Transport Properties Of Polycrystalline La0 Research Articles

Enhanced electrical transport properties of polycrystalline La0.67Sr Ca0.23-K0.1MnO3 ceramics through A-site multielement co-doping

Current research on perovskite materials is mainly focused on how to achieve a high temperature coefficient of resistivity (TCR) in anticipation of application in infrared detection. In this study, we report the superior electrical transport properties of polycrystalline La0.67SrxCa0.23-xK0.1MnO3 (LSCKMO) (0.03 ≤ x ≤ 0.13) ceramics produced through the sol-gel process using different Sr doping contents. Based on previous studies, polycrystalline manganite ceramics with a higher TCR at room temperature were obtained by optimising the composition ratio of Sr or Ca. In the process of continuous doping, the crystal structure of the polycrystalline LSCKMO ceramics changed significantly from Pnma to R 3‾ c. The final polycrystalline La0.67Sr0.10Ca0.13K0.1MnO3 ceramic material was obtained with a TCR of 17.16% K-1 and peak TCR temperature of 289.42 K, demonstrating that suitable candidates can be obtained for infrared detection technology.

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.

Study on Extraordinary Transport Behaviors of Polycrystalline La-Sb-Mn-O Ceramic

The transport properties of polycrystalline La0.9Sb0.1MnO3 (LSMO) bulk prepared by the solid-state reaction were investigated. We find that transport behaviors heavily depend on the synthesis process. The resistivity of LSMO1 for less rubbing time shows one metal-insulator transition (MIT) peak at temperature of 201 K, while the resistivity of LSMO2 for more rubbing time shows a MIT and a shoulder at about 240 and 140 K, respectively. The magnetoresistance (MR) ratio of LSMO2 reaches 41% under magnetic field of 2 T. Moreover, the MR ratio keeps significant value within broad temperature range. The infrared (IR) absorption spectra of LSMO2 show that the stretch-mode peak split into two Gaussian peaks with the gap about 70 cm-1. This large splitting indicates there are strong distortion and disorder in LSMO2 sample. The results are interpreted in terms of the disorder system and phase separation in perovskite manganites.

DC current effect on the magnetic phase and transport properties of polycrystalline La0.7Ca0.3MnO3

The influence of DC current on the resistivity and phase transition of polycrystalline La0.7Ca0.3MnO3 has been investigated. The specific heat measurement found that charge carriers and ferromagnetic spin-wave contributions were changed after applied DC current. Applying high electric fields leads to the formation of ferromagnetic regions. The resistivity drops abruptly once the percolating current path is established. As current through the sample disappears, the larger ferromagnetic (FM) clusters, however, remain and are frozen in giving a measurable contribution to the specific heat of the system. The larger clusters should give rise to the value of spin-wave stiffness constant (D), as it is expected to increase the strength of the ferromagnetic coupling. The metallic ferromagnetic regions would make the charge carrier delocalization and attribute to specific heat linear term γ.

Effect of Sintering Temperature on Microstructure, Electrical and Magnetic Properties of La0.85K0.15MnO3 Prepared by Sol-Gel Method

The influence of sintering temperature on the microstructure and transport properties of polycrystalline La0.85K0.15MnO3(LKMO) samples via sol-gel method is studied. Powder X-ray diffraction (XRD) shows that all the LKMO samples have single phase with hexagonal structure. The data obtained from XRD were analyzed by using the Rietveld refinement technique. The increase of the sintering temperature considerably promotes grain growth and improves grains connectivity. The increase of the average grain size throughout the sintering temperatures has affected the transport properties of LKMO samples. The magnetization is improved with the reduction of coercivity. The Curie temperature (Tc) was obtained from AC susceptibility data and the results were inversely proportional to the sintering temperature of the samples because the ferromagnetic properties are reduced by the increase of unit cell volume and Mn–O bond length. The electrical resistance is decreased and the metal-insulator transition temperature (Tp) is shifted towards the high temperature side, due to the improvement of grain connectivity. A phase diagram based on the measurement of Tp and Tc is constructed. All the LKMO samples are in the ferromagnetic-insulator phase at room temperature.

