Room-temperature Temperature Coefficient Of Resistivity Research Articles

The structure, magnetic properties, magnetotransport and temperature coefficient of resistivity of hexagonal 4H-SrMnO3 manganite

The perovskite hexagonal SrMnO3 manganite with four layers (4H-SrMnO3) have been one of the hot topics in materials science due to the physical characteristics of antiferromagnetic, ferroelectric, and thermoelectric effects. The transport properties and magnetoresistance (MR) effect of 4H-SrMnO3 have seldom been reported. The structure, temperature coefficient of resistivity (TCR), magnetic and magnetotransport properties of the 4H-SrMnO3 SrMnO3 manganite obtained by solid state reaction have been investigated in this work. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) measurements at room temperature reveal that the SrMnO3 sample exhibits a pure hexagonal symmetric structure, with uniform distribution of particles and elements. Under applied magnetic fields of 2000 Oe, the SrMnO3 sample exhibits a transition from antiferromagnetic (AFM) to paramagnetic (PM) behavior at approximately 280 K, known as the Néel temperature (TN). The resistance is influenced by the magnetic field, but overall exhibits an insulating state. Remarkably, the SrMnO3 sample shows significant MR effect near room temperature. The negative MR near room temperature varies from 5.8 % with 1 T field to 16.8 % with 6 T field, indicating an existence of obvious MR in the hexagonal AFM SrMnO3 manganite. Furthermore, the maxmium value of TCR reaches 4.34 % K−1 near room temperature. These findings of room-temperature TCR and room-temperature MR in the AFM 4H-SrMnO3 hold immense value for the research and potential application of the AFM spintronics and devices.

Optimized electrical transport properties of La0.7Ca0.18Sr0.12MnO3 film by adjusting sintering temperature

Perovskite manganites Lax(Ca1-ySry)1-xMnO3 have conspicuous electrical transport properties used for the application of uncooled bolometers. Thus, considerable attention has paid to the researches on electrical transport properties of Lax(Ca1-ySry)1-xMnO3. Temperature coefficient of resistivity (TCR) and the corresponding peak temperature (Tk) are crucial parameters for uncooled bolometers. Optimal La0.7Ca0.18Sr0.12MnO3 (LCSMO) films with highly oriented growth were prepared on (00l) LaAlO3 substrate at different sintering temperature (Ts) using a facile sol-gel spin coating method. Based on the analysis of microstructure, ionic valence, surface morphology and electrical transport properties, LCSMO films exhibit high crystallinity and large room-temperature TCR at higher Ts. Theoretical Curie temperature and the coupling of the electron lattice weaken gradually with the increase in Ts, which is the dominant factor for the optimization of electrical transport properties. Additionally, the results suggest that the active energy and theoretical Curie temperature play a crucial role in adjusting TCR and Tk. With the increase in Ts, the former increases while the latter decreased, resulting in a high TCR value (12.10%/K) at room temperature (297.38 K). The peak TCR value of LCSMO sintered at 1673 K is about 25% higher than that of the film sintered at 1473 K. The resulting LCSMO films demonstrate great potential for application in uncooled bolometers. Further theoretical basis on the effects of Ts on electrical transport properties was provided.

Comparative study of La0.7Ca0.18Sr0.12MnO3 films with room-temperature TCR grown on SrTiO3, La0.3Sr0.7Al0.65Ta0.35O3 and LaAlO3 substrates

Perovskite La-based manganites have distinctive electrical transport properties; thus, them has become a research focus because of its advanced application in room-temperature infrared bolometers. To assess the influences of different substrates on the crystallinity, surface morphology and electrical transport properties, La0.7Ca0.18Sr0.12MnO3 (LCSMO) films were grown on the (00l) SrTiO3 (STO), La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) and LaAlO3 (LAO) substrates through sol–gel spin coating method. As determined by crystallinity, morphology and electrical transport properties, LCSMO/STO film with largest temperature coefficient of resistivity (TCR) were obtained compared with LCSMO/LSAT and LCSMO/LAO films. The LCSMO film grown on STO exhibited a maximum TCRmax of 9.40%/K (299.05 K), which is about 19% higher than that of the film prepared on LAO. In the LCSMO film, the electron-lattice couplings were optimized effectively owing to the low lattice mismatch between LCSMO/STO, thereby TCRmax of the film can be significantly enhanced. The results suggest that the LCSMO film grown on STO substrate possesses remarkable potential for advanced uncooled infrared bolometers.

