Perovskite Manganates Research Articles

Advanced Anti-icing and Deicing Strategies for Overhead Power Transmission Lines Based on Giant Magnetocaloric Effect of La0.7Ca0.254Sr0.046MnO3.

Perovskite manganates (AMnO3) exhibit diverse structural, thermal, electrical, and magnetic properties. Their strong magnetocaloric effect (MCE) near the Curie temperature (TC) makes them ideal for magnetic-thermal anti-icing and deicing in power transmission lines. Below TC, ferromagnetic AMnO3 produces heat through multiple mechanisms, with the changing magnetic field induced by the strong AC current, causing heat through magnetic hysteresis and eddy currents, alongside the direct MCE. Above TC, no heating is generated, as MCE is unfavorable, thus preventing additional energy loss at elevated temperatures. In this work, La0.7Ca0.254Sr0.046MnO3 with TC close to 0 °C were synthesized by solid-state reaction. It is found that particle size >10 μm is beneficial for a large MCE, based on the results of particle size dependence of MCE. The resulting maximum magnetic entropy change at 277 K is 7.69 J·kg-1·K-1, and an adiabatic temperature change of 3.87 K at 277 K is achieved under 5 T. The prototype cable is fabricated using a well-established wire drawing process. A climate-simulation chamber is employed for the anti-icing and deicing experiments. The prototype cables demonstrated a strong capability for deicing and anti-icing. This simple and cost-effective prototype cable shows significant potential for mitigating the icing problem of overhead high-voltage power transmission lines.

Local lattice distortions and electronic phases in perovskite manganite Pr0.5Sr0.5MnO3

We use variable temperature and magnetic field total x-ray scattering to study the crystal structure of the strongly correlated Pr0.5Sr0.5MnO3 perovskite, which is a paramagnetic insulator at room temperature, becomes a ferromagnetic metal at 272 K and, upon further decreasing the temperature, turns into an antiferromagnetic insulator at 105 K. We find that a model featuring a monoclinic symmetry captures the structure and its temperature and field evolution well, eliminating the need to evoke a phase segregation scenario as done in prior studies. It appears that coupled variations in Mn–oxygen bonding distances and angles from their values in an undistorted perovskite lattice, i.e., coupled local lattice distortions, assist the phase transitions in Pr0.5Sr0.5MnO3, contributing to its unique physical properties. Local structural distortions thus emerge as an important degree of freedom in strongly correlated systems, in particular perovskite manganates, and, therefore, they should be fully accounted for when their fascinating physics is considered.

Synthesis and Characterization of Perovskite Manganate Based on La0.7Ca0.3MnO3 with Ni and Ti doping as Microwave Absorber Material

Research has been carried out on the effect of Ni and Ti doping on the microwave absorption properties of the perovskite manganate material La0.7Ca0.3Mn1-xNix/2Tix/2O3 (LCMNTO) with variations x = 0; 0.03; 0.05; and 0.1, which were synthesized by the sol-gel method. The effect of Ni and Ti doping on the structure, grain size, magnetic properties, and microwave absorption properties were investigated in detail by various analytical methods. XRD (x-ray diffraction) characterization showed that the material La0.7Ca0.3Mn1-xNix/2Tix/2O3 has a single phase with an orthorhombic crystal system. The SEM (scanning electron microscope) results showed a tendency to decrease in grain size when the composition of Ni and Ti dopants began to increase. VSM (vibrating sample magnetometer) characterization shows that La0.7Ca0.3Mn1-xNix/2Tix/2O3 is a soft magnet with magnetic properties that decrease with increasing Ni and Ti dopant composition. The characterization of VNA (vector network analyzer) in the 8-12 GHz shows that the highest ability to absorb microwaves is 98% at 8.24 GHz, and there is an addition of absorption areas point and widening of the absorption bandwidth. Thus, the material La0.7Ca0.3Mn1-xNix/2Tix/2O3 has the potential to become a microwave absorber material.

