Perovskite CaTiO3 Research Articles

Experimental study of trivalent rare-earth element incorporation in CaTiO3 perovskite: evidence for a new substitution mechanism

Samples of calcium titanate perovskite (CaTiO3) substituted with variable amounts of trivalent La, Pr, Nd or Sm were synthesized by solid-state reaction. The synthesized compounds were characterized by means of electron microprobe (EMPA), powder X-ray diffraction and µ-Raman spectroscopy. The incorporation of the studied lanthanides in the CaTiO3 perovskite leads to the formation of complex (Ca1-2xLn2x)(Ti1-xCax)O3 perovskites with a Pbnm disordered structure. This mechanism was revealed by the Ca/Ti ratio analyses of the samples, the study of the lattice parameter evolution and the Raman A1g octahedral breathing mode frequency comparison for all systems.

Creating multiferroic and conductive domain walls in common ferroelastic compounds

Domain walls in ferroelectrics and ferroelastics often present peculiar functional properties, offering an intriguing route toward the design of nano-devices. Here we use first-principles simulations to illustrate an approach for engineering such walls, working with representative ferroelastic perovskites LaGaO3 and CaTiO3 (insulating, non-magnetic, non-polar). We show that a wide range of substitutional dopants can be used to create long-range-ordered structures confined within the walls of these compounds, yielding functional interfaces with tailor-made properties. We thus identify clear-cut strategies to produce metallic walls within an insulating matrix. Further, we find ways to create magnetic walls that also display ferroelectric order (proper or improper), thus providing an original route to obtain magnetoelectric multiferroics. Given the recent developments on the preparation of high-density domain structures in perovskite films, our results suggest a definite path toward new functional nano-materials.

High-temperature Mass Spectrometry Study of the Thermodynamic Properties of CaTiO3 Perovskite

Values of the activity of oxides in CaTiO3 perovskite in the temperature range of 1791–2398 K are calculated from the data obtained via Knudsen effusion mass spectrometry. The values of the Gibbs energy, and the enthalpy and entropy of the formation of perovskite from individual oxides (−39.88 ± 0.54 kJ/mol and 3.15 ± 0.28 J/(mol K), respectively) are determined. The melting enthalpy of perovskite is 47.61 ± 1.84 kJ/mol at 2241 ± 10 K.

Mass-Spectrometric Study of Evaporation of Perovskite

The evaporation of perovskite CaTiO3 at 1700–2200 K was studied by the high-temperature mass-spectrometric Knudsen effusion method. The molecular components typical of simple oxides and a small amount of complex gaseous oxide CaTiO3 were identified in the gas phase over perovskite. The partial vapor pressures of the molecular components of the gas phase over perovskite were compared with those corresponding to simple oxides; it was found that the character of evaporation of perovskite is mainly affected by the calcium component.

CaTiO3 Perovskite in the Photocatalysis of Textile Wastewater

Perovskite-type CaTiO3 material was synthesized by the polymeric precursor method and characterized. The powder was applied as a promising alternative to TiO2 photocatalyst. Photocatalytic reaction parameters were optimized by surface analysis methodology on the degradation of methylene blue under UV radiation. After optimization, complex textile- and tannery wastewaters were treated and the COD reduction was evaluated. At optimized conditions (pH=11.2 and 1 g L-1 of catalyst concentration), the results obtained for the photodegradation of the real wastewater after 240 min of irradiation were 45% COD reduction for both effluents. The reactions were adjusted to the pseudo first order kinetic and the rate constants were 2.07 x 10-3 (min-1) and 2.23 x 10- 3 (min-1) for COD reduction for textile- and tannery wastewaters, respectively.

Upconversion luminescent perovskite CaTiO3:Yb3+/Er3+ nanocubes

Perovskite CaTiO3:Yb3+,Er3+ nanocubes with tunable upconversion luminescence (UCL) were prepared by a solvothermal method. The structure and morphology of the final product after being sintered at 700 °C for 2 h were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The upconversion emissions of CaTiO3:Yb3+,Er3+ under the excitation of 980 nm diodes laser consist of two typical emission bands from 4F9/2 → 4I15/2 and 4S3/2, 2H11/2 → 4I15/2 transitions. The UCL properties depending on the doping contents of Yb3+ to Er3+ were investigated in detail. The maximum R/G ratio was observed at Yb3+ concentration of 15 mol%. The multiphotonic upconversion mechanism of controllable red-to-green ratio in CaTiO3:Yb3+,Er3+ nanocubes was addressed based on both steady state and transient spectroscopy data.

