Peak Temperature Coefficient Of Resistance Research Articles

Effect of Y doping on transport properties of La0.8Sr0.2MnO3 polycrystalline ceramics

In this study, La0.8-xYxSr0.2MnO3 (LYSMO) polycrystalline ceramics were prepared by means of sol-gel technique using methanol as solvent. X-ray diffraction (XRD) showed all samples to possess standard perovskite structure. Scanning electron microscopy (SEM) revealed samples with high compactness and grain size from 27.80 to 29.73 μm. Resistivity–temperature tests indicated sharp metal-insulator transition behavior of all samples accompanied by rapid transformation from ferromagnetism to paramagnetism (FM-PM). As Y3+ doping amounts rose, radius of A-site ions decreased, metal-insulator transition temperature (Tp) of polycrystalline samples shifted to lower temperatures, and resistivity increased. Temperature coefficient of resistance (TCR) and magnetoresistance (MR) were affected by introduction of Y3+. At x = 0.06, peak TCR and peak MR reached 4.85% K−1 and 52.34%, respectively. Using double exchange (DE) interaction mechanism, electric transport performances of as-prepared ceramics were explained. These findings look promising for future applications of LYSMO materials in magnetic devices and infrared detectors.

Electrical transport properties of (Pr1-xLax)0.7Sr0.3MnO3 (0 ≤ x ≤ 0.3) polycrystalline ceramics prepared by sol-gel process for potential room temperature bolometer use

High density (Pr1-xLax)0.7Sr0.3MnO3 (PLSMO, x = 0, 0.10, 0.20, 0.25, and 0.30) polycrystalline ceramics were fabricated by the sol-gel method followed by sintering at 1723 K for 12 h. The doping effects of lanthanum on structural, surface morphology and electrical transport properties of obtained ceramics were systematically investigated. X-ray diffraction patterns (XRD) confirmed that all samples crystallized in typical single orthorhombic perovskite phase with Pnma space group. Field emission scanning electron microscopy (FESEM) showed slight increase in grain size, and energy dispersive spectroscopy (EDS) mapping displayed uniformly distributed elements on the sample surface. Resistivity dependence of temperature (R-T) curves of PLSMO specimens were investigated by standard four-probe method, and results indicated decline in resistivity with the increase in La content. In addition, as the lanthanum doped content increased, the metal-insulator transition temperature (Tp) improved significantly. The average ionic radius increased as Pr3+ ions were replaced by La3+ ions with larger ion radius, which further affected the Mn–O band angle and Mn–O band length. These changes enhanced the double-exchange interaction, increasing Tp value. The temperature coefficient of resistance (TCR) curves revealed that peak TCR temperature improved with La content rose. The peak TCR temperature of PLSMO at molar ratio x = 0.25 was significantly increased from 258.47 K to 299.37 K (room temperature 300 K) and value reached 5.03% K−1. Obviously, obtaining relatively high room temperature TCR value in Pr system materials was interesting as this was not observed previously. In sum, the proposed (Pr0.75La0.25)0.7Sr0.3MnO3 ceramics look potential candidates for use in advanced room temperature uncooled infrared bolometers.

Electrical transport and magnetoresistive properties of Nd-doped La0.8Sr0.2MnO3 ceramics

In this paper, La0.8−xNdxSr0.2MnO3 (x = 0.03, 0.04, 0.05, and 0.06) ceramics were synthesized by a sol–gel method. The structure, surface morphology, electrical transport, and magnetoresistive properties of these materials were studied. X-ray diffraction (XRD) revealed samples to be single-phase with a distorted perovskite structure belonged to the ( $${\text{R}}\bar 3{\text{c}}$$ ) space group. Scanning electron microscopy (SEM) revealed the samples to contain compact grains, with the grain size increasing slightly with the amount of doping Nd3+. The standard four-probe method was used to test the electrical resistivity of the samples as a function of temperature (ρ–T). The metal–insulator transition temperature (Tp) shifted to lower temperatures and the resistivity (ρ) increased with the content of Nd3+. Peak temperature coefficient of resistance (TCR) and magnetoresistance (MR) were both affected by the Nd3+ substitution. At x = 0.05, peak TCR and MR reached 5.12% K−1 and 19.78%, respectively. The mechanism responsible for both electrical and magnetoresistive properties of these materials was discussed in the frame of double-exchange (DE) interaction.

