Resistance-temperature Curves Research Articles

In-situ electrical resistance measurement of the selenization process in the CuInGa–Se system

In this work the selenization reactions and reaction paths in CuIn xGa 1-xSe 2 thin films prepared by sputtering and post-selenization process are investigated. The in-situ electrical resistance measurement technique is applied to monitor all the selenization reactions. The crystal structure is determined by X-ray diffraction (XRD) measurement. From the analysis of resistance-temperature curves and the XRD patterns, the phase evolutions of various crystalline and selenization reaction paths have been obtained. From these measurements, the reaction mechanisms and kinetics in the CuInGa–Se system are further understood.

Impact of substrate temperature on the microstructure, electrical and optical properties of sputtered nanoparticle V 2O 5 thin films

Applying reactive direct current (DC) magnetron sputtering method, nanoparticle vanadium pentoxide thin films were deposited onto glass slides and KBr substrates at different substrate temperatures. The films were characterized by X-ray photoelectron spectroscopy and atomic force microscope. Infrared spectra were recorded with a Fourier transform infrared spectrophotometer. It was found that, excepting the compositions, the film growth and vanadium oxygen bonds were strongly affected by the substrate temperature. Electrical measurements indicated that the square resistances of films showed an exponential decrease from 46 MΩ/□ to 33 kΩ/□ with substrate temperature increasing from 433 K to 593 K, and that the square resistance–temperature curves of films exhibited typical semiconducting behavior. Optical investigations were carried out in the near infrared and ultraviolet–visible range. Transmittance varied from about 95 to 55% in near-infrared range when the substrate temperature was elevated. In ultraviolet–visible range, optical band gaps and refractive indexes of films were deduced according to the transmission and reflection spectra.

Robust charge and magnetic orders under electric field and current in multiferroicLuFe2O4

We performed elastic neutron scattering measurements on the charge- and magnetically-ordered multiferroic material LuFe(2)O(4). An external electric field along the [001] direction with strength up to 20 kV/cm applied at low temperature (~100 K) does not affect either the charge or magnetic structure. At higher temperatures (~360 K), before the transition to three-dimensional charge-ordered state, the resistivity of the sample is low, and an electric current was applied instead. A reduction of the charge and magnetic peak intensities occurs when the sample is cooled under a constant electric current. However, after calibrating the real sample temperature using its own resistance-temperature curve, we show that the actual sample temperature is higher than the thermometer readings, and the "intensity reduction" is entirely due to internal sample heating by the applied current. Our results suggest that the charge and magnetic orders in LuFe(2)O(4) are unaffected by the application of external electric field/current, and previously observed electric field/current effects can be naturally explained by internal sample heating.

Resistivity-Temperature Feature of Ga36.5Sb63.5 Melt

In the present work, the resistivity of Ga36.5Sb63.5 alloy during cooling process was studied by the method of DC Four electrodes . The result of the experiment showed that there is an anomalous point at 710°C－735°C on the resistivity-temperature curve of Ga36.5Sb63.5 melt. At the same time, The relevance of the resistivity and the liquid structure of the alloy was analyzed. The physical properties of Ga36.5Sb63.5 alloy melt was discussed.

Reversible resistivity–temperature anomalies of liquid Pb–Bi–Sn alloys

The patterns of electrical resistivity of (Pb–Bi56.1)1− x –Sn x alloys, along with liquid Pb–Bi56.1 wt% alloy and pure Pb, Sn and Bi have been investigated as a function of temperature, using the DC four-probe technique. Evident reversible changes are observed on resistivity–temperature curves of different liquid Pb–Bi–Sn alloys, and there are clear turning points both in the heating and cooling process, which are similar to that of liquid Sn. Moreover, the turning temperatures vary with differing compositions of alloys. In the case of the Pb–Bi alloy, however, no reversible changes are observed on resistivity–temperature curves. Since resistivity is one of the physical properties sensitive to structures, it is suggested that there are reversible temperature-induced liquid–liquid transitions in (Pb–Bi56.1)1− x –Sn x alloys, and that Sn plays an important role in the change.

