Ruddlesden-Popper Manganite Research Articles

Structural, magnetic and field-driven abrupt magnetocaloric properties of La1.4-xSmxCa1.6Mn2O7 Ruddlesden-Popper manganites

Evolution in the structural, magnetic and magnetocaloric (MCE) properties for a series of samarium (Sm) doped La1.4-xSmxCa1.6Mn2O7 (0.0 ≤ x ≤ 0.4) Ruddlesden-Popper manganites prepared by using the solid-state reaction method have been investigated. Structural refinement of XRD profiles established that the MnO6 octahedral structural units were distorted upon Sm-substitution. The effect of Sm-concentration on the microstructure was also very well observed in terms of increased average grain size and absolute density. Discrepancy in MCE parameters by implementing the conventional isothermal curve method was appeared which was resolved with a separate calorimetric method. The isothermal entropy change was enhanced from 2.52 J/kgK for x = 0.0 sample up to 4.61 J/kgK and 4.2 J/kgK for x = 0.1 and x = 0.2 samples respectively. The temperature averaged entropy change (TEC) was also remarkably improved from 4.04 J/kgK up to 8.5 J/kgK and 7.77 J/kgK for the same compounds respectively.

Methane steam reforming in water-deficient conditions on a new Ni-exsolved Ruddlesden-Popper manganite: Coke formation and H2S poisoning

This research deals with the catalytic behavior of the methane steam reforming reaction over a new Ni-exsolved Ruddlesden-Popper manganite during prolonged reaction time (up to 100 h) with special focus on the possible carbon deposition and H2S poisoning. La1.5Sr1.5Mn1.5Ni0.5O7±δ material was synthesized and reduced in diluted hydrogen to induce Ni exsolution. Its catalytic behavior in long reaction times was compared to Ni-impregnated manganite and Ni/YSZ cermet. The catalytic measurements for the steam reforming reaction were carried out at 850 °C in low steam-to-carbon conditions. All materials are susceptible to H2S poisoning (50 ppm), forming undesired sulfide compounds with damaging impact on their catalytic activity. In contrast, during tests without H2S, the activity for cermet and impregnated materials drops at relatively short reaction time due to coking formation, as evidenced by TEM and TGA/MS analysis, while the behavior of new exsolved material remains stable throughout the test. This high stability of the new exsolved catalyst over a prolonged reaction time is a noticeable advantage due to its potential use as SOFC anode fed with natural gas free of H2S.

Performance of La0.5Sr1.5MnO4±δ Ruddlesden-Popper manganite as electrode material for symmetrical solid oxide fuel cells. Part B. the hydrogen oxidation reaction

The electrochemical performance of La0.5Sr1.5MnO4±δ (L5S15M) in reducing atmosphere was investigated using Electrochemical Impedance Spectroscopy (EIS) measurements on Au/L5S15M/GDC/YSZ/GDC/L5S15M/Au symmetrical cell. In this research, the electrochemical performance of symmetrical cells sintered at different temperatures cells was evaluated in various reducing atmospheres: 3% H2/Ar (3% H2O), dry 3% H2/Ar, and pure H2 (3% H2O). The lowest values for the area specific resistance (ASR) were acquired for the L5S15M electrode sintered at 1150 °C. For the hydrogen oxidation reaction, three rate limiting processes were identified and for all the electrode elaboration conditions, the low frequency response assigned to surface diffusion represents the highest contribution to the total polarization resistance.

Coupling of magnetoresistance switching and glassy magnetic state at the metal–insulator transition in Ruddlesden-Popper manganite Ca4Mn3O10

Electronic phase separation is a frequent ingredient of the physics of manganites for which the colossal magnetoresistance (CMR) phenomenon is at debate. We investigate the switchable magnetoresistance (MR) effect of the Ruddelsden-Popper (RP) oxide Ca4Mn3O10 (CMO), which shows a metal-to-insulator transition (MIT) at 70 K (TMIT). The static (DC) and dynamic (AC) magnetic susceptibilities of CMO indicate an unusual magnetic phase coexistence below the Néel temperature (TN) i.e., at TMIT, which we describe as a glassy magnetic behavior. Furthermore, by means of synchrotron X-ray diffraction, we observed a structural anomaly directly associated with the MIT. Hence, the onset of glassiness correlates with a slight structural distortion. Interestingly, CMO displays a large positive magneto-resistance (PMR) effect (up to 550% at 4 K) in the metallic state below TMIT, while a small negative magneto-resistance (NMR) effect (-3.5% at 112 K) in the insulating region above TMIT. At TMIT, the PMR switches to NMR behavior. PMR is probably induced via enhancing the exchange interaction by localization of itinerant moment resulting in formation of magnetic polarons, whereas NMR is possibly due to reduced electron-spin scattering. This appears to be a special type of magnetoresistance, different from regular observations, and may open a new avenue in searching for exotic phenomena in manganese-based CMR materials.

