Large Temperature Interval Research Articles

Orientation and temperature dependence of superelasticity caused by reversible γ-α′ martensitic transformations in FeNiCoAlTa single crystals

Reversible thermoelastic γ-α′ martensite transformations (MTs) have been studied in Fe-28%Ni-17%Co-11.5%Al-2.5%Ta (at. %) single crystals under cooling/heating and loading conditions. It is established that the precipitation of dispersed γ′ phase particles with an average size of d ≤ 5 nm leads to thermoelastic γ-α′ MTs with a small temperature hysteresis (ΔT = 20 K). The [001] oriented crystals favor the attaining of maximum superelasticity (SE) ɛSE = 6.8%, minimum mechanical hysteresis Δσ = 130 MPa, and large SE temperature interval ΔTSE = 130 K. In contrast, in the [111] oriented crystals, small values of ɛSE = 2.0%, high values of Δσ = 350–400 MPa and narrow SE interval ΔTSE = 55 K are found.

Heat Capacity Studies of Nanocrystalline Magnetite (Fe3O4)

The Verwey transition in magnetite (Fe3O4) has been studied extensively with a wide assortment of experimental techniques to investigate the effects of impurities, oxygen stoichiometry, and crystal quality; however, no studies have tested the effects of crystal size on the Verwey transition. In this study, the heat capacity of a magnetite powder with an average crystallite size of 13 nm was measured in the temperature range of 0.5−350 K. No obvious anomaly was observed in the heat capacity in the vicinity of 120 K, yet the measurements exhibited unusual thermal behaviors between 50 and 90 K with relaxation times increasing from an average of 25 min to as much as 5 h in this temperature interval. The behavior is typical of a phase transition, so the lack of a distinct anomaly suggests either the phenomenon is spread out over a large temperature interval with little enthalpy or an insulating phase with different thermal conductivities appears. The heat capacity below 90 K was dependent on cooling rate with an inconsistent anomaly found below 4 K. The results suggest that the Verwey transition has a particle-size dependence. Additionally, theoretical fits below 15 K suggest that magnetite nanoparticles display anisotropic ferrimagnetic behavior and a superparamagnetic contribution to the heat capacity which are properties not observed in bulk magnetite.

Selection of ULIRGs in infrared and submm surveys

We examine the selection characteristics of infrared and sub-mm surveys with IRAS, Spitzer, BLAST, Herschel and SCUBA and identify the range of dust temperatures these surveys are sensitive to, for galaxies in the ULIRG luminosity range (12<log(LIR)<13), between z=0 and z=4. We find that the extent of the redshift range over which surveys are unbiased is a function of the wavelength of selection, flux density limit and ULIRG luminosity. Short wavelength (<200{\mu}m) surveys with IRAS, Spitzer/MIPS and Herschel/PACS are sensitive to all SED types in a large temperature interval (17-87K), over a substantial fraction of their accessible redshift range. On the other hand, long wavelength (>200{\mu}m) surveys with BLAST, Herschel/ SPIRE and SCUBA are significantly more sensitive to cold ULIRGs, disfavouring warmer SEDs even at low redshifts. We evaluate observations in the context of survey selection effects, finding that the lack of cold ULIRGs in the local (z<0.1) Universe is not a consequence of selection and that the range of ULIRG temperatures seen locally is only a subset of a much larger range which exists at high redshift. We demonstrate that the local luminosity-temperature (L-T) relation, which indicates that more luminous sources are also hotter, is not applicable in the distant Universe when extrapolated to the ULIRG regime, because the scatter in observed temperatures is too large. Finally, we show that the difference between the ULIRG temperature distributions locally and at high redshift is not the result of galaxies becoming colder due to an L-T relation which evolves as a function of redshift. Instead, they are consistent with a picture where the evolution of the infrared luminosity function is temperature dependent, i.e. cold galaxies evolve at a faster rate than their warm counterparts.

Thermotropic and Thermo-optical Properties of Nematic Mesophase at Direct and Reverse Phase Transitions

Comparative investigations of the thermo-optical, thermotropic, and thermo-morphologic properties of aligned and non-aligned textures in the nematic mesophase over a large temperature interval and in regions of direct and reverse phase transitions between the nematic mesophase and the isotropic liquid have been carried out. The character of the optical transmission and adsorption coefficient has been compared with that of the texture transformations. Nonlinearity of the thermo-optical and thermotropic behavior at the nematic mesophase–isotropic liquid and isotropic liquid–nematic mesophase phase transitions has been observed. Differences in the temperatures of phase transitions for the aligned and non-aligned textures of the nematic liquid crystals have been found.