New PTCR thermistors, switching current, and electromagnetic shielding effectiveness from nanosized vanadium sesquioxides ceramic reinforced epoxy resin nanocomposites

AbstractA new polymer nanocomposites of an epoxy resin matrix with randomly dispersed nano‐vanadium sesquioxides (V2O3) in various amounts were prepared. The structure of the nanocomposites were characterized by scanning and transmission electron microscopy (SEM and TEM), X‐ray diffraction, hardness, packing factor, extent of filler reinforcement, glass transition temperature, and sound velocity. The percolation threshold in the conductivity of the composites is lesser than 8 wt % and the dielectric constant can reach as high as 103. The resistivity—temperature curve of the composites shows a positive temperature coefficient (PTC) effect. The thermal stability of the composites was examined in terms of thermal gravimetry and differential scanning calorimetry (TG and DTA) and isothermal resistivity–time check. Because of the interfacial interaction among filler particles and the epoxy matrix, the nanocomposites exhibit higher thermal stability. The current–voltage–temperature curves behave as switching current. The temperature increases linearly with the applied voltage which makes this PTC nanocomposites very useful for temperature probe. Finally, electromagnetic interference shielding effectiveness (SE) values have been calculated and measured for the nanocomposites in the frequency range 1–12 GHz. It is found that the SE properties of the nanocomposite improve with increase in wt % of V2O3. A maximum SE of 42 dB for V20 sample at 12 GHz has been achieved. These nanocomposites are potentially useful in suppression of electromagnetic interference and reduction of radar signature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Design and fabrication of superconducting HEB mixer

This paper describes the design and fabrication of superconducting hot electron bolometer (HEB) mixer based on ultra-thin superconducting NbN films. The high quality films were epitaxially grown on high resistance Si substrates. The device was fabricated by magnetron sputtering, electron beam lithography (EBL), reactive ion etching (RIE), lithography, and so on. The device’s resistance-temperature (R-T) curves and current-voltage (I-V) curves were studied. The results of THz response of the device are presented. Y-factor technique was used to measure the device’s noise temperature. When the device was irradiated with a laser radiation of 2.5 THz, the obtained lowest noise temperature of the device was 2213 K.

Superconducting Films for Absorber-Coupled MKID Detectors for Sub-Millimeter and Far-Infrared Astronomy

We describe measurements of the properties, at dc, gigahertz, and terahertz frequencies, of thin (10 nm) aluminum films with 10 Omega/square normal state sheet resistance. Such films can be applied to construct microwave kinetic inductance detector arrays for submillimeter and far-infrared astronomical applications in which incident power excites quasiparticles directly in a superconducting resonator that is configured to present a matched-impedance to the high frequency radiation being detected. For films 10 nm thick, we report normal state sheet resistance, resistance-temperature curves for the superconducting transition, quality factor and kinetic inductance fraction for microwave resonators made from patterned films, and terahertz measurements of sheet impedance measured with a Fourier Transform Spectrometer. We compare properties with similar resonators made from niobium 600 nm thick.

Effect of Sintering Temperature on the Microstructural and Flux Pinning Characteristics of Bi1.6Pb0.5Sr1.8La0.2Ca1.1Cu2.1O8+δ Ceramics

We evaluated the microstructure, superconducting, and flux pinning properties of La‐doped (Bi,Pb)‐2212 bulk sample by varying its sintering temperature (Tsinter) between 846° and 860°C. Significant variations in microstructure, self‐ and in‐field JCs at 64 K and flux pinning properties have been observed for La‐substituted samples with respect to Tsinter. The sample sintered at 858°C shows best self‐field JC while that sintered at 846°C shows the best in‐field JC due to the changes in microstructure. The activation energy of flux motion (pinning potential Uo) is estimated from the field dependent resistivity–temperature curves, and the flux pinning force (FP) from the field‐dependent JC values. It is found that the La‐doped samples, sintered at 846°C show maximum FP and Uo of 463 kN/m3 and 0.380±0.001 eV as against 93.6 k/Nm3 and 0.140±0.001 eV, respectively, for the sample sintered at 858°C. The undoped (Bi,Pb)‐2212 shows a maximum FP and Uo of 12.7 k/Nm3 and 0.074±0.001 eV, respectively. The origin of these enhanced properties is mainly from the normal‐like defects introduced by optimum La‐doping at the Sr‐site, at an optimum sintering temperature.

A new understanding of melt overheating treatment of Sn–20 wt-%Sb from viewpoint of TI-LLST

Investigations of the electrical resistivity of liquid Sn–20 wt-%Sb alloy as a function of temperature were carried out by dc four probe method. An abnormal change on the resistivity–temperature curve was observed in temperature interval of 850–980°C, which indicated that temperature induced liquid–liquid structure transitions (TI-LLST) occurred with temperature rising. Further explorations of effects of TI-LLST on solidification showed that the undercooling for primary or peritectic phase crystallisation increased for the samples solidified from the melt experienced the TI-LLST, and the size of primary phase decreased markedly.

