Showing papers on "Transition temperature published in 1985"
TL;DR: In this paper, the authors investigated ionic conductivity σ and mobility σ in amorphous network polymers from poly(propylene oxide) (PPO) containing lithium perchlorate (LiClO4) at the concentration of 0.042 and 0.076.
Abstract: Ionic conductivity σ and mobility μ in the amorphous network polymers from poly(propylene oxide) (PPO) containing lithium perchlorate (LiClO4) at the concentration of [LiClO4]/[PO unit]=0.042 and 0.076 were investigated by means of complex impedance and time‐of‐flight methods. The σ values of the PPO–LiClO4 complexes reached 10−5 S cm−1 at 70 °C. The temperature dependence of σ deviated from a single Arrhenius behavior above a critical temperature (−1 °C and 11 °C) which approximately corresponded to the glass transition temperature Tg. The μ values were relatively high and changed from 10−6 to 10−5 cm2 V−1 s−1 in the temperature range of 40–100 °C. The Nernst–Einstein equation correlated μ with the ionic diffusion coefficient D. The Williams–Landel–Ferry equation with C1≂5 and C2≂30–50 held with a temperature dependence of D in the order of 10−8–10−7 cm2 s−1. The change in the number of ionic carriers n with temperature obeyed the Arrhenius equation with the activation energy of 0.26 and 0.34 eV. The deg...
259 citations
TL;DR: It is argued that the modes contribute to the cooling of the quark-gluon plasma by being analogous to the fluctuations of the order parameter in a superconductor above the critical point.
Abstract: Fluctuations of the order parameter of chiral transition in a hot and dense quark gas are examined in the random-phase approximation with the use of a QCD-motivated effective Lagrangian. We show that there arise soft modes having a large strength and a narrow width above the critical temperature, which are analogous to the fluctuations of the order parameter in a superconductor above the critical point. It is argued that the modes contribute to the cooling of the quark-gluon plasma.
235 citations
TL;DR: The sensitivity of the bilayer to hexagonal phase transition temperature to the presence of additives is at least as great as that which has been observed for any other lipid phase transition.
Abstract: The bilayer to hexagonal phase transition temperatures of dielaidoylphosphatidylethanolamine and 1-palmitoyl-2-oleoylphosphatidylethanolamine are 65.6 and 71.4 degrees C, respectively. Using high-sensitivity differential scanning calorimetry, I have shown that these transition temperatures are extremely sensitive to the presence of small amounts of other lipid components. For example, at a mole fraction of only 0.01, dilinolenin lowers the bilayer to hexagonal phase transition temperature of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine by 8.5 degrees C. Other diacylglycerols have similar effects on this transition temperature, although the degree of unsaturation of the acyl chains has some effect, with distearin being less potent. In comparison, the 20-carbon alkane eicosane lowers this transition temperature by 5 degrees C, while palmitoyl-lysolecithin raises it by 2.5 degrees C. Similar effects of these additives on the bilayer to to hexagonal phase transition temperature are observed with dielaidoylphosphatidylethanolamine. At these concentrations of additive, there is no effect on the gel-state to liquid-crystalline-state transition temperature. The observed shifts in the temperature of the bilayer to the hexagonal phase transition can be qualitatively interpreted in terms of the effects of these additives on the hydrophilic surface area and on the hydrophobic volume. Substances expanding the hydrophobic domain promote hexagonal phase formation and lower the bilayer to hexagonal phase transition temperature. The sensitivity of the bilayer to hexagonal phase transition temperature to the presence of additives is at least as great as that which has been observed for any other lipid phase transition.
217 citations
TL;DR: In this article, a computer simulation is employed to demonstrate that a vapordeposited thin film of low adatom mobility undergoes a sudden change from a porous columnar microstructure to a densely packed film if the substrate temperature is increased to a certain value.
Abstract: A computer simulation is employed to demonstrate, in a two‐dimensional growth model, that a vapor‐deposited thin film of low adatom mobility undergoes a sudden change from a porous columnar microstructure to a densely packed film if the substrate temperature is increased to a certain value. The temperature where this structural transition occurs is shown to be related to the lower boundary temperature of the empirical structure‐zone model. The dependence of the transition temperature and range on the vapor deposition rate is discussed.