Impact of Ag doping on the structural, surface morphologic and electrical properties of La0.625(Ca0.285Sr0.09)MnO3 polycrystalline ceramics

In this study, Ag-doped La0.625(Ca0.285Sr0.09)MnO3:Agz (LCSMO:Agz, z = 0, 0.1, 0.2, 0.3, and 0.4) polycrystalline ceramics were prepared by sol-gel method, then characterized by various techniques. X-ray diffraction (XRD) showed that all bulk prepared specimens crystalized in LCSMO phase with orthogonal cubic structure (space group of Pnma) and without impurities. Scanning electron microscopy (SEM) revealed good compactness with fewer holes. Average grain sizes and quantity of grain boundaries (GBs) correlated with Ag doping amounts. As z content rose, resistivity dropped, and both peaks temperature coefficient of resistance (TCR) and magnetoresistance (MR) first increased and then decreased. Several previous studies indicated that Ag doping amount could affect TCR and MR peaks. At z = 0.3, TCR peaks reached maxima of 10.27% (289.56 K), at z = 0.1, MR peaks reached maxima of 15.63% (293.08 K). As z increased from 0 to 0.4, the temperature of peak TCR (Tk) was adjusted to room temperature from 289.56 to 294.22 K. TCR peak of La0.625(Ca0.285Sr0.09)MnO3:Agz material was improved at room temperature when compared to values reported in the literature. This could be related to changes in tolerance factor (τ) and average A-site cationic radius (rA). Overall, LCSMO:Agz ceramics look promising for infrared detectors and colossal magnetoresistance (CMR) radiant heating instruments at room temperature.

La0·7Ca0.3−xSrxMnO3:Ag0.2 (0.0165 ≤ x ≤ 0.1) ceramics with large and stable TCR in different magnetic field environments

La0·7Ca0.3−xSrxMnO3:Ag0.2 (LCSMO:Ag) ceramics with varying strontium (Sr) content (x = 0.0165, 0.03, 0.05, 0.07, and 0.1) were synthesized using a combination of sol–gel and solid-state doping methods and studied as colossal magnetoresistance materials. Significant improvements in the peak temperature coefficient of resistivity (TCR) and resistivity (ρ) were observed across all ceramic samples when the mol% of Sr was adjusted. The low ρ and large TCR values resulted from a combination of two factors. First, the presence of Sr led to the increase in the grain size and decrease in the number of boundaries, which improved the electrical transport and reduced the boundary scattering effects. This resulted in additional improvement in the grain arrangement order. Second, the cell volume (Vcell) and octahedron volume (Voct) both decreased first and then increased. The MnO6 octahedron underwent gradual deformation into a flattened shape, which facilitated carrier migration and increased electrical sensitivity of the material. The ceramic with x = 0.03 maintained high and stable TCR values in different working environments, both without a magnetic field (TCRo, 54.76% K−1) and in the presence of a vertical field (TCR⊥, 33.33% K−1). Furthermore, the material exhibited a low resistivity and a higher insulator–metal transition temperature (Tp). Performance differences among the samples were comprehensively and systematically explained by conducting cross magnetic field tests with field directions parallel and perpendicular to the flat surface of the bulk material, respectively. Overall, the findings of this study indicate that these ceramics act as promising candidates for future applications in information storage devices and magnetic sensors.

