Properties Of La0 Research Articles

Role of divalent doping at A-sites (A=Ca2+, Sr2+, Ba2+ & Pb2+) on thermoelectric and magnetoresistive properties in La0.67(Bi0.0835Na0.0835) A0.165MnO3

The present work reports on the effect of divalent ion doping (Ca2+, Sr2+, Pb2+ & Ba2+) ions at A-site in the compound with compositional formula La0.67(Bi0.0835Na0.0835)A0.165MnO3 on structural, magnetic, magneto-transport and thermoelectric properties. X-ray diffraction reveals orthorhombic structure for calcium and barium doped with no peak splitting observed at ~ 32o whereas rhombohedral structure for strontium and lead dopants with a peak splitting in the main intensity. Doping with divalent ions at A-site in La0.67(Bi0.0835Na0.0835)A0.165MnO3 manganites has introduced Mn2+ ions, changing the ratio of Mn3+/Mn4+ in octahedral site and this has been confirmed from X-ray photospectroscopy studies. The field emission scanning electron microscope images confirm different grain sizes and morphologies for different doping elements and distinguished variation is noticed for strontium doped manganites with a grain size of 1.08µm. Room temperature ferromagnetic behavior was observed in the samples at room temperature except for calcium doped sample and magnetic behavior has been discussed on the basis of the various interactions between mixed valence manganese ions and Mn3+/Mn4+ ratio. Electrical resistivity (ρ) as a function of temperature (T) without magnetic field indicates the double peak behavior and with the application of external magnetic fields, the double peak disappears, in all the investigated samples. Highest MR% at their respective transition temperatures (TP1) has been obtained for lead doped samples when compared to barium, strontium and calcium samples. Activation energies (EP) estimated decreases initially for calcium and strontium whereas it increases for lead and barium dopants i.e. for further increases in ionic radii. The change of sign from positive to negative in Seebeck coefficient (S) was noticed with increasing ionic radii suggesting the variation in the nature of charge carriers. The electron-electron, electron-magnon, magnon-magnon scattering mechanism contributes to the temperature dependent resistivity and thermopower in the low temperature region while in the paramagnetic insulating region is governed by a small polaron hopping mechanism.

Optical temperature-sensing properties in La1.55SiO4.33:Yb3+,Ho3+ phosphors affected by Ho3+-doping concentration

In this paper, the Yb3+-Ho3+ co-doped La1.55SiO4.33 (LSO) phosphors were synthesized by the conventional solid-state reaction method. The phase purity and morphology of the samples were studied by XRD and SEM, respectively. Under 980 nm excitation, the upconversion (UC) luminescence of the LSO:Yb3+,Ho3+ phosphors was checked for different Ho3+ doping content and pump power. The corresponding UC mechanism was interpreted from the changing decay lifetimes and the energy transfer processes between Yb3+ and Ho3+ ions. Meanwhile, the temperature-dependent emission spectra were analyzed to learn the optical temperature-sensing behaviors with the fluorescence intensity ratio (FIR) method. The results revealed that the FIR (I658/I544) value increased when the temperature rose, which followed a linear function. The sensor sensitivity was evaluated, and the LSO:10%Yb3+,2%Ho3+ phosphor showed the highest absolute sensitivity. Besides, the main population way on 5F5 level of Ho3+ for red emission was clarified by the comparison of the UC spectra excited by continuous-wave and pulse light. Based on the above results, the LSO:Yb3+,Ho3+ phosphor can be considered as a new UC luminescent material for optical temperature sensors.

Influence of A-Site Modifications on the Properties of La0.21Sr0.74−xCaxTi0.95Fe0.05O3−δ Based Fuel Electrode for Solid Oxide Cell

