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Thermal Hysteresis (thermal + hysteresi)
Selected AbstractsThermal hysteresis of the phase-transition temperature of single-crystal GdB6PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006M. Reiffers Abstract The phase transition of a single-crystal sample of GdB6, oriented along the ,111, axis using the temperature dependence of electrical resistivity , (T ), susceptibility , (T ) and heat capacity C (T ) under an applied magnetic field was studied. , (T ) has shown 2 anomalies , a sharp drop at TN1 = 15.4 K and a small maximum at TN2 = 9.1 K with thermal hysteresis effect. , (T ) shows the anomalies at both transition temperatures. C (T ) shows similar thermal hysteresis effect at TN2. The small maximum at TN2 decreases its position to lower temperatures with increasing magnetic field. The peak at TN1 is practically unaffected by an applied magnetic field up to 9 T. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical, Magnetic and Structural Properties of the Spin-Crossover Complex [Fe(btr)2(NCS)2]·H2O in the Light-Induced and Thermally Quenched Metastable StatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2007Vincent Legrand Abstract [Fe(btr)2(NCS)2]·H2O [btr = 4,4,-bis(1,2,4-triazole)] is thearchetype of highly cooperative and low-dimensional spin-crossover complexes, which exhibit low-spin (LS) to high-spin (HS) light-induced conversion at very low temperature. The structural reorganizations related to the light-induced and thermally induced LS,HS transitions were characterized by single-crystal X-ray diffraction below the relaxation temperature (T = 15 K < TLIESST) and at 130 K within the thermal hysteresis loop. We show that the LIESST and thermal spin transitions lead to the same structural variations, namely an elongation of the Fe,N bonds by 0.18 Å (Fe,NNCS) and 0.20 Å (Fe,Nbtr), on going from LS to HS, together with a reorientation of the NCS group by nearly 13°. The atomic displacement amplitudes, derived from the crystal structures, indicate lattice vibration modes of larger amplitudes and correlatively lower vibration frequencies in the HS state. The deformation of the crystal lattice as a function of temperature and laser excitation was quantitatively analyzed in terms of the HS and LS thermal-expansion (,HS and ,LS) and spin-transition spontaneous-strain (,) tensors. The eigendirections and eigenvalues of the , and , tensors correlate well with the weak and strong interactions in the solid and are responsible for the high cooperativity and low-dimensional behaviour. Magnetic and spectroscopic measurements were performed in all the different spin states and related to the structural findings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] A Study of the Electronic Spin-State Crossover in {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2004Daniel L. Reger Abstract The synthesis, structural, magnetic, and Mössbauer spectroscopic properties of {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 are reported. The single-crystal X-ray structure results indicate that at 150 K {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 has a structure which is very similar to that observed at 220 K for the trigonally distorted octahedral, high-spin {Fe[HC(3,5-Me2pz)3]2}(BF4)2 complex. Both the magnetic and Mössbauer spectroscopic results indicate that {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 is high spin between 160 and 296 K. Upon cooling, {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 exhibits a complete electronic spin-state crossover from the high-spin to the low-spin state at approximately 110 K and remains completely low spin down to 4.2 K; upon subsequent warming from 4.2 K, the transition from the low-spin to the high-spin state occurs at 148 to 150 K. {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 exhibits a rather large thermal hysteresis of 38 K in its spin-state crossover. Thus, {Fe[HC(3,4,5-Me3pz)3]2}(BF4)2 behaves differently from both {Fe[HC(3,5-Me2pz)3]2}(BF4)2, which is known to show a unique spin-state crossover of one-half of its iron(II) ions associated with a phase transition, and Fe[HB(3,4,5-Me3pz)3]2, which is known to remain high-spin even upon cooling to 1.7 K. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Co-operative effect of the isoforms of type III antifreeze protein expressed in Notched-fin eelpout, Zoarces elongatus KnerFEBS JOURNAL, Issue 2 2005Yoshiyuki Nishimiya We found that Notched-fin eelpout, which lives off the north east coast of Japan, expresses an antifreeze protein (AFP). The liver of this fish contains DNAs that encode at least 13 type III AFP isoforms (denoted nfeAFPs). The primary sequences of the nfeAFP isoforms were categorized into SP- and QAE-sephadex binding groups, and the latter were further divided into two subgroups, QAE1 and QAE2 groups. Ice crystals observed in HPLC-pure nfeAFP fractions are bipyramidal in shape with different ratios of c and a axes, suggesting that all the isoforms are able to bind ice. We expressed five recombinant isoforms of nfeAFP and analyzed the thermal hysteresis (TH) activity of each as a function of protein concentration. We also examined the change in activity on mixing the isoforms. TH was estimated to be 0.60 °C for the QAE1 isoform, 0.11 °C for QAE2, and almost zero for the SP isoforms when the concentrations of these isoforms was standardized to 1.0 mm. Significantly, the TH activity of the SP isoforms showed concentration dependence in the presence of 0.2 mm QAE1, indicating that the less active SP isoform becomes ,active' when a small amount of QAE1 is added. In contrast, it does not become active on the addition of another SP isoform. These results suggest that the SP and QAE isoforms of type III AFP have different levels of TH activity, and they accomplish the antifreeze function in a co-operative manner. [source] Developmental and environmental regulation of antifreeze proteins in the mealworm beetle Tenebrio molitorFEBS JOURNAL, Issue 21 2000Laurie A. Graham The yellow mealworm beetle, Tenebrio molitor, contains a family of small Cys-rich and Thr-rich thermal hysteresis proteins that depress the hemolymph freezing point below the melting point by as much as 5.5 °C (,T = thermal hysteresis). Thermal hysteresis protein expression was evaluated throughout development and after exposure to altered environmental conditions. Under favorable growth conditions, small larvae (11,13 mg) had only low levels of thermal hysteresis proteins or thermal hysteresis protein message, but these levels increased 10-fold and 18-fold, respectively, by the final larval instar (> 190 mg), resulting in thermal hysteresis >,3 °C. Exposure of small larvae (11,13 mg) to 4 weeks of cold (4 °C) caused an ,,20-fold increase in thermal hysteresis protein concentration, well in excess of the less than threefold developmental increase seen after 4 weeks at 22 °C. Exposure of large larvae (100,120 mg) to cold caused 12-fold and sixfold increases in thermal hysteresis protein message and protein levels, respectively, approximately double the maximum levels they would have attained in the final larval instar at 22 °C. Thus, thermal hysteresis increased to similar levels (> 4 °C) in the cold, irrespective of the size of the larvae (the overwintering stage). At pupation, thermal hysteresis protein message levels decreased >,20-fold and remained low thereafter, but thermal hysteresis activity decreased much more slowly. Exposure to cold did not reverse this decline. Desiccation or starvation of larvae had comparable effects to cold exposure, but surprisingly, short daylength photoperiod or total darkness had no effect on either thermal hysteresis or message levels. As all environmental conditions that caused increased thermal hysteresis also inhibited growth, we postulate that developmental arrest is a primary factor in the regulation of T. molitor thermal hysteresis proteins. [source] Shape Memory Materials: Identification of Quaternary Shape Memory Alloys with Near-Zero Thermal Hysteresis and Unprecedented Functional Stability (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Mater. On page 1917, R. Zarnetta et al. report that for the reversible martensitic transformation in shape memory alloys the compatibility at the austenite/martensite interface is directly related to the width of the thermal hysteresis and to the functional stability. A "perfect" compatibility results in the growth of twinless martensite (blue) within the austenite (red), as shown in the TEM image for a Ti50Ni39Pd11 shape memory alloy (image provided courtesy of R. Delville). [source] Identification of Quaternary Shape Memory Alloys with Near-Zero Thermal Hysteresis and Unprecedented Functional StabilityADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Robert Zarnetta Abstract Improving the functional stability of shape memory alloys (SMAs), which undergo a reversible martensitic transformation, is critical for their applications and remains a central research theme driving advances in shape memory technology. By using a thin-film composition-spread technique and high-throughput characterization methods, the lattice parameters of quaternary Ti,Ni,Cu,Pd SMAs and the thermal hysteresis are tailored. Novel alloys with near-zero thermal hysteresis, as predicted by the