The resistivity evolution with temperature of 7050 aluminium alloy by different casting methods

The resistivity-temperature curve of 7050 aluminium alloy prepared by different casting methods (DC and LFEC) has been measured with D.C. four-probe method. By analysing the curve, it was found that a change occurred to the slope at 250℃ when the samples were heated, and the resistivity of LFEC sample changed with temperature more quickly than that of DC. Both the solidus and liquidus temperatures of LFEC samples were higher than those of DC samples during the process of temperature rise from room temperature to 900℃. However, the resistivity of DC samples increased remarkably when the temperature was kept at 900℃ and before it was decreased to 600℃. With the help of microstructure observation, the characteristics and phenomenon of the resistivity evolution with temperature were studied.

Fabrication and characterization of La0.7Sr0.3MnO3 sandwich structure separated by （La0.7Sr0.3MnO3）m（BiFeO3）n superlattice

The La0.7Sr0.3MnO3 sandwich structure separated by （La0.7Sr0.3MnO3）m（BiFeO3）n superlattices is grown in situ on SrTiO3（001） substrates by RF magnetron sputtering. The X-ray diffraction scans indicate that the films are obviously superlattice structures. The resistivity-temperature curves measured in the case of current perpendicular to the plane geometry show that the films undergo metal-insulator transition at 290 K, which is a little lower than the temperature of single La0.7Sr0.3MnO3 film. When the current is within 0.01—10 mA, the peak resistivity of the （La0.7Sr0.3MnO3）m（BiFeO3）n films decreases with the increasing current.The change rate which is higher than that of single La0.7Sr0.3MnO3 film increases with the increasing thickness of the period films. The current-voltage curves indicate that the conduction mechanism in superlattices is space-charge-limited con-duction and a big bias voltage which is a characteristic of Schottky junction is also found in the current-voltage curves at low temperatures.

Effect of second introduced phase on magnetotransport properties of La 2/3Sr 1/3MnO 3/0.33(CuO, ZnO, Al 2O 3) composites

The structure, magnetic and magnetotransport properties of La 2/3Sr 1/3MnO 3(LSMO)/0.33(CuO, ZnO, Al 2O 3) composites were investigated to explore the role of second introduced phase. The microstructural analysis shows two kinds of grain boundaries: LSMO/LSMO and LSMO/second phase/LSMO. Two maximal resistivities appear in LSMO/0.33CuO and LSMO/0.33ZnO composites while the resistivity of LSMO/0.33Al 2O 3 decreases monotonically with increasing the temperature from 200 K to 400 K. Moreover, the temperature dependence of magnetoresistance(MR) of LSMO/0.33Al 2O 3 that decreases monotonically with increasing the temperature is different from that of LSMO/0.33CuO and LSMO/0.33ZnO. A developed two-channel model consisting of scattering model and tunneling model was proposed to fit the resistivity—temperature curves of these composites. The role of second introduced phase and the magnetotransport mechanism of these composites were elucidated.

Resistivity Evolution with Temperature of 7050 Aluminium Alloy in Different Casting Methods

The resistivity-temperature curve of 7050 aluminum alloy prepared in different casting methods (DC and LFEC) has been measured with D.C. four-probe method. By analyzing the curve, it was found that a change occurred to the slope at 250°C when the samples were heated, and the resistivity of LFEC sample changed with temperature more quickly than that of DC. Both the solidus and liquidus temperatures of LFEC samples were higher than those of DC samples during the process from room temperature to 900°C. However, the resistivity of DC samples increased remarkably while the temperature was kept at 900°C, and even before it was decreased to 600°C. With the microstructure observation, the characteristics and phenomenon of the resistivity evolution with temperature were studied.