Superior La0.67K0.33-xSrxMnO3 films with room-temperature TCR prepared by spin coating method

La0.67K0.33-xSrxMnO3 thin films were grown on LaAlO3 (010) substrates via sol–gel and spin coating methods. The replacement of K ions with Sr ions affected the eg electron bandwidth and concentration of Mn3+/Mn4+ pairs as well as effectively modulated the magnetic/orbital order and lattice structure. Consequently, the ferromagnetic metal to paramagnetic insulation transition was affected, which further optimized the resistivity, temperature coefficient of resistivity (TCR), peak TCR temperature (TK), and peak resistivity temperature (TP). At temperatures below 230 K, temperature-independent scattering and electron-electron scattering were practically not observed in the films. Overall, electrical properties of films improved with an increase in the Sr doping content. The superior La0.67K0.27Sr0.06MnO3 film exhibited a maximum TCR of 11.88% K−1 (298.3 K), which is approximately 31% higher than that of bulk ceramic with the same composition. The as-developed films exhibit significant potential for application in uncooled infrared bolometers.

Optimization of room-temperature temperature coefficient of resistivity of La0.75-xK0.19+xSr0.06MnO3 (0.00 ≤ x ≤ 0.06) ceramics by La and K content adjustment

Herein, La0.75-xK0.19+xSr0.06MnO3 (LKSMO, x = 0.00, 0.02, 0.03, 0.04, and 0.06) polycrystalline ceramics were prepared by sol–gel method. Crystal structure, surface morphology, and electrical properties of these ceramic samples were characterized and analyzed in detail. All LKSMO ceramics had rhombohedral structure (R3¯c space group) with excellent crystallinity and homogeneity. With increasing x value, Mn–O bond lengths were increased, and the number of Mn3+/Mn4+ pairs was reduced in LKSMO samples. Increasing K content in these LKSMO ceramics suppressed double-exchange mechanism and significantly promoted Jahn–Teller effect. Consequently, temperature coefficient of resistivity (TCR) was optimized and the temperature of TCR peak was adjusted to room temperature. By adjusting La and K content ratio at A-site, obtained LKSMO (x = 0.03) ceramics exhibited high TCR (11.4% K−1) at room temperature (292.35 K). These results indicate that La0.72K0.22Sr0.06MnO3 polycrystalline ceramics are suitable materials for the preparation of uncooled infrared bolometers.

Co-optimization of Na and K doping for improved room-temperature TCR of La0.7(Na0.3-K )MnO3 polycrystalline ceramics

Polycrystalline La 0.7 (Na 0.3- x K x )MnO 3 (LNKMO, x = 0.10, 0.15, 0.20, 0.25, and 0.26) ceramics were successfully compounded by adopting conventional sol-gel technology. The physical properties of as-prepared specimens were closely related to their morphology and internal structure, which were characterized and analyzed via X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. Results confirmed that La + ions located at A-sites in crystal lattice were partially substituted by doped Na + and K + ions, which resulted in rotation and distortion of MnO 6 octahedron. Lattice distortion was primary factor behind double exchange (DE) mechanism and Jahn-Teller (JT) effects. In addition, Na and K dopants altered relative amount of Mn 3+ and Mn 4+ ions, causing intensity variation in DE effect. These changes contributed to a decline in resistivity and an increase in peak resistance temperature ( T k ) with increasing K doping level. Meanwhile, optimal temperature coefficient of resistance ( TCR ) value of LNKMO ceramics reached 8.48% K −1 at 292.14 K when x = 0.25. This work reveals the mechanism of Na and K co-doping to optimize electrical transport properties of LNKMO manganese oxides and provides excellent material for the fabrication of uncooled infrared bolometers.