Room-temperature TCR and low-field MR of La0.7Ca0.3-xSrxMnO3 (0.06 ≤ x ≤ 0.1) polycrystalline ceramics

In this study, La0.7Ca0.3-xSrxMnO3 (LCSMO, 0.06 ≤ x ≤ 0.1) ceramics were synthesized via a sol-gel method. The perovskite microstructure, electrical transport properties, low-field magnetoresistance (MR) and peak temperature coefficient of resistivity (TCR) behaviors of the as-obtained materials were all studied and the results were discussed. Grain size of LCSMO ceramics expanded as more Sr was added but grain boundaries (GBs) decreased. Field emission scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS) and vibrating sample magnetometry (VSM) analyses suggested that addition of Sr greatly enhanced the electrical/magnetic properties of the prepared specimens. The metal-insulator transition temperature rose as doping concentration x enhanced, and increased Ca2+ substitution led to reduced peaks of MR and TCR. For single-phase LCSMO, large room-temperature TCR and low-field MR effects (0.8 T magnetic field) were obtained by controlling the level of Sr2+ substituted Ca2+. For x = 0.095, the optimized room-temperature TCR and MR reached 13.78% K−1 (299.2 K) and 26.41% (302.6 K), respectively. Overall, LCSMO ceramics have broad application prospects in photoelectronic or magnetic devices at room-temperature.

La0.67(Ca0.24Sr0.09)MnO3:xAg2O (0 ≤ x ≤ 0.25) composites with improved room–temperature TCR and MR for advanced uncooling infrared bolometers and magnetic sensors

In this research, high–density La0.67(Ca0.24Sr0.09)MnO3:xAg2O (LCSMO: xAg2O, x = 0, 0.05, 0.1. 0.15, 0.2, and 0.25) composites were successfully fabricated through the conventional sol-gel method. Scanning electron microscopy (SEM), X–ray photoelectron spectroscopy (XPS) and XRD data confirmed presence of silver at A sites (La3+/Ca2+/Sr2+) as Ag+ and segregates at grain boundaries (GBs) to form metallic silver. The electrical properties greatly improved by adding Ag2O. Significant enhancements in peak temperature coefficient of resistivity (TCR) and magnetoresistance (MR) at room–temperature (300 K) were observed for LCSMO:xAg2O composites. The peak TCR increased from 3.7% K−1 (299.3 K, for x = 0) to 14.8% K−1 (301.0 K, for x = 0.2), and MR rose from 16.9% (303.0 K, for x = 0) to 34.1% (300.6 K, for x = 0.2). These improvements in peak TCR were attributed to increased grain size and formation of metallic silver at GBs or within the composites. Moreover, peak MR was higher in Ag2O doped composites, which was mainly due to large spin polarization effect and strong coupling ferromagnetic domains under external magnetic field. Overall, the large room-temperature TCR and MR values of LCSMO:0.2Ag2O composites look promising for future advanced uncooling infrared bolometers and magnetic sensors.

Dependence of the electrical and magnetic properties of La0.845Sr0.155MnO3:Ag0.4 ceramics on its sintering time

In this work, polycrystalline La0.845Sr0.155MnO3:Ag0.4 (LSMO:Ag) ceramics were synthesized via a combined sol–gel and solid-state method with various sintering times. The structure and unique electrical and magnetic properties of the synthesized ceramics were examined in detail. The optimized sintering temperature was determined to be 1723 K. At this temperature, by changing the sintering time from 5 to 14 h, the temperature coefficient of resistivity (TCR) and the magnetic resistance (MR) of the LSMO:Ag samples could be quickly improved. The results show that La3+ and Sr2+ ions were gradually substituted by Ag+ ions with increasing sintering time. The substitution resulted in changes to the Mn3+–O–Mn4+ pairs and a distortion of the MnO6 octahedron, which could be attributed to the double exchange (DE) and Jahn–Teller (JT) effects. At a sintering time of t = 10 h, a peak TCR value of 17.82% K−1 was attained and was achieved at room-temperature (Tk, 299.9 K). This work demonstrates an effective approach to obtain high TCR and MR values at room-temperature for uncooled manganite devices by optimizing the sintering time.