195 citations
TL;DR: A mechanism is proposed for the lamellar/hexagonal phase transition that does not involve large or energetically expensive molecular rearrangements, incorporates facile reversibility, repeatability, and cooperativity, and is consistent with the experimental observation of a predominantly two-state transition.
Abstract: A study of the kinetics and mechanism of the thermotropic lamellar gel/lamellar liquid-crystalline and lamellar/inverted hexagonal phase transition in dihexadecylphosphatidylethanolamine (DHPE) at various hydration levels has been carried out. Measurements were made by using a real-time X-ray diffraction method at the Cornell High Energy Synchrotron Source. This represents an extension of an earlier study concerning the lamellar gel/lamellar liquid-crystalline phase transition in dipalmitoylphosphatidylcholine [Caffrey, M., & Bilderback, D. H. (1984) Biophys. J. 45, 627-631]. With DHPE, the chain-melting and the nonbilayer transitions were examined under active heating and passive cooling conditions by using a temperature jump to effect phase transformation. Measurements were made at hydration levels ranging from 0% to 60% (w/w) water, and in all cases, the transitions were found to be repeatable, be reversible, and have an upper bound on the transit times (time required to complete the transition) of less than or equal to 3 s. The shortest transit time recorded for the chain-melting and lamellar/hexagonal transitions was less than 1 s. At 8% (w/w) water, the transit times were still on the order of seconds even though the transition does not involve the intermediate L alpha phase. Note, the measured transit times are gross values incorporating the intrinsic transit time in addition to the time required to heat or cool the sample through the transition temperature range and to supply or remove the latent heat of the transition. Regardless of the direction of the transition, both appear to be two state to within the sensitivity limits of the real-time method. From simultaneous wide- and low-angle measurements at the lamellar chain-melting transition, loss of long-range order in the lamellar gel phase appears to precede the chain-melting process. On the basis of the real-time X-ray diffraction measurements, a mechanism is proposed for the lamellar/hexagonal phase transition. The mechanism does not involve large or energetically expensive molecular rearrangements, leads directly to a hexagonal lattice coplanar with the lamellar phase, incorporates facile reversibility, repeatability, and cooperativity, accounts for an observed, apparent memory in the hexagonal phase of the original lamellar phase orientation, and is consistent with the experimental observation of a predominantly two-state transition. In conjunction with the kinetic measurements, the DHPE/water phase diagram was constructed. At and above 12% (w/w) water, the thermotropic transition sequence is L beta'/L alpha/HII.(ABSTRACT TRUNCATED AT 400 WORDS)
158 citations
TL;DR: Superconductivity in the simple hexagonal phase of silicon is predicted on the basis of an electron-phonon-coupling calculation and measured experimentally up to a pressure of 25 GPa in a Bridgman-type opposed-anvil device.
Abstract: Superconductivity in the simple hexagonal phase of silicon is predicted on the basis of an electron-phonon-coupling calculation and measured experimentally up to a pressure of 25 GPa in a Bridgman-type opposed-anvil device. The highest measured superconducting transition temperature is 8.2 K at 15 GPa for the simple hexagonal phase.
150 citations
TL;DR: In this article, the phase diagram of zirconia was determined by optical microscopy and X-ray diffraction techniques using a diamond anvil pressure cell, and the initial transformation pressure for the monoclinic-tI-tII transition on a virgin ZrO/sub 2/ crystal can be as high as 4.4 GPa; on subsequent cycling the transition pressure ultimately lowers to 3.29 + or 0.06 GPa.