Improved room-temperature TCR of La0.7Ag0.125K0.175MnO3 films by optimizing sintering temperatures

Cation-doped perovskite manganite has unique electrical transport properties; therefore, it has attracted attention due to its promising applications in the field of uncooled infrared bolometers. For the bolometer applications, high temperature coefficient of resistivity (TCR) at room-temperature is essential for the perovskite materials. To investigate the effect of sintering temperature (Ts) on TCR and obtain high TCR values of manganite films at room temperature, La0.7Ag0.125K0.175MnO3 (LAKMO) films were prepared on the (001) SrTiO3 substrate at various Ts via sol–gel spin coating method. Using analysis of structure, morphology, ionic valence, and electrical transport properties, LAKMO films with better crystalline quality and larger TCR values were obtained at higher Ts. The TCR value of LAKMO films reached a maximum value (9.46 % K−1) and the TCR peak temperature (Tk) reached room-temperature (298.75 K) at Ts of 1000 °C, indicating that the material has great potential for the uncooled infrared bolometer applications.

High room-temperature TCR and MR of La1-xSrxMnO3 thin films for advanced uncooled infrared bolometers and magnetic sensors

Perovskite manganese films had promising applications in the field of photoelectronic materials and devices. However, the utilization of manganese films remained severely challenging due to high fabrication cost and inferior electrical and magnetic properties. Herein, La1-xSrxMnO3 (LSMO) thin films were fabricated on La0.3Sr0.7Al0.65Ta0.35O3 (LSATO) substrates using a facile sol–gel spin-coating technique. All the LSMO films displayed (001)-orientation with orthorhombic structure. The LSMO films exhibited high temperature coefficient of resistivity (TCR) and magnetoresistance (MR) values at room-temperature. The maximum TCR value was 10.4 % K−1 (301.2 K, for x = 0.175). This result can be attributed to high carrier concentration and mobility of optimal × content LSMO films with low film-substrate lattice mismatch (-0.4%), leading to low resistivity, and thus, increased TCR value. The maximum MR value reached 42.85% (290.95 K, for x = 0.150). The LSMO films with high room-temperature TCR and MR values are potential materials for advanced uncooled infrared bolometers and magnetic sensors.

Enhancement of magnetoresistance and near room-temperature temperature coefficient of resistivity in polycrystalline La0.7Ca0.24Na0.06MnO3 by silver doping

Enhancement of magnetoresistance and near room-temperature temperature coefficient of resistivity in polycrystalline La0.7Ca0.24Na0.06MnO3 by silver doping

Significantly enhanced room-temperature TCR and MR of La0.67K0.33-xSrxMnO3 ceramics by adjusting Sr content

Strontium (Sr)-doped La0.67K0.33-xSrxMnO3 (LKSMO) ceramics were obtained by traditional sol-gel method. With increasing Sr content, full width at half maximum (FWHM) for temperature-dependent resistivity curves increased, resistivity decreased, and peak resistivity temperature (TP) shifted toward high temperature. Microstructure of LKSMO ceramics was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoemission spectroscopy, energy dispersive spectrometry, and Fourier transform infrared spectroscopy, etc. Connection between microstructure and properties of ceramics was studied by combining double exchange mechanism, Jahn-Teller effect, and phenomenological percolation model. Electrical transport mechanism of ferromagnetic metal (FMM) and paramagnetic insulator (PMI) regions was employed to explain temperature coefficient of resistivity (TCR) and magnetoresistance (MR) behaviors of as-obtained samples. Various scattering factors, effective mass of itinerant electron, and energy difference between FMM and PMI phases affected FWHM of ρ-T curves in Sr-doped LKSMO ceramics. In sum, these findings provide physical mechanism and experimental guidance for synthesis of high-TCR and MR polycrystalline ceramics at room temperature.

