Electrical Transport Properties Of La0 Research Articles

Improved electrical transport properties of La0.7Ca0.3−xKxMnO3 (0.0 ≤ x ≤ 0.3) films grown on La0.3Sr0.7Al0.65Ta0.35O3 (00l) substrates by sol–gel spin coating method

Herein, La0.7Ca0.3−xKxMnO3 (LCKMO) films with highly oriented growth were prepared on La0.3Sr0.7Al0.65Ta0.35O3 (00l) substrates by sol–gel spin coating method. Comprehensive analysis of microstructure, surface morphology, ion valence, and electrical transport properties of LCKMO films indicates that the substitution of K+ ions for Ca2+ ions increased the ratio of Mn4+/(Mn3+ + Mn4+), narrowed the one electron bandwidth, and enhanced double exchange mechanism and electron–lattice coupling. Moreover, the doping of K+ ions induced the dense and uniform conical-structured growth of grains on the surface of the films. Results demonstrated that at x = 0.1, LCKMO film exhibited the maximum TCR of 17.84% K−1 at 253.07 K, which was 31.76% higher than that of previously reported La1−x−yCaxKyMnO3 ceramic with the highest TCR. Further theoretical insights into the effects of Ca/K co-doping on electrical transport properties were supplemented.

Theoretical simulation of pre-sintering effect and improvement of electrical transport properties of La0.7Ca0.18Sr0.12MnO3 film prepared by spin coating method

Perovskite manganites Lax(Ca1-ySry)1-xMnO3 have drawn the plentiful attention owing to their distinctive physical properties. Their unique properties make them an ideal candidate for high-sensitivity and uncooled bolometric applications. Optimized La0.7Ca0.18Sr0.12MnO3 (LCSMO) films were grown on (00l) LaAlO3 substrate at different pre-sintering temperature (Tps) via sol–gel spin coating method. According to the test results of microstructure, internal strain, Mn ion valences and surface morphology, electrical transport properties are restricted by MnO6 octahedron distortion and film crystallinity affected by the change in Tps. The microstructure growth was improved and the surface morphology tended to grow in a cross-like structure with high crystallinity by optimizing Tps. Double exchange mechanism and internal strain were enhanced with the increase in Tps. Thereby, due to the enlarging MnOMn bond angle and enhancing MnO covalency, the temperature (Tk) corresponding to temperature coefficient of resistivity (TCR) was increased gradually as Tps increased. The TCR value of LCSMO film reached a maximum value (10.82 %/K) and Tk reached room temperature (302.03 K) at Tps = 1123 K. The theoretical foundation of the pre-sintering effect has been supplemented, helping to understand the influence of pre-sintering on film growth and electrical transport properties.

Tuning strain-stress and electron-lattice effects to enhance electrical transport properties of La0.7Ca0.25K0.05MnO3 films via optimizing sintering temperatures

Facile-prepared films with a high-temperature coefficient of resistivity (TCR) are crucial for application in high-sensitivity bolometers. In this study, La0.7Ca0.25K0.05MnO3 (LCKMO) films were grown on (001)-oriented La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrates using the spin-coating method. Various sintering temperatures (900 °C ≤ Ts ≤ 1050 °C) were utilized in the film preparation, causing the lattice mismatch between films and substrate degraded. The effect of Ts on the strain state of films was investigated through X-ray diffraction (XRD) analysis. The distortion of MnO6 octahedra and the Mn–O bond were assessed using Raman and FTIR spectra, respectively. The structural perfection and elemental valence of films were adjusted via optimizing Ts. Meanwhile, the strain state and defect structure were effectively improved with Ts increasing. These results indicate that the LCKMO films with high crystalline quality can be achieved by optimizing the sintering process. The TCR of LCKMO films was modified. When Ts at 1000 °C, the LCKMO films exhibit the remarkable TCR of 16.29% K-1 at 269.54 K, indicating the substantial potential of LCKMO films in infrared bolometers.

