Phase Of La0 Research Articles

Time dependant switchover of competing phases in La0.40Pr0.10Ca0.50MnO3

By employing impedance spectroscopy, switchover of one phase (RLF) into another phase (RHF) is reported with time for polycrystalline La0.40Pr0.10Ca0.50MnO3 compound. An irreversible increase in the impedance is explored in terms of the competition of two coexisting contending phases. An increasing along with switchover tendency of the impedance of RLF with RHF with time is conferred having different kinetics of the two coexisting competing phases. The increase in the resistance of the La0.40Pr0.10Ca0.50MnO3 sample is originated in terms of the polar nature of RHF (O-deficient related traps) and structural as well as trap associated nature of RLF.

Effect of Pr on phase structure and cycling stability of La–Mg–Ni-based alloys with A2B7- and A5B19-type superlattice structures

Fast capacity degradation is a significant drawback hindering La–Mg–Ni-based alloys from wide application as anode electrode materials of nickel metal hydride batteries. Herein, the effect of Pr element on the phase structure and cycling stability of La0.8−xPrxMg0.2Ni3.4Al0.1 (x=0, 0.1, 0.2 and 0.3) alloys is investigated. All the alloys contain (La,Mg)2Ni7 and (La,Mg)5Ni19 main phases as well as LaNi5 minor phase. It is found that Pr tends to form [AB5] subunits more than [A2B4] subunits, thus increasing the content of (La,Mg)5Ni19 phase with higher [AB5]/[A2B4] ratio in sacrifice of (La,Mg)2Ni7 phase. The increased (La,Mg)5Ni19 phase network with good structural stability increases the anti-pulverization and anti-amorphization resistance of the alloys. After 100 charge/discharge cycles, part of the superlattice phases in La0.6Mg0.2Ni3.4Al0.1 alloy decomposes into amorphous phase and LaNi5 phase, leading to the decrease in superlattce phase abundance; while little amorphization is observed for La0.6Pr0.2Mg0.2Ni3.4Al0.1 alloy and its phase contents remain almost unchanged. Correspondingly La0.6Pr0.2Mg0.2Ni3.4Al0.1 alloy electrode has a slighter oxidation degree after 100 cycles in alkaline electrolyte and exhibits good electrochemical cycling stability with a discharge capacity of 340mAhg−1 and a cycling stability of 90.7% at the 100th cycle.

Multiferroic properties of SBN–LSMO, SBN–NZCFO and SBN–LSMO–NZCFO particulate composites

Recent studies on nanocrystalline magnetodielectric (MD) composites have shown interesting results. Further, the Sr0.5Ba0.5Nb2O6 (0.5SBN) has proved to be a promising lead free ferroelectric phase to form the magnetoelectric (ME) composites. However, no detailed report on the investigations of MD properties of these composites is available in the literature. Therefore, the present paper reports synthesis and characterization of Sr0.5Ba0.5Nb2O6 (0.5SBN) based ME and MD composites. The ferromagnetic phases La0.67Sr0.33MnO3 (0.33LSMO) and Ni0.85Zn0.1Co0.05Fe2O4 (0.1NZCFO) are so synthesized that both the compositions possess crystallites of nearly 80 nm. 0.5SBN is synthesized using conventional ceramic sintering process, while 0.33LSMO and 0.1NZCFO are synthesized via hydroxide co-precipitation route followed by annealing at higher temperatures. The crystal structure is determined to confirm correct phases of individual compositions. The composites are investigated for the crystal structure, microstructure, dielectric properties, ME coefficients and MD properties. Further, the magnetoelectric coefficient α is sufficiently large. Here, the magnetodielectric properties show presence of stress induced and interfacial polarization induced contributions to the magnetocapacitance (Mc).

Synthesis and thermoelectric properties of La0.8Sr0.2CuO2.4+δ

Oxygen deficient perovskites are potential candidate materials for thermoelectric power generation and applications in solid oxide fuel cells. In this study, single phase La0.8Sr0.2CuO2.4+δ compound was synthesized by a citrate method. The room temperature DC electrical conductivity was 1774S/cm which decreased to 650S/cm with an increase in temperature, suggesting the on-set of semi-metallic behavior. The Seebeck measurements indicated p-type conduction in La0.8Sr0.2CuO2.4+δ which was low at room temperature and increased with increasing temperature. The maximum ZT value (7.24×10−3) was obtained at 700°C.

