Ca MnO Research Articles

Perovskite-structured ultrasensitive CaMnO3 nanoenzyme enables highly efficient ultrasound-amplified and catalysis-involved synergistic tumor therapy

Catalytic nanoenzyme-mediated therapy with reactive oxygen species generation feature and tumor microenvironment regulation characteristic has demonstrated high therapeutic efficacy in oncological field, whereas its low enzyme-mimicking reaction efficacy typically results in dissatisfied therapeutic effect and outcome. Herein, an ultrasensitive CaMnO3 (CMO) nanoenzyme has been rationally designed and engineered for enzyodynamic-calcium overload synergistic tumor therapy. CMO nanoenzyme with oxidase (OXD)-, peroxidase (POD)- and glutathione peroxidase (GPx)-mimic activities is responsible for the generation of reactive oxygen species, the consumption of intra-tumor glutathione and mitochondrial damage. For the evaluation of OXD and POD-mimicking activities, CMO with ultra low concentration (1 μg ml−1) can rapidly catalyze the color reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) hydrochloride and reach the reaction termination in a very short time (1 s). Moreover, the release and overload of Ca2+ strengthen the tumor cell death. Exogenous ultrasound stimulation further amplifies the enzyodynamic-Ca2+ overload synergistic tumor-therapeutic efficacy. In vitro and in vivo results affirm the transcendent antineoplastic outcomes of CMO. Meanwhile, the existence of Mn2+ endows nanoenzyme with T1-weighted MR imaging capacity. This work provides new strategies for efficient enzyme-mimicking activity and tumor synergistic treatment based on new perspectives on the engineering of multifunctional therapeutic nanomedicine.

Multifaceted Roles of Ag+ Ions within and outside La–Ca–MnO3 Perovskite Manganites: Unveiling the Room Temperature Magnetocaloric Effect

Multifaceted Roles of Ag⁺ Ions within and outside La–Ca–MnO₃ Perovskite Manganites: Unveiling the Room Temperature Magnetocaloric Effect

Magnetic, Antiferroelectric-like Behavior and Resistance Switching Properties in BiFeO3-CaMnO3 Polycrystalline Thin Films

The effect of ferromagnetic CaMnO3 (CMO) addition to structural, magnetic, dielectric, and ferroelectric properties of BiFeO3 is presented. X-ray diffraction and Raman investigation allowed the identification of a single pseudocubic perovskite structure. The magnetic measurement showed that the prepared films exhibit a ferromagnetic behavior at a low temperature with both coercive field and remnant magnetization increased with increasing CMO content. However, a deterioration of magnetization was observed at room temperature. Ferroelectric study revealed an antiferroelectric-like behavior with a pinched P–E hysteresis loop for 5% CMO doping BFO, resulting in low remnant polarization and double hysteresis loops. Whereas, high remnant polarization and coercive field with a likely square hysteresis loop are obtained for 10% CMO addition. Furthermore, a bipolar resistive switching behavior with a threshold voltage of about 1.8 V is observed for high doped film that can be linked to the ferroelectric polarization switching.

Response characteristics of (La,Ca)Mn1+δO3 films for heat fluxes based on the transverse thermoelectric effect

Inclined epitaxial (La,Ca)Mn1+δO3 films (-0.3 ≤ δ ≤ 0.1) have been prepared on the miscut 12° STO single crystal substrates. The conductivity gradually increases from 1.51 × 103 S/m for (La,Ca)Mn0.7O3 to 1.23 × 104 S/m for (La, Ca)MnO3, and then slightly decreases to 1.12 × 104 S/m for (La, Ca)Mn1.1O3 films. The enhanced conductivity results in the increase of electron thermal conductivity, so the sensitivity gradually decreases from 12.44 μV/(kW/m2) for (La,Ca)Mn0.7O3 to 7.69 μV/(kW/m2) for (La,Ca)MnO3. As the Mn content continues to increase, even if the conductivity of (La,Ca)Mn1.1O3 decreases, the sensitivity still decreases to 6.12 μV/(kW/m2) due to the deteriorated Seebeck coefficient anisotropy. Additionally, the response time decreases to 22 ns for (La,Ca)MnO3 with increased conductivity, and then slightly increases to 24 ns for (La,Ca)Mn1.1O3 due to the decrease in conductivity. The above results indicate that the sensitivity and response time show a similar trend with the conductivity, which could serve as a reference to fabricate heat flux sensors based on the TTE effect by designing materials.