Nonlinear thermotropic and thermo-optical behaviour of planar oriented textures in nematic liquid crystals at phase transitions

Thermotropic, thermo-morphologic and thermo-optical properties of the planar oriented nematic liquid crystals have been investigated for large temperature interval and especially for the direct nematic - isotropic liquid and the reverse isotropic liquid - nematic phase transition regions. Temperature dependences of the optical transmission, absorption coefficient and optical birefringence for both heating and cooling processes were obtained. Nonlinear thermotropic and thermo-optical behaviour and temperature hysteresis for the optical transmission, absorption coefficient and optical birefringence at the phase transitions has been found.

Evidence from anisotropic penetration depth for a three-dimensional nodal superconducting gap in single-crystallineBa(Fe1−xNix)2As2

The London penetration depth, $\lambda$, is directly related to the density, $n_{s}$, of the Cooper pairs ($\lambda^{2}\propto 1/n_{s}$) and its variation with temperature provides valuable insight into the pairing mechanism. Here we study the evolution with doping of the temperature dependence of the in-plane ($\lambda_{ab}$) and out-of-plane ($\lambda_{c}$) penetration depths in single crystals of electron-doped Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$. As is the case for other pnictides, $\lambda(T) \sim T^n$ over the whole doping range and this behavior extends down to at least $T=T_c/100$, setting a very small upper limit on the gap minimum. Furthermore, in the overdoped regime: 1) the exponent $n$ becomes substantially smaller than 2, which is incompatible with the models that explain power-law behavior to be due to scattering; 2) the exponent $n$ becomes anisotropic, with $\lambda_{c}(T)$ showing a clear $T$-linear behavior over a large temperature interval. These findings suggest that in the overdoped regime the superconducting gap in iron-based pnictide superconductors develops nodal structure, which unlike in the cuprates, cannot be understood within a two-dimensional picture.

Compositionally graded ferroelectric multilayers for frequency agile tunable devices

Recently, there has been significant interest toward the development of tunable dielectric materials for voltage-controlled, frequency-agile phase shifters and filters operating in the microwave regime. The fundamental challenge in designing materials systems for such tunable devices is the simultaneous requirement of high dielectric tunability (>40%) over a large temperature interval (−10 °C to +90 °C) coupled with low dielectric losses (between 3.0 dB and 4.0 dB in operational bandwidths ranging from several hundred MHz up to 30 or more GHz). We show that a high- and temperature-insensitive tunability can be realized in compositionally graded ferroelectrics and provide a brief review of the results of experimental and theoretical studies on the dielectric properties of Barium Strontium Titanate (Ba1−xSrxTiO3 or BST) multilayer heterostructures. Theoretically, we discuss the role of thermal stresses on the dielectric properties using a non-linear thermodynamic model coupled with basic electrostatic considerations to describe the interlayer interactions between the ferroelectric layers. We show that the thermal strains arising from the thermal expansion coefficient mismatch between the multilayered film and the substrate may have a significant effect on the dielectric permittivity and tunability of BST multilayers. Experimentally, compositionally graded BST multilayers (5 mol% MgO doped and undoped) were grown via metallo-organic solution deposition (MOSD) on Pt–Si substrates and electrically characterized. Optimum conditions were found to exist in BST multilayers consisting of three distinct layers of ~220 nm nominal thickness with compositions corresponding to Ba0.60Sr0.40TiO3 (BST 60/40), BST 75/25, and BST 90/10. At room temperature, the BST heterostructure has a small-signal dielectric permittivity of 360 with a dissipation factor of 0.012 and a dielectric tunability of 65% at 444 kV/cm. These properties exhibit minimal dispersion as a function of temperature ranging from 90 °C to −10 °C. Our results also show that MgO doping improves dielectric loss (tan δ = 0.008), but results in a moderate dielectric tunability of 29% at 444 kV/cm. Electrical measurements at microwave frequencies display a decrease in the dielectric permittivity and tunability for both undoped and MgO-doped BST multilayers. At 10 GHz, the dielectric response, tunability, and the loss characteristics for graded undoped BST are 261, 25% (at 1,778 kV/cm), and 0.078, respectively, and 189 and 15% (at 1,778 kV/cm), and 0.039, respectively, for the MgO-doped graded BST.

