Maximum Transition Temperature Research Articles

Comparative study of structure, dielectric and electrical behavior of Ba(Fe0.5Nb0.5)O3 ceramics and their solid solutions with BaTiO3

Dielectric properties of (1-x)Ba(Fe0.5Nb0.5)O3-xBaTiO3 (where x = 0.00, 0.05 and 0.10) solid solution ceramics at high temperature range of RT ~ 270 o C have been characterized in this paper. The above said polycrystalline ceramics with (x = 0.0, 0.05 and 0.10) have been produced via a mixed oxide route. The effects of BaTiO3 substitution on the structure and on the electrical and ferroelectric properties of Ba(Fe0.5Nb0.5)O3 samples have been studied by performing x-ray diffraction and dielectric measurements. The dielectric properties (e¢ and tan d) were investigated in the temperature range of 30-270 °C and in the frequency range of 100 Hz-5 MHz. The variation of relative dielectric permittivity (tan d) and tangent loss (tan d) has suggested a significant role of hopping of trapped charge carriers, which is resulted in an extra dielectric response in addition to the dipole response. It is observed that: (i) the relative dielectric permittivity and tangent loss (tan d) are dependent on frequency, (ii) the temperature of dielectric permittivity maximum shifts toward lower temperature side and (iii) dielectric permittivity and tangent loss rapidly increase by making solid solution of BFN with BaTiO3. X-ray diffraction analysis of the compound suggests the formation of single-phase compound with monoclinic structure. SEM photographs exhibit the uniform distribution of grains. The maximum ferroelectric transition temperature (Tc) of this system was 250-270 °C with the dielectric constant peak of 72500 at 1.09 kHz for x = 0.05.

Characterization of the Low Temperature Superconductor Niobium Carbonitride

Niobium carbonitride's superior radiation tolerance , coupled with the recently reported increase in its upper critical magnetic field when made nanocrystalline, increases its potential importance in future technological high-field superconductor applications. The maximum transition temperature for the composition NbC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> is ~17.8 K and its upper critical magnetic field is ~11 T; this increases to ~12 T for the composition NbC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> ,. Using solid-state processing, we have fabricated microcrystalline bulk niobium carbonitride with a transition temperature of ~ 7.6 K. A comprehensive characterization of this material, which includes susceptibility, resistivity, magnetization, heat capacity and XRD measurements is provided. Comparisons between the heat-treated material and the same material subjected to hot isostatic pressing are made so that the values of the intrinsic fundamental properties can be identified and their sensitivities to different fabrication processes determined.

FERROELECTRIC AND MAGNETIC PROPERTIES OF PEROVSKITE STRUCTURED Bi1-x-yGdxBayFe1-yTiyO3 MAGNETOELECTRIC CERAMICS

Ternary solid solutions of BiFeO3 , GdFeO3 and BaTiO3 have been prepared by solid-state reaction method. Dielectric properties of these ceramics have been characterized in the temperature range between room temperature and 673 K and magnetic properties between 5 K and 300 K. For the understanding of the multiferroic property, the relation between the crystal structures, magnetic transition and ferroelectric transitions with increasing temperature have been analyzed. All ceramic samples show single perovskite phase. When Ba content exceeds 0.2 wt%, the sintering ability is weakened and the phase structure of Bi 1-x-y Gd x Ba y Fe 1-y Ti y O 3 (with x = 0.2 and y = 0.1, 0.2, 0.3, 0.4, 0.5) solid solution changes from rhombohedral to tetragonal phase. The maximum ferroelectric transition temperature (Te of this system was in the range 154–165°C with the dielectric constant peak of 6000 for y = 0.5 at 100 kHz. Well-saturated piezoresponse hysteresis loops were observed for all compositions indicating room temperature ferroelectricity. With increasing Ba content (up to 0.3 wt%) the remanent magnetization Mr increased and the coercive magnetic field decreased.

