Perovskite Manganese Oxides Research Articles

Electron-lattice coupling effect to improve electrical transport properties of La0.7Ca0.3−xKxMnO3 (0.22 ≤ x ≤ 0.28) films via large-radius K doping

For uncooled infrared bolometers, the traditional thermal sensing materials such as vanadium oxide and amorphous silicon have a relative low value of temperature coefficient of resistivity (TCR). In contrast, perovskite manganese oxide films exhibit 3–5 times higher TCR values than traditional materials. The important challenge is to achieve both high TCR and peak TCR temperatures (Tk) at room temperature. Herein, La0.7Ca0.3−xKxMnO3 (LCKMO, 0.22 ≤ x ≤ 0.28) films were fabricated on La0.3Sr0.7Al0.65Ta0.35O3 (00l) substrates using a combined sol–gel and spin coating process. It was found that by optimizing the K doping amount at x = 0.24, on the one hand, double exchange mechanism becomes the strongest. On the other hand, with minimal lattice strain, electron scattering is inhibited, and the electron-lattice coupling effect improves. Furthermore, the film exhibits a dense surface structure and a uniform distribution of grains. Finally, TCR value reaches 15.95 % K−1 at the corresponding temperature of 283.28 K. Obviously, the prepared LCKMO films effectively combine the high TCR of La1−xCaxMnO3 with the high Tk of La1−xKxMnO3 by optimizing the K doping level. The results show that LCKMO films are a promising candidate for fabricating uncooled infrared bolometers.

Exploration of electrical conduction mechanisms via modulating sintering period of La0.67Ca0.33MnO3 films in various phase regions

Perovskite manganese oxide films have garnered significant attention due to their unique and diverse physical properties. In this work, La0.67Ca0.33MnO3 (LCMO) films are prepared on LaAlO3 (00l) substrates using the sol−gel spin coating method with varying sintering period (Ps). By optimizing Ps, improvements were observed in the films’ structure, morphology, ionic valence, and temperature−dependent resistivity. The reduction in Mn−O bond length and the increase in Mn−O−Mn bond angle change the degree of MnO6 distortion, resulting in an increased eg bandwidth. As Ps increased, the LCMO films exhibited better crystalline quality. The improved Mn4+/Mn3+ ratio strengthened the double exchange effect, facilitating the carrier hopping of the eg electrons. Analyses of various electrical conduction mechanisms showed that optimized electron scattering behavior, reduced hopping distance, energy and theoretical Curie temperature collectively enhance the temperature coefficient of resistivity (TCR) of LCMO films under optimal Ps. The TCR of the LCMO films reached a maximum value (31.64 % K−1) at Ps = 18 min. These findings offer valuable insights into the main electrical conduction mechanisms in both metallic and semiconducting phases, providing a deeper understanding of the underlying physical processes and offering experimental guidance for optimizing the electrical transport properties of perovskite films.

Perovskite manganese oxide-based superposed multilayer film with high emittance tunability for smart radiation devices

Smart radiation devices (SRDs) with the ability to switch emittance according to the radiator surface’s temperature are significant for spacecraft thermal control on exploration missions with drastic changes in thermal environments. However, it is quite urgent to improve the performance of the intelligent thermal control films in SRDs due to the limitations such as low emittance tunability and inappropriate phase transition temperature. Consequently, a film with self-adaptive infrared emittance based on anti-reflective design is proposed in this paper. The main structure is a superposed multilayer film based on a doped perovskite manganese oxide La0.825Sr0.175MnO3 (LSMO) and BaF2 stacks. The emittances of the designed multilayer film are 0.18 and 0.83 at the temperatures of 100 K and 295 K, and therefore the emittance tunability achieves 0.65. Compared with single-layer LSMO, the emittance tunability has increased 25 % approximately. The enhancement in emittance tunability can be explained by the fact that multilayer films with staggered low and high refractive index dielectric layers may cause destructive interference and suppress the Fresnel reflections at high temperatures. In addition, the thickness of dielectric part is carefully designed to avoid the formation of high emissivity Fabry-Perot (FP) resonance when LSMO switches to metallic state at low temperatures. This perovskite manganese oxide-based multilayer film exhibits remarkable intelligent thermal control properties. It provides a significant opportunity to improve the performance of SRDs and a promising potential for maintaining the optimal operating temperature of the spacecraft.