Abstract: The pressure-temperature phase diagram of zirconia was determined by optical microscopy and X-ray diffraction techniques using a diamond anvil pressure cell. At room temperature, monoclinic ZrO/sub 2/ transforms to a tetragonal phase (tII) which is related to the high-temperature tetragonal structure (tI). The transformation pressure exhibits hysteresis and is cycle dependent. At room temperature, the initial transformation pressure for the monoclinic-tII transition on a virgin monoclinic crystal can be as high as 4.4 GPa; on subsequent cycling the transition pressure ultimately lowers to 3.29 + or 0.06 GPa. The pressure for the reverse transition is essentially constant at 2.75 + or - 0.06 GPa. At pressures > 16.6 GPa, the tII form transforms to the orthorhombic cotunnite (PbCl/sub 2/) structure. With increasing temperature, the tII form transforms to the high-temperature tetragonal phase. For increasing P and T, the monoclinic-tI-tII triple point is located at T = 596/sup 0/ + or - 18/sup 0/C and P = 2.26 + or - 0.28 GPa, whereas for decreasing P and T, the triple point is found at T = 535/sup 0/ + or - 25/sup 0/C and P = 1.7 + or - 0.28 GPa.
146 citations
TL;DR: In this article, the thermal variation of atomic beam diffraction intensities on (1, 1, 2n + 1) faces of Cu is discussed for large n. The main parameter of the theory is the energy W0 of a kink on a step.
Abstract: The thermal variation of atomic beam diffraction intensities on (1, 1, 2n + 1) faces of Cu is discussed for large n. the dramatic decrease of intensity at about 600K is attributed to a roughening transition, above which the steps are fuzzy. The steps are assumed to repel themselves with a repulsion energy proportional to (2n+1)-2, of elastic or electrostatic nature or both. The main parameter of the theory is the energy W0 of a kink on a step. Experimental data are consistent with a value of W0 between 0.2 and 0.3 eV, in agreement with very rough theoretical evaluations. Predictions are presented concerning the lineshape of diffraction spectra in the high-temperature rough phase, where intensities cannot be written as delta functions. The Bragg peak intensity vanishes just below the roughening transition temperature, TR, as exp(-constant*(TR-T)-12/), where the constant depends on the particular Bragg peak.
139 citations
TL;DR: A model is presented which gives a unique magnetic-field-induced transition from a two-dimensional open-orbit metal to a semimetal, which can explain some of the anomalous quantum oscillations and the Hall steps observed in the tetramethyltetraselenafulvalenium compounds.
Abstract: A model is presented which gives a unique magnetic-field-induced transition from a two-dimensional open-orbit metal to a semimetal. A magnetic field causes the open-orbit electron motion to become progressively more one dimensional, with an effective density of states proportional to H at low field. This leads to a Fermi-surface instability with a transition temperature which varies approximately as ${T}_{c}$=${T}_{0}$exp(-A/H). The resulting gap, which is both temperature and magnetic field dependent, can explain some of the anomalous quantum oscillations and the Hall steps observed in the tetramethyltetraselenafulvalenium compounds [(TMTSF${)}_{2}$X].
85 citations
TL;DR: In this paper, the dielectric permittivity and loss of 1-cyanoadamantane have been measured under isothermal conditions in the frequency range, 100-2*105 Hz and the temperature range, 80-350K in the glassy crystal, supercooled (metastable) and stable (disordered) crystals and partially ordered crystalline states.
Abstract: The dielectric permittivity and loss of 1-cyanoadamantane have been measured under isothermal conditions in the frequency range, 100-2*105 Hz and the temperature range, 80-350K in the glassy crystal, supercooled (metastable) and stable (disordered) crystals and partially ordered crystalline states. Two relaxation regions were observed, one above the glass-like transition temperature (170K) and the other below it. (The latter finding is contrary to the observations of Amoureux et al., for which reasons are given.) The characteristics of the two relaxations are remarkably similar to those found in other isotropic and anisotropic glasses and glassy crystals. The implications of this similarity for concepts of the glass transition and configurational states are pointed out. The static permittivity of 1-cyanoadamantane shows that it is only partially disordered even at high temperatures and that its disorder-order transformation occurs over a wide temperature range. Isothermal measurements in this range show no time dependence of the ordering process.
69 citations
TL;DR: In this article, X-ray diffraction patterns from melt-crystallized Nylon ll films showed significant discrepancies with the proposed alpha-form structure, and these discrepancies did not disappear after annealing the samples.