To make solid oxide fuel cell (SOFC) systems commercially attractive it’s essential to reduce manufacturing cost and improve the stability of membrane electrode assembly (MEA). In this research, the influence of A-site modification on electrical and electrochemical performance of 5% A-site deficient La0.21Sr0.74−xCaxTi0.95Fe0.05O3−δ (x = 0.26 − 0.69) (LSCTF5-x) hydrogen electrode has been studied. Results indicate that the magnitude of A-site deficiency and Ca concentration in A-site influence the conductivity, catalytic activity and stability of the electrodes considerably. The highest stability was observed in the case of La0.21Sr0.26Ca0.48Ti0.95Fe0.05O3−δ anode composition. The maximal total electrical conductivity of porous electrode layer made of LSCFT5-x was 3.5 S cm−1 at 850 °C characteristic of the La0.211Sr0.26Ca0.48Ti0.95Fe0.05O3−δ material in 97% H2 + 3% H2O atmosphere. The best electrochemical performance was observed in the case of La0.21Sr0.37Ca0.37Ti0.95Fe0.05O3−δ , which showed polarization resistance value equal to 0.44 Ω cm2 after 100 h of stabilization at 800 °C in humidified (1.7% H2O) H2 atmosphere. During the stability test the fuel cell with optimal anode composition 50 wt% La0.21Sr0.26Ca0.48Ti0.95Fe0.05O3−δ + 50 wt% Ce0.9Gd0.1O2-δ showed power density of 437 mW cm−2 at 850 °C in 98.3% H2 + 1.7% H2O atmosphere.

Impact of sintering temperature on the structural, magnetic and magnetocaloric properties in La0.75Eu0.05Sr0.2MnO3 manganite

This work concerns a profound study on the structural, magnetic properties and the influence of gradual decrease of the sintering temperature TS on the magnetocaloric properties of La0.75Eu0.05Sr0.2MnO3 manganite elaborated by adopting sol-gel method with TS = 800 °C, 1000 °C and 1200 °C. The refinement of X-ray diffraction patterns at room temperature has shown the coexistence of both rhombohedral R3¯c and orthorhombic Pnma structural phases. The grain size of the sample sintered at 800 °C is around 56 nm. The Curie temperature TC slightly shifts from 305 K to 298 K with decreasing particle size. The magnetic behavior has been discussed based on the core-shell structure. Reducing TS induces the broadening of the magnetic transition. According to the magnetocaloric study, the maximum relative cooling power (RCP) value was recorded for the sample sintered at 800 °C (RCP = 90.11 J/kg for a magnetic field of 2 T at 298 K) suggesting that this sample represents a promising candidate for magnetic refrigeration at room temperature.

Effects of impurities on the cooling of photoexcited carriers in La1−xSrxCoO3−δ: A DFT and nonadiabatic molecular dynamics study

Photo-carrier relaxation in semiconductors determines their photon-conversion efficiency. Impurities have been proven to play an essential role in improving the efficiency and stability of perovskites. We studied the effects of Sr-doping and O-vacancies on the electronic band structure and photoexcited carrier cooling of perovskite-type LaCoO3 using density functional theory and nonadiabatic molecular dynamics methods. We found that the substitution of Sr2+ for La3+ in LaCoO3 leads to a semiconductor–metal transition, while a stoichiometric oxygen vacancy restores semiconductor properties in La1−xSrxCoO3−δ (δ = x/6). In addition, the oxygen vacancy basically changes the electronic band structures, and for visible light with low oxygen vacancy intensity, the photo-electron cooling can be reduced fourfold relative to that of pure LaCoO3. We clarify the functions of impurities, Sr-dopants, and O-vacancies in LaCoO3 and find that the average coupling strength between carriers (electrons/holes) and phonons can be used as a descriptor to characterize carrier relaxation, which is of great value for the further development of practical photo-conversion based on perovskites.

Structural, magnetic and magnetocaloric properties in La0.67(Sr1−xMgx)0.33MnO3 (x = 0, 0.1, 0.3) compounds

Structural, magnetic and magnetocaloric properties in La0.67(Sr1−xMgx)0.33MnO3 (x = 0, 0.1, 0.3) compounds

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

For the perovskite manganite La1-xCaxMnO3, achieving high temperature coefficient of resistance (TCR) and magnetoresistance (MR) is the key to realize its potential applications. In this study, high-quality La0.67Ca0.33Mn0.97Co0.03O3:Agx 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 (TCRpeak) and the MR peak (MRpeak) values are significantly improved. The TCRpeak reaches 65.2%·K−1 at x = 0.1, while the MRpeak 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.