Sign reversal and symmetry change of anisotropic magnetoresistance in antiferromagnetic LSMO films

The study of anisotropic magnetoresistance (AMR) holds dual significance in both theoretical and applied contexts. The underlying mechanisms of AMR remain unclear, and the phenomenon of AMR sign reversal (positive and negative transitions in values) has garnered multiple interpretations, demanding experimental verification. In this work, the effect of epitaxial strain on magnetic and transport properties of perovskite manganese oxide La0.35Sr0.65MnO3 films is investigated. The AMR demonstrates sign reversal and symmetry change behaviors. The symmetry changes of AMR stem from the competition between Zeeman energy, exchange interaction energy, and magnetocrystalline anisotropy energy. The sign reversal of AMR is attributed to the change in the density of states of spin up and spin down of conduction electrons during the magnetic phase transition induced by epitaxial strain. Our work offers experimental evidence and a reasonable explanation for the origin of the sign reversal of AMR.

Obtained large room-temperature TCR of La0.67Ca0.25Sr0.08MnO3 ceramics by optimizing sintering temperature

Over the past few decades, perovskite manganese oxide Lax(CaSr)1-xMnO3 has presented new opportunities for uncooled infrared bolometers due to its exceptional electrical transport performance. In this study, La0.67Ca0.25Sr0.08MnO3 (LCSMO) ceramics were prepared at different sintering temperatures (Ts, Ts = 1450, 1470, 1490, 1510, 1530 °C) by changing the previous sol-gel preparation process parameters. The research results indicated that the tolerance factor (τ) of the ceramics is τ = 0.935, and all ceramics exhibit a Pnma space group perovskite structure with excellent crystallinity. LCSMO ceramics exhibit good crystal quality and higher room-temperature TCR (14.58 % K−1) at Ts = 1510 °C. As Ts increases, the grain size, Mn–O bond length (dMn-O), Mn–O–Mn bond angle (θMn-O-Mn) and cell volume (V) of ceramics have a slight affected. The decrease of grain boundary scattering, electron-electron scattering, and strong coupling between electrons, so the peak resistivity value of all sintered samples firstly decreases and then increases with the increase in Ts, which effectively yields ceramics with high TCR. The peak TCR value (TCRmax) increased from 8.38 % K−1 (Ts = 1450 °C) at 296.91 K to 14.58 % K−1 (Ts = 1510 °C) at 298.18 K. On the same component, the TCRmax was increased by 42 % from 8.38 % K−1 to 14.58 % K−1 at Ts = 1450 °C–1510 °C. The high room-temperature TCR of LCSMO is expected to be used in advanced uncooled infrared bolometers, providing a basis for studying the influence of Ts on the electrical transport performance of ceramics.

Changing the Ca2+ ion ratio to modulate the temperature coefficient of resistivity (TCR) of La1-xCaxMnO3 films prepared by the sol-gel spin coating method

Perovskite manganese oxides are highly desirable for infrared acquisition owing to their characteristics of ferromagnetic metal-paramagnetic insulators. In this work, the sol-gel spin-coating technique was employed to prepare La1-xCaxMnO3 (LCMO) films with varying Ca2+ content (x = 0.1, 0.2, 0.3, 0.4, 0.5) on the (l00) LaAlO3 (LAO) substrates. In comparison to previous studies, the pre-sintering temperature, final sintering temperature, and final sintering period were modified. The crystal structure, surface topography, elemental valence states, and electrical transport performance of the LCMO films were characterized and analyzed as well. The results demonstrated that the diffraction peaks of the above films were aligned with those of the LAO single-crystal substrate. The change in Ca2+ content caused an increase in the Mn–O bond length, the amount of Mn4+, and the Mn–O–Mn angle in LCMO films, promoting the double exchange effect. These modifications had a considerable impact on the resistivity of LCMO films, increasing their TCR value. The maximum TCR of 22.92% K−1 was reached at x = 0.3 and peak TCR temperature (Tk) of 241.93 K. Therefore, the film has great application potential for infrared bolometers.