Abstract: : Careful examination of the X-ray diffraction patterns from melt-crystallized Nylon ll films showed significant discrepancies with the proposed alpha-form structure. These discrepancies did not disappear after annealing the samples. The temperature dependence of the d-spacings of the two strongest peaks showed further evidence that the melt-crystallized and solution cast films (alpha-form) possess different crystal structures. These results suggest a different crystal structure for the melt-crystallized films, and this would help explain the rather low piezoelectric response of these films and also the failure to observe a rapid decrease in polarization at the transition temperature.
TL;DR: In this paper, the superconductivity with onset temperature as high as 8 K in the organic conductor of β-(BEDT-TTF)2I3, which was achieved by an application of a soft pressure, i.e. 1.3 kb, remains stable with even higher transition temperature after a subsequent release of pressure to the ambient pressure.
TL;DR: In this paper, small-angle neutron scattering (SANS) studies of an amorphous Fe91Zr9 alloy have shown that there is no transition to long-range magnetic order in contrast to previous bulk magnetization results which indicated a transition to a ferromagnetic state at 220 K followed by a reentrant spinglass state near 60 K.
Abstract: Small‐angle neutron scattering (SANS) studies of an amorphous Fe91Zr9 alloy have shown that there is no transition to long‐range magnetic order in contrast to previous bulk magnetization results which indicated a transition to a ferromagnetic state at 220 K followed by a reentrant spin‐glass state near 60 K. The scattering line shape is Lorentzian in Q down to below 150 K and yields a spin correlation length which reaches a maximum of only 27 A at the transition T C=210 K and exhibits an essentially constant plateau of 23 A down to helium temperature, with no evidence of a second transition in the 60–80 K range. The line shape departs from Lorentzian below about 120 K and can be represented by a Lorentzian plus Lorentzian‐squared cross section as appropriate for a system in which long‐range order has been replaced by a frozen cluster configuration. The absence of ferromagnetic order in Fe91Zr9 at Fe concentrations far above the percolation threshold suggests the presence of a very broad distribution of ex...
TL;DR: In this article, the α-modification of (BEDT-TTF)2 I3 undergoes a metal-to-insulator transition at T = 135 K. The β-modifcation, on the other hand, exhibits ambient pressure volume superconductivity below Tc = 1.05 K.
Abstract: The α-modification of (BEDT-TTF)2 I3 undergoes a metal-to-insulator transition at T = 135 K. Application of hydrostatic pressure shifts the transition temperature to lower values. Above 12 kbar semimetallic behavior is observed, but no superconductivity is detected up to a pressure of 17 kbar and temperatures down to l00 mK. The β-modifcation, on the other hand, exhibits ambient pressure volume superconductivity below Tc = 1.05 K. Measurements of the anisotropy of the diamagnetic shielding- as well as the Meissner-magnetization are presented.
TL;DR: In this article, the a(T) curve for the monodomain and polydomain regions of a flux-grown SrTiO3 crystal was observed below the transition temperature without applying external stress.
Abstract: In a flux-grown SrTiO3 crystal, monodomain and polydomain regions have been observed below the transition temperature without applying external stress. For each region, measurements of the lattice constant as a function of temperature are made by means of high-angle double-crystal X-ray diffractometry (HADOX) with a precision better than one part in 106. The a(T) curve for the monodomain clearly shows a critical contraction in the region Tc ± 2 K, where the curve deviates from the relation 1—a/a 0 ∞ (1-T/Tc )βa . The phenomenon is discussed in terms of the fluctuation of the order parameter and related to the precursor effect reported for KMnF3 and for SrTiO3 Verneuil crystals for T > Tc . This means, on the other hand, that the determination of the critical exponent of spontaneous strain of SrTiO3 is intrinsically difficult. An anomalous temperature dependence of the intensity of the 400 and 004 reflections found for Verneuil crystals is observed in a very similar manner.
TL;DR: The dc reactive magnetron sputtering process yields stoichiometric NbN films with superconducting transition temperature T(c) as high as 15.7 K on substrates as varied as glass, glazed ceramic, fused quartz, and sapphire as discussed by the authors.
Abstract: The dc reactive magnetron sputtering process yields stoichiometric NbN films with superconducting transition temperature T(c) as high as 15.7 K on substrates as varied as glass, glazed ceramic, fused quartz, and sapphire. These films posses fcc (B1) structure and (111) texture. The most dominant factors governing the formation of the transition metal nitrides are the relative metal and nitrogen fluxes incident on the substrate and the background argon pressure (which dictates the overall reactive sites and residence times for nitrogen).