Photocatalytic hydrogen production with purification of wastewater from nuclear power plant under irradiation of liquid phase plasma

Liquid phase plasma process was applied in production of hydrogen and purification of wastewater. Ethanolamine released from a nuclear power plant was degraded by photocatalytic decomposition using the liquid phase plasma with perovskite photocatalysts. Eu-doped CaTiO3 and Eu-doped SrAl2O4 perovskites were compared with that of commercial TiO2 photocatalyst. The photocatalytic decomposition of ethanolamine-contained water induced the degradation of ethanolamine and H2 evolution, simultaneously. The degradation of ethanolamine and H2 evolution were elevated on Eu-doped CaTiO3 perovskite which having less bandgap energy. The rate of H2 evolution in the ethanolamine-containing water was higher than that in pure water, which was attributed to the additional H2 evolution by the photo-decomposition of ethanolamine in water.

Photoluminescence of Eu3+-doped CaTiO3 perovskites and their photocatalytic properties with a metal ion loading

Abstract Eu3+-doped CaTiO3 perovskites were prepared using a sol-gel reaction method. Two solvent materials were employed to the synthesis process to produce higher emitting phosphors. Eu3+-doped CaTiO3 perovskite synthesized using an ethanol mixture solvent exhibited higher photoluminescence intensities for red emission than those synthesized using distilled water as a solvent. Ni ion-loaded CaTiO3:Eu3+ perovskite showed enhanced red emission and higher photocatalytic activities compared to those of bare CaTiO3:Eu3+ perovskite. The improvement of the photocatalytic degradation of toluene was attributed to the lower bandgap of Ni ion-loaded CaTiO3:Eu3+ perovskite, as determined by UV–visible diffuse reflectance spectroscopy.

Effect of magnesium on structural and optical properties of CaTiO3: A DFT study

The electronic bandstructure, optical and structural properties of pure and Mg-doped CaTiO3 are calculated by using first-principle calculation which is based on the density functional theory. The effect of Mg-dopant on the properties of CaTiO3 perovskite explored by using ultra soft pseudo-potential (USP) and generalized gradient approximation (GGA). The incorporation of Mg at Ca site affected the electronic band structure of CaTiO3 meaningfully by introducing new gamma point. The incorporation of Mg increases the band gap from 1.84 eV to 1.92 eV. The partial density of states of pure CaTiO3 changed after doping cleared the effect of dopant on pure system. Optical properties of both the systems are examined which reveals that the absorption edge shifting from 2.1 eV to 2.5 eV indicates a blue shift whereas the refractive index also increases from 2 to 2.4 after doping. Thus Mg-doped CaTiO3 not only affect the optical properties of the system but also make it and appealing candidate for optical devices.

Hydrothermal synthesis of perovskite CaTiO3 tetragonal microrods with vertical V-type holes along the [010] direction

CaTiO3 tetragonal microrods with vertical V-type holes along the [010] direction are synthesized successfully and their growth mechanism is discussed.

Improved functional response of spark plasma sintered hydroxyapatite based functionally graded materials: An impedance spectroscopy perspective

Owing to the inherent polarization regulated functionality of living bone, the present study aims to enhance the polarizability of hydroxyapatite (HA) without affecting its’ surface chemistry i.e., excellent biocompatibility. This concept has been materialized by the development of functionally graded materials (FGMs) using perovskites BaTiO3 and CaTiO3 as intermediary layers. These perovskites were sandwiched between HA layers via buffer interlayers to provide the structural integrity to the FGMs. FGMs were optimally processed using spark plasma sintering route at 1100°C for 10 min. Microstructural analyses of fractured surfaces revealed no sign of delamination between HA/BaTiO3 or HA/CaTiO3 layers, despite of differences in their coefficients of thermal expansions. Further, detailed impedance spectroscopic analysis was performed over a wide range of temperature (35–500°C) and frequency (1 Hz - 1 MHz). Almost two times increase in polarizability has been observed in both types of FGMs as compared to HA. Overall, the developed FGMs can be suggested as potential materials for polarized bone applications.

Cost-effective and dynamic carbon dioxide conversion into methane using a CaTiO3@Ni-Pt catalyst in a photo-thermal hybrid system

This research focuses on the synergy of converting carbon dioxide (CO2) into methane (CH4) by simultaneously introducing light and heat as dynamic sources to activate the catalyst. A CaTiO3@Ni-Pt catalyst, loaded with 30.0 wt.% Ni and 1.0 wt.% Pt on a perovskite CaTiO3 support was introduced. The photo-thermal catalytic hybrid system has two features that distinguish it from other photo- or thermal-catalytic systems. First, unlike the CO2 thermal-methanation reaction where CO2 and H2 react at a molar ratio of 1:4, 2.0 mol of H2 was replaced with 2.0 mol H2O in the photo-thermal catalytic hybrid system compared to the thermal-methanation reaction requiring 4.0 mol of H2. Second, by loading Ni and Pt, which are catalytic active species with excellent CO2 and H2 adsorption abilities, the CO2 reduction (46.48%) was promoted and the CH4 selectivity (99.46%) in the product was increased compared to the photo-methanation reaction. The CaTiO3@Ni-Pt not only inhibited the recombination of the photo-generated charges, but also facilitated the adsorption of the reactants in the photo-thermal hybrid system. The quantum efficiency of the CaTiO3@Ni-Pt catalyst measured for the photo-thermal hybrid system steadily increased to 180 °C. Nevertheless, this study implies that a photo-thermal hybrid system can be useful to photo-reducing CO2 by adding a small amount of heat. From a thermal reaction standpoint, a photo-thermal hybrid system can be used to reduce the reaction temperature during CO2 thermal-methanation and to reduce the consumption of H2 in half.