Synthesis and properties of La1 – x Sr x NiO3 and La1–x Sr x NiO2

Superconductivity has been realized in films of La1−x Sr x NiO2. Here we report synthesis and characterization of polycrystalline samples of La1−x Sr x NiO3 and La1−x Sr x NiO2 (0 ≤ x ≤ 0.2). Magnetization and resistivity measurements reveal that La1−x Sr x NiO3 are paramagnetic metal and La1−x Sr x NiO2 exhibit an insulating behavior. Superconductivity is not detected in bulk samples of La1−x Sr x NiO2. The absence of superconductivity in bulk La1−x Sr x NiO2 may be due to the generation of hydroxide during reduction, a small amount of nickel impurity, or incomplete reduction of apical oxygen. The effect of interface in films of La1−x Sr x NiO2 may also play a role for superconductivity.

Theoretical study of the magnetic and magnetocaloric properties of La0.7Sr0.3Mn0.95Fe0.05O3 perovskite manganites at low and high applied magnetic fields: Landau theory and phenomenological models

Theoretical study of the magnetic and magnetocaloric properties of La0.7Sr0.3Mn0.95Fe0.05O3 perovskite manganites at low and high applied magnetic fields: Landau theory and phenomenological models

Effect of Cr Substitution on Magnetic and Magnetocaloric Properties for La0.62Nd0.05Ba0.33MnO3

Effect of Cr Substitution on Magnetic and Magnetocaloric Properties for La0.62Nd0.05Ba0.33MnO3

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 Ag doping on structure and electrical properties of La0.7Ca0.26K0.04MnO3 ceramics

Effect of Ag doping on structure and electrical properties of La0.7Ca0.26K0.04MnO3 ceramics

The investigation of the effect of K doping on the structural, magnetic, and magnetocaloric properties of La1.4−xKxCa1.6Mn2O7 (0.0 ≤ x ≤ 0.4) double perovskite manganite

The investigation of the effect of K doping on the structural, magnetic, and magnetocaloric properties of La1.4−xKxCa1.6Mn2O7 (0.0 ≤ x ≤ 0.4) double perovskite manganite

Comparative study on the effect of synthesis route on the structural, magnetic, and magnetocaloric properties of La0 .5Ca0.5Mn0.95V0.05O3 manganite

ABSTRACT The influence of the synthesis method on structural, magnetic and magnetocaloric properties of the La0.5Ca0.5Mn0.95V0.05O3 compound has been investigated. The compound was prepared by glycine nitrate process (GNP) and compared to counterparts obtained with solid-state route (S-S) and ball milling (B-M). The structural analysis shows a pure and single-orthorhombic crystalline phase for the GNP compound. A secondary phase LaVO4 was detected for S-S and B-M samples. From magnetization versus temperature analysis, different magnetic behaviors were distinguished when moving from one technique to another. The nature of transition was determined and a crossover from second order to first-order magnetic transition was observed with the decrease of crystallite size. Landau theory was performed to confirm the order of magnetic transition of the sample consistent with the Banerjee criterion. The magnetic entropy change (ΔSm) and the relative cooling power RCP, which decreased by reducing the particle size, were calculated.

Effects of Cu doping on electrochemical NOx removal by La0.8Sr0.2MnO3 perovskites

Electrochemical removal of nitrogen oxides (NOx) by perovskite electrodes is a promising method due to its low cost, simple operation and no secondary pollution. In this study, a series of La0.8Sr0.2Mn1-xCuxO3 (x = 0, 0.05, 0.1 and 0.15) perovskites are fabricated as the improved electrodes of solid electrolyte cells (SECs) for NOx removal and the effects of Cu doping are investigated systematacially. Multiple characterization methods are carried out to analyze the physicochemical properties of perovskites firstly. Then the performances of cells based on various perovskites are evaluated by the measurements of electrochemical properties and NOx conversions. The results show that the Cu-doped electrode has more surface oxygen vacancies and a better redox property, thus having a higher NOx conversion and smaller polarization resistance. The electrode based on La0.8Sr0.2Mn0.9Cu0.1O3 has the maximum 70.8% NOx conversion and the lowest 36.3 Ω cm2 Rp value in the atmosphere of 1000 ppm NO at 700 °C. First-principle calculation reveals that the Cu-doped electrode is easier to form surface oxygen vacancy, while the surface oxygen vacancy plays an important role on electron transfer between electrode and NOx molecule. This study not only provides a new strategy to enhance the electrode performance for NOx removal in SECs but reveals the fundamental effect of Cu doping on the properties of La0.8Sr0.2MnO3 perovskites.