TL;DR: In this paper, the Verwey phase transition in magnetite has been investigated by thermomagnetic analysis of the initial permeability, revealing that the transition temperature is a maximum for pure stoichiometric Fe3O4 and is strongly depressed by departures from ideal stoichiometry.
Abstract: A systematic investigation of the dependence of the Verwey phase transition in magnetite on the metal‐to‐oxygen ratio, by thermomagnetic analysis of the initial permeability, reveals that the transition temperature is a maximum for pure stoichiometric Fe3O4 and is strongly depressed by departures from ideal stoichiometry Homogeneous single crystalline samples were prepared by subsolidus controlled oxygen fugacity annealing at 1400 °C Heat capacity measurements by relaxation calorimetry techniques indicate a drastic reduction in the entropy, as well as temperature, of the transition with departures from ideal stoichiometry For high levels of cation deficiency, a second, instead of a first‐order, transition is observed
TL;DR: In this article, a simple, three-constant pressure-volumetemperature PVT equation of state was applied to polymer solids, both crystalline and amorphous.
Abstract: A simple, three‐constant pressure‐volume‐temperature PVT equation of state, previously applied to polymer liquids, is applied to polymer solids, both crystalline and amorphous. In terms of reduced variables P=P/B0, V=V/V0, and T=T/T0, the equation P V5=T3/2−ln V fits experimental volume data taken from the literature for 19 polymers to within the accuracy of the measurements, about 0.1%. Using the different sets of reducing parameters for the liquid and glassy states of an amorphous polymer, a second order phase transition is predicted. At zero pressure, this transition temperature T2 lies about 20 K below the glass transition temperature Tg but has a greater pressure dependence. It was also found that the combination of reducing parameters RT0/B0V0 is approximately constant for amorphous and crystalline polymers.
IBM1
TL;DR: In this paper, it was found that, far above the transition temperature, Tc, certain ferroelectric systems show a temperature dependent index of refraction, n(T), that is qualitatively different from ordinary ferroelectrics.
Abstract: It is found that, far above the ferroelectric transition temperature, Tc, certain ferroelectric systems show a temperature dependent index of refraction, n(T), that is qualitatively different from ordinary ferroelectrics. We review measurements in these systems and show how some aspects of this n(T) data can be quantitatively understood. This is done by considering the polarization in these materials to arise from very small localized clusters of a few unit cells far above Tc. The strongly broken long range symmetry allows these effects to occur. Furthermore, we find a one-to-one correspondence between ferroelectrics that show this unusual high temperature behavior and those that show glass-like excitations at very low temperatures; this clarifies the ambiguities in the low temperature heat capacity and thermal conductivity results.
TL;DR: In this article, the dielectric constants along the c'axis of Cs 3 H(SeO 4 ) 2 and its deuterated crystal were measured in a temperature range from 5 K to 460 K.
Abstract: The dielectric constants along the c ' axis of Cs 3 H(SeO 4 ) 2 and its deuterated crystal were measured in a temperature range from 5 K to 460 K. It was found that Cs 3 H(SeO 4 ) 2 undergoes three phase transitions at 451 K, 364 K and 50 K. The dielectric constant of Cs 3 H(SeO 4 ) 2 shows a small peak at 50 K, and it obeys the Curie-Weiss law above 50 K. The transition temperature (50 K) is increased to 168 K by deuteration, showing a large isotope effect, while other two transition temperatures do not change appreciably.
TL;DR: In this article, the use of large volume sealed stainless steel capsules has allowed the measurement of a transition temperature in wool at a range of moisture contents using differential scanning calorimetry.
Abstract: The use of large volume sealed stainless steel capsules has allowed the measurement of a transition temperature in wool at a range of moisture contents using differential scanning calorimetry. Aged wool showed an endothermic peak that disappeared after cooling from above the transition temperature, but was restored with subsequent ageing at ambient temperature. Similar behavior is characteristic of amorphous polymers annealed below their glass transition temperature. Moisture appeared to act as a plasticizer in wool and lowered the transition temperature. At moisture contents of 22% the transition temperature approached 35°C, and the application of this result to the formation of severe wrinkles in wool garments during wear is discussed.