Effect of sintering temperature on room-temperature electrical and magnetic properties of La0.625(Ca0.315Sr0.06)MnO3 polycrystalline ceramics

Polycrystalline La0.625(Ca0.315Sr0.06)MnO3 (LCSMO) ceramics were prepared by conventional sol-gel method at different sintering temperatures (Ts) of 1273, 1373, 1473, 1573, and 1673 K. Structures, electrical and magnetic properties of obtained LCSMO ceramics were investigated by various analytical techniques. X−ray diffraction (XRD) identified structures of all ceramics as pure perovskite LCSMO phase with Pnma space group. Scanning electron microscopy (SEM) revealed improvements in surface compactness and homogeneity of LCSMO ceramics prepared at various Ts. As Ts rose, resistivity (ρ) dropped and both peak temperature coefficient of resistance (TCR) and magnetoresistance (MR) increased. This, in turn, improved crystalline quality and microstructure of LCSMO ceramics. For LCSMO ceramics sintered at 1673 K, the TCR and MR peaks reached maxima of 4.15% (294.5 K) and 17.4% (296.7 K), respectively. X−ray photoelectron spectroscopy (XPS) suggested no change in La, Ca and Sr, indicative of stable proportion of Mn3+ and Mn4+. The increase in Ts caused lattice distortion and suppressed double exchange (DE) interaction. The latter changed the metal to insulator transition temperature (Tp) of the materials. Overall, room−temperature (295–300 K) electrical and magnetic properties of LCSMO ceramics could significantly be enhanced by increasing Ts.

Enhanced room temperature coefficient of resistivity (RT-TCR) and broad metal-insulator transition temperature (TMI) of La0.67Ca0.33-Ag MnO3 polycrystalline ceramics

Abstract Polycrystalline La0.67Ca0.33-xAgxMnO3 (LCAMO, x = 0, 0.06, 0.15, 0.18, and 0.24) ceramics were fabricated by conventional sol-gel route at relatively low sintering temperature of 1100 °C for 12 h. Effects of silver content (x) on crystal structure, grain size, resistivity and magnetic properties of as-prepared LCAMO specimens were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), elemental mapping and energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), and standard four-probe method (ρ-T). The data from XPS, XRD and EDS revealed that silver existed as Ag+ ions in the lattice matrix position of LCAMO ceramics. Broad metal-insulator transition temperature (TMI) values ranging from 267.0 K (x = 0) to 302.6 K (x = 0.24) were obtained with LCAMO specimens prepared with variable Ag+ added contents. Peak temperature coefficient of resistivity (TCR) enhanced from 4.1% K−1 at 263.2 K (for x = 0) to 10.9% K−1 at 278.5 K (for x = 0.18), and reached 7.5% K−1 at room-temperature (295.9 K) for x = 0.24. Meanwhile, magnetoresistance (MR) of materials reached 17.7% at room-temperature (299.2 K) for x = 0.24. Overall, these findings demonstrated that Ag doping was beneficial for improving electrical and magnetic properties of LCAMO materials. In summary, LCAMO ceramics achieved RT-TCR and MR at optimal Ag stoichiometric ratio, promising for applications in infrared bolometers or magnetic sensors.

Structural and electrical properties of La0.67(Ca0.3Sr0.03)MnO3 composites prepared with added Ag