Correlation of Magnetic and Superconducting Properties with the Strength of the Magnetic Proximity Effect in La0.67Sr0.33MnO3/SrTiO3/YBa2Cu3O7-δ Heterostructures.

The effect of the stacking sequence on magnetic and superconducting properties in La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7-δ (YBCO) and LSMO/SrTiO3/YBCO heterostructures, which consequently affected the magnetic proximity effect (MPE), was investigated using spin-polarized neutron reflectivity experiments. The results established the intrinsic nature of MPE and its correlation with stacking sequence-dependent magnetic and superconducting properties in these oxide heterostructure systems. We found an increase in the superconducting transition temperature (Tsc) and magnetization for both of the heterostructures as compared to heterostructures with a reversed stacking order. The evolution of the magnetization of the interfacial ferromagnetic (FM) layer, studied as a function of temperature for both heterostructures, showed a decrease in the MPE-induced magnetic depleted layer thickness for heterostructures at a higher Tsc. A comparison of the results of different studies with the present results suggested that the average magnetization and transition temperatures of a FM and a superconductor (SC) were important parameters that dictate the strength of the proximity effect due to the complex interaction of SC and FM in these systems. Tuning the strength of MPE in FM/SC and FM/I/SC oxide heterostructures may provide a promising platform for the effective realization of devices.

Nanostructured Manganite Films Grown by Pulsed Injection MOCVD: Tuning Low- and High-Field Magnetoresistive Properties for Sensors Applications.

The results of colossal magnetoresistance (CMR) properties of La0.83Sr0.17Mn1.21O3 (LSMO) films grown by pulsed injection MOCVD technique onto various substrates are presented. The films with thicknesses of 360 nm and 60 nm grown on AT-cut single crystal quartz, polycrystalline Al2O3, and amorphous Si/SiO2 substrates were nanostructured with column-shaped crystallites spread perpendicular to the film plane. It was found that morphology, microstructure, and magnetoresistive properties of the films strongly depend on the substrate used. The low-field MR at low temperatures (25 K) showed twice higher values (−31% at 0.7 T) for LSMO/quartz in comparison to films grown on the other substrates (−15%). This value is high in comparison to results published in literature for manganite films prepared without additional insulating oxides. The high-field MR measured up to 20 T at 80 K was also the highest for LSMO/quartz films (−56%) and demonstrated the highest sensitivity S = 0.28 V/T at B = 0.25 T (voltage supply 2.5 V), which is promising for magnetic sensor applications. It was demonstrated that Mn excess Mn/(La + Sr) = 1.21 increases the metal-insulator transition temperature of the films up to 285 K, allowing the increase in the operation temperature of magnetic sensors up to 363 K. These results allow us to fabricate CMR sensors with predetermined parameters in a wide range of magnetic fields and temperatures.

Temperature and Frequency Dependence of Negative Capacitance, Dielectric and Electric Properties in La0.57Nd0.1Sr0.13Ag0.2MnO3 Ceramic

Temperature and Frequency Dependence of Negative Capacitance, Dielectric and Electric Properties in La0.57Nd0.1Sr0.13Ag0.2MnO3 Ceramic

Effect of Structure and Electron Configuration on the Magnetic Properties of La0.7Ca0.3– x Sr x Mn0.95Al0.05O3 Manganites

Effect of Structure and Electron Configuration on the Magnetic Properties of La_0.7Ca_0.3– <i> _x </i>Sr<i> _x </i>Mn_0.95Al_0.05O₃ Manganites

Electrical properties of La0.72Ca0.28MnO3: Ag0.2 thin films of different deposition time prepared by deposited pulsed laser method

Electrical properties of La0.72Ca0.28MnO3: Ag0.2 thin films of different deposition time prepared by deposited pulsed laser method