Phase diagram of the iron arsenide superconductors Ca(Fe1−xCox)2As2(0⩽x⩽0.2)

Platelet-like single crystals of the Ca(Fe1-xCox)2As2 series having lateral dimensions up to 15 mm and thickness up to 0.5 mm were obtained from the high temperature solution growth technique using Sn flux. Upon Co doping, the c-axis of the tetragonal unit cell decreases, while the a-axis shows a less significant variation. Pristine CaFe2As2 shows a combined spin-density-wave and structural transition near T = 166 K which gradually shifts to lower temperatures and splits with increasing Co-doping. Both transitions terminate abruptly at a critical Co-concentration of xc = 0.075. For x \geq 0.05, superconductivity appears at low temperatures with a maximum transition temperature TC of around 20 K. The superconducting volume fraction increases with Co concentration up to x = 0.09 followed by a gradual decrease with further increase of the doping level. The electronic phase diagram of Ca(Fe1-xCox)2As2 (0 \leq x \leq 0.2) series is constructed from the magnetization and electric resistivity data. We show that the low-temperature superconducting properties of Co-doped CaFe2As2 differ considerably from those of BaFe2As2 reported previously. These differences seem to be related to the extreme pressure sensitivity of CaFe2As2 relative to its Ba counterpart.

Effect of a hyperbranched polymer over the thermal curing and the photocuring of an epoxy resin

In this study, the authors study by calorimetry the influence of hyperbranched polyester Boltron®H40 on the thermal curing and the photocuring of a diglycidyl ether of bisphenol epoxy resin (DGEBA) using ytterbium (III) trifluoromethanesulfonate and triarylsulfonium hexafluorantimonate as thermal and photo cationic initiators, respectively. In the dynamic thermal curing at different heating rates, the authors have seen a decelerating effect when H40 is added to DGEBA, the system with 10% of H40 being the slowest. An isoconversional method has been used to determine the apparent activation energy of the thermal curing. In the isothermal photocuring at low temperatures, the authors have also appreciated a decelerating effect on adding H40, obtaining a minimum conversion when the H40 proportion is 15%. However, at high temperatures, the photocuring process can be accelerated at the first part of this process. This behavior is a consequence of the temperature dependence of H40 solubility in DGEBA, the viscosity of the system, and the hydroxyl-induced chain-transfer reaction. The values found of the maximum glass transition temperature in the thermal curing and in the photocuring, show that H40 is not completely solubilized in the reacted system.

Superconductivity and magnetism in platinum-substitutedSrFe2As2single crystals

Single crystals of SrFe2-xPtxAs2 (0 < x < 0.36) were grown using the self flux solution method and characterized using x-ray crystallography, electrical transport, magnetic susceptibility, and specific heat measurements. The magnetic/structural transition is suppressed with increasing Pt concentration, with superconductivity seen over the range 0.08 < x < 0.36 with a maximum transition temperature Tc of 16 K at x = 0.16. The shape of the phase diagram and the changes to the lattice parameters are similar to the effects of other group VIII elements Ni and Pd, however the higher transition temperature and extended range of superconductivity suggest some complexity beyond the simple electron counting picture that has been discussed thus far.

Electronic Energy Levels in High-Temperature Superconductors

Parent materials of high-temperature superconductors (HTSC) need to be doped to become superconducting. The optimum doping for maximum critical transition temperature T c has been analyzed for more than 20 materials. Assuming a uniform doping distribution the distance x between doped unit cells—projected into the CuO2 plane for cuprates—shows a strong linear correlation to the inverse of T c in the form (2x)2=m 11/T c with a slope of m 1=(2.786±0.029)×10−15 m2 K. The mercury cuprate homologous series HgBa2Ca n−1Cu n O2n+2+δ with n=1,2,3 has been used to demonstrate the procedure deriving the doping distance x from the optimum doping value δ.

Type I collagen from the skin of ornate threadfin bream ( Nemipterus hexodon): Characteristics and effect of pepsin hydrolysis

Type I collagen from the skin of ornate threadfin bream ( Nemipterus hexodon) was purified and characterised. Purified type I collagen contained [α1(I)] 2α2(I) as the dominant component with the co-presence of α1(I)α2(I)α3(I). It was rich in glycine and alanine with high content of imino acids (188 residues/1000 residues). The maximum transition temperature ( T m) and the total denaturation enthalpy (Δ H) of purified type I collagen was 33.35 °C and 0.819 J/g, respectively. The isoelectric point (pI) of purified type I collagen was estimated to be 6.40. After hydrolysis of purified type I collagen using pepsin, the band intensity ratios of α1/α2-chains were increased ( P < 0.05). The cross-linked components were effectively hydrolysed by pepsin 1 and 2 from skipjack tuna stomach and porcine pepsin at 4 °C without the cleavage of β- and α-chains. At 50 °C, they were more susceptible to porcine pepsin hydrolysis, followed by pepsin 2 and 1, respectively.

