The reduction at low temperatures is much smaller as would be expected from the saturation magnetization. The optical absorption is drastically increased by the irradiation. Annealing leads to heal‐out of the irradiation induced effects. The saturation magnetization is restored after 10 h annealing at 833 K. The Faraday rota...
TL;DR: In this article, a superconducting thin film of BaPb1−xBixO3 with transition temperature above 9 K was successfully prepared by rf diode sputtering and subsequent annealing.
Abstract: Superconducting thin films of BaPb1−xBixO3 with transition temperature above 9 K were successfully prepared by rf diode sputtering and subsequent annealing. It was found that sputtered films tended to lack Pb and Bi during deposition, so that targets with excess Pb and Bi were used in order to achieve the film stoichiometry. Sufficient oxygen partial pressure during discharge was found to be requisite for obtaining thin films with low resistivity, high Tc, and sharp superconducting transition. The films admit optical transmission to a small extent in the wavelength range from 500 to 700 nm. Based on these results, some aspects of the band structure are discussed.
TL;DR: In this article, the transition temperature and upper parallel critical field of layered Nb-Ti alloys for layer wavelengths between 6 and 6250 A were measured for a single-input single-out (SISO) configuration.
Abstract: We present measurements of the transition temperature and upper parallel critical field, to 15 kG, of layered Nb-Ti alloys for layer wavelengths between 6 and 6250 A.