Synthesis and catalytic application of nanostructured metal oxides and phosphates.

The design and development of new high-performance catalysts is one of the most important and challenging issues to achieve sustainable chemical and energy production. This Feature Article describes the synthesis of nanostructured metal oxides and phosphates mainly based on earth-abundant metals and their thermocatalytic application to selective oxidation and acid-base reactions. A simple and versatile methodology for the control of nanostructures based on crystalline complex oxides and phosphates with diverse structures and compositions is proposed as another approach to catalyst design. Herein, two unique and verstile methods for the synthesis of metal oxide and phosphate nanostructures are introduced; an amino acid-aided method for metal oxides and phosphates and a precursor crystallization method for porous manganese oxides. Nanomaterials based on perovskite oxides, manganese oxides, and metal phosphates can function as effective heterogeneous catalysts for selective aerobic oxidation, biomass conversion, direct methane conversion, one-pot synthesis, acid-base reactions, and water electrolysis. Furthermore, the structure-activity relationship is clarified based on experimental and computational approaches, and the influence of oxygen vacancy formation, concerted activation of molecules, and the redox/acid-base properties of the outermost surface are discussed. The proposed methodology for nanostructure control would be useful not only for the design and understanding of the complexity of metal oxide catalysts, but also for the development of innovative catalysts.

Effect of Mn content on the structure, electromagnetic properties, and electromagnetic wave absorption characteristics in La0.7Sr0.3Mn1+xO3

The perovskite manganese oxide, La0.7Sr0.3Mn1+xO3 (x = −0.4, −0.2, 0, 0.2, 0.4, 0.6, 0.8, 1.0), was synthesized using the solid-state reaction method. A single-phase perovskite structure was obtained at the stoichiometric composition (x = 0). However, with an increase in Mn excess (x > 0), secondary phases of Mn2O3 and Mn3O4 formed and increased, while La2O3 and Sr-rich phases emerged when Mn is deficient (x < 0). The electrical conductivity, permittivity, and permeability of the samples showed significant variations with x, as both charge transport and magnetism originate from the presence of Mn. Complex permittivity (ε', ε") and permeability (μ', μ") spectra were utilized to calculate RL maps based on a transmission line theory. For samples with x ≥ 0, which exhibited relatively high values of ε' and ε", there was no significant absorption of electromagnetic (EM) waves within the measured frequency range (0.1 ≤ f ≤ 18 GHz) due to high EM wave reflection. Conversely, the Mn-deficient samples (x = −0.2, −0.4) demonstrated excellent EM wave absorption properties in the GHz range. This can be attributed to their favorable impedance matching characteristics, resulting from significantly reduced ε' and ε" values in the Mn-deficient samples. Notably, the sample with x = −0.2 exhibited the most outstanding EM wave absorption characteristics, with an RL value of −56 dB at a frequency of 2.33 GHz and a thickness of 7.59 mm. Additionally, it achieved an RL value of −50 dB at 9.8 GHz and 2.90 mm thickness.

Perovskite manganese oxides with tunable metal–oxygen covalency for efficient bisphenol A degradation

The metal–oxygen covalency of manganese oxides is the main factor affecting the degradation efficiency of persistent organic pollutants in water.

