Perovskite Calcium Research Articles

Performance of a perovskite-structured calcium manganite oxygen carrier produced from natural ores in a batch reactor and in operation of a chemical-looping combustion reactor system

The potential for low cost of CO2 capture using chemical-looping combustion (CLC) should not be compromised by costs associated with the oxygen carrier. This justifies studies of oxygen carrier materials with reasonable production costs. In this study, a perovskite calcium manganite (CaMnO3-δ), was synthesized from manganese ore and limestone through a straightforward process involving mixing with polyvinyl-alcohol, sintering, crushing and sieving. The calcium manganite produced exhibited two primary crystalline phases: CaMnO3 (perovskite) and CaMn2O4 (marokite). Experiments were conducted using both a batch fluidized-bed reactor and a 300 W CLC reactor system in continuous operation to assess the oxygen uncoupling and reactivity of the calcium manganite. The results show that the oxygen uncoupling ability increases with temperature. Full syngas conversion was achieved at relatively low temperatures and low fuel-reactor bed mass over fuel power ratio in the 300 W unit. Elevated temperatures and ratio of fuel-reactor bed mass over fuel power enhance methane conversion significantly. The attrition of the calcium manganite was low, around 0.1 wt%/h for the last 15 h operation with methane. Batch reactor tests of fresh and used materials showed that there was no reduction in reactivity after 29 h of fuel operation.

Photocatalytic treatment of landfill leachate using CaTiO3 nanoparticles

Perovskite Calcium titanate (CaTiO3)is a versatile material that can be used in several applications, such as biomedicine, electronic devices, photocatalysis, and wastewater treatment.In this study, CaTiO3nanoparticles were synthesized using the sol–gel method at 600 °C with the help of tetra butyl titanate, calcium nitrate, and citric acid as chelating agents. FESEM and TEM analysis shows the synthesized nanoparticle has particle sizes of less than 26.23 and 23.71 nm respectively with a bandgap of 3.57 eV. By using DTA, TGA, XRD, FESEM, TEM, EDX, and UV–Vis, the thermal, structural, and optical properties were examined. Several studies examined the photocatalytic capabilities of CaTiO3for the photocatalytic treatment of simulated dye solution and wastewater produced by the textile industry. In this study, the CaTiO3 nanoparticles are used in the photocatalytic treatment of landfill leachate. The results are promising, showing a 72 % reduction in chemical oxygen demand (COD),a 43.62 % decrease in colour,a 41.75 % improvement in turbidity, 59.01 % removal of total dissolved solids, and35.71 % removal of NH3-N from the landfill leachate under the optimum condition of 33 W UV irradiation for 8 h at a catalyst dose of 3.33 g/L and a pH of 6. After nano-photocatalytic treatment, the percentages of Cr, Ni, and Zn removed are 52.30 %, 63.46 %, and 87.50 %, respectively.

Hardware-based security devices using a physical unclonable function created by the irregular grain boundaries found in perovskite calcium titanate

The IoT era necessitated the need for hardware-based security devices due to their strong resistance to hacking compared to software-based systems, which are limited by CPU usage and performance. Hardware-based systems are more unpredictable due to their unique and non-discernible external properties. This research focused on developing a security device based on lead-free metal oxide CaTiO3 perovskite material with irregular electrical characteristics, known as physical unclonable functions. These irregularities were created by increasing the number of grain boundaries on the device surface through high-temperature annealing, resulting in greater adsorbed oxygen. The outcome was a highly random and unique security key using irregular electrical characteristics with 49.53% uniformity and a 46.55% inter-Hamming distance.