Transition Insulator-Metal and Antiferromagnetic-Paramagnetic Cu Doped in La<sub>0.47</sub>Ca<sub>0.53</sub>MnO<sub>3</sub>

The study of the perovskite manganites La0.47Ca0.53Mn1-xCuxO3 with x = 0, 0.06, 0.09, and 0.13 has been done. The magnetic structure was determined using high-resolution neutron scattering at room temperature and low temperature. All samples were paramagnetic at room temperature and antiferromagnetic at low temperature. Using the SQUID Quantum Design, the samples showed that the doping of the insulating antiferromagnetic phase La0.47Ca0.53MnO3 with Cu doping resulted in the temperature transition from an insulator to metal state, and an antiferromagnetic to paramagnetic phase. The temperature transition from an insulator to metal state ranged from 23 to 100 K and from 200 to 230 K for the transition from an antiferromagnetic to paramagnetic phase.

Dielectric properties and alternating current conductivity of sol–gel made La0.8Ca0.2FeO3 compound

In this work, single phase La0.8Ca0.2FeO3 nanomaterial has been synthesized by the sol–gel method using the citric acid route. By employing impedance spectroscopy, ac electrical properties have been measured over a temperature range from 300 to 673K at various frequencies. With the analysis based on Debye's theory and a series of Arrhenius relations, the relaxation was argued to be associated with the hopping motions of charge carriers between Fe ions. The relaxation in the La0.8Ca0.2FeO3 compound was ascribed to be a polaronic relaxation. The ac electrical conduction was studied and associated to the non-overlapping small polaron tunneling (NSPT) model.

1:13 phase formation mechanism and first-order magnetic transition strengthening characteristics in (La,Ce)Fe13–x Si x alloys

The effects of the introduction of Ce to La1−xCexFe11.5Si1.5 alloys on 1:13 phase formation mechanism, the first-order magnetic phase transition strengthening characteristics, and magnetocaloric property were studied, respectively. The results show that the formation mechanisms of 1:13 and LaFeSi phases in La1−xCexFe11.5Si1.5 alloys are the same as those of Ce2Fe17 and CeFe2 phases in Ce–Fe binary system, respectively. The substitution of Ce in 1:13 phase which is limited can make the first-order magnetic phase transition characteristics strengthen, which can make thermal and magnetic hysteresis increase, the temperature interval of temperature-induced phase transition decrease, and the critical magnetic field of field-induced magnetic phase transition (HC) increase, respectively. Owing to the lattice shrink of 1:13 phase with the increase in Ce content, the Curie temperatures (TC) show a linear decrease. The maximum change in magnetic entropy gradually increases due to the decrease in temperature interval of temperature-induced phase transition, but the relative cooling capacities are all about 80 J·kg−1 at magnetic field of 2 T.

On the Origin of CE-Type Orbital Fluctuations in the Ferromagnetic Metallic Phase of La2−2xSr1+2xMn2O7 near x = 0.4

We investigate the orbital fluctuations in the ferromagnetic–metallic phase of La2−2xSr1+2xMn2O7 near x = 0.4 by considering a two orbital model within a tight-binding description which reproduces the ARPES Fermi surface. We find strong antisymmetric transverse orbital fluctuations at wavevector \((0.5\pi ,0.5\pi )\) resulting from the Fermi-surface nesting between the portions of bonding and antibonding bands instead of the widely believed nesting between the portions of bonding band despite their flat segments, which provide an insight into the origin of so called CE-type orbital fluctuations in the ferromagnetic–metallic phase. Subsequent renormalization of the phonons near wavevector \((0.5\pi ,0.5\pi )\) and the behavior of the phonon linewidth as a function of momentum are in agreement with the inelastic neutron scattering experiments.

Griffith phase-induced ferromagnetic diffuse phase transition

A ferromagnetic transition is generally regarded as a diffusionless process, exhibiting a sharp change of magnetic properties with temperature. In this paper, however, we report a ferromagnetic diffuse phase transition (FDPT) induced by Griffiths phase in La1 − xSrxMnO3 (0·06 ≤ x ≤ 0·2). Such a FDPT experiences a broad transition temperature range, resulting in temperature-controlled ferromagnetic cluster owing to the existence of Griffiths phase during the diffusion process. The transition temperature range calculated from M–T curve is as large as 146 K for the FDPT sample. Further analysis suggests that this novel FDPT has the same scenario with that in the ferroelectric relaxor, where the ferroelectric clusters are embedded in the paraelectric matrix.