How Does Solute-Polarization Affect the Hydrophobic Hydration of Methane?

Abstract We simulate the solubility and solvation free energy of methane dissolved in water at infinite dilution. Molecular dynamics simulations of TIP4P-Ew model water are carried out at ambient pressure conditions over a large temperature interval, ranging from 250 K to 370 K. Solvation free energies are determined using the Widom particle insertion method. The fitted temperature dependent data is used to calculate solvation enthalpies, entropies, as well as the heat capacity of solvation. In particular we study the effect of polarizability of methane on those thermodynamic parameters. Solute polarization leads to a lowering of the solvation free energy at 298 K to 8.3 kJ mol−1, almost exactly matching the experimental value. A close inspection of the enthalpic and entropic contributions, however, reveals that this coincidence is a consequence of a compensation of enthalpic and entropic contributions, each of them deviating even larger from their respective experimental values. Surprisingly, the solute polarizability is apparently affecting the solvation entropy more strongly than the solvation enthalpy, leading to an about 5 J K−1 mol−1 smaller (less negative) solvation entropy compared to the non-polarizable model. The solute-water radial distribution functions of the polarizable particle reveals significant modifications, favoring small distances, as well as structural changes, very similar to those caused by a temperature increase. This is suggesting that the reduced negative solvation entropy of a polarizable methane particle is related to a more disordered, "high-temperature"-like hydration shell.

Peculiarities of inversion walls and singular points in oriented textures of nematic mesophase

AbstractIn this work the nature and peculiarities of the inversion walls and singular points, which can spontaneously arise or can be stimulated in the homeotropic and planar oriented textures of the thermotropic nematogens, have been investigated for large temperature interval. The interaction force and mean approach velocity of the singular points, having opposite optical sign, have been calculated. The optical mappings and sketches of the inversion walls and singularities, taking place in the oriented textures of the nematogens, are presented. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

High density quark matter in the Nambu–Jona-Lasinio model with dimensional versus cutoff regularization

We investigate color superconducting phase at high density in the extended Nambu--Jona-Lasinio model for two-flavor quarks. Because of the nonrenormalizability of the model, physical observables may depend on the regularization procedure; that is why we apply two types of regularization, the cutoff and the dimensional one to evaluate the phase structure, the equation of state, and the relationship between the mass and the radius of a dense star. To obtain the phase structure we evaluate the minimum of the effective potential at finite temperature and chemical potential. The stress tensor is calculated to derive the equation of state. Solving the Tolman-Oppenheimer-Volkoff equation, we show the relationship between the mass and the radius of a dense star. The dependence on the regularization is found not to be small, interestingly. The dimensional regularization predicts color superconductivity phase at rather large values of $\ensuremath{\mu}$ (in agreement with perturbative QCD in contrast to the cutoff regularization), in the larger temperature interval, the existence of heavier and larger quark stars.

Correlations in hot dense helium

Hot dense helium is studied with first-principle computer simulations. By combining path integral Monte Carlo and density functional molecular dynamics, a large temperature and density interval ranging from 1000 to 1 000 000 K and 0.4 to 5.4 g cm−3 becomes accessible to first-principle simulations and the changes in the structure of dense hot fluids can be investigated. The focus of this paper is on pair correlation functions between nuclei, between electrons, and between electrons and nuclei. The density and temperature dependence of these correlation functions is analyzed in order to describe the structure of the dense fluid helium at extreme conditions.

Temperature dependence of Eu-related EPR spectra in CsBr:Eu needle image plates

Vacuum-deposited CsBr needle plates doped with ${\text{Eu}}^{2+}$ have been investigated with $Q$ $(\ensuremath{\sim}34\text{ }\text{GHz})$ and $W$ $(\ensuremath{\sim}95\text{ }\text{GHz})$ band electron paramagnetic resonance in a large temperature interval (4 K: room temperature). At low temperatures $(&lt;35\text{ }\text{K})$, two Eu-related centers were found with different symmetry (tetragonal and orthorhombic), while in earlier studies at room temperature only one center was found with tetragonal symmetry. Possible models for the three defects are investigated, taking into account their temperature behavior, their symmetry, and the atypical values of their zero-field splitting parameters.