TL;DR: In this paper, the authors used the molecular dynamics technique to simulate patches of solid nitrogen adsorbed on the basal plane of graphite and showed that an isotropic site-site interaction predicts a melting transition 9 K below the experimentally observed temperature and leads to an adorbed liquid patch on melting.
Abstract: The molecular dynamics technique has been used to simulate patches of solid nitrogen adsorbed on the basal plane of graphite. A model of the molecule-surface interaction involving an isotropic site-site interaction predicts a melting transition 9 K below the experimentally observed temperature and leads to an adsorbed liquid patch on melting. By including the anisotropy in the site-site interaction the lateral surface barriers are increased and a site-site potential of the form with γA = 0·4, γR = -1·05 will reproduce the experimental transition temperature. The nature of the phase above the melting transition cannot be determined with certainty. The simulation does not give a uniform density distribution for the anisotropic model, but we speculate that the spreading of the patch occurs on a time-scale longer than the simulation. There is clear evidence for a periodic density fluctuation in the adsorbed liquid associated with the molecule-surface potential.
TL;DR: In this article, a binary ferroelectric liquid-crystal mixture with room-temperature Ferroelectricity and a large spontaneous polarization has been developed and a guest-host-type device was fabricated using the mixture, and some potential problems in the application of the materials to electro-optical switching devices are pointed out on the basis of the optical properties of this device.
Abstract: A binary ferroelectric liquid-crystal mixture having both room-temperature ferroelectricity and a large spontaneous polarization has been developed. The temperature range is from 20°C to 34°C. The spontaneous polarization is almost the same value, 4 nC/cm2, as that in DOBAMBC. Five material constants for the mixture; the transition temperature, spontaneous polarization, helical pitch, tilt angle and birefringence, are reported. A guest-host-type device was fabricated using the mixture, and some potential problems in the application of the materials to electro-optical switching devices are pointed out on the basis of the optical properties of this device.
TL;DR: In this article, the Peierls transition in the quasi-one-dimensional conductor K03MoO3 has been studied to clarify its dynamical nature and the electron correlation problem.
Abstract: The Peierls transition in the quasi-one-dimensional conductor K03MoO3 has been studied to clarify its dynamical nature and the electron correlation problem A giant Kohn anomaly and the central peak in S(q, omega ) were observed The amplitude below the transition temperature Tc was also measured An asymmetry of the elastic diffuse scattering above Tc around the reciprocal point which corresponds to the superlattice point can be explained by taking into account the structure factor of the charge-density wave A detailed type of modulation of Mo atoms is presented by the X-ray study No evidence for the correlation effect was observed and the transition of K03MoO3 seems to be explained by a simple band picture
TL;DR: The existence of a TiSi2 phase in the C49 (ZrSi2) structure prior to formation of the stable low resistivity C54 (C54) structure has been justified for Ti-Si thin film diffusion couples after low temperature anneal.
Abstract: The existence of a TiSi2 phase in the C49 (ZrSi2) structure prior to formation of the stable low resistivity C54 TiSi2 structure has been justified for Ti-Si thin film diffusion couples after low temperature (500°C to 650°C) anneal The transition temperature (Ttr) to the C54 phase is shown to be dependent on layer thickness, thinner films yielding higher Ttr We could not detect an influence of oxygen on Ttr Moreover the growth rate of C49 TiSi2 is independent of oxygen contamination in the Ti layer up to a mean concentration of 23 at% It is postulated that the transition from the C49 to the C54 phase actually is a recrystallization process
TL;DR: In this article, the authors measured the heat capacity (C p ) of quartz near the α-β phase transition temperature, and confirmed the existence of the intermediate phase (IP) was confirmed.
Abstract: The heat capacity ( C p ) of quartz was measured by AC calorimetry near the α-β phase transition temperature. The existence of the intermediate phase (IP) was confirmed. A sharp increase of C p was observed at T C , the lower transition temperature. The value of T C in heating runs (HR) was higher than that in cooling runs (CR) by about 0.9 K. A hump of C p was clearly observed at T Q , the higher transition temperature in CR and also in HR of a special heating cycle without passing through T C . It was obscure, however, in the ordinary HR because of the hysteresis. The temperature range of IP was 1.15±0.05 K in CR, which is significantly narrower than the range where the X-ray satellite reflections are observable.