Visible-light photoelectric performance of RMnO3 (R = La, Pr and Nd) epitaxial films with structural distortion

All-inorganic perovskite has aroused extensive attention as the light absorption layer of solar cells due to the high photoelectric conversion efficiency and chemical stability. In this work, RMnO3 (RMO, R = La, Pr and Nd)/(001) LaAlO3 (LAO) epitaxial films were prepared by the polymer assisted deposition method. All of the RMO films were grown epitaxially with tetragonal distortion (like Jahn-Taller distortion) of MnO6 octahedron. Owing to lattice mismatch between RMO and LAO, the tetragonal distortion of MnO6 octahedron increases when the radius of trivalent R ions increases. This reduces the crystal field splitting energy of MnO6 octahedron, resulting in a reduction in the band gap and enhancement of the visible-light photoelectric performance. It also reveals that the surface-adsorbed oxygen plays a crucial role in the photoelectric process of the RMO epitaxial films. More surface-adsorbed oxygen, existing in RMO films with larger R ions, can enhance the double exchange of electrons in Mn3+ - O2− - Mn4+, thus preventing the recombination of photogenerated electron-hole pair and improving the photoelectric performance. These results provide a channel to tune the structure and photoelectric performance of perovskite manganese oxide.

Adjusting the K-doping of La1-xKxMnO3 (0.1 ≤ x ≤ 0.35) films to obtain high TCR and LFMR at room-temperature

Compared with conventional thermal and magnetic sensing materials, perovskite manganese oxide films with a rapid shift from ferromagnetic metals to paramagnetic insulators can be more suitable for the fabrication of uncooled infrared bolometers and magnetic sensors. However, the main challenge is to obtain perovskite manganese oxide films with high temperature coefficient of resistivity (TCR) and low field magnetoresistance (LFMR) at room temperature. In this study, La1-xKxMnO3 (LKMO, 0.10 ≤ x ≤ 0.35) films with different K-dopant amounts were prepared on SrTiO3 substrates using sol–gel spin coating method. A comprehensive analysis of their structure, morphology, and ionic valence enabled one to conclude that varying K-dopant content from 0.10 to 0.30 caused a decrease in Mn-O bond lengths and an increase in Mn-O-Mn bond angles, as well as caused the grain growth and the rise in Mn4+ content in LKMO films. All these changes resulted in a significant alteration in the resistivity of LKMO films, thereby providing the larger TCR and LFMR values at room temperature. According to the results, La0.7K0.3MnO3 with 13.13 % K−1TCR and La0.85K0.15MnO3 with 46.39% LFMR (under an external magnetic field of 1 T) are promising materials for the manufacturing of uncooled infrared bolometers and magnetic sensors, respectively.

Critical field analysis and magnetic properties of perovskite manganese oxide La0.8Ca0.2Mn1-xNixO3(x = 0.0,0.1,0.2)

Critical field analysis and the magnetocaloric effect of the polycrystalline perovskite manganese oxide samples, La0.8Ca0.2Mn1-xNixO3 (x = 0.0,0.1,0.2), which were prepared using a traditional solid phase reaction method, were explored. The data obtained from X-ray diffraction (XRD) measurements of the polycrystalline samples show good single-phase properties. The replacement of a given Mn3+ ion fraction by Ni2+ions decreased the crystal parameters and unit cell volume, Curie temperature (Tc), and the magnetic and the magnetic entropy change. These property changes originate from the partial substitution of Mn3+ ions by Ni2+, which changes the Mn3+/Mn4+ ratio and consequently weakens the double exchange (DE) effect. At an applied magnetic field of 7 T, the maximum difference in magnetic entropy of the undoped sample is 6.15 J/kg•K, and the refrigeration efficiency is 422.94 J/kg. The critical parameters of the parent material and the doped sample fit well to the Tricritical model. The La0.8Ca0.2Mn1-xNixO3 samples with x = 0.0 exhibit crossover of the phase transitions, which can be first or second order. The observed phase transitions of samples with x = 0.1 and 0.2 are exclusively second order. Around the TC of La0.8Ca0.2Mn1-xNixO3 (x = 0.0, 0.1 and 0.2) compounds, the correlation of the magnetic field with the maximum change in magnetic entropy follows a power law.

