A-site Ca/Sr co-doping to optimize room-temperature TCR of La0.7Ca0.3-xSrxMnO3 films

Based on the analysis of crystal structure, Mn³⁺/Mn⁴⁺ pairs, distortion of MnO₆ octahedron, and electrical transport properties of La_1-xCa_xMnO₃ and La_1-xSr_xMnO₃ materials, room-temperature coefficient of resistivity (TCR) of La_0.7Ca_0.3-xSr_xMnO₃ (LCSMO) films was optimized by Ca/Sr co-doping at the A-site. LCSMO films are successfully fabricated on LaAlO₃ (100) substrates via facile spin coating technology. The microstructure of LCSMO films is characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy and X-ray photoemission spectroscopy. Results reveal that A-site Ca/Sr co-doping significantly influenced crystal structure, formation of Mn³⁺/Mn⁴⁺ pairs, and distortion of MnO₆ octahedron. The correlation between microstructure and electrical transport properties was explained through the phenomenological percolation model, double-exchange mechanism and Jahn-Teller effect. Furthermore, the TCR reached 10.2% K^-1 at 296.1 K in La_0.7Ca_0.18Sr_0.12MnO₃ films.     

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

High-density La_0.9-xSr_xK_0.1MnO₃ 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.     

Enhanced room-temperature TCR of La0.67Ca0.33-xSrxMnO3 (0.06 ≤ x ≤ 0.11) polycrystalline ceramics by Sr content adjustment

Herein, the influence of Sr doping on chemical composition, microstructure, and electrical transport properties of La_0.67Ca_0.33-xSr_xMnO₃ (LCSMO, 0.06 ≤ x ≤ 0.11) polycrystalline ceramics is systematically investigated. The study was performed by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), elemental mapping, energy dispersive spectrometry (EDS), X-ray photoemission spectroscopy (XPS), and four-probe method (ρ-T). XRD results verified the synthesis of high-purity orthogonal perovskite structure with Pnma space group. EDS and XPS results confirmed presence and uniform distribution of La, Ca, Sr, Mn and O. Furthermore, ρ-T curves indicated that the resistivity decreased with increasing Sr content, whereas metal-insulator transition temperature (T_MI) gradually increased. Moreover, cell volume (V) and electron bandwidth (W) increased with the increase in Sr content, which effectively reduced the resistivity of LCSMO ceramics. One should note that double exchange (DE) enhancement between Mn³⁺ and Mn⁴⁺ is responsible for gradually increasing T_MI. Finally, maximum TCR value of 14.3% K⁻¹ was achieved at x = 0.08, which rendered TCR peak temperature of 299.0 K. High room-temperature TCR of LCSMO ceramics is promising for next-generation infrared bolometers, operating at room-temperature.     

La1−xCaxMnO3:Ag0.2 (0.25 ≤ x ≤ 0.31) ceramics with high temperature coefficient of resistivity under magnetic field

The polycrystalline La_1?xCa_xMnO₃ ceramics exhibit good electromagnetic performance, i.e., high temperature coefficient of resistivity (TCR), which can be tuned flexibly with respect to structures. Unfortunately, the magnetic field applied to these materials causes a massive decrease in TCR, which hinders their practical applications. In this study, polycrystalline ceramic La_1?xCa_xMnO₃:Ag_0.2 was fabricated by sol–gel and solid–phase doping methods, and subsequently vast TCR was obtained in the magnetic field for ceramic with x = 0.2. For this polycrystalline material, high value of TCR (58.65%·K^?1, 62.00%·K^?1) could be maintained with or without magnetic field with metal–insulator (M ? I) transition temperature near room temperature range. Extremely high value of TCR in the presence of magnetic field is attributed to the spin–spin coupling effect, which is beneficial to the sensitivity of M ? I transition, generating vast TCR in the magnetic field. Overall, these findings provide new prospects for future applications in infrared bolometers.     

Effect of Fe substitution on temperature coefficient of resistance and magnetoresistance of La0.67Ca0.33MnO3 polycrystalline ceramics

La_0.67Ca_0.33MnO₃ perovskite manganate exhibits high temperature coefficient of resistance (TCR) and large magnetoresistance (MR) effect, these enable novel multifunctionalities. Mn site substitution can change magnetic order of the manganates, thereby tailoring both electrical and magnetic transport. Herein, La_0.67Ca_0.33Mn_1-xFe_xO₃(0 ≤ x ≤ 0.06) polycrystalline ceramics were prepared by sol-gel route. The effect of Fe substitution on TCR and MR of La_0.67Ca_0.33MnO₃ was studied. Fe replacing Mn ions, would weaken double exchange, and significantly reduced Curie temperature and ferromagnetism. Additionally, Fe doping promoted the development of grain. TCR increased first with Fe content x and then decreased, and reached 45.2%·K^-1 at x = 0.01, which is the highest value reported. Notably, with Fe doping, MR gradually increased and reached 81.1% (1 T) at x = 0.06. Fe doping can significantly enhance TCR and MR, which generates promising potential in (uncooled) thermistor/infrared detecting and magnetic sensors.     