A-site Na-doping to enhance room-temperature TCR of La1-xNaxMnO3 polycrystalline ceramics

During the exploration on the temperature coefficient of resistance (TCR) of A-site cation-doped perovskites, divalent cation-doped material systems have received increasing attention; however, the TCR performance of monovalent cation-doped perovskites has been less studied. In order to investigate the effect of monovalent Na cation doping on the TCR of La1-xNaxMnO3 (LNMO, x = 0.1, 0.2, 0.3, 0.4, and 0.5) and obtain LNMO materials possessing high TCR values at room temperature, the LNMO perovskite ceramics were synthesized by the Pechini sol–gel method. The effect of sodium cation doping on their structural and electrical properties was investigated by various characterization methods. An increase in Na content affected the grain size and Mn4+ ion concentration in the LNMO ceramics. Furthermore, increasing quantity of Na significantly increased the TCR from 5.89 % K−1 at x = 0.1 to 8.56 % K−1 at x = 0.4. For a Na-doping level x = 0.4, the peak TCR temperature (Tk) at room temperature reached 299.42 K. Among the feasible reasons that could improve the above electrical parameters are the weakened grain boundary scattering, the increase in A-site vacancy, the enhanced double-exchange effects, and the generation of Jahn–Teller distortions. According to the results of this study, the obtained LNMO ceramics seem to be promising for the application in uncooled infrared bolometer technology.

Impact of K doping on room-temperature temperature coefficient of resistivity of La0.7(Ag0.3-xKx)MnO3 (0.160 ≤ x ≤ 0.180) polycrystalline ceramics

Herein, La0.7(Ag0.3-xKx)MnO3 (LAKMO, x = 0.160, 0.165, 0.170, 0.175 and 0.180) polycrystalline ceramics are prepared by the sol-gel method and the influence of K content on the structure of LAKMO ceramics is investigated using X-ray powder diffraction (XRD), field-emission scanning electron microscope (FESEM), Fourier transform infrared (FTIR) and Raman spectroscopy, demonstrating that variations in K content cause significant structural changes. For instance, K doping led to the distortion of MnO6 octahedron and grain growth. Moreover, the energy dispersive spectrometer (EDS), elemental mapping and X-ray photoemission spectroscopy (XPS) confirmed the uniform distribution of constituent elements on the surface. The increase in K-doping ratio resulted in the distortion of MnO6 octahedron, weakening grain boundaries scattering and enhancing the double exchange effect. Consequently, the electrical transport properties of LAKMO ceramics were improved with the increase of K doping, especially the decrease in resistivity and increase in temperature coefficient of resistivity (TCR) values. At x = 0.175, the peak TCR value was found to be 11.15% K−1 at room temperature (Tk = 292.22 K). These results indicated that the K-doped LAKMO ceramics are promising candidates for uncooled infrared bolometers.

Using spin coating method to prepare near room-temperature TCR of La0.7Ca0.205Sr0.095MnO3 films for uncooled infrared bolometers

La0.7Ca0.205Sr0.095MnO3 (LCSMO) thin films were grown on LaAlO3 (100) substrates via facile spin coating at different sintering temperatures (Ts; Ts = 750, 900, 1100, and 1300 °C). The crystal structures of the films were detected by X-ray diffraction. The distortion of MnO6 octahedral was analyzed by Fourier transform infrared spectroscopy, while the surface morphology was observed using atomic force microscopy. In addition, the concentrations of itinerant electron and Mn3+/Mn4+ pairs were determined by X-ray photoemission spectroscopy. The electrical performance was analyzed using double exchange interaction, Jahn–Teller effect, and phenomenon percolation model. In general, the electrical properties of the films improved by increasing Ts. The peak temperature coefficient of resistivity (TCR) enhanced from 1.9% K−1 at 210.5 K (for Ts = 750 °C) to 11.1% K−1 at 276.8 K (for Ts = 1300 °C). These LCSMO films with optimized electrical properties exhibited a peak TCR temperature close to room temperature (290–300 K), making these films potential candidates for the uncooled infrared bolometers.