Optimization of the electrical transport properties of La0.7Ca0.3MnO3 films by sintering temperature adjustment

With the development of the radiation thermometers, perovskite manganites have been fallen into the focus of highly sensitive infrared bolometers due to its metal-insulator transition properties. In this study, La0.7Ca0.3MnO3 (LCMO) films were prepared on (l00) LaAlO3 substrates using sol-gel spin-coating technology by adjusting different sintering temperatures (Ts, 1000 °C ≤ Ts ≤ 1400 °C). The analysis of the microstructure, surface morphology, ion valence state, and electrical transport properties revealed that the crystalline quality enhanced and the concentration of Mn4+ increased with the increasing of sintering temperature, promoting the DE effect and improving the electrical properties of the LCMO films. At Ts = 1200 °C, the temperature coefficient of resistivity (TCR) value of the LCMO film reached the maximum value (22.95% K−1) and corresponding peak TCR temperature of 246.85 K indicating that the LCMO film has great potential in infrared bolometers.

Effect of ethylene glycol on preparation and electrical transport properties of La0.67Ca0.33MnO3 ceramics

Perovskite manganates La1-xCaxMnO3 (LCMO) has attracted wide attention due to its unique physical properties such as metal-insulator transition (IMT), colossal magnetoresistance (CMR), which has potential application value in infrared detection, magnetic sensor, and other fields. LCMO precursor powder was prepared using the sol-gel method with a large surface area, high surface energy, and unstable thermodynamic system. To reduce the free enthalpy of the system, powder particles will spontaneously form agglomeration, affecting the structure and properties of materials. Ethylene glycol is selected as a dispersant, and the content of ethylene glycol is changed to obtain LCMO ceramics with excellent uniformity. To achieve the purpose of regulating the electrical transport properties, temperature coefficient of resistance (TCR), and magnetoresistance (MR) of LCMO. In this study, when the amount of ethylene glycol was 4 %, TCR is 42.58 %·K−1 (262.69 K), and MR is 59.96 %. Therefore, the excellent preparation process promotes the application of such materials in the fields of uncooled thermal radiation infrared detection and magnetic sensitivity.

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.

Effect of Nd doping on the electrical transport properties of La0.67Ca0.33MnO3 thin films

Effect of Nd doping on the electrical transport properties of La0.67Ca0.33MnO3 thin films

Effect of sintering temperature on structure and electrical transport properties of La0.7Ca0.26Na0.04MnO3 ceramics

LCNMO (La0.7Ca0.26Na0.04MnO3) ceramics are prepared via the sol-gel method and sintered at different temperatures, ranging from 1000 to 1300 °C. The influences of sintering temperature on structure and electrical properties are systematically investigated. X-ray diffraction analysis reveals that uniform phase of perovskite structure is formed after sintering. Furthermore, scanning electron microscope (SEM) images demonstrate the presence of on the surface, a highly dense grain boundary and an average grain size of ~2.5 μm. The resistivity-temperature (ρ-T) measurement shows that the resistivity decreases with increased sinter temperature. Moreover, the metal-insulation transition temperature (Tp) and peak resistivity (ρmax) gradually decreased with increasing sintering temperature. The influence of various scattering mechanisms on resistivity at low temperatures is studied, revealing that the residual resistivity (ρ0) dictates the electrical transport performance of the LCNMO ceramics. Also, the different models employed to analyze the ρ-T curves in the temperature range of 100–300 K, confirming the occurrence of phase-separation mechanism in the entire temperature range. The resistance temperature coefficient (TCR) of 10.6%·K−1 and maximum magnetic resistance (MRmax) of 57.12% are achieved after sintering at 1200 °C. These results indicate that LCNMO are promising candidates for infrared detector and magnetic sensor.

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

Gd doped La0.8Sr0.2MnO3 (La0.8-xGdxSr0.2MnO3, LGSMO) ceramics were prepared by a sol-gel method. X-ray diffraction (XRD) patterns showed that all samples exhibited distorted perovskite structures, R3c. 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, TP, 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.