Magnetic and critical behavior studies of Ni2+-doped perovskite manganese oxides

Magnetic and critical behavior studies of Ni2+-doped perovskite manganese oxides

High-performance La0.75K0.25MnO3:xAg2O composites based on electron-lattice and electron-magnetic coupling mechanism

Perovskite manganese oxides possess a large room-temperature coefficient of electrical resistivity (TCR), thereby suitable for fabrication of high-performance uncooled infrared bolometers. Herein, La0.75K0.25MnO3:xAg2O (LKMO:xA, 0.0 ≤ x ≤ 0.4) composites were prepared by combining the sol-gel with solid-state methods. LKMO:0.3A composite revealed TCRmax reaching 18.32% K−1 at 300.4 K, a value higher than those of reported perovskite manganese oxides at room temperature. The electrical transport properties of LKMO:xA composites were also investigated by combining electron-lattice and electron-magnetic coupling and the results were shown promising. In sum, the provided physical mechanism and experimental foundation could optimize high room-temperature TCR of perovskite manganese oxides.

Silver addition in polycrystalline La0.7Ca0.3MnO3: Large magnetoresistance and anisotropic magnetoresistance for manganite sensors

Perovskite manganite La1−yCayMnO3 has giant and tunable magnetoresistance (MR) and anisotropic magnetoresistance (AMR), still the following two challenges are of great concern: (i) large magnetic field is required for achieving excellent electromagnetic performance; and (ii) metal–insulator (M–I) transition temperature (TMI) significantly different from room temperature; both these factors limit its practical applications. In this study, polycrystalline La0.7Ca0.3MnO3:Agx composites were fabricated by sol–gel and solid–phase addition methods, and large MR and AMR (84.1% and 32%, respectively) were obtained at near room temperature in 1 T magnetic field when x = 0.2. Evidently, it was found that the grain boundary scattering effects were weakened due to Ag−addition, which resulted in an enhancement of MR. The tremendously high AMR value was attributed to the anisotropic spin–orbit coupling (SOC) effect. The electron–scattering and small–polaron hopping models were used to successfully fit the resistivity data, which support the SOC effect under different magnetic fields that enhance the AMR. These results support further development of the perovskite manganese oxide with potential applications in manganite devices.

Electrical transport properties driven by magnetic competition in hole-doped perovskite Pr1-xBaxMnO3 (0.25 ≤ x ≤ 0.36)

In this work, polycrystalline Pr1-xBaxMnO3 (0.25 ≤ x ≤ 0.36) ceramics were synthesized, and their magnetic and electrical transport properties were systematically studied. All samples show two metal-insulator transitions (MITs) corresponding to the high temperature TMI1 and low temperature TMI2, respectively, besides the non-Griffith phase above the ferromagnetic (FM) transition temperature TC. Combining the results of the transport and magnetic properties, it is found that the FM transition temperature TC coincides with the temperature TMI1, which is linearly related to the A-site ionic radius mismatch variance σ2, indicating the enhancement of FM interactions due to the increase of the degree of B-site ordering of Mn3+/Mn4+ ions. The positive correlation between ferromagnetic insulators (FMI) and magnetic interactions, including the FM and short-range antiferromagnetic (AFM) interactions, is confirmed. It is suggested that the first MIT at TMI1 is attributed to the Mn3+/Mn4+ double exchange interactions and the second MIT at TMI2 is closely related to the suppression of the AFM interactions under the internal FM field induced by the Mn3+/Mn4+ DE interactions. This work provides not only a theoretical understanding on the origin of MIT at low temperature, but also a new way for adjusting the FMI in perovskite manganese oxide Pr1-xBaxMnO3 for application.