In this account, La0.67(Ca0.3Sr0.03)MnO3:mol%Agx (LCSMO:Agx, 0 ≤ x ≤ 0.5) high-density composites were successfully prepared by the conventional sol-gel method using deionized water as solvent. The structures, surface morphologies and electrical transport properties of obtained composites were analyzed by various analytical methods. The X-ray diffraction (XRD) profiles of LCSMO:Agx exhibited single perovskite structure with pure orthorhombic crystal structure (Pnma space group) and without presence of traces secondary phases. Field emission scanning electron microscopy (FESEM), XRD and X-ray photoemission spectroscopy (XPS) depicted good grain surface connectivity of the specimens. In addition, grain size increased with Ag doping. The influences of Ag2O doping on materials electrical properties were also explored. The results indicated the presence of silver as Ag+ ions substituting A-site ions. Furthermore, small amounts of metallic silver gathered at the grain boundaries (GBs) were detected. This increased both the MnO bond length and MnOMn bond angle, and slightly expanded both cell volume (V) and lattice constant (a, b, c). The maximum value of temperature coefficient of resistivity (TCR) reached 11.2% K−1 with peak TCR temperature (Tk) of 281.5 K. The improved electrical transport performances of LCSMO:Agx materials were attributed to Ag doping, which enhanced Mn4+ ion amounts and GBs connectivity in each specimen. In addition, excess replacement of A-site ions by Ag+ expanded the metal-insulator transition characteristics and reduced the temperature coefficient of resistivity. Finally, a double exchange based mechanism was proposed to explain the above results.

Polycrystalline La0.845Sr0.155MnO3:Ag ceramics (0 ≤ x ≤ 0.5) with room-temperature TCR and MR for improved uncooling photoelectric and magnetic devices

The structural, electrical and magnetic properties of polycrystalline La0.845Sr0.155MnO3:mol%Agx (LSMO:Agx, 0 ≤ x ≤ 0.5) ceramics fabricated by the sol-gel process were systematically investigated. The Rietveld refinements of X-ray diffraction (XRD) patterns confirmed that LSMO:Agx were crystallized in rhombohedral texture belonging to R3¯c space group. As Ag addition rose, grain sizes of LSMO:Agx specimens increased and grain boundaries (GBs) amount decreased accordingly. The optimal values of magnetoresistance (MR) and temperature coefficient of resistivity (TCR) of LSMO:Agx specimens significantly enhanced as Ag content changed. For LSMO:Agx (x = 0.2), the maximum values of TCR and MR reached 17.54% K−1 (peak TCR temperature Tk = 300.04 K) and 34.58% (peak MR temperature Tm = 303.83 K), shifting temperature to room value (300 K). The optimization of the electrical/magnetic performance of the LSMO:Agx samples were ascribed to the Ag doping, which improved the GBs connectivity in LSMO:Agx. Overall, these results indicated the promise of LSMO:Agx ceramics for broad use to uncooling infrared bolometers or magnetic sensors.

Modulation of room-temperature TCR and MR in La1−xSrxMnO3 polycrystalline ceramics via Sr doping

La1−xSrxMnO3 (LSMO) polycrystalline samples with x content from 0.1 to 0.2 were synthesized via the optimized sol–gel method. The effect of Sr doping (x) on crystal structure, surface morphology, magnetic, and electrical transport properties of LSMO ceramics were investigated systematically. X-ray diffraction (XRD) results showed that all samples crystallized in single phases with rhombohedral structure (R $$\bar 3$$ c space group), without any detectable impurity phases. With the increase of x content, lattice parameters expanded, whereas grain size of LSMO ceramic enlarged and grain boundaries (GBs) decreased accordingly. For LSMO ceramics with x = 0.16, peak value of temperature coefficient of resistance (TCR) reached 2.7% K−1 as the peak-TCR temperature (TK) approached room temperature at 292.5 K, as well as the maximum magnetoresistance (MR) value arrived 17.9% at 300.2 K. In addition, peak TCR of LSMO (x= 0.2) was obtained at 6.4% K−1 as TK at 329.4 K. These properties of modulation TCR and MR at room temperature in LSMO ceramics were interpreted by the interaction of double exchange mechanism and Jahn-Teller effects.