Neodymium-Doping Induced Superconductivity in 1111-SrFeAsF Iron-Pnictide System

Polycrystalline Sr1−x Nd x FeAsF samples at various Nd-doping levels have been prepared by conventional solid-state synthesis close to ambient pressure. Susceptibility and resistivity were studied down to 4 K showing superconductivity competing with a low-temperature magnetic ordering and probably the coexistence of both, well into the superconducting region. The temperature dependence of the resistivity of all the Nd-doped samples clearly show the presence of this transition below 15 K, most likely originating from the magnetic ordering of Nd moments. This transition is gradually attenuated but not completely suppressed even at optimum-doping region at x≈0.54. The spin-density wave anomaly at 175 K survives up to 0.35 Nd-doping, while superconductivity occurs only above x=0.40. The maximum onset transition temperature, T c , reaches as high as 54.3 K for x=0.70, but superconductivity disappears beyond that. The estimated upper critical fields, H c2, are high, with values exceeding 98 Tesla obtained from two samples of different doping level.

Superconductivity induced by doping platinum inBaFe2As2

By substituting Fe with the 5d-transition metal Pt in BaFe2As2, we have successfully synthesized the superconductors BaFe2-xPtxAs2. The systematic evolution of the lattice constants indicates that the Fe ions were successfully replaced by Pt ions. By increasing the doping content of Pt, the antiferromagnetic order and structural transition of the parent phase is suppressed and superconductivity emerges at a doping level of about x = 0.02. At a doping level of x = 0.1, we get a maximum transition temperature Tc of about 25 K. The synchrotron powder x-ray diffraction shows that the resistivity anomaly is in good agreement with the structural transition. The superconducting transitions at different magnetic fields were also measured at the doping level of about x = 0.1, yielding a slope of -dHc2/dT = 5.4 T/K near Tc. A phase diagram was established for the Pt doped 122 system. Our results suggest that superconductivity can also be easily induced in the FeAs family by substituting the Fe with Pt, with almost the similar maximum transition temperatures as doping Ni, Co, Rh and Ir.

Hidden low‐temperature instability in PrOs4Sb12

AbstractThe low‐temperature behavior of many correlated electron systems is characterized by the appearance of macroscopically ordered states that show a dome‐shaped evolution of their transition temperatures as a function of non‐thermal control parameters. In the heavy‐fermion compound PrOs4Sb12, a field‐induced phase emerges in a magnetic field range between $B \approx 4.5$ and 13.5 T. The phase is characterized by antiferroquadrupolar (AFQ) ordering of the Pr3+ ions. We measured the specific heat of PrOs4Sb12 single crystals in magnetic fields up to $B = 14$ T parallel to the crystallographic [100] direction to determine the entropy S as a function of T and B. Above the maximum AFQ transition temperature, the entropy $S(T = {\rm const},B)$ reveals a pronounced maximum. We show that this maximum can be related to a low‐temperature instability which is produced by the degeneracy of the lowest crystalline electric field (CEF) energy levels.

Purification and Characterization of Pepsin-Solubilized Collagen from Skin and Connective Tissue of Giant Red Sea Cucumber (Parastichopus californicus)

Pepsin-solubilized collagen (PSC) was extracted from giant red sea cucumbers ( Parastichopus californicus ) and characterized for denaturation temperature (T(d)), maximum transition temperature (T(m)), enzyme-digested peptide maps, and gel-forming capability. SDS-PAGE showed that PSCs from giant red sea cucumber skin and connective tissue were both type I collagens, consisting of three alpha(1) chains of approximately 138 kDa each. The amino acid composition and peptide maps of PSCs digested by V8 protease were different from those of calf skin type I collagen. The T(d) and T(m) are 18.5 and 33.2 degrees C, respectively, for skin PSC and are 17.9 and 32.7 degrees C, respectively, for connective tissue PSC. Both skin and connective tissue PSCs exhibited good gel-forming capability at pH 6.5 and at an ionic strength of 300 mM salt (NaCl). Collagen isolated from giant red sea cucumbers might be used as an alternative to mammalian collagen in the food and pharmaceutical industries.