A-Site Doped in Perovskite La(1-x)Bax/2Srx/2Mn0.4Ti0.6O3 (x = 0, 0.1, and 0.3) for Absorbing Microwave Material

Microwave radiation can have harmful effects on our bodies. With increased exposure due to online activities, it is essential to use absorber materials like perovskite manganate to reduce radiation. In this study, perovskite manganate La(1-x)Bax/2Srx/2Mn0.4Ti0.6O3 (x = 0, 0.1, and 0.3) was synthesized using the sol-gel method. X-ray diffraction (XRD) analysis revealed that the two samples were multi-phased, LaMnO3 and La2Ti2O7, and were formed, exhibiting a rhombohedral crystal structure (R -3 c). Morphological characterization of the sample surface using a Scanning Electron Microscope (SEM) showed that as doping increases, the grain size decreases from 282.02 to 245.63 nm at x=0 and x=0.3, respectively. This result implies that doping leads to more uniform grain distribution and enhanced grain refinement. Characterization via Vibrating Sample Magnetometer (VSM) revealed that the maximum saturation value, 0.79 emu/g, was attained when x = 0. This sample exhibits soft magnetic properties, as evidenced by its coercivity (Hc) value of < 1kOe. Results from the Vector Network Analyzer (VNA) indicate that the absorption capacity of La(1-x)Bax/2Srx/2Mn0.4Ti0.6O3 increases, with a maximum reflection loss value of -25.5 dB with 1.5 mm thickness. Consequently, La(1-x)Bax/2Srx/2Mn0.4Ti0.6O3 demonstrates potential as a microwave absorber material.

Effect of ethylene glycol on preparation and electrical transport properties of La0.67Ca0.33MnO3 ceramics

Perovskite manganates La1-xCaxMnO3 (LCMO) has attracted wide attention due to its unique physical properties such as metal-insulator transition (IMT), colossal magnetoresistance (CMR), which has potential application value in infrared detection, magnetic sensor, and other fields. LCMO precursor powder was prepared using the sol-gel method with a large surface area, high surface energy, and unstable thermodynamic system. To reduce the free enthalpy of the system, powder particles will spontaneously form agglomeration, affecting the structure and properties of materials. Ethylene glycol is selected as a dispersant, and the content of ethylene glycol is changed to obtain LCMO ceramics with excellent uniformity. To achieve the purpose of regulating the electrical transport properties, temperature coefficient of resistance (TCR), and magnetoresistance (MR) of LCMO. In this study, when the amount of ethylene glycol was 4 %, TCR is 42.58 %·K−1 (262.69 K), and MR is 59.96 %. Therefore, the excellent preparation process promotes the application of such materials in the fields of uncooled thermal radiation infrared detection and magnetic sensitivity.

Manipulation and observation of atomic-scale superlattices in perovskite manganate

Superlattices in crystals, particularly in perovskite oxides with strong correlation effects, can create new states of matter and produce peculiar physicochemical phenomena. However, the newfangled perovskite superlattices depend on physical deposition with unit-cell precision. It has been challenging to explore a new suitable chemical method to tailor perovskite superlattices. Herein, we present a new bottom-up strategy to precisely prepare atomic-scale oxide superlattices of (LaMnO3)1-(La1-x-yCaxKyMnO3)2 in a monodispersed perovskite La0.66Ca0.29K0.05MnO3 (LCKMO). The special atomic-scale perovskite superlattices are demonstrated using SAED, HAADF-STEM, XRD, and atomic-resolution elemental mapping. Our experiments reveal that the perovskite superlattices can be fabricated under extreme hydrothermal conditions utilizing ultra-high concentrations of KOH. An approximate molten salt system in the hydrothermal process can induce the disproportionation reaction of MnO2 solids, which is vital to the growth of ordered perovskite superlattices. This work not only clarifies the hydrothermal growth process of perovskite oxides in extreme conditions, but also proposes a novel engineering route toward perovskite superlattices.