Remarkable magnetic relaxation and metamagnetic transition in phase-separated La0.7Ca0.3Mn0.9Cu0.1O3 perovskite

The magnetic and electrical properties in phase-separated La0.7Ca0.3Mn0.9Cu0.1O3 perovskite were studied in detail. Experimental results show that the substitution of Cu at Mn-site suppresses the ferromagnetic (FM) phase of La0.7Ca0.3MnO3 matrix and induces a charge ordering transition at ∼146 K. At ∼256 K, a Griffiths-like behaviour is observed. At low temperatures, the occurrence of an irreversible metamagnetic transition associated with a large relaxation rate is analyzed, clearly indicating the dynamic phase coexistence and evolution of FM islands. A magnetic phase diagram is finally constructed based on the magnetic measurements, summarizing the dynamic evolution process of phase separation.

Flash Sintering of (La, Sr)(Co, Fe)O3–Gd‐Doped CeO2 Composite

Sintering of composites constituted by two nonstoichiometric phases (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) and Gd0.1Ce0.9O2 (GDC) under constant electric field in constant heating rate experiment is studied in this work. The requirements of field and temperature for composite systematically increase with GDC amounts this indicating the importance of material conductivity. Sintering/grain growth rate is higher in the composite compared to pure LSCF phase. Flash‐sintering phenomenon in the composite is explained on the basis of three factors: (1) large and continuous increase in conductivity of LSCF acts as source of defects, (2) maintenance of sufficient local temperature because of GDC during continuous conductivity increase facilitates the cationic diffusion, and (3) reduction reactions of LSCF, during polaron hopping conduction, and of GDC phase at higher temperature activate the sintering process.

Mössbauer spectroscopy studies of phase evolution in SrFe12O19/La0.5Ca0.5MnO3 composites

A composite system composed of SrFe12O19 (SFO) and La0.5Ca0.5MnO3 (LCMO) was prepared by a two-stage sol–gel/hydrothermal synthesis technique. Starting conditions were varied to obtain products with 1:1 and 1:2M ratios of SFO:LCMO. The morphology and composition of the composites were characterized by SEM and room-temperature Mössbauer spectroscopy, revealing the growth of nanocrystalline La0.5Ca0.5MnO3 particles (d⩽150nm) on the surface of SrFe12O19 platelets. Mössbauer spectra not only confirm the presence of well-formed M-type hexagonal ferrite in the composite materials, but also demonstrate the formation of a new, intermediate phase La0.5Ca0.5Mn(Fe)O3 at the interface between SFO and LCMO. The signature of the intermediate Fe-containing phase increases with the starting molar content of La0.5Ca0.5MnO3, as a greater fraction of the SrFe12O19 surface is covered by La0.5Ca0.5MnO3, increasing the total interfacial area. The trends in coercivity in the series of samples between 10K and 300K are reported and discussed in terms of sample morphology.

Size-dependent multiple magnetic phases and exchange bias effect in hole-doped double perovskite La1.6Sr0.4NiMnO6

La1.6Sr0.4NiMnO6 nanoparticles of different sizes (18–150 nm) have been prepared by a sol–gel method, and the size effects on their magnetic properties are investigated. It is found that there is a ferromagnetic (FM) transition at TC ∼ 245 K for the sample with particle size D ∼ 150 nm. As the particle size decreases, a spin glass (SG) transition appears at TG ∼ 60 K and becomes more obvious. Meanwhile, the TC shifts to a lower temperature and the FM transition becomes indistinct. The size dependent saturation magnetization MS, which is in the range 0.78 ∼ 1.27 μB/f.u., shows a non-monotonic variation with a maximum of 1.27 μB/f.u. at the particle size DC ∼ 42 nm. The exchange bias (EB) effect is clearly observed for D > 32 nm and becomes indistinct as D ⩽ 32 nm. As the particle size decreasing, the EB field HE decreases and becomes near nil at DC. Meanwhile, the coercive field HC first increases to a maximum at DC and then decreases. All the results indicate the coexistence of AFM APBs related to the anti-site disorders, FM domains, and SG phase in La1.6Sr0.4NiMnO6 nanoparticles. The magnetic properties of the nanoparticles are understood by a complex core-shell model, i.e. both AFM APBs and FM domains coexist in the core, and the SG phase mainly resides on the surface (shell) of each particle, which reveals that the size effects on the FM phase, AFM APBs and surface SG phase in grain are different, even are opposite. The nanometer size effect is a crucial factor to influence the magnetic properties of La1.6Sr0.4NiMnO6 nanoparticles.