TL;DR: In this paper, a Hall coefficient and an electrical conductivity of NbO 2 were measured just below the metal-insulator transition temperature and it was concluded that the conduction is mainly a band conduction of large polarons above 550 K with an energy gap decreasing to zero toward the transition.
Abstract: A Hall coefficient and an electrical conductivity of NbO 2 were measured just below the metal-insulator transition temperature. It is concluded that the conduction is mainly a band conduction of large polarons above 550 K with an energy gap decreasing to zero toward the transition. A reflectivity measurement was consistent with the narrowing of the gap.
TL;DR: In this paper, micro-indentation sizes, dislocation rosette sizes and median/radial crack lengths were measured on the surface of germanium crystals of three different dopings (intrinsic, heavily-doped p-type and heavily doped n-type) over the temperature range 20 to 420°C.
Abstract: Vickers micro-indentation tests have been performed in the temperature range 20 to 420° C on the {0 0 1} surfaces of germanium crystals of three different dopings: “intrinsic”, heavily doped p-type and heavily doped n-type. Indentation sizes, dislocation rosette sizes and median/radial crack lengths were measured. Rosette sizes were found to depend strongly on doping, being respectively larger and smaller than in intrinsic material for n-type and p-type specimens, over the temperature range 20 to 420° C. This result correlates well with dislocation velocity measurements in germanium. Indentation size (hardness) was found to vary with doping above ~ 300° C, hardness increasing from n-type through intrinsic to p-type material. Crack lengths, as a function of temperature, showed a sharp transition (to much shorter crack lengths) at a well-defined temperature; this ductile/brittle transition temperature was found to depend on doping, being lowest for n-type (~ 290° C) and highest for p-type (~ 400° C). This is the first observation of a relation between a fracture parameter and bulk electronic doping.
TL;DR: An anisotropic softening of the acoustic mode in the ferroelastic phase transition of LaNbO 4 has been observed by the Brillouin scattering experiment as discussed by the authors.
Abstract: An anisotropic softening of the acoustic mode in the ferroelastic phase transition of LaNbO 4 has been observed by the Brillouin scattering experiment. The transverse mode propagating along a direction deviated from the crystal axis by 23° in the a b -plane shows a complete softening at the transition temperature T 0 . The direction is parallel or normal to the ferroelastic domain boundary as predicted by the phenomenological analysis of the phase transition from 4/ m to 2/ m symmetry. Thc temperature dependence of the elastic susceptibility is well described by the classical indices γ=γ'=1 in both phases, suggesting a typical proper ferroelastic transition.
TL;DR: In this article, the Schawlow-Devlin self-inductance method of direct measurement of the penetration depth has been adopted for layered superconductors, for which this method is especially suitable because the calibration procedure is very simple for them.
Abstract: The Schawlow-Devlin self-inductance method of direct measurement of the penetration depth has been adopted for layered superconductors, for which this method is especially suitable because the calibration procedure is very simple for them. The ratio of coherence length to mean free path xi/sub 0//l within the layer is deduced from the penetration depth measured by the new method and the resistivity, and is found to be 0.14 for a pure crystal of 2H-NbSe/sub 2/ with RRR of about 50. The effect of the CDW transition on the superconductivity in 2H-NbSe/sub 2/ is investigated through the measurement of the penetration depth. In addition to pure crystals, some modified crystals are investigated where the CDW transition is suppressed. The London penetration depth lambda/sub L/(0) as well as the superconducting transition temperature T/sub c/ show a slight but apparent increase with decreasing CDW transition temperature T/sub D/ of the samples. Both behaviors may be explained by a decrease in the reduction of N(E/sub f/) due to the suppression of the CDW transitions, where N(E/sub F/) is the density of states at the Fermi energy. The result also suggests a systematic increase of the ratio of effective mass to electron density m/sub parallel//n ofmore » the electron system with the suppression of the CDW transition.« less