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

In this study, high-density La_1-xSr_xMnO₃:Ag_0.2 (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 La_1-xSr_xMnO₃:Ag_0.2 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 La_1-xSr_xMnO₃:Ag_0.2 ceramics, the peak TCR value reached 14.7% K⁻¹, and peak TCR temperature (T_K, 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 La_0.85Sr_0.15MnO₃:Ag_0.2 ceramics could be used to prepare room-temperature uncooled infrared bolometers.     

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

In this study, La_0.8-xY_xSr_0.2MnO₃ (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 (T_p) 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.     

Utilization of Ag ions to improve room-temperature TCR of La0.85-xSr0.15AgxMnO3 polycrystalline ceramics

In this work, silver-doped La_0.85-xSr_0.15Ag_xMnO₃ (LSAMO, 0.05 ≤ x ≤ 0.20) polycrystalline ceramics were prepared by the sol-gel method. The experimental characterization of ceramics revealed that Ag ions were bounded with the lattice matrix. The resistivity and the corresponding peak temperature coefficient (TCR) of LSAMO ceramics were systematically tuned by changing the Ag dopant content. Adjusting the proportion of Ag enabled one to vary the metal-insulator transition temperature (T_MI) for LSAMO specimens in a wide range, and their peak resistivity temperature (T_p) was increased from 299.6 to 335.7 K. At the same time, the peak TCR value achieved its maximum of 15.2% K^?1 at the doping molar ratio x of 0.15 and the peak resistivity temperature (T_k) of 294.1 K. In addition, the electrical transport was described in the context of the small polaron hopping (SPH) model and the phenomenological percolation model (PP) over the metal-insulator transition region. Under the combined action of the Jahn-Teller (JT) effect, the double exchange (DE) mechanism and the PP model, LSAMO ceramics possessing high TCR at room temperature were obtained by varying the amount of Ag doping. The observed properties suggest LSAMO material can be used in advanced uncooled infrared bolometers.     

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

Strontium (Sr)-doped La_0.67K_0.33-xSr_xMnO₃ (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 (T_P) 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.     

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

Perovskite manganites La_x(Ca_1-ySr_y)_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 La_x(Ca_1-ySr_y)_1-xMnO₃. Temperature coefficient of resistivity (TCR) and the corresponding peak temperature (T_k) are crucial parameters for uncooled bolometers. Optimal La_0.7Ca_0.18Sr_0.12MnO₃ (LCSMO) films with highly oriented growth were prepared on (00l) LaAlO₃ substrate at different sintering temperature (T_s) 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 T_s. Theoretical Curie temperature and the coupling of the electron lattice weaken gradually with the increase in T_s, 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 T_k. With the increase in T_s, 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 T_s on electrical transport properties was provided.     

Enhanced temperature coefficient of resistance and magnetoresistance of Co-doped La0.67Ca0.33MnO3 polycrystalline ceramics

Recently, La_0.67Ca_0.33MnO₃ has garnered significant research attention due to its peculiar physical properties, such as colossal magnetoresistance and metal insulator transitions. The practical applications of these materials are mainly determined by the temperature coefficient of resistance (TCR) and magnetoresistance (MR). As a mature synthesis route, the sol-gel method can prepare high-quality ceramic targets. Herein, using methanol as a solvent, La_0.67Ca_0.33Mn_1-xCo_xO₃ (0 ≤ x ≤ 0.06) polycrystalline ceramics are prepared using the sol-gel method and the influence of Co doping on electrical and magnetic properties is systematically studied. Co doping increases the grain size, and is helpful to improve TCR and MR. In addition, with increased Co doping, the double exchange is weakened, and the ferromagnetism is depressed, which leads to a decrease in T_MI. The results reveal that the TCR and MR can be optimized by tuning the Co content. For instance, we have achieved a TCR value of 44.2% · K^?1 at x = 0.02 and an MR value of 76.3% at x = 0.04, showing the promise of Co-doped La_0.67Ca_0.33MnO₃ ceramics in a wide array of applications, such as bolometers and magnetic sensors.     