Influence of disorder on the appearance of Griffiths phases in La0.8−x□xCa0.2MnO3 (x=0.15 and 0.2) compounds

The La0.8−x□xCa0.2MnO3 (x=0.15 and 0.2) compounds were synthesized by the solid state reaction method. The X-ray diffraction (XRD) and magnetic measurements were used to study their physical and chemical properties. The structural characterization has revealed that these samples are crystallized in the orthorhombic structure with Pnma space group. Then, the magnetic properties of these compounds are discussed in detail, building on the magnetization and the susceptibility. The temperature dependence of magnetic susceptibility at higher temperature confirms the presence of the Griffiths phase above the Curie temperature which proves the existence of ferromagnetic clusters in the paramagnetic domain.

Appearance of Griffiths phase in La0.62Er0.05Ba0.33Fe0.2Mn0.8O3 manganite

Structural and magnetic properties of La0.62Er0.05Ba0.33Fe0.2Mn0.8O3 (LEBFMO) compound have been investigated. Rietveld refinement of powder X-ray diffraction data reveals that the sample crystallizes in the rhombohedral (R3¯c) structure. The dc and ac magnetic studies demonstrate aspects of Griffiths phase-like behavior above the Curie temperature. The observed anomalous paramagnetic behavior is attributed to the magnetic heterogeneity which is caused by the segregation of short-range ferromagnetic clusters within the paramagnetic matrix. A large deviation is usually observed between zero fields cooled (ZFC) and field cooled (FC) M(T) at a low temperature below the blocking temperature. At 50K a spin-glass state is seen to arise from a ferromagnetic state. This is caused by the competition between the ferromagnetic and antiferromagnetic interaction. From isothermal magnetization versus magnetic applied field, we deduced the magnetic entropy change ΔSM. The large RCP and ΔSM found in Fe-substituted sample are found to be interesting for magnetic refrigeration below room temperature.

Impact of Co3O4 phase on the magnetocaloric effect and magnetoresistance in La0.7Sr0.3MnO3/Co3O4 and La0.7Ca0.3MnO3/Co3O4 ceramic composites

We report the magnetic transition, magnetocaloric effect and magnetoresistance in Co3O4 modified La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 perovskites manganite. The composite, samples with nominal composition of (La0.7Ca0.3MnO3 or La0.7Sr0.3MnO3)0.9/(Co3O4)0.1 were prepared using the conventional solid-state reaction method. The phase purity and structure were confirmed by using X-ray diffraction. The scanning electron micrographs show that Co3O4 is mainly distributed at the grain boundaries and surface of the pervoskite matrix. Temperature dependent magnetization measurements and Arrott analysis reveal second order of phase transition (ferromagnetic to paramagnetic) in composite samples. A large magnetic entropy change (~3.04J/kgK at 1T) has been observed in La0.7Ca0.3MnO3 sample, and is suppressed due to the impact of Co3O4 phase in composite sample. On the other hand, the addition of Co3O4 as secondary phase in La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 samples enhances their relative cooling power (RCP). The RCP values of ~128 and 160J/kg were obtained for La0.7Sr0.3MnO3/Co3O4 and La0.7Ca0.3MnO3/Co3O4 composite samples, respectively at magnetic field of 3T. The resistivity of the composite sample was measured at the applied magnetic fields of 0.0T and 0.5T. The MR of 24.6% was observed for La0.7Ca0.3MnO3/Co3O4 composite at 200K which is 12.1% higher than that of La0.7Ca0.3MnO3 pure sample. The enhanced RCP and MR of these composites make them attractive for potential applications.