TEMPERATURE PROFILE OF RESISTIVITY OF MANGANITES

In the resistivity–temperature curves of La 0.7 Ca 0.3 MnO 3 and La 0.75 Ca 0.25 MnO 3, five distinct regions have been identified. For example, in La 0.7 Ca 0.3 MnO 3, the regions are: (1) from the lowest temperature of measurement to 200 K where resistivity is directly proportional to temperature with a small slope, (2) the reciprocal of resistivity follows Bloch's T3/2 law, (3) resistivity is directly proportional to temperature with a large slope, (4) the cusp region, where there are FM clusters of reduced dimensions and varying degrees of correlated polarons or bipolarons and small polarons, (5) the semiconducting region having small polarons. The regions 1, 2 and 3 together appear to replicate the spontaneous magnetization curves of the materials. The effect of magnetic field on the resistivity–temperature curves are as follows: (a) resistivity is reduced. In particular, the resistivity peak with magnetic field occurs at a temperature μH/K downward from the T c of the curve without magnetic field; (b) resistivity peak is displaced by μ · μH/K towards the higher temperature side compared to the resistivity peak without magnetic field; (c) cusp region is broadened; (d) magnetoresistance is appreciable only within 10% of Tp on both sides. All these observations suggest that temperature profile of resistivity of manganites is controlled by magnetic effects.

Hump phenomenon on resistivity–temperature curve in liquid Bi, Sb and their alloys

The electrical resistivities of liquid Bi, Sb, and some of their alloys Pb–Bi, Pb–Sb have been investigated as a function of temperature, and the effect of heating-rate on the turning points of liquid Bi has also been investigated. Obvious and interesting hump phenomena are observed on resistivity–temperature curves of liquid Bi, Sb, and Pb–Bi, Pb–Sb alloys on heating at the temperature far above their liquidus. Moreover, the transition temperature of liquid Bi increases with heating-rate increasing, which shows that this kind of transition is in accordance with kinetic characteristics. However, comparing the heating curve with the cooling one, we found that the anomalous hump phenomenon is irreversible in liquid Bi, Sb, and Pb–Bi, Pb–Sb alloys.

Characteristics of La0.7Ca0.3MnO3–Cu composites fabricated by an electroless process

Ferromagnet–metal-type composites, La0.7Ca0.3MnO3(LCMO)–Cu, have been fabricated by a three-step route. We got LCMO powder using the conventional solid state method. Then, LCMO powders coated by Cu are obtained using a novel electroless plating technique, in which the contents of copper are controlled by changing the plating time. Finally these powders are pelletized and then sintered at different temperatures in argon. The powders coated by Cu are characterized by x-ray powder diffraction and scanning electron microscope. The temperature dependence of resistivity and the magnetoresistance in the applied field of 3000 Oe are measured. It is observed that the metal–insulator transition temperature (Tp) is improved above 20 K approximately up to 280 K compared with that of LCMO powder using the conventional solid state method without being coated by Cu; meanwhile, a second broad peak occurs in low temperature in the resistivity-temperature curve when sintering temperature is changed. Also an anisotropic magnetoresistance effect is observed.

Effect of Sn on reversibility of liquid–liquid transition in Bi–Sb–Sn alloys

The temperature dependence of electrical resistivity of (Bi–Sb20)1−x–Snx alloys, along with liquid Bi–Sb20% alloy, have been investigated using the D.C. four-probe technique. Obvious reversible changes are observed on resistivity–temperature curves of the investigated (Bi–Sb20)1−x–Snx alloys, and there are clear turning points both on heating and cooling process in several experimental cycles. In case of Bi–Sb20% alloy, however, no reversible changes are observed on resistivity–temperature curves. Since resistivity is one of the physical properties sensitive to structures, it is suggested that there are reversible temperature-induced liquid–liquid transition in (Bi–Sb20)1−x–Snx alloys and the Sn plays an important role on the liquid–liquid transition.

Photoinduced effect in charge-ordering La0.5Ca0.5MnO3 film

Charge-ordered La0.5Ca0.5MnO3 film has been deposited on (100)-LaAlO3 substrate using rf magnetron sputtering method. X-ray diffraction analysis shows that the bulk has orthorhombic structure and the film has the better epitaxial character. The charge-ordering transition temperature is about 280 K by fitting the resistance-temperature curve using the variable-range hopping model. The decrease in the resistance of the film irradiated by the laser is caused by the delocalization effect of the correlated electron system. The photoinduced relaxation exhibits different processes when the laser is on and off, which can be attributed to thermal fluctuation.

Resistivity-Temperature Properties of La(Ti<sub>x</sub>Mn<sub>1-x</sub>)O<sub>3</sub> Ceramics

Samples of La(TixMn1-x)O3 (0.1 ≤ x ≤ 0.7) were sintered at different temperatures. The experimental results showed that the resistivity-temperature curves of the samples match NTC characteristic. The crystal structure was analyzed using X-ray diffraction and the microstructure was observed by scanning electron microscope.