Low‐Symmetry 2D Perovskite CaNb2O6 for Polarization‐Sensitive UV Photodetection

AbstractPolarization‐sensitive photodetection in ultraviolet (UV) range has demonstrated broad applications in both military and civilian fields. As the key component of polarized UV photodetectors, semiconducting materials with wide bandgaps and intrinsic low‐symmetry are highly desired. Herein, perovskite calcium niobate (CaNb2O6) is re‐introduced to the family of two‐dimensional (2D) layered materials for UV‐polarized photodetection. Using a simple vapor phase epitaxy growth process, CaNb2O6 nanosheets are successfully synthesized, which can be scaled down to monolayers with thickness of about 0.8 nm. The anisotropic structural, vibrational, and optical properties of CaNb2O6 are systematically investigated. Photodetectors based on 2D CaNb2O6 present a large dichroic ratio of 2.1 at 375 nm light irradiation, exceeding most of reported UV photodetectors, and the large anisotropic ratio also contributes to a high‐resolution polarization imaging. This work demonstrates that the 2D CaNb2O6 has promising potential for developing next‐generation polarized UV detecting and imaging technology.

High pressure-temperature phase relations of basaltic crust up to mid-mantle conditions

A substantial amount of subducted basaltic crusts may exist in the lower mantle. It features distinct chemical composition from the peridotitic mantle and plays important roles in the chemical and dynamic evolution of Earth's interior. However, the chemical composition of mineral phases present in basaltic crust in the lower mantle is still poorly constrained. Here, we determined phase relations of normal mid-ocean ridge basalt (MORB) up to 52 GPa at 2000 K by multi-anvil press. Throughout our experiments, the mineral assemblages consist of five phases including bridgmanite, stishovite, calcium perovskite (davemaoite), calcium ferrite and new hexagonal aluminous phases. The density of MORB calculated from our phase assemblages and previously published thermoelastic data is 2-3% higher than that of the average mantle, which is consistent with literature. The new hexagonal aluminous phase is a host of potassium but only occupies 1-2 vol.% due to limited abundance of potassium in normal MORB. This indicates that the new hexagonal aluminous phase doesn't affect the elastic properties of basalt. Electron energy-loss spectra of recovered basaltic Al-rich bridgmanite show significant enrichment of ferrous iron (75-85%) compared with peridotitic Al-poor bridgmanite (∼30%), which is against previous studies showing that ferric iron ratio in bridgmanite increases with Al content. Ferric iron exhibits strong partitioning into the new hexagonal aluminous phase (41-64%), whereas bridgmanite (14-28%) and calcium ferrite phase (5-27%) remain Fe2+-enriched. The oxygen vacancy component of MgAlO2.5 in bridgmanite is ∼11% up to 40 GPa, which is much higher than that in peridotitic bridgmanite (2-3%), possibly producing a viscosity contrast in the mid-mantle that would explain slab stagnation and plume thinning between 660 km and 1000 km depth. The presence of ferrous iron-rich bridgmanite in the deep lower mantle may contribute to seismic features of large low-shear-velocity provinces.

Role of Ca doping on oxygen vacancy production in modulating dielectric, ferroelectric and magnetic polarization in BaTiO3 thin films

Chemical bath deposition, being an application oriented electroless technique, is used for the deposition of calcium doped barium titanate (Ba1-xCaxTiO3) thin films using glass substrate. Ca concentration is varied as x = 0.0, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.12. As-deposited thin films show amorphous behavior, whereas, annealed thin films show crystalline nature. X-ray diffraction (XRD) analysis of annealed thin films shows a pure tetragonal phase of Perovskite barium calcium titanate thin films up to x = 0.08 dopant concentration, while XRD peak corresponding to CaO is observed at x = 0.10 and 0.12. Maximum optical transmission of 65% is observed under undoped and as-deposited conditions. Annealed thin films show 83% transmission under undoped condition. While decrease in transmission is observed with the increase of dopant concentration due to the presence of sub bands. High value of dielectric constant (i.e. ∼3800 at log f = 1.3) and low value of tangent loss (i.e.∼0.15 at log f = 1.3) is observed for x = 0.08 dopant concentration. Cole–Cole plots reveal the presence of two electrically active grains and grain boundary regions. Maximum value of spontaneous polarization Pmax (18.46 μC/cm2) is observed for x = 0.08 dopant concentration. Mixed para-ferromagnetic response is observed under undoped condition. S-shaped magnetic response is observed for x = 0.02–0.04 whereas, ferromagnetic curves are observed for x = 0.06–0.12. It is important to mention here that tetragonal Perovskite calcium doped barium titanate thin films with U-shaped dielectric constant and good ferroelectric properties are hard to find in literature.