High-density sol-gel derived, cold-isostatically pressed La0.67Ca0.27Sr0.06MnO3 polycrystalline ceramics and their room-temperature TCR improvement

In this study, high-density La0.67Ca0.27Sr0.06MnO3 (LCSMO) ceramics were successfully obtained by sol-gel method followed by cold isostatic pressing (CIP) under 250 MPa. Effects of sintering temperature (TS, 1250 °C ≤ TS ≤ 1450 °C) on structure, surface chemical, electrical, and optical properties of as-obtained LCSMO ceramics were investigated by X-ray diffraction (XRD, BDX3200), X-ray photoemission spectroscopy (XPS, Thermo Fisher Scientific), a four-probe system (East changing ET9005), Fourier transform infrared spectrometry (FTIR, TENSOR 27), Raman microscopy (RENISHAW inVia) and UV–vis spectrophotometry (HITACHI U-4100), respectively. All prepared samples showed orthorhombic structure with Pnma space group. As TS increased, grain size gradually rose from 2.71 to 7.30 μm. XRD refinement, Raman, and FTIR all depicted constant of bond angle and length of Mn–O. Hence, variation in TS did not cause lattice distortion inside samples. The best electrical properties were obtained at 1450 °C, where resistivity (ρ) fell below 0.008 Ω cm and temperature coefficient of resistivity (TCR) reached 13.0% K−1 at 289.2 K (room temperature).It is worth noting that electrical performance was indeed improved due to high densities of samples under processing of CIP. Overall, the change in TS from 1250 to 1450 °C greatly influenced electrical behaviors but showed little effect on structural and optical properties of LCSMO ceramics.

Optimization of room-temperature TCR of polycrystalline La0.9-xSrxK0.1MnO3 ceramics by Sr adjustment

High-density La0.9-xSrxK0.1MnO3 ceramics (LSKMO, A-site = La, Sr and K, 0 ≤ x ≤ 0.25) are successfully fabricated by using facile sol-gel method. Electrical properties are performed by using combination of phenomenological percolation (PP) model, double exchange (DE) mechanism, and Jahn-Teller (JT) effect. Moreover, X-ray diffraction and scanning electron microscopy are employed to analyze the structure and morphology of LSKMO ceramics. Valence states and ionic stoichiometry are assessed by using X-ray photoemission spectrometry. Results reveal that Sr2+ ions, substituting La3+ ions, significantly influenced DE mechanism and JT effect. In addition, Sr-doping plays essential role in improving electrical properties of LSKMO ceramics. At optimal doping content of x = 0.09, peak temperature coefficient of resistance (TCR) of the resistivity is found to be 11.56% K−1 at 297.15 K, which is optimal TCR for A-site K-occupied perovskite manganese oxides. These results confirm that polycrystalline LSKMO ceramics render high room-temperature TCR values due to Sr-doping.

A-site K-doping to enhance room-temperature TCR of polycrystalline La0.8Sr0.2-xKxMnO3 ceramics

Herein, polycrystalline La0.8Sr0.2-xKxMnO3 (LSKMO, 0 ≤ x ≤ 0.2) ceramics with varying K concentration are successfully synthesized via a facile sol-gel method. The electrical transport properties and microstructural of the prepared samples are characterized and analyzed in detail. The different characterization results show that K+ ion substituted La3+ and Sr2+ ions significantly influenced the double exchange (DE) mechanism and Jahn-Teller (JT) effects. The electrical resistivity studies suggest that as the K doping content rose, the resistivity increased and peak resistance temperature decreased. Electrical transport properties of samples are analyzed via the combination of DE mechanism, JT effects, variable-range hopping and small-polaron hopping model. The temperature coefficient of resistance (TCR) measurement demonstrates the enhanced temperature sensitivity for the K-doped polycrystalline ceramics samples as compared to the pure La0.8Sr0.2MnO3 samples. The optimized x content for the polycrystalline LSKMO ceramics is determined to be x = 0.08. At this x value, the peak TCR of the resistivity measured 9.11% K−1 at 292.44 K. These results confirm that high room-temperature TCR values can be achieved by optimizing A-site K doping and demonstrate the potential of polycrystalline La0.8Sr0.12K0.08MnO3 ceramic in room-temperature infrared bolometers.