Effect of Fe substitution on temperature coefficient of resistance and magnetoresistance of La0.67Ca0.33MnO3 polycrystalline ceramics

La0.67Ca0.33MnO3 perovskite manganate exhibits high temperature coefficient of resistance (TCR) and large magnetoresistance (MR) effect, these enable novel multifunctionalities. Mn site substitution can change magnetic order of the manganates, thereby tailoring both electrical and magnetic transport. Herein, La0.67Ca0.33Mn1-xFexO3(0 ≤ x ≤ 0.06) polycrystalline ceramics were prepared by sol-gel route. The effect of Fe substitution on TCR and MR of La0.67Ca0.33MnO3 was studied. Fe replacing Mn ions, would weaken double exchange, and significantly reduced Curie temperature and ferromagnetism. Additionally, Fe doping promoted the development of grain. TCR increased first with Fe content x and then decreased, and reached 45.2%·K-1 at x = 0.01, which is the highest value reported. Notably, with Fe doping, MR gradually increased and reached 81.1% (1 T) at x = 0.06. Fe doping can significantly enhance TCR and MR, which generates promising potential in (uncooled) thermistor/infrared detecting and magnetic sensors.

Theoretical investigation on orthorhombic XMnO3 (X = Nd, Dy and Ho) perovskite manganates using DFT

The structural, electronic, magnetic and optical properties of the orthorhombic oxide perovskite XMnO3 (X = Nd, Dy and Ho) compounds are performed using DFT calculations. The calculated lattice parameters and bond length between content atoms agree with previous studies. From the formation energy value, the present compounds are expected to be thermodynamically stable and can be created. The electronic band structure and Fermi surface calculations suggest major involvement of ionic bond and metallic attributes for the studied compounds. The magnetism calculations portray a ferromagnetic behavior for XMnO3 compounds. From the electronic properties and the high total magnetic moment, useful electronic and magnetic applications are predicted, such as spintronic, especially for DyMnO3. The different calculated optical properties show that XMnO3 are promising optical compounds in a special energy zone.

Structure and Morphology of Copper Subtituted in La<sub>0.667</sub>Ba<sub>0.333</sub>Mn<sub>1-x</sub>Cu<sub>x</sub>O<sub>3 </sub>(x = 0.35 and 0.40)

A perovskite manganate material La0,667Ba0,333Mn1-xCuxO3 (x = 0.35 and 0.40) were prepared. The samples were synthesized by sol gel method. The samples were sintered at 1000OC for 6 hours. Rietveld refinement shows that both samples are crystallized in orthorhombic structure with Pnma space group. This results is in accordance with Goldschmidt’s tolerance factor value which are 0.8698 and 0.8701 for x = 0.35 and 0.4, respectively. Subtitutions with large amount of copper ions in B-sites caused the unit cell to decrease from 236.234 Å3 to 236.088 Å3 . Futher calculation from crystallography Refinement also shows that copper subtitutions increase the crystallite size of the samples from 74.8 nm to 94.49 nm. It has been found from the SEM results that copper subtitutions also alter the morphology of the samples.

Magnetic excitations in the spin-spiral state ofTbMnO3andDyMnO3

We calculate spectra of magnetic excitations in the spin-spiral state of perovskite manganates. The spectra consist of several branches corresponding to different polarizations and different ways of diffraction from the static magnetic order. Goldstone modes and opening of gaps at zero and non-zero energies due to the crystal field and the Dzyaloshinski-Moriya anisotropies are discussed. Comparing results of the calculation with available experimental data we determine values of effective exchange parameters and anisotropies. To simplify the spin-wave calculation and to get a more clear physical insight in the structure of excitations we use the {\sigma}-model-like effective field theory to analyze the Heisenberg Hamiltonian and to derive the spectra.

Magnetic and dielectric properties of multiferroic Tb0.5Eu0.5MnO3

The structural, magnetic and dielectric properties of multiferroic compound Tb0.5Eu0.5MnO3 are reported near the boundary of the multiferroic phase of the Eu-doped Tb1−xEuxMnO3 system. The Mn3+ moments order in an incommensurate antiferromagnetic manner below TN = 50 K, followed by a spin canting-like response around 25 K. Below TN, extra hysteresis loops were observed for applied fields Ba around 1-2 T, with decreasing magnetic / K moment for increasing magnetic fields. The dielectric constant ϵ' showed a peak at 28, which was attributed to the ferroelectric transition in analogy with the parent compound TbMnO3. Structural analysis indicates the Mn-O2-Mn bond angle within the ab-plane is 145.9° suggesting that there exists a critical angle in the perovskite manganate multiferroic systems.