The Effect of Calcium Perovskite and Newly Developed Magnetic CaFe2O4/CaTiO3 Perovskite Nanocomposite on Degradation of Toxic Dyes Under UV–Visible Radiation

The Effect of Calcium Perovskite and Newly Developed Magnetic CaFe2O4/CaTiO3 Perovskite Nanocomposite on Degradation of Toxic Dyes Under UV–Visible Radiation

Magnetic and dielectric features of Yb3+, Dy3+, and Nd3+ subrogated perovskite calcium manganite bulk materials

Magnetic and dielectric features of Yb3+, Dy3+, and Nd3+ subrogated perovskite calcium manganite bulk materials

The miscibility of calcium silicate perovskite and bridgmanite: A single perovskite solid solution in hot, iron-rich regions

Calcium silicate perovskite and bridgmanite are two phases believed to coexist throughout the lower mantle, which at some temperature, at least theoretically, dissolve into each other to form a single perovskite solid solution (CaxMg1−xSiO3). This may have large seismic and geochemical implications due to the changes in density, elasticity and element partition coefficients between single and mixed phase perovskites. DFT Molecular Dynamics has been used to estimate the miscibility of bridgmanite and calcium perovskite at pressures between 25 and 125 GPa. At 125 GPa (where mixing is the greatest in our pressure range) to mix 1% of Ca-pv into bridgmanite requires a temperature of 2042 K, 5% 2588 K, 10% 2675 K and 50% 2743 K. Therefore, in a simplified lower mantle chemistry an extensive MgSiO3–CaSiO3 solid solution is not expected to occur. However, a simple model was employed to test whether the presence of other elements might influence this mutual solid solution and it was demonstrated that if sufficient concentrations (>1 at.%) of additional elements are present then miscibility may become favourable. Of the elements likely to be present at these concentrations it appears that ferrous iron promotes, whilst aluminium inhibits, a single-phase perovskite solid solution. To a lesser extent ferric iron may both increase and decrease perovskite miscibility. Modelling for realistic mantle compositions suggests that basaltic lithologies will always retain two perovskite components, whereas a single perovskite solid solution may be preferred in hot and/or iron-rich pyrolytic bulk compositions near the base of the lower mantle. Static calculations indicate perovskite miscibility may cause pyrolytic lithologies (with 12.5% CaSiO3) to possess lower density (−0.14–0.25%), Vs (−1.5–3.5%) and Vp (−0.5–1.2%), and higher VΦ (+ 0.00–0.75%) than predicted for assemblages containing two perovskites. These seismic changes, while preliminary, are similar to those observed in the LLSVPs which are also regions that are likely hotter than the surrounding mantle and thus possess conditions promoting the formation of a single perovskite phase.

Near-infrared anti-Stokes luminescence from neodymium doped perovskite calcium titanate particles for optical temperature sensors

The optical thermometer materials have drawn tremendous attention for their excellent performances, such as fast response, well-adapted, and non-contact. However, most phosphors present thermally quenched emissions, which greatly weakens temperature sensing. In this work, we synthesized Yb3+/Nd3+ codoped CaTiO3 microcrystals by solid state reaction. Under the excitation of 980 nm, the developed perovskite particles present anti-Stokes emissions at the near-infrared range. More importantly, the near-infrared anti-Stokes emissions gradually get enhanced as the temperature rises. An optical ratiometric thermometer has been constructed based on the energy level transitions of Nd3+ ions (4F7/2/4F5/2 →4I9/2). On account of the thermally enhanced emissions, the prepared thermometer only needs 16 mW/mm2 power density, and has a relatively high sensitivity of 1.52 % K−1. Therefore, the prepared Yb3+/Nd3+ codoped CaTiO3 crystal is a promising optical thermometer material with great application prospects.