Uncompensated-spins induced weak ferromagnetism in Ca3Mn2O7: Magneto-conductive and dual magneto-capacitive effects

Temperature dependent magnetization study on single phase orthorhombic Ruddlesden-Popper manganite Ca3Mn2O7 evidences antiferromagnetic (AFM) ordering below 123 K. Field-dependent magnetization M(H) depicts off-centered hysteretic loops below ~110 K—confirming the existence of both weak ferromagnetism (WFM) and exchange bias, whose development upon cooling is examined in detail. WFM is attributed to the formation of uncompensated-spin-clusters within the AFM-matrix, stabilized by the high-anisotropy in the manganite, favoring Dzyaloshinskii-Moriya (D-M) interaction. Temperature dependence of an evaluated average canting angle from the M(H) loops provides a quantitative measure of the WFM-evolution. Dielectric measurements exhibit magneto-conductive effects concurrent to the WFM-onset. Temperature dependence of the low-frequency/dc-limit of Jonscher-fits to the conductivity isotherms confirms the presence of relatively more-conductive clusters, embedded in the insulating-bulk. Nyquist impedance-analysis of complex impedance reveals two relaxations, yielding dual magnetic-field effects; the lumped circuit parameters feature anomalies across the magnetic phase changes.

LaSr2Mn2O7 Ruddlesden-Popper manganites for oxygen reduction and electrochemical capacitors

LaSr2Mn2O7, a Ruddlesden-Popper type bilayered perovskite, was investigated as oxygen catalyst for oxygen reduction reaction (ORR) and active electrode material for electrochemical capacitors in KOH solutions. XPS results show that Mn takes a mixed Mn2+, Mn3+ and Mn4+ valence state with an average valence of 3.4. As catalyst towards ORR, LaSr2Mn2O7 and LaSr2Mn2O7/acetylene black composite favor four electron pathways for ORR. LaSr2Mn2O7/C composite shows a comparable onset potential for ORR to that of Pt/C electrode. The improved ORR activity of LaSr2Mn2O7/acetylene black composite is attributed to the synergy between catalytic LaSr2Mn2O7 and conductive acetylene black. As electrode material for electrochemical capacitors, LaSr2Mn2O7 exhibits a maximum specific capacitance of 167.2 F/g with 62% faradic contribution at a scan rate of 1 mV/s in cyclic voltammetry test.

Performance of La0.5Sr1.5MnO4±δ Ruddlesden-Popper manganite as electrode material for symmetrical solid oxide fuel cells. Part A. The oxygen reduction reaction

The electrochemical performance of La0.5Sr1.5MnO4±δ (L5S15 M) as SOFC cathode was studied using Electrochemical Impedance Spectroscopy (EIS) measurements. The influence of the sintering temperature on the electrochemical performance was examined in air for Au/L5S15 M/GDC/YSZ/GDC/L5S15 M/Au symmetrical cell. For the oxygen reduction reaction, the electron transfer between the electrode and oxygen, and the incorporation of oxygen ions into the electrode are the main controlling processes of oxygen reduction reaction for electrodes sintered at 1150 and 1200 °C. Increasing the sintering temperature up to 1250 °C increases the Sr diffusion through GDC interlayer, which leads to Sr accumulation at the GDC/YSZ interface with SrZrO3 formation and subsequent cell performance degradation. The lowest area specific resistance (ASR) values was obtained for the L5S15 M electrode sintered at 1150 °C.

Expanding the Ruddlesden–Popper Manganite Family: The n = 3 La3.2Ba0.8Mn3O10 Member

La(3.2)Ba(0.8)Mn(3)O(10), a representative of the rare n = 3 members of the Ruddlesden-Popper manganites A(n+1)Mn(n)O(3n+1), was synthesized in an evacuated sealed silica tube. Its crystal structure was refined from a combination of powder X-ray diffraction (PXD) and precession electron diffraction (PED) data, with the rotations of the MnO(6) octahedra described within the symmetry-adapted mode approach (space group Cccm, a = 29.068(1) Å, b = 5.5504(5) Å, c = 5.5412(5) Å; PXD R(F) = 0.053, R(P) = 0.026; PED R(F) = 0.248). The perovskite block in La(3.2)Ba(0.8)Mn(3)O(10) features an octahedral tilting distortion with out-of-phase rotations of the MnO(6) octahedra according to the (Φ,Φ,0)(Φ,Φ,0) mode, observed for the first time in the n = 3 Ruddlesden-Popper structures. The MnO(6) octahedra demonstrate a noticeable deformation with the elongation of two apical Mn-O bonds due to the Jahn-Teller effect in the Mn(3+) cations. The relationships between the octahedral tilting distortion, the ionic radii of the cations at the A- and B-positions, and the mismatch between the perovskite and rock-salt blocks of the Ruddlesden-Popper structure are discussed. At low temperatures, La(3.2)Ba(0.8)Mn(3)O(10) reveals a sizable remnant magnetization of about 1.3 μ(B)/Mn at 2 K, and shows signatures of spin freezing below 150 K.

Artificial construction of the layered Ruddlesden-Popper manganite La2Sr2Mn3O10 by reflection high energy electron diffraction monitored pulsed laser deposition.

Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden–Popper structure La2Sr2Mn3O10 in epitaxial thin film form by sequentially layering La1–xSrxMnO3 and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr2+ predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature Tg ≈ 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state.