Contents and Chemical Science

The substitution of cobalt and nickel for manganese in the perovskite manganate LaBiMn2O6+d; has been realized, leading to the perovskites LaBiMn2-x(M)xO6+d, with M = Co, Ni and x =0-2/3. In contrast to the literature those phases are found to be orthorhombic with Pnma symmetry. More importantly, it is shown that ferromagnetism is enhanced, TC being increased from 80 K for the parent compound (x = 0) to 97 K for Ni-phase, and to 130 K for the Co-phase. Moreover, a strong competition between ferromagnetism and a glassy-ferromagnetic state in the case of nickel or a spin-glass behaviour in the case of cobalt is observed. These phenomena are interpreted in the frame of a phase separation scenario, where the ferromagnetic Mn4+/Ni2+ and Mn4+/Co2+ interactions reinforce the Mn3+/Mn4+ interactions. These compounds are found to be insulating with a relatively large positive value of thermoelectric power.

Enhancement of ferromagnetism by Co and Ni substitution in the perovskite LaBiMn2O6+δ

The substitution of cobalt and nickel for manganese in the perovskite manganate LaBiMn2O6+δ has been realized, leading to the perovskites LaBiMn2−MxO6+δ, with M = Co, Ni and 0 ≤ x ≤ 2/3. In contrast to the literature these phases are found to be orthorhombic with Pnma symmetry. More importantly, it is shown that ferromagnetism is enhanced, TC being increased from 80 K for the parent compound (x = 0) to 97 K for the Ni phase, and to 130 K for the Co phase. Moreover, strong competition between ferromagnetism and a glassy-ferromagnetic state in the case of nickel or spin-glass behaviour in the case of cobalt is observed. These phenomena are interpreted in the frame of a phase separation scenario, where the ferromagnetic Mn4+/Ni2+ and Mn4+/Co2+ interactions reinforce the Mn3+/Mn4+ interactions. These compounds are found to be insulating with a relatively large positive value of thermoelectric power.

Spin-cluster effect and lattice-deformation-induced Kondo effect, spin-glass freezing, and strong phonon scattering in La0.7Ca0.3Mn1−xCrxO3

Besides the Kondo effect observed in dilute magnetic alloys, the Cr-doped perovskite manganate compounds La0.7Ca0.3Mn1−xCrxO3 also exhibit Kondo effect and spin-glass freezing in a certain composition range. An extensive investigation for the La0.7Ca0.3Mn1−xCrxO3 (x=0.01, 0.05, 0.10, 0.3, 0.6, and 1.0) system on the magnetization and ac susceptibility, the resistivity and magnetoresistance, as well as the thermal conductivity is done at low temperature. The spin-glass behavior has been confirmed for these compounds with x=0.05, 0.1, and 0.3. For temperatures above Tf (the spin-glass freezing temperature) a Curie–Weiss law is obeyed. The paramagnetic Curie temperature θ is dependent on Cr doping. Below Tf there exists a Kondo minimum in the resistivity. Colossal magnetoresistance has been observed in this system with Cr concentration up to x=0.6. We suppose that the substitution of Mn with Cr dilutes Mn ions and changes the long-range ferromagnetic order of La0.7Ca0.3MnO3. These behaviors demonstrate that short-range ferromagnetic correlation and fluctuation exist among Mn spins far above Tf. Furthermore, these interactions are a precursor of the cooperative freezing at Tf. The “double bumps” feature in the resistivity-temperature curve is observed in compounds with x=0.05 and 0.1. The phonon scattering is enhanced at low temperatures, where the second peak of double bumps comes out. The results indicate that the spin-cluster effect and lattice deformation induce Kondo effect, spin-glass freezing, and strong phonon scattering in mixed perovskite La0.7Ca0.3Mn1−xCrxO3.

Hall-effect studies of Pr0.7Sr0.3MnO3

Hall-effect measurements of the perovskite manganate Pr0.7Sr0.3MnO3 have been obtained at a magnetic field of 0.6 T in the temperature range 77–400 K. The results show peculiarities in the Hall-coefficient behavior. This is likely to be due to the coexistence of charge ordering and ferromagnetism. Obviously, the transformation between different magnetic phases with increasing temperature is significant for the physical properties, and influences the current transport in the compound.