Improvement of electrical and magnetic properties in La0.67Ca0.33Mn0.97Co0.03O3 ceramic by Ag doping

For the perovskite manganite La_1-xCa_xMnO₃, achieving high temperature coefficient of resistance (TCR) and magnetoresistance (MR) is the key to realize its potential applications. In this study, high-quality La_0.67Ca_0.33Mn_0.97Co_0.03O₃:Ag_x polycrystalline ceramics were prepared by the sol-gel method. The results show that Ag doping has important impact on metal-insulator and ferromagnetic-paramagnetic transitions. A Ag doping amount increases, the grain size of the samples increases at x = 0.05 and then decreases. The doping of Ag can improve the crystalline quality of the samples and enhance the connectivity between grains, thereby improving the metallicity of the system. Additionally, with Ag doping amount increases, the resistivity of the samples gradually decreased, while the Curie temperature and the metal-insulator transition temperature gradually increased. Especially after Ag doping, both the TCR peak (TCR_peak) and the MR peak (MR_peak) values are significantly improved. The TCR_peak reaches 65.2%·K^?1 at x = 0.1, while the MR_peak is as high as 82.6% at x = 0.05 under 1 T magnetic field. Doping perovskite manganite ceramics with Co and Ag can greatly optimize their TCR and MR, favoring the potential applications of these materials.     

Nd1-xSrxMnO3 (x = 0.3): A perovskite manganite ceramic that exhibits PTC and NTC double properties

Nd_1-xSr_xMnO₃ (NSMO, x = 0.280, 0.300, 0.330, 0.350, and 0.375) polycrystalline ceramics were fabricated using the sol-gel method. The crystal structure, surface morphology, valence state, elements distribution, and electrical properties were examined to understand the effect of Sr doping on NdMnO₃ ceramics. The resistivity of the NSMO ceramics was measured using a standard four-probe method. The results obtained revealed that Sr doping significantly decreased the resistivity of the ceramics, which can be explained by the double exchange (DE) interaction and small-polaron hopping (SPH) model. The Nd_0.70Sr_0.30MnO₃ ceramic had a positive temperature coefficient (PTC) of resistivity (16.69% K^?1) at 197.5 K, and is expected to be used for preparing electronic switches with high sensitivity. Additionally, the NSMO ceramics maintained a stable negative temperature coefficient (NTC) of resistivity (?1% K^?1) for x = 0.300 in the temperature range of 210.6–342.5 K. In conclusion, it is worth exploring materials with a high PTC and NTC over an extended temperature range, possessing the double potential function for high sensitivity or wide-temperature detection for electronic switches or infrared bolometers.     

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

Gd doped La_0.8Sr_0.2MnO₃ (La_0.8-xGd_xSr_0.2MnO₃, LGSMO) ceramics were prepared by a sol-gel method. X-ray diffraction (XRD) patterns showed that all samples exhibited distorted perovskite structures, R_3c. When the Gd³⁺ content x > 0.03, the crystal structure changed to orthorhombic, Pnma. Scanning electron microscopy (SEM) images showed that the ceramics characterize high density and grain boundary connectivity, and higher Gd³⁺ doping decreased the grain size from 26.72 μm to 7.42 μm. The temperature dependence of resistivity showed a transition from a low-temperature metal to a high-temperature insulator. The resistivity increased with Gd doping content, and the metal-insulator transition temperature, T_P, increased first and then decreased, while the temperature coefficient of resistance (TCR) of the samples first decreased and then increased with Gd³⁺, and the magnetoresistance (MR) increased first and then decreased. The peak TCR at x = 0.06 was 5.18%·K^?1, and MR at 0.04 was 34.57%. The electrical transport properties of the ceramics were explained based on the double exchange (DE) interaction mechanism. The obtained material may have application prospects in magnetic devices and infrared detectors.     

Robust temperature coefficient of resistance of polycrystalline La0.6Ca0.4MnO3 under magnetic fields at room temperature

In the presence of magnetic field, reducing the loss in temperature coefficient of resistance (TCR) and increasing metal−insulator transition point (T_MI) to room temperature are the most important concerns for the application of perovskite manganites in high−precision thermistors. Based on emerging evidence, relevant factor to address these problems lies in the interaction between Jahn−Teller (JT) distortion and magnetic field, which results in spin−orbital coupling (SOC) effect and significantly influences TCR and T_MI. In this work, we studied the magnetic field induced SOC effect in polycrystalline La_1−xCa_xMnO₃ (x = 0.225–0.45) materials synthesized via sol−gel technique. Compounds undergo the JT distortions with increasing Ca dopant content, and the most pronounced distortion of 0.0144 at x = 0.40 is correlated with a basal−plane distortion mode. All samples exhibit T_MI values between 262 K and 288 K, indicating the enhancement of doping−induced double−exchange interaction. In the magnetic field of 1 T, SOC effect sufficiently suppresses the deterioration of TCR caused by deficient magnetization in La_0.6Ca_0.4MnO₃ to a value of 2.9%·K⁻¹ at room temperature (287 K).     