Unconventional magnetism in ThCr2Si2-type phosphides, La1−xNdxCo2P2

Quaternary phases La1−xNdxCo2P2 (x = 0, 0.12, 0.25, 0.37, 0.50, 0.63, 0.75, 0.88, 1.0) have been synthesized from Sn flux to investigate the origins of drastic differences in properties between ferromagnetic LaCo2P2 and antiferromagnetic NdCo2P2. Powder and single-crystal X-ray diffraction indicate that all La1−xNdxCo2P2 samples are isostructural and crystallize in the ThCr2Si2 structure type. The unit cell parameters and volume change non-linearly with the Nd content (x), with the x 0.50 being closer to NdCo2P2. These structural differences are also reflected in the magnetic behavior. The samples with lower Nd content are characterized by ferromagnetic ordering in the Co sublattice with the TC increasing from 132 K for x = 0 to 262 K for x = 0.50, while the samples with higher Nd content exhibit suppressed magnetization in the Co sublattice and canted antiferromagnetic ordering with TC ∼ 270 K. Refinement of neutron powder diffraction patterns for x = 0.50 and 0.75 reveals a gradual ordering of the Nd 4f moments under the influence of Co 3d moments below 100 K. At low temperatures and zero field, these samples exhibit antiferromagnetic ordering of both Nd and Co magnetic moments, but under applied field they demonstrate the stabilization of a ferrimagnetic state with antiparallel alignment of the 4f and 3d moments, as indicated by isothermal magnetization measurements. The re-entrant ferrimagnetic transition is also observed in samples with x > 0.50 if the temperature is lowered below 5 K. The occurrence of this low-temperature magnetic transition was confirmed by alternating-current susceptibility measurements.

Phase decomposition and electrochemical properties of single phase La1.6Mg0.4Ni7 alloy

The Ce2Ni7-type (hexagonal, 2H) single phase La1.6Mg0.4Ni7 alloy has been obtained by annealing the induction melting as-cast sample at 1223 K for 12 h. The relationship between phase structural stability and volume change rate of the three kinds of slabs in Ce2Ni7-type structure is studied. It is found that the volume change rate of Mg-containing [La1.22Mg0.78Ni4] slab after hydrogenation/dehydrogenation is larger than that of [LaNi5] I (outer) and [LaNi5] II (inner) slabs, and the consecutive cell volume change of [La1.22Mg0.78Ni4] slab ultimately results in the decomposition of Ce2Ni7-type phase La1.6Mg0.4Ni7 to amorphous La and Mg phases, nanocrystalline Ni, and CaCu5-type LaNi5 phases, as well as the reduction of electrochemical discharge capacity. Electrochemical studies show that the single phase alloy electrode possesses good discharge capacity (400 mAh g−1) and cycling stability (84.2% after 100 cycles). The improvement in phase structure stability and the cycling stability of the superlattice structure alloys can be achieved by inhibiting the significant volume change of Mg-containing slabs during hydrogenation/dehydrogenation.

Effect of Cu doping on the electrochemical properties and structural phases of La0.8Sr0.2Mn1−xCuxO3 (0≤x≤0.2) at elevated temperature

Abstract The electrochemical properties of La 0.8 Sr 0.2 Mn 1 − x Cu x O 3 (0 ≤ x ≤ 0.2)–Gd 0.2 Ce 0.8 O 2 − δ (GDC) composite cathodes are determined in the intermediate-temperature range (600–850 °C), and their cathode performance is analyzed in the context of their phase transition behavior at elevated temperatures. The addition of Cu to LSM forces Mn 3 + to Mn 4 + , thereby increasing the Mn 4 + concentration with increasing Cu doping. The increased Mn 4 + concentration increases the cubic phase fraction, and thus enhances the low-temperature performance of the LSM cathode. The La 0.8 Sr 0.2 Mn 0.8 Cu 0.2 O 3 –GDC yields the greatest low-temperature cubic phase fraction and shows the smallest area specific resistance (0.49 Ω cm 2 at 750 °C) of the compositions tested.

The role of the hybridization between Mn 3d and O 2p orbitals in the existence of the Griffiths phase in La0.85Ca0.15MnO3

Favourable conditions for the existence of the Griffiths phase in the La0.85Ca0.15MnO3 compound are experimentally investigated in terms of electronic and lattice structure by temperature-dependent x-ray absorption spectroscopy, valence band photoemission spectroscopy, and x-ray diffraction experiments. The chemical shifts of Mn L-edge and O K-edge x-ray absorption lines in the Griffiths phase are understood to be related to the hybridization between Mn 3d and O 2p states instead of the variation of Mn valence states. Valence band spectra also indicate that the hybridization of O 2p with Mn 3d is enhanced in the Griffiths phase. From a 2D diluted Ising ferromagnet model, this hybridization between Mn 3d and O 2p orbitals surely enhances the Griffiths phase feature.