Effect of sintering temperature on structural and electrical transport properties of La0.7Ca0.28K0.02MnO3 ceramics

Manganites with large temperature coefficient of resistance (TCR) have been considered as potential candidate for infrared detecting. To date, A-site doping with alkaline-earth metal (+2 oxidation state) has been widely used to improve the TCR. However, doping with alkali ions (+1 oxidation state) was less explored. In this study, 2% K doped La0.7Ca0.28K0.02MnO3 (LCKMO) ceramics were prepared by sol-gel method and sintered within the temperature range of 1000–1300 °C for structural and electrical transport properties investigation. X-ray diffraction (XRD) analysis demonstrated that all samples exhibited an orthorhombic perovskite structure with space group Pnma. Elevated sintering temperature would lead to an increase in grain size, which could account for the concurrent decrease of the resistivity (ρ). By optimizing the sintering process, the magnetoresistance (MR) and TCR reached their maxima of 60.95% and 13.54% K−1, respectively, for sintering temperature of 1200 °C. By fitting the temperature dependence of resistivity (ρ-T), grain boundary scattering and small-polaron hopping (SPH) were found to dominate in the low-temperature ferromagnetic and high-temperature paramagnetic regions, respectively. In addition, the ρ-T in the whole temperature range of 100–300 K can also be explained by the percolation model.

Effect of Incident Light on Transport Properties of Pulsed Laser Deposited Manganite Thin Films

In this communication, we report the results of different light illumination on electrical transport properties of La0.67Ca0.33Mn0.9Ga0.1O3 (LCMGO) thin films grown on Si (100) ( n-type phosphorus-doped) wafer using Pulsed Laser Deposition (PLD) System. The variation in deposition time changes the thickness of the films. X-ray Diffraction (XRD) reveals the polycrystalline structure of LCMGO thin films. The cross-sectional SEM were taken to determine the thickness of the films with changing deposition time. Atomic Forced Micrographs (AFM) show that island type grains diffuse into one another to form a more uniform distribution of grains as the thickness of the film increases. The charge transport properties have been studied using the I-V measurement at LCMGO/Si interfaces. I-V measurement shows the backwards-diode like the behaviour of the LCMGO/Si p-n junction. The reverse bias current changes under the influence of different incident light illumination. The built-in electric field is generated at the interface when the film was illuminated with UV light. The tunnelling process for backward diode like p-n junction is explained using a modified Simmons model.

Effect of oxygen non-stoichiometry on magnetic and electrical transport properties of La0.67Sr0.33MnO3

The effect of oxygen deficiency and oxygen excess on the magnetic and electrical transport properties of La0.67Sr0.33MnO3 has been investigated. The thermal and isothermal magnetization measurement results show that the Curie temperature and saturation magnetization of oxygen deficient sample (defined as A) are higher than those oxygen excess sample (defined as B). The electrical resistivity of A is lower than that of B in studied temperature range. The magnetoresistance (MR) of B is larger than that of A in the temperature range from 280 to 360 K, which agrees with the magnetic field needed full spin polarization at room temperature. The colossal MR (CMR) around transition temperature from ferromagnetic metal to paramagnetic insulator (TMI) for A is larger than that for B, which arises from assistance of stronger lattice deformation for A.

Influence of sintering temperature on the structure and electrical transport properties of La0.7Ba0.1Sr0.2Mn0.85Cu0.15O3 manganites

A systematic study of the La0.7Ba0.1Sr0.2Mn0.85Cu0.15O3 manganites have been conducted, mainly to understand the influence of sintering temperature on structure, microstructure, and electrical transport properties in the materials. Polycrystalline sample of La0.7Ba0.1Sr0.2Mn0.85Cu0.15O3 were prepared using sol-gel method and sintered at 1100 °C and 1200 °C. X-ray diffraction result shows that sintering temperature does not affect the crystal structure of the materials which remain rhombohedral with R-3c space group. a more detailed examination shows that sintering temperature change the unit cell volume, <Mn-O-Mn> bond length, and <Mn-O> bond angle of the samples. The electrical resistivity decreases followed by the decrease in the grain size with the increase in sintering temperature. Analysis using theoretical model shows that both samples can be well explained using percolation model. Fitting result suggests that the transport properties of the materials at low temperature were governed by the scattering and interaction between electron, phonon, and magnon. At high temperature, the electrical transport of the samples was governed by the hopping of polarons.