Structural changes and pseudo-piezoelectric behaviour of field assisted sintered calcium titanate

The polycrystalline perovskite calcium titanate has an orthorhombic crystal structure at room temperature, which belongs to a centro-symmetric point group. Due to this fact, it does not show piezoelectric behaviour. However, such behaviour is observed in nanostructured calcium titanate prepared by sol-gel synthesis and field assisted sintering. Whereas, the conventionally sintered sample does not show this behaviour. Presumably, the instability of regular TiO6 octahedra results in the off-centering of titanium positions of the field assisted sintered calcium titanate. This phenomenon leads to the generation of electric dipoles due to the lattice distortions produced by the formation of highly localized defects, i.e. oxygen vacancies, during densification by the field assisted sintering. As a result, pseudo-piezoelectric behaviour is observed, which confirms that the field assisted sintering triggers the piezoelectric effect but not the conventional sintering. The charge (Q) produced in the field assisted sintered sample and the piezoelectric constant (d33*) values have been determined to be Q = (2.1 ± 0.3) pC and d33+* ~ (7.13 ± 0.4) pm/V or d33-* ~ (-5.95 ± 0.3) pm/V, respectively. This particular response of nanostructured calcium titanate is of great interest in biomedicine because it can improve the osseointegration of an implant.

Electrical conductivity increase by order of magnitude through controlling sintering to tune hierarchical structure of oxide ceramics

Perovskite calcium manganate CaMnO3-δ is representative of an essential group of semiconductors with unique physical phenomena including colossal magnetoresistance and thermoelectric properties. For the large-scale applications that require the utilization of oxide ceramics, the polycrystalline materials’ physical properties such as conductivity can be controlled and ultimately optimized through tuning the ceramics sintering conditions. In the present study, the impact of the sintering temperature on the structure and thermoelectric performance of CaMnO3-δ is systematically studied. For the ceramics pellets made of precursors powders synthesized using the chemical sol-gel reaction, the increase in the sintering temperature dramatically increases the electrical conductivity by order of magnitude and simultaneously increases the Seebeck coefficient. Meanwhile, the thermal conductivity increases with the rise of the sintering temperature. Among the samples sintered at different temperatures, the peaking thermoelectric Figure of Merit ZT of pristine CaMnO3-δ reached 0.28, which is a factor of 2.5 higher than the highest reported ZT for pristine CaMnO3-δ and approached that of the doped single-phase CaMnO3-δ. The electrical and thermal properties changes were interpreted based on the oxide ceramics hierarchical structure evolutions, from unit cell level to micron scales, induced by changes of sintering temperatures.

The Role of Redox on Bridgmanite Crystal Chemistry and Calcium Speciation in the Lower Mantle

AbstractThe amount of ferric iron Fe3+ in the lower mantle is largely unknown and may be influenced by the disproportionation reaction of ferrous iron Fe2+ into metallic Fe and Fe3+ triggered by the formation of bridgmanite. Recent work has shown that Fe3+ has a strong effect on the density and seismic wave speeds of bridgmanite and the incorporation of impurities such as aluminum. In order to further investigate the effects of ferric iron on mineral behavior at lower mantle conditions, we conducted laser‐heated diamond‐anvil cell (LHDAC) experiments on two sets of samples nearly identical in composition (an aluminum‐rich pyroxenite glass) except for the Fe3+ content; with one sample with more Fe3+ (“oxidized”: Fe3+/ΣFe ~ 55%) and the other with less Fe3+ (“reduced”: Fe3+/ΣFe ~ 11%). We heated the samples to lower mantle conditions, and the resulting assemblages were drastically different between the two sets of samples. For the reduced composition, we observed a multiphase assemblage dominated by bridgmanite and calcium perovskite. In contrast, the oxidized material yielded a single phase of Ca‐bearing bridgmanite. These Al‐rich pyroxenite samples show a difference in density and seismic velocities for these two redox states, where the reduced assemblage is denser than the oxidized assemblage by ~1.5% at the bottom of the lower mantle and slower (bulk sound speed) by ~2%. Thus, heterogeneities of Fe3+ content may lead to density and seismic wave speed heterogeneities in Earth's lower mantle.