Photocatalyst of Perovskite CaTiO3 Nanopowder Synthesized from CaO derived from Snail Shell in Comparison with The Use of CaO and CaCO3

Calcium titanate belongs to the important group of compounds with a perovskite structure having high dielectric loss for various applications including photocatalysis mechanism. Refer to the principles of green chemistry, in this work preparation of CaTiO3 was conducted by using CaO derived from snail shell. Aim of this research are to study the physicochemical character of perovskite derived from snail shell and its comparison with CaO and CaCO3 as Ca sources. Material preparation was performed by solid reaction of Ca sources with TiO2 under comparison with CaO and CaCO3 precursors. Mixture of Ca sources with TiO2 in certain proportion were ground and calcined at the temperature of 200 °C for 2 hs. Materials were characterized by using X-ray diffractometer (XRD), Fourier Transform-Infra Red (FTIR) and the photocatalytic activity was tested by using methylene blue photooxidation. Perovskite synthesized using CaO derived from snail shell exhibits the similar XRD pattern with that were prepared by using CaO and CaCO3. From the photooxidation activity test, it is proven that CaTiO3 shows similar photocatalytic activity correspond to that were prepared by CaO and CaCO3. Utilazation of shell as agricultural waste of the synthesis of CaTiO3 perovskite is the novelty of this work. Furthermore, the study on material structure and photoactivity is the main focuses for the application in industry and environment.

Preparation of CaTiO<sub>3</sub> Asymmetric Membranes Using Polyetherimide as Binder Polymer

Asymmetric dense and thin membranes have been prepared from powders of perovskite oxide-type CaTiO3 without cracking by phase inversion method. Polyetherimide was used as a polymeric binder in the method. The resulting green membranes, composed of CaTiO3 powder and polyetherimide binder, were sintered at 890, 1100 or 1200 °C. The crystal phase of CaTiO3 was analyzed using X-Ray Diffraction (XRD). The XRD pattern of the synthesized CaTiO3 powder was matched with the reference indicating the formation of CaTiO3 structure. Sintering at 890 °C fails to form a strong membrane. Scanning Electron Microscope (SEM) images of the membranes showed that the membrane had the asymmetric structure with dense layer on one side and porous layer on the other side. The pores in the porous layer were both finger-like and sponge-like structure. The mechanical strength of the membranes, which were determined by Vickers micro hardness method, varied from 3.5 to 25.8 Hv. The strongest membrane without any crack was resulted from sintering at 1200°C with hardness values between 19.4 and 25.8 Hv. Thermal expansion coefficients of the asymmetric membranes sintered at 1100 and 1200 °C, measured with Thermomechanical Analyzer (TMA), were 10.82 × 10-6 and 12.78 × 10-6.C-1 respectively.

CaTiO3 perovskite in the framework of activated carbon and its effect on enhanced electrochemical capacitance

Modifications of activated carbon materials (ACs) towards an increase in the electronic and ionic conductivities are expected to improve their capacitance in the absence of a conductive agent. Char derived from cotton straw feed were heat-treated at 800 °C in the presence of TiO2. Simultaneously KOH and K2CO3 were used as activation agents. That process resulted in the formation of perovskite CaTiO3 with an involvement of calcium present in carbon as an impurity. The composite were extensively characterized from the point of view of a texture, surface chemistry and electrochemical performance. The results indicated that perovskite with impurities affected the ionic conductivity and enhanced the capacitive performance of ACs. The capacitance measured on the electrode made of the best performing sample in both three- and two-electrode cell systems in the absence of a conductive agent - carbon black was 270 F g−1 and 185 F g−1 at current density of 0.5 A g−1, respectively. The results suggest that the AC/perovskite composites are promising electrodes of the high-performance supercapacitors.