New oxypnictide superconductors: PrOFe 1−xCo xAs

Oxypnictides of the type PrOFe 1− x Co x As ( x≤0.3) were synthesized for the first time by the sealed tube method. All the compounds were found to be monophasic and crystallize in the tetragonal ZrCuSiAs type structure (space group= P4/ nmm) and the lattice parameters ( a and c) decrease with increase in cobalt content. Mössbauer measurements of the compounds indicate low spin Fe 2+ in tetrahedral coordination. Resistivity and magnetization studies reveal superconducting transitions in compounds with ‘ x’=0.05, 0.10 and 0.15, with maximum transition temperature ( T c ) at ∼14 K in the compound with ‘ x’=0.1. The variation of resistivity with temperature under different magnetic field has been studied to estimate the upper critical field ( H c 2) (∼50.2 T for the ‘ x’=0.1 composition). The Seebeck and Hall coefficient ( R H ) suggests electron type charge carriers in these compound and the charge carrier density increases with increase in Co-doping.

Annealing effects on superconductivity in [formula omitted

Superconductivity has been explored in single crystals of the Ni-doped FeAs-compound SrFe2-xNixAs2grown by self-flux solution method. The antiferromagnetic order associated with the magnetostructural transition of the parent compound SrFe2As2 is gradually suppressed with increasing Ni concentration x and bulk-phase superconductivity with full diamagnetic screening is induced near the optimal doping of x=0.15 with a maximum transition temperature Tc∼9.8K. An investigation of high-temperature annealing on as-grown samples indicate that the heat treatment can enhance Tc as much as ∼50%.

Ferroelectric and ferromagnetic properties of Gd-doped BiFeO 3–BaTiO 3 solid solution

The solid solutions of Bi 1− x− y Gd x Ba y Fe 1− y Ti y O 3 have been prepared via solid-state reaction method with the aim to obtain magnetoelectric coupling (i.e., linear relation between magnetization and electric field) at room temperature. Optimum calcination and sintering strategies for obtaining pure perovskite phase, high density ceramics and homogeneous microstructures have been determined. All the samples of the composition Bi 1− x− y Gd x Ba y Fe 1− y Ti y O 3 ( x = 0.1 and y = 0.1, 0.2, and 0.3) reported in the present work are tetragonal at room temperature. The maximum ferroelectric transition temperature ( T c) of this system was 150–170 °C with the dielectric constant peak of 2300 at 100 kHz for y = 0.1. Above T c the dielectric constant is decreasing up to a certain temperature and then increasing with temperature similar to that observed in other perovskites due to chemical inhomogeneities in both A and B sites of the ABO 3 cell. The variation of ferroelectric and magnetic properties was followed by piezoresponse force microscopy and vibrating sample magnetometer, respectively. Well-saturated piezoelectric loops were observed for all composition indicating room temperature ferroelectricity.

Dielectric, ferroelectric and pyroelectric properties of Pb[(Ni1/3Sb2/3)xTiyZrz]O3 ceramics

In the present study, various Pb[(Ni1/3Sb2/3)xTiyZrz]O3 where x+y+z=1, x=0.08 and y=0.44–0.49, ceramics in the morphotropic phase boundary (MPB) range were studied by dielectric and pyroelectric methods. The results of the investigations revealed an MPB composition range of y≅0.46. The study of the dielectric properties of these compounds as a function of temperature suggests that with increase in y the permittivity maximum increases and transition temperature shifts towards higher temperature. Well-saturated polarization versus electric field (P–E) hysteresis loops were obtained and values of Pr were calculated. The samples revealed good pyroelectric properties for y=0.44 and y=0.45 at room temperature with large figures of merit Fv=0.019 m2/C and FD=1.34×10–5Pa1/2.