A study of calcium ion intercalation in perovskite calcium manganese oxide

Abstract We report on the synthesis and characterization of perovskite calcium manganese oxide (CaMnO3) as an intercalation compound for calcium ion insertion and extraction. Cyclic voltammetry measurements indicate calcium ion insertion and de-insertion into and from the CaMnO3 host. Differential capacity analysis delineates the potentials at which the insertion and extraction redox processes occur (at −0.4 V and + 0.1 V vs. Ag/Ag+, respectively). The insertion and extraction of calcium ions is supported by post-mortem x-ray analysis, which indicates loss of Ca2+ ions from the native CaMnO3 phase as well as the presence of manganese oxide phases. This study shows that perovskite calcium manganese oxide is a promising intercalation host.

Effect of B2O3 Content on the Sintering Basic Characteristics of Mixed Ore Powder of Vanadium-Titanium Magnetite and Hematite

The sintering basic characteristics of iron ore play a key role in the process of sintering. In this study, the effects of B2O3 on the assimilation characteristics, softening temperature, fluidity of liquid phase, compressive strength of bonding phase, and microstructure of the mixed fine powder of hematite and vanadium-titanium magnetite (H-VTM) are studied. Results show that B2O3 content from 0%–5% (wt%) could improve the assimilation characteristics of the H-VTM and increase the amount of the liquid phase. The liquidity of the bonding phase index (LBPI) of the H-VTM increases from 3.7 to 24.2. When B2O3 content exceeds 2%, the diameter of the pore in the H-VTM sintered samples enlarges. However, the compressive strength gradually decreases. Boron and calcium-magnesium-aluminium elements are abundant in the bonding phase, which can reduce the formation of calcium silicate and perovskite in H-VTM sintered samples.

An improved setup for radial diffraction experiments at high pressures and high temperatures in a resistive graphite-heated diamond anvil cell.

We present an improved setup for the experimental study of deformation of solids at simultaneous high pressures and temperatures by radial x-ray diffraction. This technique employs a graphite resistive heated Mao-Bell type diamond anvil cell for radial x-ray diffraction in combination with a water-cooled vacuum chamber. The new chamber has been developed by the sample environment group at PETRA III and implemented at the Extreme Conditions Beamline P02.2 at PETRA III, DESY (Hamburg, Germany). We discuss applications of the new setup to study deformation of a variety of materials, including ferropericlase, calcium perovskite, bridgmanite, and tantalum carbide, at high-pressure/temperature.

Phase Formation and Morphological Features of Calcium Copper Titanate by Modified Solid State Process

Perovskite calcium copper titanate posses giant dielectric constant making it a suitable candidate for possible applications in microelectronic components, advanced transistors, energy storage capacitors. Generally, this grade of material is synthesized by the chemical route to improving homogeneity, controlled size growth for enhanced properties. In the present research, a simple synthesis process was adopted using precursors of high purity oxides like Calcium carbonate, titania, Copper oxide without any use of complicated synthesis routes and costly chemical precursors. The molar ratio of oxides used was about 1:3:4 with mechano-chemical activation in an agate mortar for 20, 25 and 30 hours respectively in dry condition. After milling, powders obtained were made to undergo annealing at a fixed temperature of 900°C for 26 hours soaking period. Phase analysis was carried to determine the phase along with crystallite size calculation. Bonding information of the synthesized sample was analyzed to obtain the M-O coordination and vibration-stretching analysis of the bonds. Morphological features were also noted using FESEM (Field Emission Scanning Electron Microscopy) for understanding grains and granular boundaries. Both FTIR (Fourier Transform Infra-Red Spectroscopy) and XRD (X-Ray Diffractogram) analyses confirm the compound formation in terms of molecular structure responsible to obtain the proper phase.