Ba(Zn1/3Ta2/3)O3 Ceramics for Microwave and Millimeter‐wave Applications

The Ba(Zn(1/3)Ta(2/3))O(3) (BZT) ceramic samples were prepared by solid-state reaction and sintered in the range 1550-1650 degrees C for 2 h. Several methods--X-ray diffraction (XRD) and scanning electron microscopy (SEM)--were used for structural and morphological characterization. The unit cell distortion and the presence of the secondary phase content were studied by XRD. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was noticed with the increase of the sintering temperature. SEM investigations revealed polyhedral well-faceted grains and large grain size distribution. The dielectric properties in the microwave range were measured at room temperature and at 1 kHz on a large temperature interval (+/-150 degrees C). The dielectric parameters were correlated with morphological and structural properties. Ceramic samples were annealed at 1410 degrees C for 30 h to improve the microwave properties. The dielectric constant of BZT samples measured at 6 GHz and at 1 kHz was between 27 and 28 on the whole temperature range, that is, typical values for BZT material. The temperature coefficient of the resonance frequency at 6 GHz exhibits positive values less than 6 ppm/degrees C.

Low temperature electrical transport properties of carbon matrix containing iron nanoparticles

We present a comparative study of the low temperature electrical transport properties of the carbon matrix containing iron nanoparticles and the films. The conductivity of the nanoparticles located just below the metal-insulator transition exhibits metallic behavior with a logarithmic temperature dependence over a large temperature interval. The zero-field conductivity and the negative magnetoresistance, showing a characteristic upturn at liquid helium temperature, are consistently explained by incorporating the Kondo relation and the two dimensional electron-electron interaction. The films, in contrast, exhibit a crossover of the conductivity from power-law dependence at high temperatures to an activated hopping law dependence in the low temperature region. The transition is attributed to changes in the energy dependence of the density of states near the Fermi level. The observed magnetoresistance is discussed in terms of quantum interference effect on a three-dimensional variable range hopping mechanism.

Effect of quantum critical fluctuations on the amplitude of de Haas-van Alphen oscillations

A simple model of spinless fermions with nested Fermi surface leading to a charge density wave is considered. A quantum critical point (QCP) is obtained by tuning the nesting mismatch of the Fermi surface so that the critical temperature is zero. The amplitudes of de Haas-van Alphen oscillations are calculated using a Lifshitz-Kosevich expression modified by the quasi-particle selfenergy. The amplitudes are considerably reduced by the interaction. The effects of the QCP extend over a large temperature interval.

Phase Transformations During the Reaction Heat Treatment of Internal Tin Nb&lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;$_{3}$&lt;/tex&gt; &lt;/formula&gt;Sn Strands With High Sn Content

The phase transformations that occur during the reaction heat treatment (HT) of Nb3Sn superconductors depend on the overall elemental composition of the strand subelements. In the case of modern high Jc strands with a relatively low Cu content, liquid phases are present during large temperature intervals and phases that can be detrimental for the microstructural and microchemical homogeneity of the fully reacted strand are formed. We report synchrotron X-ray diffraction measurements during in-situ reaction HT of a state-of-the-art high Jc Nb3 Sn internal tin strand. In this strand, Cu3Sn is formed upon Cu 6Sn 5 decomposition at 415degC, a Sn-rich ternary Cu-Nb-Sn phase is detected in the approximate temperature interval 345degC-575degC, and NbSn2 is present in the temperature interval 545degC-630degC. The formation of voids in the strand subelements has been monitored by synchrotron microtomography during in-situ reaction HT.