Evolution of bulk superconductivity inSrFe2As2with Ni substitution

Single crystals of the Ni-doped FeAs-based superconductor ${\text{SrFe}}_{2\ensuremath{-}x}{\text{Ni}}_{x}{\text{As}}_{2}$ were grown using a self-flux solution method and characterized via x-ray measurements and low-temperature transport, magnetization, and specific heat studies. A doping phase diagram has been established where the antiferromagnetic order associated with the magnetostructural transition of the parent compound ${\text{SrFe}}_{2}{\text{As}}_{2}$ is gradually suppressed with increasing Ni concentration, giving way to bulk-phase superconductivity with a maximum transition temperature of 9.8 K. The superconducting phase exists through a finite range of Ni concentrations centered at $x=0.15$ with full diamagnetic screening observed over a narrow range of $x$ coinciding with a sharpening of the superconducting transition and an absence of magnetic order. An enhancement of bulk superconducting transition temperatures of up to 20% was found to occur upon high-temperature annealing of samples.

Magnetic phases and transitions of the two-species Bose-Hubbard model

A model of two-species bosons moving on the sites of a lattice is studied at nonzero temperature, focusing on magnetic order and superfluid-insulator transitions. First, Landau theory is used to find the general structure of the phase diagram and in particular to demonstrate the presence of first-order transitions and hysteresis in the vicinity of a multicritical point. Second, an explicit thermodynamic phase diagram is calculated using an approach based on a field-theoretical description of the Bose-Hubbard model, which incorporates the crucial effects of particle-number fluctuations. The maximum transition temperature to a magnetically ordered Mott insulator is found to be limited by the presence of the superfluid phase.

Bose-Einstein condensation of triplons inBa3Cr2O8

By performing heat-capacity, magnetocaloric effect, torque magnetometry, and force magnetometry measurements up to 33 T, we have mapped out the $T\text{\ensuremath{-}}H$ phase diagram of the $S=1/2$ spin dimer compound ${\text{Ba}}_{3}{\text{Cr}}_{2}{\text{O}}_{8}$. We found evidence for field-induced magnetic order between ${H}_{c1}=12.52(2)\text{ }\text{T}$ and ${H}_{c2}=23.60(5)\text{ }\text{T}$, with the maximum transition temperature ${T}_{c}\ensuremath{\sim}2.7\text{ }\text{K}$ at $H\ensuremath{\sim}18\text{ }\text{T}$. The lower transition can likely be described by Bose-Einstein condensation of triplons theory, and this is consistent with the absence of any magnetization plateaus in our magnetic torque and force measurements. In contrast, our measurements uncovered magnetic field irreversibility associated with a symmetric specific heat versus temperature near ${H}_{c2}$ suggesting that the upper transition is first order.

Thermal properties and heat-induced aggregation of natural actomyosin extracted from goatfish ( Mulloidichthys martinicus) muscle as influenced by iced storage

Thermal properties and aggregation of natural actomyosin (NAM) extracted from fresh and 9 days ice-stored goatfish were comparatively studied. Myosin of fresh goatfish had the higher thermal stability than that of ice-stored counterpart as indicated by the higher maximum transition temperature ( T max). Additionally, the thermal inactivation rate constant ( K D ) of Ca 2+-ATPase in NAM from fresh goatfish was lower than that of ice-stored counterpart when incubated at the temperature range of 20–40 °C, indicating the lower thermal stability of the latter NAM. NAM from fresh goatfish exhibited the higher turbidity, surface hydrophobicity and disulfide bond formation than did NAM of iced-stored sample when heated at temperature from 35 to 75 °C, suggesting the higher extent of aggregation of the former. However, goatfish NAM showed the lower extent of heat-induced aggregation than did bigeye snapper NAM. As visualized by transmission electron microscopy, network strands of aggregates from bigeye snapper NAM were finer and more uniform than those from goatfish. NAM from goatfish stored in ice showed the lower extent of heat-induced aggregation than did NAM from fresh counterpart. Therefore, heat-induced aggregation of goatfish muscle proteins was governed by freshness.