Interaction of Titanium Minerals and Their Melts with Diamond-Forming Media (Experiments at 7–8 GPa)

Melting relations in the multicomponent diamond-forming systems of the upper mantle with a boundary of K–Na–Mg–Fe–Ca carbonate, phases of the model peridotite and eclogite, carbon, and titanium minerals from kimberlite (ilmenite FeTiO3, perovskite CaTiO3, and rutile TiO2) were studied experimentally at 7–8 GPa and 1600–1650°C. Perovskite reacts with the formation of rutile in the diamond-forming silicate–carbonate melts. We discovered liquid immiscibility between melts of titanium minerals, on the one hand, and carbonate–carbon, peridotite–carbonate–carbon, and eclogite–carbonate–carbon diamond-forming melts, on the other. The solubility of titanium mineral in diamond-forming melts is negligible independent of their concentration in the experimental systems. Growth melts retain high diamond-forming efficiency. In general, the experimental results are evident for the xenogenic nature of titanium minerals in inclusions in diamond and, therefore, in diamond-forming melts. It is shown that the physicochemical factors that may correlate the diamond content with the concentration of Ti in kimberlite do not occur during the diamond genesis in silicate–carbonate–carbon parental melts containing titanium minerals and their melts.

A quantum-mechanical investigation of oxygen vacancies and copper doping in the orthorhombic CaSnO3perovskite

In this study we explore the implications of oxygen vacancy formation and of copper doping in the orthorhombic CaSnO3 perovskite, by means of density functional theory, focusing on energetic and electronic properties. In particular, the electronic charge distribution is analyzed by Mulliken, Hirshfeld-I, Bader and Wannier approaches. Calculations are performed at the PBE and the PBE0 level (for doping with Cu, only PBE0), with both spin-restricted and spin-unrestricted formulations; unrestricted calculations are used for spin-polarized cases and for the naturally open-shell cases (Cu doping). An oxygen vacancy is found to have the tendency to reduce Sn neighbors by giving rise to an energy band within the energy band-gap of the pristine system, close to the valence band. At variance with what happens in the CaTiO3 perovskite (also investigated here), an oxygen vacancy in the CaSnO3 perovskite is found to lose two valence electrons and thus to be positively charged so that no F-center is formed. Regarding Cu doping, when one Sn atom is substituted by a Cu one, the most stable configuration corresponds to having the Cu atom as a first neighbor to the vacancy. These findings shed some light on the catalytic and phosphorous host properties of this perovskite.

Low Cost CaTiO3 Perovskite Synthesized from Scallop (Anadara granosa) Shell as Antibacterial Ceramic Material

Research on perovskite CaTiO3 synthesis from scallop (Anadara granosa) shell and its test as material for antibacterial ceramic application have been conducted. The synthesis was performed by calcium extraction from the scallop shell followed by solid-solid reaction of obtained calcium with TiO2. Physicochemical character of the perovskite wasstudied by measurement of crystallinity using x-ray diffraction (XRD), diffuse-reflectance UV Visible spectrophotometry, scanning electrone microscope-energy dispersive x-ray (SEM-EDX) and Fourier-Transform InfraRed. Considering the future application of the perovskite as antibacterial agent, laboratory test of the peroskite as material in antibacterial ceramic preparation was also conducted. Result of research indicated that perovskite formation was obtained and the material demonstrated photocatalytic activity as identified by band gap energy (Eg) value. The significant activity was also reflected by the antibacterial action of formed ceramic.

Near-infrared persistent luminescence of Yb^3+ in perovskite phosphor

Here we report the observation of near-infrared persistent luminescence (NIR PersL) of Yb3+ in perovskite CaTiO3. Sensitized by the Bi3+ codopants, it exhibits intense NIR PersL of Yb3+ at about 1000nm. In addition, this phosphor can be excited by the near ultraviolet and even visible light, and the PersL signals can be recorded for more than 80h. The PersL enhancement by Bi3+ is revealed to be due to the suitable Bi3+ induced deeper traps and the possible PersL quantum cutting. The results suggest that the NIR PersL of the CaTiO3:Yb3+, Bi3+ phosphor has potential applications for biomedical imaging in the second biological window.

Systematic trends in (0 0 1) surface ab initio calculations of ABO3 perovskites

By means of the hybrid exchange–correlation functionals, as it is implemented in the CRYSTAL computer code, ab initio calculations for main ABO3 perovskite (001) surfaces, namely SrTiO3, BaTiO3, PbTiO3, CaTiO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3, were performed. For ABO3 perovskite (001) surfaces, with a few exceptions, all atoms of the upper surface layer relax inward, all atoms of the second surface layer relax outward, and all third layer atoms, again, inward. The relaxation of (001) surface metal atoms for ABO3 perovskite upper two surface layers for both AO and BO2-terminations, in most cases, are considerably larger than that of oxygen atoms, what leads to a considerable rumpling of the outermost plane. The ABO3 perovskite (001) surface energies always are smaller than the (011) and especially (111) surface energies. The ABO3 perovskite AO and BO2-terminated (001) surface band gaps always are reduced with respect to the bulk values. The B–O chemical bond population in ABO3 perovskite bulk always are smaller than near the (001) and especially (011) surfaces.