Substrate-induced strain effect on magnetic and electrical transport properties of La0·67Ca0·33MnO3 thin films with varying orientation

This paper carries out a detailed study on magnetic and electrical transport properties of La0·67Ca0·33MnO3 (LCMO) thin films deposited on SrTiO3 substrates with different orientations, which provide varying degrees of in-plane tensile strain. As confirmed by the structure and morphology analyses, the homogeneous LCMO thin films with columnar grains are epitaxially grown along the orientations of the substrates, and the suffered tensile strain in the film is increasing from (100) LCMO to (111) LCMO. The obtained data suggest that the magnetic and electrical transport properties of the thin films are sensitive to the substrate-induced tensile strain. The resistivity, temperature coefficient of resistivity (TCR) and magnetoresistance (MR) of the thin films were in ascending order of (1 0 0) < (1 1 0) < (1 1 1), while the ferromagnetic-paramagnetic transition temperature (TC), magnetization and metal-insulator transition temperature (TIM) were in descending order of (1 0 0) > (1 1 0) > (1 1 1).

Effect of film thickness and strain state on the structure, magnetic and transport properties of La0.9Sr0.1CoO3 films

In this paper, we investigate the effects of film thickness and strain state on the structure, magnetism and electrical transport properties of La0.9Sr0.1CoO3 (LSCO) thin films. The x-ray diffraction analysis shows that the out-of-plane lattice parameters of LSCO films grown on different substrates gradually approach those of the bulk LSCO with increasing film thickness, indicating that the strain induced by the substrates is partially relaxed in thick films, i.e. 100 nm. The film magnetism is gradually enhanced with increasing film thickness. For the 20-nm-thick film, it is almost non-magnetic. However, the film becomes ferromagnetic when its thickness increases up to 100 nm. The magnetism is stronger for the film under compressive strain than that under tensile strain. The change in the magnetic properties of films is attributed to the lattice strain, which can affect the spin state of Co ions. Regarding the conductivity, all the samples show a semiconducting-like behavior, and the resistivity is inversely proportional to the film thickness. The electrical transport mechanism of the films with different thickness transforms from a three-dimensional variable range hopping (VRH) to a small-polaron hopping conduction (SPC) with increasing temperature. Fascinatingly, the temperature for transport mechanism transformation decreases gradually with increasing film thickness. This work could shed light on the electrical transport mechanism of LSCO films with different thickness.

Effect of sintering temperature on structural, magnetic and electrical transport properties of La0.67Ca0.33MnO3 ceramics prepared by Plasma Activated Sintering

La0.67Ca0.33MnO3 (LCMO) ceramics were prepared by Plasma Activated Sintering (PAS). The effect of sintering temperature on structural, magnetic and electrical transport properties of the LCMO ceramics were investigated. XRD and SEM characterizations of the LCMO ceramics indicated that all samples exhibited single orthorhombic phase. Also, through PAS dense LCMO ceramics were obtained. Certain interesting phenomena were observed from the PAS sintering temperature effect on the magnetic and transport behaviors of LCMO ceramics, which were significantly different from traditional sintering methods The magnetization decreased and the resistivity increased as the sintering temperature increased, whereas the TC and TIM shifted towards the lower temperature side. The conduction mechanism of all samples was electron-magnon scattering process in the ferromagnetic low-temperature region, while the paramagnetic high-temperature region mechanism was explained with the variable range hopping (VRH) model. All these behaviors were explained through the oxygen vacancy effect in combination with the grain size effect.