A Refined Approach to Model Anisotropy in the Lowermost Mantle

Seismic anisotropy in the lowermost mantle has been attributed to texture development during mantle convection. This study models texture evolution in a subducting slab impinging on the core-mantle boundary. Using a 3-dimensional geodynamic model with tracers recording the deformation history, a visco-plastic self-consistent (VPSC) model for polycrystal deformation, and relying on experimentally determined slip systems, aggregate grains with volume fractions of 60% orthorhombic silicate perovskite (MgSiO3), 20% cubic calcium perovskite (CaSiO3), and 20% cubic ferropericlase ((Mg,Fe)O) were deformed plastically and developed crystal preferred orientation. Forward and reverse perovskite (Pv)-postperovskite (PPv) phase transitions were included by allowing for likely orientation variant selections. Grain orientations, P (compression) and S (shear) wave velocity pole figures were calculated for each phase as well as the aggregate. The results show that dominant (001) slip on PPv can produce strong texture and shear wave anisotropy of 0.01-3.07% with VSH >VSV which agrees with seismological observations in selected areas of the D” layer.

Phase relations and mineral chemistry in pyrolitic mantle at 1600–2200 °C under pressures up to the uppermost lower mantle: Phase transitions around the 660-km discontinuity and dynamics of upwelling hot plumes

We determined phase relations of pyrolite at 12–28 GPa and 1600–2200 °C using a 6–8 Kawai-type multianvil apparatus. A large number of high pressure and high temperature experiments were conducted to constrain the phase relations especially around 660-km depth, compared with previous studies. The phase relations drastically change between 19 and 23 GPa with temperature as follows. At 19–22 GPa, a phase transition of ringwoodite (Rw) to garnet (Gt) + magnesiowüstite (Mw) occurs at 1800 °C, and no Rw is observed at 2200 °C. The mineral proportion of Gt increases with increasing temperature due to this decomposition reaction and becomes larger than that of Rw above 1800 °C. At 23 GPa, pyrolite crystallizes to a mineral assemblage of bridgmanite (Bm) + Mw + Gt + calcium perovskite by the post-spinel (pSp) transition at 1600–2000 °C and the post-garnet (pGt) transition at 2100–2200 °C, the latter of which is defined as a phase transition of a part of Gt to Bm. Clapeyron slopes of the pSp transition and the pGt transition are determined to be −1 and 5 MPa/°C, respectively, in this study. Gt is stable at any temperatures around the 660-km discontinuity (D660), and Gt-disappearance reaction occurs at 25 GPa with no temperature dependence. Densities of pyrolite were calculated in various pressure and temperature conditions by using the mineral proportions and available data of equations of state. The density at 1600 °C is higher than that at 1800–2200 °C at any pressure-temperature conditions in this study. In particular, the drastic density drop occurs at 19–24 GPa between 1600 and 1800–2200 °C because of increase of Gt proportion with increasing temperature. These suggest that upwelling hot plumes composed of pyrolite from the lower mantle do not stagnate and their ascent is promoted across D660. The mineral proportions and the density changes also suggest that the phase transition which causes D660 changes around 1800 °C from the pSp to the pGt transitions because of the mineral proportion inversion between Rw and Gt.

Synthesis of Calcium Titanate Powder with Hollow Square Based Prism Morphology via One-Step Surfactant Free Hydrothermal Method: Temperature Effect and Optical Properties

ABSTRACTIn this work, we report a morphologically controlled growth of hollow micrometer-sized prism of perovskite calcium titanate via one-step surfactant free hydrothermal method. Highly concentrated potassium hydroxide is used as a mineralizer in this procedure. Single phase of CaTiO3 appears after treatment for 180 min during the one-step hydrothermal conditions. The reaction yield is 97% and no impurity is observed in the final product. The uniformly dispersed particles obtained from the hydrothermal method have hollow micro square based prism morphology with an average size of about 2 μm in length and 200 nm in diameter. The results indicate that the hydrothermal method is a suitable procedure to prepare CaTiO3 microparticle with a desired morphology for industrial applications. The optical properties of the prepared samples are also investigated.