Thermoelectric properties of hot‐pressed Ruddlesden‐Popper phases CaO(CaMnO3)m

AbstractWe investigated the Ruddlesden‐Popper series CaO(CaMnO3)m with m = 1, 2, 3, ∞, to study the impact of the varying amounts of CaO layers on their thermoelectric properties. Previous studies showed that highly dense samples are difficult to obtain due to the refractory nature of these materials. In this study, we managed to obtain dense pellets during a classical hot‐pressing step, if and only if the samples were subjected to extended ball‐milling prior to pressing, resulting in crystallite sizes of 30–35 nm after hot‐pressing. The sample with the largest amount of CaO layers (m = 1) had the lowest electrical and thermal conductivity, and the highest Seebeck coefficient, as predicted. Ultimately the perovskite CaMnO3 (m = ∞, no CaO layers) exhibited the best thermoelectric properties.

Insights into multi-pathway peroxymonosulfate activation by copper-doped Ca/Mn perovskite oxides for diethyl phthalate degradation

Peroxymonosulfate (PMS) activation based on metallic catalysts with versatile mineral structures and superior catalytic properties has attracted much attention. In this study, we built a CaMnO3(CMO) with copper dopped to promote PMS activation by Mn(III)/Mn(IV) and Cu(I)/Cu(II) redox cycles with the synergistic effect of bimetal for efficient degradation of diethyl phthalate (DEP). Under optimal conditions, 95.7% of DEP (10 mg L−1) degradation was realized in 60 min, and the mineralization reached 75%, while only 26.9% of DEP was removed with little TOC removal by CaMnO3. Unexpectedly, not only •OH, O2•− and SO4•−, but also nonradical pathway singlet oxygen (1O2) was found to be involved in the CMO-Cu/PMS system. The redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) effectively promoted PMS activation to reactive oxygen species (ROS), which were responsible for DEP degradation. Furthermore, density functional theory (DFT) calculations and liquid chromatograph-mass spectrometer (LCMS) were combined to explore the degradation pathway. This work provides a new insight for developing heterogeneous perovskites for PMS activation to construct more efficient method for water treatment.

Anomalous Lattice Evolution-Mediated Electrical Properties in Transparent KNN-Based Lead-Free Ferroelectric Films.

The epitaxial (K0.49Na0.49Li0.02)(Ta0.2Nb0.8)O3 with 2 wt % MnO2 addition (KNNLT-M) film on the transparent La0.03Ba0.97SnO3-coated LaAlO3 (001) substrate is chosen to investigate how the lattice evolution, as well as the electrical properties, optical bandgap energy, and thermal stability, changes with the growth oxygen pressure [P(O2)]. Compared to the other perovskite oxide films, for example, (La,Ca)MnO3, PbTiO3, and BaTiO3, an anomalous lattice evolution with an increased (decreased) out-of-plane (in-plane) lattice constant was observed in KNNLT-M films as P(O2) increases. Such anomalous lattice evolution can improve the electric properties of KNNLT-M films; for example, the ferroelectricity is significantly optimized and the dielectric constant is enhanced from 451 to 1248 at 1 kHz. The X-ray photoelectron spectra results have demonstrated that high P(O2) can make more K cations to enter the perovskite lattice and the Mn2+/Mn3+ existing in KNNLT can effectively suppress the leakage behavior, thus promoting the electrical nature of KNNLT-M films. The optical measurements show that the KNNLT-M film heterostructures are highly transparent with a maximum transmittance of ∼80%, and both direct and indirect bandgap energies increase with increasing P(O2). Meanwhile, all these KNNLT-M films exhibit good thermal stability with stable ferroelectricity up to the high temperature of at least 125 °C. These results demonstrate that the control of the lattice structure and electrical properties by P(O2) is one of the important prerequisites for the application of KNN-based films.

High electrical power designing the horizontal shaped of bulk Ca3Co4O9/CaMnO3

A horizontal-shaped cell of a bulk oxide thermoelectric material was constructed using misfit layered Ca3Co4O9 (CCO) and perovskite CaMnO3 (CMO). The electrical power was measured based on the operating parameters. The horizontal shape can improve the efficiency of the thermoelectric cell because it reduces the heat loss through the sidewalls to the junction of the thermoelectric legs, resulting in an improved thermoelectric efficiency. The pair was connected to a series circuit to generate an open-circuit voltage (VOC) of 107.98 mV. The maximum output power (Pmax) of the thermoelectric cell was 7.1 μW at ΔT = 473 K. A significant increase in the output characteristics of the cell indicates that the bulk was effective. The horizontal-shaped cell of the bulk thermoelectric oxide exhibited promising output characteristics.