Hydrothermal synthesis,sintering and characterization of nano La-manganite perovskite doped with Ca or Sr

Two lanthanum manganite perovskite-nanostructures, namely; La_xCa_(1-x)MnO₃ and La_xSr_(1-x)MnO₃ (x?=?0.1, 0.3, 0.5 and 1.0), were synthesized by hydrothermal method. To follow up the composition of formed phases, the synthesized powders were calcined at different temperatures. The obtained materials were investigated by X-ray diffraction (XRD) and transmission electron microscope (TEM). Moreover, the calcined powders were pressed at 100?MPa and sintered at variable temperatures; i.e. 1250, 1300, 1350 and 1450?°C. The phase composition and microstructural characteristics of sintered pervoskites were examined by XRD and scanning electron microscope (SEM). Furthermore, physical (bulk density and apparent porosity), electrical resistivity and magnetic properties were also determined. The results revealed that La_xCa_(1-x)MnO₃ and La_xSr_(1-x)MnO₃ nanostructures were successfully prepared by hydrothermal method. The physical properties of sintered pervoskites were strongly depended on dopant type and concentration. The maximum sintering temperature for La_xCa_(1-x)MnO₃ was 1400?°C while for La_xSr_(1-x)MnO₃ was 1450?°C, after which the materials have been fused. Materials doped with Ca or Sr exhibited lower resistivity. On the other side, the magnetic properties have been also improved after addition of Ca or Sr. This has been discussed based on the double exchange mechanism. La_xSr_1-xMnO₃ exhibited better magnetic properties than La_xCa_1-xMnO₃ and LaMnO₃. La_0.5Ca_0.5MnO₃ and La_0.5Sr_0.5MnO₃ exhibited the highest magnetization among the other pervoskites.     

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

Polycrystalline La_0.7(Na_0.3-xK_x)MnO₃ (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 MnO₆ 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 Mn³⁺ and Mn⁴⁺ 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.     

Structural,electrical, and magnetic transport properties of La0.72Ca0.28Mn1−xCrxO3 (0 ≤ x ≤ 0.06) ceramics

To obtain comprehensive materials with both high temperature coefficient of resistivity (TCR) and magnetoresistance (MR) at low magnetic fields, polycrystalline La_0.72Ca_0.28Mn_1?xCr_xO₃ (x = 0, 0.02, 0.04, 0.06) ceramics were prepared herein by sol–gel method. Electronic configuration of Cr³⁺ ions is similar to that of Mn⁴⁺ ions, therefore, successive substitution of Mn with Cr increases electrical resistivity and decreases metal–insulator transition temperature of ceramics, even yielding hump-like feature for Cr-rich (x = 0.06) samples. The best TCR (28.50%·K^?1) and MR (72.37%) values were obtained simultaneously at Cr dopant content of 0.02 (La_0.72Ca_0.28Mn_0.98Cr_0.02O₃). Strong response of the material to temperature and magnetic field was caused by minimal symmetry of orthorhombic structure and the most robust Jahn–Teller distortion. With increasing Cr content, Mn³⁺/Mn⁴⁺ or Mn³⁺/Cr³⁺ double exchange was diluted, and Cr³⁺/Cr³⁺ or Cr³⁺/Mn⁴⁺ superexchange was promoted. However, the internal competition effect was not conducive to the improvement of material properties.     

(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 (Pr_0.75La_0.25)_0.7Sr_0.3MnO₃:Ag_x (PLSMO:Ag_x, 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:Ag_0.15 ceramic with large room-temperature TCR value look prospective candidates for future advanced uncooled infrared bolometers.     

Electrical transport properties of Sm-doped La0.7Ca0.3MnO3 polycrystalline ceramics

Improving the magnetoresistance effect of perovskite ceramic materials under a low applied magnetic field to expand its application range is one of the main research directions of this type of material. In this study, La_0.7Ca_0.3MnO₃ was doped with different levels of Sm by the sol-gel method to yield a series of La_0.7-xSm_xCa_0.3MnO₃ (LSCMO) polycrystalline ceramics. X-ray diffraction (XRD) results revealed that LSCMO ceramics possessed standard perovskite structures. Scanning electron microscopy (SEM) showed grains closely connected without obvious holes. In addition, the grain size gradually decreased with the increase in Sm doping content. The resistivity temperature curves displayed a clear metal-insulator transition behavior of LSCMO accompanied by a steep change from ferromagnetic to paramagnetic behavior (FM-PM). The metal-insulator transition temperature (T_p) values of the as-obtained LSCMO gradually shifted toward lower temperatures with increase in Sm content. Moreover, resistivity temperature coefficient (TCR) and magnetoresistance (MR) values also gradually increased with Sm doping content. The transport properties in polycrystalline ceramics could be adequately explained by the double exchange model, which would be useful for interpreting the CMR effects when used in magnetic devices.