La-Doping and External Pressure Effects on the Crystal Structure of Layered Perovskite-Like Manganate Ca3Mn2O7

The effects of La-doping and external pressure on the crystal structure of layered perovskite-like manganate Ca3Mn2O7 have been investigated by substituting La3+ for Ca2+ in Ca3Mn2O7 and in situ high pressure energy dispersive X-ray diffraction measurements on Ca3Mn2O7, respectively. With the increase of La3+ content in compounds with nominal compositions, La2—2xCa1+2xMn2O7 (x = 1.0–0.5), single-phase compounds with a tetragonal structure are formed only in the range x = 1.0–0.6 and the lattice parameter a increases with increasing La-doping level while c decreases. Similarly, with the increase of external pressure in the range 0–1.3 GPa, the lattice parameter a of the layered perovskite manganate Ca3Mn2O7 increases while c decreases, and the structure of Ca3Mn2O7 undergoes a phase transition from a tetragonal to a orthorhombic structure at about 1.3 GPa. The La-doping and external pressures have the same effect on the lattice structure of the layered perovskite manganate Ca3Mn2O7.

N=2 Member of the hexagonal perovskite-intergrowth manganate family A n+1 Mn nO 3 n+3 (Ca 2O)

The n=2 member in hexagonal perovskite manganate family A n+1 Mn n O 3 n+3 (Ca 2O) was obtained in a complex composition La 2Ba 0.8Sr 0.6Ca 1.6Mn 2O 10, but simple hexagonal structure. It crystallizes in the hexagonal P6 3/ mmc space group [ a=5.63591(5) A ̊ , c=16.2843(3) A ̊ , V=447.948(9) A ̊ 3 ; Z=2] and consists of double hexagonal perovskite layers (2H-type) and graphite-like [Ca 2O] layer. The manganese octahedra share faces resulting in localized magnetic property.

The structure and properties of the manganate with nominal composition La 1.0Ca 2.0Mn 2O 7

The manganate with nominal composition La 1.0Ca 2.0Mn 2O 7 was prepared using a standard solid-state reaction method under ambient pressure. The structure of the compound was investigated using powder X-ray diffraction, Rietveld analysis and TEM experiments. The results show that the compound forms multiphase mixtures comprising the layered perovskite manganate La 1.0Ca 2.0Mn 2O 7 with 91.3% weight fraction as majority phase, the perovskite manganate La 0.5Ca 0.5MnO 3 with weight fraction 8.7% as the minority phase. The occurrence of weak magnetization at 250 K and the presence of weak magnetization in the lower temperature region of 5–135 K are linked to the perovskite manganate La 0.5Ca 0.5MnO 3 and the layered perovskite manganate La 1.0Ca 2.0Mn 2O 7, respectively. The magnetoresistance (MR) occurred in the lower temperature range arises mainly from the layered perovskite manganate La 1.0Ca 2.0Mn 2O 7.

Study of phase components of La1.5Ca1.5Mn2O7

The manganate with nominal composition La1.5Ca1.5Mn2O7, which is regarded as a single-phase compound with layered perovskite structure in the literature, was prepared using a standard ceramic process. The structures and morphology of the manganate were investigated by x-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy, and energy-dispersive x-ray microanalysis. However, no direct evidence of layered Sr3Ti2O7-type structure was observed in TEM experiments; instead, we observed multiphase mixtures of an orthorhombically distorted perovskite phase as majority and cubic perovskite phase as minority, as well as a small amount of calcium oxide. The measured magnetic and transport properties of this manganate arise mainly from the presence of hole-doped multiphase perovskite manganates. These physical properties demonstrated again the correctness of our phase component analysis.

Comment on `The metal-insulator transition and ferromagnetism in theelectron-doped layered manganates La2.3-xYxCa0.7Mn2O7(x = 0.0,0.3,0.5)'

We show that the report of Raychaudhuri et al (1998 J. Phys.: Condens. Matter 10 L191), that the samples of nominal compositionsLa2.3-xYxCa0.7Mn2O7 (x = 0.0,0.3,0.5) are electron doped layered manganates,is incorrect. Rietveld profile refinement of the x-ray diffraction data of thesample La2.3Ca0.7Mn2O7 (x = 0.0) synthesized by us following the samesynthesis process as reported by Raychaudhuri et al clearly shows that itforms a multiphase mixture comprising hole doped perovskite manganates andlanthanum oxide.