Comparative Study in Ca3Co4O9 and CaMnO3 Perovskite Structure-Based Thermoelectric Oxide

The p-type Ca3Co4O9 (CCO) and n-type CaMnO3 (CMO) thermoelectric oxide were synthesized stoichiometrically by the solid-state reaction technique. Both systems were investigated comparatively in aspects of thermoelectric and electrical properties. The material appearance, crystal structure, density, hardness, thermoelectric properties including Seebeck coefficient, electrical resistivity, and thermal conductivity, and electrical properties including dielectric constant, dielectric loss, and complex impedance of both systems were observed. Moreover, the P-E hysteresis loop of ferroelectric property and electrostriction were also investigated. The difference in the crystal structure, phase formation, and crystal growth conducts to the difference in physical, thermoelectric, and electrical properties. CMO was a cubic-perovskite type structure oxide with a higher density, less porosity, and smaller grain size with more thorough distribution as compared to orthorhombic structure CCO. Thus CMO could perform better values in terms of Seebeck coefficient, electrical resistivity, and thermal conductivity. In contrast, CCO possessed a larger grain size with an orthorhombic structure which has more favorable directions for dipole displacement. Hence, CCO exhibited a higher dielectric constant with lower dielectric loss. The complex impedance of both systems was in accordance with the RLC series circuit principle. Unfortunately, the P-E and S-E hysteresis loops of both systems could not be verified due to their electrical conductivity.

Tailoring c‐Axis Orientation in Epitaxial Ruddlesden–Popper Pr0.5Ca1.5MnO4 Films

AbstractInterest in layered Ruddlesden–Popper (RP) strongly correlated manganites of Pr0.5Ca1.5MnO4 as well as in their thin film polymorphs is motivated by the high temperature of charge orbital ordering above room temperature. The c‐axis orientation in epitaxial films is tailored by different SrTiO3 (STO) substrate orientations and CaMnO3 (CMO) buffer layers. Films on STO(110) show in‐plane alignment of the c‐axis parallel to the [100] direction. On STO(100), two possible directions of the in‐plane c‐axis lead to a mosaic like, quasi 2D nanostructure, consisting of RP, rock‐salt, and perovskite blocks. With the CMO buffer layer, Pr0.5Ca1.5MnO4 epitaxial films with c‐axis out‐of‐plane are realized. Different physical vapor deposition techniques as ion beam sputtering, pulsed laser deposition and metalorganic aerosol deposition are applied in order to distinguish effects of growth conditions from intrinsic epitaxial properties. Despite their very different growth conditions, surface morphology, crystal structure, and orientation of the thin films reveal a high level of similarity as verified by X‐ray diffraction, scanning, and high resolution transmission electron microscopy. For different epitaxial relations stress in the films is relaxed by means of modified interface chemistry. The charge ordering in the films occurs at a temperature close to that expected in bulk material.

Summerfield scaling model and conduction processes defining the transport properties of silver substituted half doped (La–Ca) MnO3 ceramic

Conductivity spectra of La0.5Ca0.3Ag0.2MnO3 (LCAM) oxide have been investigated in the temperature range [80 K–680 K]. The studied system displays a semiconductor behavior over the explored temperature and frequency ranges. From direct current study, the transport of charge carries is assisted via disorder energy below θD/4. For the temperature range [θD/4- θD/2], the transport properties are governed by activation of Mott-variable range hopping (Mott-VRH) process. Beyond θD/2, the conduction phenomena are assisted through the thermally activation of the small polaron hopping (SPH) mechanism. At high frequencies, the conductivity spectra reveal a dispersive region. They are explained by the double Jonscher response. The latter side was characterized by the appearance of the overlapping-large-polaron-tunneling (OLPT), the correlated barrier hopping (CBH) and the non small polaron tunneling (NSPT) conduction processes. It is found that the calculated disorder energy is frequency independent. At elevated frequencies, the hopping energy is predicted to decrease with increasing frequency which can be related to the change in the Polarons radius. In the temperature range [80 K–220 K], the conductivity spectra follow double Jonscher law. Using the scaling model, the spectra merge into a single master curve, which confirmed the validity of the time temperature superposition principle (TTSP). A confident divergence from the Summerfield is noticed at high frequencies. It proves that the charge mobility is temperature dependant. The Summerfield correction scaling is effectuated by introducing a scaling positive parameter (α = 1.2). An excellent coalescence of conductivity spectra is observed.