Effect of laser energy on the electrical transport properties of La0.67Ca0.33MnO3:Ag0.2 films by pulsed laser deposition technique

La0.67Ca0.33MnO3 (LCMO):Ag0.2 films were grown on LaAlO3 (LAO) substrates (100) by pulsed laser deposition (PLD) technique with various incident laser energies. The surface morphologies and the thicknesses of the films were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The crystal structures were analyzed by X-ray, diffraction (XRD), and the temperature dependence of the resistivity (ρ–T) of the films was studied by the standard four-probe method. It can be found that the crystal quality, surface morphology, metal–insulator transition temperature (T p), and temperature coefficient of resistance (TCR) of the LCMO:Ag0.2 films are changed with various laser energy. The highest T p 287 K is obtained with 300 mJ laser energy; meanwhile, the optimal TCR 13.5% K−1 is achieved. The results suggest that the electrical transport properties of LCMO:Ag0.2 films are affected by the interface-induced compressive stress, the oxygen balance, and the double exchange between Mn3+–O–Mn4+.

Correlation between microstructure and electrical transport properties of La0.7(Ba1-xCax)0.3MnO3 (x = 0 and 0.03) synthesized by sol-gel

In this paper, we reported the correlation of structure, microstructure, and electrical transport properties of polycrystalline La0.7(Ba1-xCax)0.3MnO3 (x = 0 and 0.03). The materials were synthesized by sol-gel method. These materials have interesting electronic and magnetic properties which are heavily affected by the degree of crystallographic mismatch between the La and Mn sites. By tuning these sites, the double exchange (DE) and Coulomb interactions among Mn ions can be artificially controlled. La0.7Ba0.3MnO3 is one of the strong candidates for application because it has high magnetoresistance and magnetocaloric properties. Doped Ca to the La0.7Ba0.3MnO3 is aimed for reducing its transition temperature to near room temperature and increasing the magnetoresistance and magnetocaloric properties of this material. Jahn-Teller distortion can be linked to core-shell model with the result of percolation model.

Influence of Gd-content on the electrical transport properties of La0.67−x Gd x Sr0.33MnO3 polycrystalline ceramics by sol–gel method

Polycrystalline perovskite manganites La0.67−x Gd x Sr0.33MnO3 (x = 0.15, 0.20, 0.25, 0.30, 0.35, and 0.40) were prepared by sol–gel method. The crystal structure examined by X-ray powder diffraction indicates that the samples were single phase and crystallize in a rhombohedral structure with increasing Gd content. The grain size and surface morphology were investigated by scanning electron microscope, which reveals that that all the ceramic samples with better crystallization have high density. The relation between resistivity and temperature studied by the standard four-probe method shows that the metal–insulator transition temperature (T P) shifts to the lower temperature and temperature coefficient of resistivity decrease with increasing Gd doping. It is mainly due to Gd doping decreases the A-site average cationic radius 〈r A〉 and thus the Mn3+–O–Mn4+ angle decrease, which result in the reduction of double exchange between Mn3+ and Mn4+.

Magnetic and electrical transport properties of La0.7Sr0.3MnO3/LaFeO3 bilayer thin films

Bilayer films of La0.7Sr0.3MnO3/LaFeO3 (LSMO/LFO) were grown on (001) orientated LaAlO3 substrate for different thickness of LSMO layer by using RF magnetron sputtering. The analysis of X-ray diffraction patterns show the growth of both films along (001) direction and the out-of-plane lattice constant of LSMO film decreases with increase in film thickness. Both films are found to undergo out-of-plane tensile strain and the lattice strain is found to decrease with increase in film thickness. The temperature variation of magnetisation measurements show that all films exhibit ferromagnetic transition with transition temperature in the range of 290K for 30nm thick film to 332K for 200nm film. M–H loops recorded at 50K show a systematic increase in saturation magnetisation with increase in film thickness. The electron magnetic resonance spectra recorded at room temperature and at 77K show the presence of ferromagnetic resonance peak. The resonance peak becomes sharper and shifts towards lower field as the film thickness is increased. The resonance spectra recorded with magnetic field applied perpendicular to the plane of the film show an additional peak due to lattice strain and surface pinning of spins.