A-site mixed-valence co-doping to optimize room-temperature TCR of polycrystalline La0.8K0.04Ca0.16-xSrxMnO3 ceramics

Herein, polycrystalline La0.8K0.04Ca0.16-xSrxMnO3 ceramics (A-site = La, K, Ca and Sr, 0.00 ≤ x ≤ 0.16) are successfully synthesized via the sol-gel process and the influence of Sr content on microstructural and electrical transport properties is investigated in detail. The results reveal that the replacement of Ca-ions by Sr-ions resulted in a decreased resistivity and enhanced temperature coefficient of resistance (TCR) peak temperature (Tk). The influence of A-site mixed-valence co-doping, where A-site is occupied by monovalent alkali-metal, divalent alkaline-earth element and trivalent rare-earth element, on electrical transport properties can be explained by using different conduction mechanisms in different temperature regions. At optimal doping content of 0.12, peak TCR of the resistivity was found to be 12.04% K−1 at 290.38 K, which is the best reported TCR for A-site mixed-valence co-doped perovskite manganese oxides. These results confirm that high room-temperature TCR values can be achieved by optimizing A-site mixed-valence co-doping and demonstrate the potential of polycrystalline La0.8K0.04Ca0.04Sr0.12MnO3 ceramic in uncooling infrared bolometers.

(Pr0.75La0.25)0.7Sr0.3MnO3:Agx (0 ≤ x ≤ 0.25) polycrystalline ceramics with room-temperature TCR improvement for uncooled infrared bolometers

In this work, perovskite manganite (Pr0.75La0.25)0.7Sr0.3MnO3:Agx (PLSMO:Agx, x = 0, 0.05, 0.10, 0.15, 0.20 and 0.25) ceramics were successfully prepared by sol-gel route and solid-state reaction. The surface morphologies, peak temperature variation behaviors of temperature coefficient of resistivity (TCR), microstructural and electrical transport properties of all the specimens were analyzed by various testing methods like XRD, SEM, EDS, R-T and XPS. XRD Rietveld refinement data demonstrated that Mn–O bond length, Mn–O–Mn bond angles and the unit cell volume increased along with the rise in x. Consequently, the bandwidth describing the overlap between the O2p and Mn3d orbitals reduced, and this change further affected the electrical transport properties. Scanning electron microscopy (SEM) images indicated that silver was helpful in increasing the grain size. The metal-insulator transition temperature increased due to the enhancement in double exchange (DE) interaction. X-ray photoelectron spectroscopy (XPS) fitting data (percentage of Mn4+ and O2−) along with XRD Rietveld refinement data confirmed the enhancement in DE interaction. The most remarkable thing was that the reduction in resistivity occurred gradually, which resulted in a significant improvement in the TCR. The TCR value achieved 11.35% K−1 with the peak temperature being 300.69 K (room-temperature ~ 300 K) at x = 0.15. Obviously, obtaining a large room-temperature TCR value (≥10% K−1) in praseodymium perovskite oxides was encouraging since such results have not been explored previously. Overall, the proposed PLSMO:Ag0.15 ceramic with large room-temperature TCR value look prospective candidates for future advanced uncooled infrared bolometers.

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 conduction in La0.85Sr0.15MnO3:Agx (0 ≤ x ≤ 0.5) ceramics with large room-temperature TCR

Polycrystalline La0.85Sr0.15MnO3:Agx (LSMO:Agx, 0 ≤ x ≤ 0.5) ceramics were synthesized using sol-gel procedure. All specimens showed rhombohedral perovskite structures in R3‾c space group. As the amount of Ag increased, grain size of ceramics increased, and resistivity accordingly decreased. Large temperature coefficient of resistivity (TCR) of 22.9% K−1 was obtained at room temperature (289.2 K) for x = 0.4. Interestingly, analyses of resistivity-temperature (ρ-T) experimental data showed that conduction mechanism over entire temperature region perfectly matched theoretical percolation model. This reveals that electrical transport properties of LSMO:Agx ceramics are mainly affected by domains, grain boundaries (GBs), and Kondo-like spin-dependent scattering. It also demonstrates the coexistence of paramagnetic (FM) and ferromagnetic (PM) phases in LSMO:Agx ceramics. The ρ-T and scanning electron microscopy (SEM) results confirmed that the introduction of Ag weakened these scattering effects.