Thermophysical Properties of Molten Yttrium Measured by Non-contact Techniques

Understanding the nature and behavior of liquid metals requires accurate values of their physical properties (e.g., density, surface tension, viscosity). However, maintaining samples of matter in their liquid phases, in particular under supercooled conditions, is a great challenge when dealing with refractory metals. This is due mainly to their high melting temperatures (e.g., 3,695 K for W), their high vapor pressure, and the risk of melt contamination with a support or crucibles. Electrostatic levitation, laser heating in vacuum, and non-contact characterization techniques circumvented these difficulties and allowed the determination of the properties of several metals in their liquid state, above their melting temperature as well as in their supercooled phase. In this work, several thermophysical properties were successfully measured with an electrostatic levitation furnace under vacuum conditions. For the first time, density and viscosity data of yttrium were reported over large temperature intervals in the liquid phase. Over the 1,560 to 2,100 K temperature span, the density can be expressed as $\rho (T)=4.15\times 10^3-0.21\, (T - T_{\rm m})$ (kg·m − 3) with T m = 1,796 K, yielding a volume expansion coefficient of 5.1 × 10 − 5 K − 1. In addition, the surface tension can be expressed as $\sigma \left( T \right)=8.04\times 10^2-0.05\,(T - T_{\rm m})$ (mN·m − 1) and the viscosity as $\eta \left( T \right)=0.00287\,\exp \left[ {{1.1\times 10^5} \mathord{\left/ {\vphantom {{1.1\times 10^5} {\left( {\mbox{RT}} \right)}}} \right. \kern-\nulldelimiterspace} {\left( {\mbox{RT}} \right)}} \right]$ mPa·s over the 1,830 to 2,070 K interval. The results, in particular those for viscosity, suggest that performing similar experiments in microgravity could improve the accuracy of the measurements.

Relaxation processes of water confined to AlMCM-41 molecular sieves. Influence of the hydroxyl groups of the pore surface

A series of AlMCM-41 molecular sieves was prepared with constant composition (Si/Al = 14.7) and presumably same pore structure but different pore diameters (from 2.3 to 4.6 nm). The pore size distribution is narrow for each sample. The rotational fluctuations of water molecules confined inside the pores were investigated applying broadband dielectric spectroscopy (10(-2)-10(7) Hz) over a large temperature interval (213-333 K). A relaxation process, slower than that expected for bulk water, was observed which is assigned to water molecules forming a surface layer on the pore walls. The estimated relaxation time has an unusual non-monotonic temperature dependence, which is rationalized and modeled assuming two competing processes: rotational fluctuations of constrained water molecules and defect formation (Ryabov model). This paper focuses on the defects and notably the influence of the hydroxyl groups of the pore walls. The Ryabov model is fitted to the data and characteristic parameters are obtained. Their dependence on pore diameter is considered for the first time. The found results are compared with those obtained for other types of molecular sieves and related materials.

Characterization and investigation of the mesogenic, thermo-morphologic and thermotropic properties of new chiral ( S)-5-octyloxy-2-[{4-(2-methylbuthoxy)-phenylimino(methyl]phenol liquid crystalline compound

Synthesis, characterization and investigation of the mesogenic, thermo-morphologic and thermotropic properties of a new chiral liquid crystalline compound are presented in this work. This new compound has prolate molecules and exhibits the chiral smectic C* mesophase in a sufficiently large temperature interval. Two types of solid crystalline phases have been found in this compound. Typical textures and temperatures of the direct and reverse phase transitions, taking place in the compound, are given. Typical peculiarities for the first-order transition between the smectic C* mesophase and isotropic liquid have been observed.

Mg6Ni formation in rapidly quenched amorphous Mg–Ni alloys

The crystallization behavior of two Mg-rich near eutectic Mg–Ni amorphous alloys (Mg88Ni12 and Mg87Ni12Y1) was compared. The influence of Y substitution for Mg and quenching rate on the crystallization process was studied. Formation of the metastable nanocrystalline Mg∼6Ni phase as well as its decomposition were mostly studied and compared to the crystallization behavior of the recently investigated Mg83Ni17 glass with a composition corresponding to the Mg∼6Ni intermetallic compound [T. Spassov, P. Solsona, S. Surinach, M.D. Baro, J. Alloys Compd. 345 (2002) 123–129, T. Spassov, S. Todorova, V. Petkov, J. Non-Cryst. Solids, submitted for publication]. The metastable compound decomposes in a large temperature interval with a very broad exothermic effect for both alloys. Due to the very low rate of transformation its DSC peak and the associated enthalpy change can be detected only at high heating rates (>40 K/min). The isothermal crystallization kinetics analysis revealed a three-dimensional linear growth of existing nuclei mechanism for the Mg∼6Ni formation in both Mg87Ni12Y1 and Mg88Ni12 glasses, appearing as a second crystallization reaction after the primary αMg formation. The activation energies of Mg∼6Ni nanocrystallization in both glasses were determined and compared with that in Mg83Ni17.