geometric non-linear theory of martensite, are identified. The thin-film results are successfully transferred to bulk materials and near-zero thermal hysteresis is observed for the phase transformation in bulk alloys using the temperature-dependent alternating current potential drop method. A universal behavior of hysteresis versus the middle eigenvalue of the transformation stretch matrix is observed for different alloy systems. Furthermore, significantly improved functional stability, investigated by thermal cycling using differential scanning calorimetry, is found for the quaternary bulk alloy Ti50.2Ni34.4Cu12.3Pd3.1. [source] Recent Progress in Exploring Magnetocaloric MaterialsADVANCED MATERIALS, Issue 45 2009B. G. Shen Abstract The magnetic refrigeration technique based on the magnetocaloric effect (MCE) has attracted increasing interest because of its high efficiency and environment friendliness. In this article, our recent progress in exploring effective MCE materials is reviewed with emphasis on the MCE in the LaFe13,xSixbased alloys discovered by us. These alloys show large entropy changes over a wide temperature range near room temperature. The effects of magnetic rare-earth doping, interstitial atoms and high pressure on the MCE have been systematically studied. Special issues, such as appropriate approaches to determining the MCE associated with the first-order magnetic transition, the depression of magnetic and thermal hysteresis, and the key factors determining the magnetic exchange in alloys of this kind, are discussed. The applicability of giant MCE materials to magnetic refrigeration near ambient temperature is evaluated. A brief review of other materials with significant MCE is also presented. [source] Supramolecular control of spin-crossover phenomena in lipophilic Fe(II)-1,2,4-triazole complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2006Keita Kuroiwa Abstract The spin-crossover properties of lipophilic, supramolecular Fe(II) complexes bridged by 4-(3-dodecyloxy)propyl-1,2,4-triazole [Fe(II)(1)3Cl2] were investigated in chloroform and cast films. A purple low-spin (LS) complex in a powdery form was transformed into pale yellow high-spin (HS) polymers by dissolution in chloroform. The formation of lipophilic molecular wires in chloroform was observed with transmission electron microscopy. The casting of chloroform solutions onto solid supports produced purple, transparent films (LS state). The cast films exhibited sluggish spin-crossover (LS , HS) behavior without thermal hysteresis. On the other hand, the cocasting of equimolar dodecanol or tetradecanol with Fe(II)(1)3Cl2 produced composite films in which alcohol molecules were bound to the complex by ionic hydrogen bonding (ROH···Cl,) and van der Waals interactions. At room temperature, the cast films exhibited regular lamellar structures before and after alcohol doping; this was confirmed by wide-angle X-ray diffraction measurements. Interestingly, the Fe(II)(1)3Cl2/CnOH (n = 12 or 14) ternary films showed a reversible abrupt spin crossover accompanied by thermal hysteresis. The observed bistability was related to dynamic structural transformations between lamellar and hexagonal structures. This study provides a novel supramolecular approach to designing spin-crossover polymer films with controlled thermal bistability. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5192,5202, 2006 [source] Dielectric anomaly of tungsten trioxide WO3 with giant dielectric constantPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2006Toshikazu Hirose Abstract Temperature dependences of the dielectric constant and the dielectric dispersion of a WO3 single crystal have been measured in the temperature range from ,180 °C to 100 °C and at frequencies from 20 Hz to 1 MHz. A large dielectric anomaly has been observed at 16.2 °C on heating, and the peak value of the dielectric constant is as large as about 105. The anomaly has large thermal hysteresis, long relaxation time and large dielectric dispersion. A transition from ferrielectric state to ferroelectric state induced by an electric field has been observed by D,E hysteresis measurement below room temperature. In the triclinic phase, the coexistence of the monoclinic(II) and the monoclinic(I) phases was observed by EPR (ESR) measurements of doped Cr+3 ions. These results suggest that a frustration of the antiferroelectric and ferroelectric states exists at the dielectric anomaly temperature. The dielectric anomaly can be interpreted as a result of the phase transition between the triclinic phase with micro ferroelectric regions and the antiferroelectric monoclinic(I) phase. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermal hysteresis of the phase-transition temperature of single-crystal GdB6PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006M. Reiffers Abstract The phase transition of a single-crystal sample of GdB6, oriented along the ,111, axis using the temperature dependence of electrical resistivity , (T ), susceptibility , (T ) and heat capacity C (T ) under an applied magnetic field was studied. , (T ) has shown 2 anomalies , a sharp drop at TN1 = 15.4 K and a small maximum at TN2 = 9.1 K with thermal hysteresis effect. , (T ) shows the anomalies at both transition temperatures. C (T ) shows similar thermal hysteresis effect at TN2. The small maximum at TN2 decreases its position to lower temperatures with increasing magnetic field. The peak at TN1 is practically unaffected by an applied magnetic field up to 9 T. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structure,property correlation over five phases and four transitions in Pb5Al3F19ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2003S. C. Abrahams The calorimetric and dielectric properties of Pb5Al3F19 in the five phases stable under ambient pressure are correlated with structure for fuller characterization of each phase. The first-order transition between ferroelectric phase V and antiferroelectric phase IV at TV,IV = 260,(5),K exhibits a thermal hysteresis of 135,(5),K on heating, with a maximum atomic displacement ,(xyz)max = 1.21,(6),Å; the transition from phase IV to ferroelastic phase III at 315,(5),K is also first order but with a thermal hysteresis of 10,(5),K and ,(xyz)max = 0.92,(7) ,Å; that from phase III to paraelastic phase II at 360,(5),K is second order without hysteresis and has ,(xyz)max = 0.69,(4),Å; and the transition from phase II to paraelectric phase I at 670,(5),K is second or higher order, with ,(xyz)max = 0.7,(4),Å. The measured entropy change ,S at TV,IV agrees well with ,S as derived from the increased configurational energy by Stirling's approximation. For all other phase transitions, 0.5 ,,S > 0,J,mol,1,K,1 is consistent with an entropy change caused primarily by the changes in the vibrational energy. The structure of phase III is determined both by group theoretical/normal mode analysis and by consideration of the structures of phases II, IV and V reported previously; refinement is by simultaneous Rietveld analysis of the X-ray and neutron diffraction powder profiles. The structure of prototypic phase I is predicted on the basis of the atomic arrangement in phases II, III, IV and V. The introduction of 3d electrons into the Pb5Al3F19 lattice disturbs the structural equilibrium, the addition of 0.04% Cr3+ causing significant changes in atomic positions and increasing TIV,III by ,15,K. Substitution of Al3+ by 20% or more Cr3+ eliminates the potential minima that otherwise stabilize phases IV, III and II. [source] Nanoparticles of [Fe(NH2 -trz)3]Br2,3,H2O (NH2 -trz=2-Amino-1,2,4-triazole) Prepared by the Reverse Micelle Technique: Influence of Particle and Coherent Domain Sizes on Spin-Crossover PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2009Thibaut Forestier Dr. Abstract By changing the surfactant/water ratio, nanoparticles of the iron(II) spin crossover material, [Fe(NH2 -trz)3]Br2,3,H2O (with NH2 -trz=4-amino-1,2,4-triazole), have been synthesised from 1,,m down to 30,nm (see figure). Magnetic and reflectivity experiments indicate that the critical size for observing a thermal hysteresis in this 1D polymer family is around 50,nm, and powder X-ray diffraction shows that particles of about 30,nm are constituted by about one coherent domain. This paper describes the synthesis of iron(II) spin-crossover nanoparticles prepared by the reverse micelle technique by using the non-ionic surfactant Lauropal (Ifralan D0205) from the polyoxyethylenic family. By changing the surfactant/water ratio, the size of the particles of [Fe(NH2 -trz)3]Br2,3H2O (with NH2trz=4-amino-1,2,4-triazole) can be controlled. On the macroscopic scale this complex exhibits cooperative thermal spin crossovers at 305 and 320,K. We find that when the size is reduced down to 50,nm, the spin transition becomes gradual and no hysteresis can be detected. For our data it seems that the critical size, for which the existence of a thermal hysteresis can be detected, is around 50,nm. Interestingly, the change of the particle size induces almost no change in the temperature of the thermal spin transition. A systematic determination of coherent domain size carried out on the nanoparticles by powder X-ray diffraction indicates that at approximately 30,nm individual particles consist of one coherent domain. [source] | ||||||||||||||||