Magnetic exchange coupling in Fe/bilayer-manganites heterostructure

Magnetic exchange couplings among perovskite manganese oxide heterostructures (typified by SrRuO3/La0.3Sr0.7MnO3) have been widely studied as potential components of metal-oxide spintronic devices, while bi-layered manganite related magnetic coupling phenomenon has never been reported. In this work, we find an obvious enhancement of coercivity in Fe/La2−2xSr1+2xMn2O7 (x=0.35, B-LSMO) starting at the transition temperature of B-LSMO single crystal. Systematic analysis on the temperature and external field evolution of magnetization reversal behavior reveals the emergence of antiferromagnetic interfacial exchange coupling between Fe and B-LSMO. Our results shed new light on tuning of magnetic property on layered oxide interface and designing novel spintronic devices.

Effect of Eu3+ Doping on Electrical Transport Properties of LaMnO3

Perovskite manganese oxide La0.87R0.13MnO3 (R=La, Eu) polycrystalline samples were prepared by high temperature solid-phase reaction. The crystal structure was studied by X-ray diffraction (XRD). Through the resistivity-temperature (ρ-T) curve, the electrical transport properties are studied. The magnetoresistance-temperature (MR-T) curve was made to study the magnetoresistance effect. The results show that all samples in this group have good monophasic property and belong to orthorhombic system. In the measured temperature region, it belongs to semiconductor material, and the average ion radius of A position is different, and the influence of external magnetic field on electric conduction is different. The ρ-T curve fitting of the samples of this group shows that the samples of this group all follow the conduction mode of variable range jump in the measured temperature region. The magnetoresistance effect of Eu3+ doped samples is significantly increased, which is beneficial to the practical application of magnetoresistance.

Controllable Magnetic Proximity Effect and Charge Transfer in 2D Semiconductor and Double-Layered Perovskite Manganese Oxide van der Waals Heterostructure.

Optically generated excitonic states (excitons and trions) in transition metal dichalcogenides are highly sensitive to the electronic and magnetic properties of the materials underneath. Modulation and control of the excitonic states in a novel van der Waals (vdW) heterostructure of monolayer MoSe2 on double-layered perovskite Mn oxide ((La0.8 Nd0.2 )1.2 Sr1.8 Mn2 O7 ) is demonstrated, wherein the Mn oxide transforms from a paramagnetic insulator to a ferromagnetic metal. A discontinuous change in the exciton photoluminescence intensity via dielectric screening is observed. Further, a relatively high trion intensity is discovered due to the charge transfer from metallic Mn oxide under the Curie temperature. Moreover, the vdW heterostructures with an ultrathin h-BN spacer layer demonstrate enhanced valley splitting and polarization of excitonic states due to the proximity effect of the ferromagnetic spins of Mn oxide. The controllable h-BN thickness in vdW heterostructures reveals a several-nanometer-long scale of charge transfer as well as a magnetic proximity effect. The vdW heterostructure allows modulation and control of the excitonic states via dielectric screening, charge carriers, and magnetic spins.

Optimization of room-temperature TCR of polycrystalline La0.9-xSrxK0.1MnO3 ceramics by Sr adjustment

High-density La0.9-xSrxK0.1MnO3 ceramics (LSKMO, A-site = La, Sr and K, 0 ≤ x ≤ 0.25) are successfully fabricated by using facile sol-gel method. Electrical properties are performed by using combination of phenomenological percolation (PP) model, double exchange (DE) mechanism, and Jahn-Teller (JT) effect. Moreover, X-ray diffraction and scanning electron microscopy are employed to analyze the structure and morphology of LSKMO ceramics. Valence states and ionic stoichiometry are assessed by using X-ray photoemission spectrometry. Results reveal that Sr2+ ions, substituting La3+ ions, significantly influenced DE mechanism and JT effect. In addition, Sr-doping plays essential role in improving electrical properties of LSKMO ceramics. At optimal doping content of x = 0.09, peak temperature coefficient of resistance (TCR) of the resistivity is found to be 11.56% K−1 at 297.15 K, which is optimal TCR for A-site K-occupied perovskite manganese oxides. These results confirm that polycrystalline LSKMO ceramics render high room-temperature TCR values due to Sr-doping.