Investigation of the phase separation property in [formula omitted][formula omitted][formula omitted][formula omitted] manganite

We report a comprehensive investigation of La0.2Pr0.4Ca0.4MnO3 to clarify the micrometre scale phase separation phenomenon in the mixed valent manganite (La,Pr,Ca)MnO3. The compound shows multiple magnetic transitions, in which the charge-ordered state is converted into a ferromagnetic state in steps with the application of a magnetic field. The ac susceptibility measurements show that the glassy transition at low temperatures does not depend on the frequency, thus indicating the absence of any spin glass behaviour. Magnetization as well as heat capacity measurements indicate that this low temperature transition is magnetic field dependent. The field dependent resistivity at 2 K shows a sharp drop indicating that the sample behaviour changes from a high resistive state to a low resistive state, corroborating the conversion of charge-ordered insulating (COI) phase to a ferromagnetic metallic (FMM) phase. Our results point towards the existence of phase separation, rigidity of the low temperature glassy-like phase as well as the conversion of COI phase to FMM phase by the application of magnetic fields.

Thermoelectric properties of non-stoichiometric CaMnO3-δ composites formed by redox-activated exsolution

A novel synthesis route for preparing well-defined composites based on CMO (CaMnO3) has been established taking advantage of the unique phase relations in the system Ca-Mn-O at reducing- and oxidizing atmosphere, respectively. Samples corresponding to stoichiometric CMO and composites with 5 and 10 vol % of Ruddlesden-Popper (Ca4Mn3O10)- and spinel (CaMn2O4)-phases, respectively, were prepared with final densities >91 %. The presence of secondary phases significantly enhanced the electrical conductivity compared to stoichiometric CMO. The highest electrical conductivity was observed for CMO with 10 vol % spinel varying between 55 and 75 S/cm at temperatures between 100 and 900 °C. This composition also exhibited the highest figure-of-merit (zT) in this study, reaching 0.083 at 800 °C.

Broad band magnetotransport at room temperature in La0.7Sr0.3−Ca MnO3: Electrically detected magnetic resonances

Abstract We report the room temperature magnetoimpedance in bulk samples of La0.7Sr0.3−xCaxMnO3 (0 ≤ x ≤ 1) subjected to ac current excitation of frequency f = 1 MHz to 3 GHz and dc magnetic fields (−5 kOe 700 MHz. A plot of Hdc corresponding to the double peak/critical field versus frequency suggest that the curves are linear for PM samples and non-linear for FM samples. We suggest that the observed anomalies in the ac magnetoresistance are due to electron paramagnetic resonance for x ≥ 0.24 and ferromagnetic resonance for x ≤ 0.20. Thus, we are able to electrically detect paramagnetic and ferromagnetic resonances in these conducing magnetic oxides through a simple magnetoimpedance measurement.

Tailoring electronic and thermal transport properties of CaO(CaMnO3)m-based (m=1 and m=∞) composites for thermoelectric power generation

Oxide thermoelectric (TE) materials are promising for waste heat recovery at high temperatures thanks to their good chemical stability at elevated temperatures and low cost. We study Nb-doped n-type TE oxides of the CaO(CaMnO3)m-series. The CaMnO3 (m = ∞) and Ca2MnO4 (m = 1) derivatives feature extremely opposite transport coefficients, where the m = ∞ structure exhibits high electrical and thermal conductivity, and the m = 1 derivative exhibits the opposite combination. We synthesize composite materials based on these two phases of different ratios to draw correlations between the TE properties, microstructure evolution, and composition of the material. We determine the optimum sintering temperature to be 1373 K, and measure both thermal and electronic transport coefficients, then perform a thorough general effective medium (GEM) analysis. Interestingly, we find that most ratios obey to the GEM behavior, where deviations are elucidated in terms of interfacial effects. This study provides us with tools for identifying the significance of bulk vs. interfacial effects in design of composite materials with controllable transport properties.

On the origin of vibrational properties of calcium manganate based thermoelectric compounds

Vibrational properties of CaO(CaMnO3)m (m = 1, 2, 3, and ∞) thermoelectric (TE) oxides for high-temperature energy conversion applications are studied both experimentally and computationally. Density functional theory (DFT) calculations reveal strong scattering events involving dispersive acoustic phonons and non-dispersive optical modes in the frequency range of 3–5 THz. We demonstrate that the low frequency parts of the phonon spectra are strongly dominated by Ca-sublattice oscillations for all compounds of the CaO(CaMnO3)m (m = 1,2,3, ∞) series, which predicts enhanced phonon scattering upon Ca-sublattice site substitution defects. Accordingly, laser flash analysis (LFA) indicates considerable decrease of thermal conductivity (κ) due to La- substitution for Ca, whereas Nb- substitution for Mn-sites does not affect κ noticeably. It is found that thermal conductivity of CaO(CaMnO3)m compounds is governed by phonon scattering on CaO/CaMnO3 boundaries for m = 1, 2, and 3 and by Umklapp processes for m = ∞. Thermal transport in this system is strongly dominated by acoustic phonon modes possessing much larger Grüneisen parameters (γ) compared to optical ones.