Effect of dimension on charge order domain in Ruddlesden–Popper manganites

The charge order (CO) domains of dimensionally controlled manganites Pr 1− x Ca x MnO 3 and Pr 1− x Ca 1+ x MnO 4 ( x=0.5, 0.6 and 0.67), which have three-dimensional (3D) and two-dimensional (2D) Mn–O networks, respectively, have been studied by transmission electron microscopy (TEM). Although the electron diffraction data show similar dependences of the modulation wave vector on hole doping x, there are distinctive differences between the 3D and 2D systems in terms of the CO domain sizes. In the 2D system, the TEM images show that the domain size is almost constant irrespective of hole doping x. On the other hand, in the 3D system, the domain size of the incommensurate CO for x=0.6 is much smaller than those of the commensurate CO for x=0.5 and 0.67. Namely, in the 3D system, the CO states are strongly influenced by the incommensurability for the parent lattice. This difference indicates that the dimension of the Mn–O network plays a crucial role in the CO domain and suggests that the electron–lattice coupling of the 3D system is stronger than that of the 2D system.

Microstructure and defect investigations of the layered manganites La2–2xCa1+2xMn2O7 (x = 0.6, 0.8 and 0.9) by HREM

AbstractThe microstructure and defects of the n = 2 Ruddlesden–Popper manganites La2–2x Ca1+2x Mn2O7 (x = 0.6, 0.8 and 0.9) were investigated by electron diffraction and high‐resolution transmission electron microscopy. Besides the predominant n = 2 layered structure in the examined compounds, intergrowths with different number of the perovskite‐like layers were observed. Intergrowth of n = 1 (K2NiF4‐type) was observed only in x = 0.9 sample. Intergrowths with n ≥ 5, essential perovskite microdomains or inclusions, were seen in the x = 0.8 and 0.6 samples. The type of defects in x = 0.8 sample is much richer than that in x = 0.6 and 0.9 samples and two rare types were observed and analyzed. Some of edge dislocations in the x = 0.6 specimen were presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

XAS study of Ru doped n = 1, 2 Ruddlesden–Popper manganites

We report on the results of X-ray absorption near edge structure (XANES) studies at the Mn:L 2,3, Ru:K and O:K edges of novel manganites, Sr 2Mn 0.5Ru 0.5O 4 and Sr 3MnRuO 7. Measurements were carried out on polycrystalline powder samples at room temperature. From the analysis of the XANES spectra the average manganese valences of 3.4 in bilayer Sr 3MnRuO 7 and 3.1 in single layer Sr 2Mn 0.5Ru 0.5O 4 are obtained. The corresponding average valences for Ru ions are 4.6 and 4.9, respectively. This indicates that Ru doping gives rise to a decrease of Mn valence, whereas Ru valence increases, compared to Mn(IV) and Ru(IV) in undoped compounds. The effect of charge disproportionation is stronger in the single layered compound than in the bilayered one.

Synthesis and structural properties of n = 1 Ruddlesden–Popper manganites Nd1−xCa1+xMnO4

Polycrystalline samples of n=1 Ruddlesden–Popper manganites Nd1−xCa1+xMnO4 (0.55≦x≦1.00) were synthesized by a solid-state reaction. X-ray diffraction (XRD) and electron diffraction (ED) measurements confirmed that the fundamental crystal structure at room temperature consists of three distorted K2NiF4-types: orthorhombic Bmab (64) phase in 0.55≦x<0.73, orthorhombic Acam (64) phase in 0.73≦x<0.85 and tetragonal I41/acd (142) phase in 0.85≦x≦1.00. Furthermore, in a whole range of 0.55≦x≦0.75, low-temperature magnetic and ED measurements revealed charge-orbital ordering (COO) states, which are accompanied by suppression of magnetization and structural modulations with q=(1−x)a*. The COO transition temperatures are high with a maximum of ∼330K at x=0.67, and then higher than those in non-distorted n=1 Ruddlesden–Popper manganites. The observations suggest that COO states are much stabilized by the distortion in the fundamental structures.

Structural, Magnetic, and Transport Properties of the Two Electron‐Doped Ruddlesden—Popper Manganites Ca3‐xThxMn2O7.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Effect of dimensionality on the magnetic properties of Ruddlesden–Popper manganites

We have measured the muon-spin relaxation (μSR) in La 0.6Sr 0.4MnO 3 and in its layered sister system La 1.2Sr 1.8Mn 2O 7 to study the influence of dimensionality on their magnetic properties. Both compounds show ferromagnetic ordering with decreasing temperature. Above their Curie temperatures we followed the spin fluctuations. While the electron spin fluctuations in the three-dimensional La 0.6Sr 0.4MnO 3 slow down critically as the transition temperature is approached they remain finite in the layered material La 1.2Sr 1.8Mn 2O 7. We can fit them to 2D critical behaviour with a lower T C. In addition, we observe a spin precession signal in the ferromagnetically ordered state in La 1.2Sr 1.8Mn 2O 7; the temperature dependence of the muon precession frequency is in agreement with a three-dimensional character of the ordering.