Structure and electromagnetic properties of La0.7Ca0.3-xKxMnO3 polycrystalline ceramics

In this study, La0.7Ca0.3-xKxMnO3 (LCKMO) polycrystalline ceramics were synthesized by sol–gel method. Their structures, surface morphologies, and electromagnetic transmission characteristics were studied and discussed. X-ray diffraction results showed that all prepared specimens highly crystalized as single phase with orthorhombic perovskite structure and Pnma space group. Characterization by scanning electron microscopy revealed that grain size increased with the increase in the K+ content. Electrical resistivity as function of temperature (ρ-T) was investigated through standard four-probe method. With the increase in the K+ content, metal–insulator transition temperature (Tp) and the Curie temperature (TC) shifted to higher temperatures, while the resistivity (ρ) reduced. Careful analysis of data indicated that peak temperature coefficient of resistance (TCR) and magnetoresistance (MR) were affected by K+ substitution. At x = 0.02, peak TCR and MR values reached 6.03%·K−1 and 30.26%, respectively. Characteristics of resultant ceramics were explained based on double exchange interaction. Overall, LCKMO materials act as promising candidates for broad range of applications in magnetic devices and infrared detectors at room temperature.

La1-xSrxMnO3:Ag0.2 (0.1 ≤ x ≤ 0.2) ceramics with large room-temperature TCR for uncooled infrared bolometers

In this study, high-density La1-xSrxMnO3:Ag0.2 (x = 0.1, 0.125, 0.15, 0.175, and 0.2) ceramics were prepared by the conventional sol-gel method. The peak values of temperature coefficient of resistivity (TCR) in all La1-xSrxMnO3:Ag0.2 samples were systematically controlled by changing the Sr content. A significant improvement in peak TCR have been observed through adjusting the Sr content. At doping molar ratio of x = 0.15 in La1-xSrxMnO3:Ag0.2 ceramics, the peak TCR value reached 14.7% K−1, and peak TCR temperature (TK, 288.2 K) was estimated to room-temperature (290 K). Visibly, it is encouraging to get such a high room-temperature TCR value. These findings suggested that La0.85Sr0.15MnO3:Ag0.2 ceramics could be used to prepare room-temperature uncooled infrared bolometers.

Nonhysteretic Phenomena in the Metal–Semiconductor Phase-Transition Loop of $\hbox{VO}_{2}$ Films for Bolometric Sensor Applications

Hysteresis observed in the resistive semiconductor-to-metal phase transition in VO2 causes problems in bolometric readout, and thus is an obstacle in utilizing this strong phase transition in bolometric sensor applications. It is possible to avoid the unwanted hysteresis when operating in limited temperature ranges within the hysteresis loop of VO2. Nonhysteretic branches (NHB-s) traced in such limited temperature intervals turned out to have much higher temperature coefficient of resistance (TCR) than VO2 at room temperature: while TCR at 25° C in VO2 is close to 3%, peak TCR values in NHB-s reach 6% in VO2 films on Si/SiO2 substrates and 21% in films on crystalline sapphire substrates. At the same time, the nanoscopic-scale mixture of semiconducting and metallic phases in VO2 within its hysteresis loop provides for partially shunted low resistivity, thus creating an unprecedented combination of record high semiconducting TCR and metal-like low resistance. This combination may benefit the uncooled focal plane array microbolometer IR visualization technology.

Silver ion implantation in epitaxial La2/3Ca1/3MnO3 thin films: Large temperature coefficient of resistance for bolometric applications

Epitaxial films of La2/3Ca1/3MnO3 were successively implanted with 100 and 200 keV silver ions at fluences of 4.5×1015 and 1×1016 ions/cm2, respectively, to achieve a fairly uniform implant distribution. The as-implanted films are insulating and do not show a metal–insulator transition. Postimplantation annealing at 950 °C shows a recovery of the high structural quality of the films, along with an increase in the metal–insulator transition temperature (Tp), magnetoresistance, and the peak temperature coefficient of resistance (TCR) at the transition. The peak TCR of 23% for manganite films is clearly significant for bolometric applications.