Magnetic field-induced transitions in La0.42Eu0.25Ca0.33MnO3 perovskite manganite

Electrical and magnetic transport properties of polycrystalline La0.42Eu0.25Ca0.33MnO3 manganite perovskite are reported here. Temperature dependence of electrical transport, in 0 and 0.6 T external magnetic fields, shows insulating behaviour down to the lowest measured temperatures. Application of 6 T external magnetic field induces two different transitions: (1) an insulator–metal transition around 110 K and (2) a low temperature upturn in resistance values at 30 K. These field-induced transitions suggest strong competition between various interactions present in these materials; this is further supported by the observation of hysteresis in electrical resistance in thermal cooling and warming cycles of measurement. The observed upturn in resistance values below 30 K is presumably due to the combined effect of weak localization, electron–electron and electron–phonon scattering. Magnetization measurements show a paramagnetic–AFM transition at 50 K, but a deviation from a straight line in the 1/M versus T is observed well above 170 K. These results manifest the competition between various possible interactions present in the system.

The influence of oxygen vacancies on the magnetic state of La0.50D0.50MnO3−γ (D=Da, Sr) manganites

The crystal structure and magnetic and electric transport properties of polycrystalline La0.50D0.50MnO3−γmanganites (D=Ca, Sr) were studied experimentally depending on the concentration of oxygen vacancies. The La0.50Sr0.50MnO3−γ system of anion-deficient compositions was found to be stable and possess a perovskite structure only up to the γ=0.25 concentration of oxygen vacancies, whereas, for the La0.50Ca0.50MnO3−γ system, we were able to obtain samples with the concentrations of oxygen vacancies up to γ=0.50. The stoichiometric La0.50D0.50MnO3 (D=Ca, Sr) compositions had O-orthorhombic (Ca) and tetragonal (Sr) unit cells. The unit cell of the anion-deficient La0.50Sr0.50MnO3−γ manganites also became O-orthorhombic when the concentration of oxygen vacancies increased γτ;0.16). Oxygen deficiency in La0.50Sr0.50MnO3−γ first caused the transition from the antiferromagnetic to the ferromagnetic state γ∼0.06) and then to the spin glass state γ∼0.16). Supposedly, the oxygen vacancies in the reduced La0.50Sr0.50MnO3− γ samples with γ≥0.16 were disordered. The special feature of the La0.50Ca0.50MnO3−γ manganites was a nonuniform distribution of oxygen vacancies in the La0.50Ca0.50MnO2.75 phase. In the La0.50Ca0.50MnO2.50 phase, the type of oxygen vacancy ordering corresponded to that in Sr2Fe2O5, which led to antiferromagnetic ordering. The specific electric resistance of the La0.50D0.50MnO3−γ anion-deficient samples increased with increasing oxygen deficiency. The magnetoresistance of all samples gradually increased as a result of the transition to the magnetically ordered state. Supposedly, the La0.50Ca0.50MnO3−γ manganites in the range of oxygen vacancy concentrations 0.09≤γ≤0.50 had a mixed state and contained microdomains with different types of magnetic ordering. The experimentally observed properties can be interpreted based on the model of phase layering and the model of superexchange magnetic ordering.

Structural, magnetic, and transport properties in La0.7Ca0.3Mn1−xScxO3

Structural, magnetic, and transport properties of polycrystalline La0.7Ca0.3Mn1−xScxO3 have been experimentally investigated. Single-phase samples are obtained in the range 0⩽x⩽0.25 by the soft chemical synthesis route. The substitution of Sc3+ at the Mn site results in reductions in the Curie temperature Tc and in the magnetic moment per Mn ion. The Tc transition temperature becomes broader with x, and the magnetic spontaneous state has changed into a cluster glass state for the sample of x=0.1. In addition, great enhancement in resistance and magnetoresistance effect is observed in the Sc-doped samples. In our case the notable doping effects can be mainly ascribed to the variation in the Mn3+–O2−–Mn4+ network and to the magnetic disorder caused by the presence of the large and nonmagnetic Sc3+ ions in the Mn sublattice.

Doping effects arising from Fe and Ge for Mn in La0.7Ca0.3MnO3

Structural, magnetic, and transport properties of polycrystalline La0.7Ca0.3Mn1−xFexO3 and La0.7Ca0.3Mn1−xGexO3 are experimentally studied. Single-phase samples are obtained in the range x=0–0.12 for Fe, and x=0–0.06 for Ge. There are no appreciable structure changes due to the introduction of Fe and Ge. The Mn-site doping favors a reduced magnetic/resistive transition, at rates of ∼22 K for 1% Fe and ∼28 K for 1% Ge, and an elevated resistivity. No metal–insulator transition occurs when the content of Fe exceeds ∼0.1. The enhanced doping effects in La0.7Ca0.3Mn1−xGexO3 can be ascribed to the reduced hole concentration noting that the presence of Fe and Ge influence the contents of mobile eg electrons and holes in the compounds, respectively. Equivalence of the effects from Fe and Ge doping, respectively, to those due to eg electron and hole trapping and the relation between Mn- and O-site doping are discussed.