Activating the Bifunctionality of a Perovskite Oxide toward Oxygen Reduction and Oxygen Evolution Reactions.

This article presents a facile and effective approach to activate the bifunctionality of calcium-manganese perovskites toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). We substituted Nb into the Mn site of CaMnO3 (CMO) and treated the material with H2. The as-obtained CaMn0.75Nb0.25O3-δ (H2-CMNO) displays the same structure as that of CMO, and compared to that of CMO, H2-CMNO exhibits significantly improved OER performance, including a lower overpotential, a reduced Tafel slope, a higher mass activity, and enhanced stability. In addition, the ORR performance of H2-CMNO is also greatly enhanced, relative to CMO, with a higher ORR activity and a more efficient electron-transfer pathway. H2-CMNO shows an even higher activity-per-catalyst cost and superior stability than that of state-of-the-art materials, such as IrO2 and Pt/C. This great enhancement in ORR and OER activity of H2-CMNO is attributed to several factors, including phase stabilization, optimized eg filling, better OH- adsorption, and improved electrical conductivity.

Exchange interactions of CaMnO3 in the bulk and at the surface

In this work, we present electronic and magnetic properties of CaMnO3 (CMO) as obtained from ab initio calculations. We identify the preferable magnetic order by means of density functional theory plus Hubbard U calculations and extract the effective exchange parameters (Jij's) using the magnetic force theorem. We find that the effects of geometrical relaxation at the surface as well as the change of crystal field are very strong and are able to influence the lower energy magnetic configuration. In particular, our analysis reveals that the exchange interaction between the Mn atoms belonging to the surface and the subsurface layers is very sensitive to the structural changes. An earlier study [A. Filippetti and W.E. Pickett, Phys. Rev. Lett. 83, 4184 (1999)] suggested that this coupling is ferromagnetic and gives rise to the spin flip process on the surface of CMO. In our work we confirm their finding for an unrelaxed geometry, but once the structural relaxations are taken into account, this exchange coupling changes its sign. Thus, we suggest that the surface of CMO should have the same G-type antiferromagnetic order as in the bulk. Finally, we show that the suggested SF can be induced in the system by introducing an excess of electrons.

Dependence of electrical transport properties of CaO(CaMnO3)m (m = 1, 2, 3, ∞) thermoelectric oxides on lattice periodicity

The electrical transport properties of CaO(CaMnO3)m (m = 1, 2, 3, ∞) compounds are studied applying the density functional theory (DFT) in terms of band structure at the vicinity of the Fermi level (EF). It is shown that the total density of states (DOS) values at EF increase with increase in the m-values, which implies an increase in the electrical conductivity, σ, with increasing m-values, in full accordance with experimental results. Additionally, the calculated values of the relative slopes of the DOS at EF correlate with the experimentally measured Seebeck coefficients. The electrical conductivity and Seebeck coefficients were calculated in the framework of the Boltzmann transport theory applying the constant relaxation time approximation. By the analysis of experimental and calculated σ(Τ) dependences, the electronic relaxation time and mean free path values were estimated. It is shown that the electrical transport is dominated by electron scattering on the boundaries between perovskite (CaMnO3) and Ca oxide (CaO) layers inside the crystal lattice.

Structural stability of calcium-manganate based CaO(CaMnO3)m (m = 1, 2, 3, ∞) compounds for thermoelectric applications

We investigate the crystal structure and bulk properties of calcium-manganate based TE oxides of the CaO(CaMnO3)m (m = 1, 2, 3, ∞) Ruddlesden-Popper (RP) class applying the density functional theory (DFT) approach. We find that the crystal structures of all compounds in this series tend to deviate from the high-symmetry cubic perovskite structure (for the case of m = ∞) or tetragonal I4/mmm structure (for m = 1, 2, and 3). The structure of Ca2MnO4 (m = 1) is found to be tetragonal with the I41/acd space group symmetry, whereas the Ca3Mn2O7 (m = 2) and Ca4Mn3O10 (m = 3) compounds form orthorhombic structures having the Cmc21 and Pbca symmetries, respectively; all of the above are formed by combinations of tilted MnO6 octahedra. These results are corroborated by X-ray diffraction experiments. This procedure provides us with a powerful tool predicting phase stability and polymorphism.