Orthorhombic Perovskite Phase Research Articles

La-doped Sr4Fe4Co2O13-δ as a promising in-situ self-assembled composite cathode for protonic ceramic fuel cells

Protonic ceramic fuel cells (PCFCs) exhibit a lower activation energy compared to conventional oxygen-ion conducting solid oxide fuel cells, which makes them better suited for operating at low temperatures. Regrettably, the use of PCFCs at lower temperatures is restricted due to the absence of durable and highly active cathode materials. Herein, we rationally design in-situ self-assembled composite cathodes with the nominal compositions of Sr4-xLaxFe4Co2O13-δ (SLxFC, x = 0.4, 0.8, 1, and 2) for PCFCs. The SL0.4FC, displays a composite of cubic perovskite phase and spinel phase, the other compositions yield a mixture of both orthorhombic perovskite and spinel phases. The self-assembled SL1FC composite cathode has the highest electrocatalytic activity among all samples, particularly at temperatures (<650 °C). For instance, it demonstrates a very low area-specific resistance (ASR) of 0.465 Ω cm2 at 550 °C. The PCFC with the SL1FC composite cathode provides a high peak power density (PPD) of 518 mW cm−2 at the same temperature. More importantly, the SL1FC electrode demonstrates robust long-term stability (400 h for the symmetrical cell mode and 200 h for the single cell mode). This study shows how La doping enhances the electrochemical activity of Sr4Fe4Co2O13-δ and how the synergistic effect of the two phases boosts the electrochemical performance of the composite cathode.

Successful synthesis of LaFeO3 nanoporous powders with high catalytic and photocatalytic performances: Investigation of precursor effect

Porous LaFeO3 powders with high catalytic and photocatalytic activities were successfully synthesized by sol-gel method using nitrate and chloride precursors. The precursor effect on the crystal structure, morphology, specific surface area and optical properties of the prepared powders was fully determined. Thermogravimetric and X-ray diffraction analyzes showed the formation of the orthorhombic perovskite phase (Pnma, #62) at annealing temperature of 800 and 1000 °C for powder prepared by nitride and chloride salts, respectively. The scanning electron microscopy images revealed a significant effect of precursor type on nanoparticles morphology. It was found that powder prepared from chloride salts is more porous than that prepared with nitrate salts. The estimated surface area of LaFeO3 nanoparticles ranges between 5.94 and 11.56 m2/g and the band gap varies from 2.19 to 2.27 eV. Methylene blue (MB) dye was used to investigate the catalytic and photocatalytic properties of LaFeO3 powders. Both prepared powder types showed good catalytic activity and high photocatalytic performance under visible irradiation in removing MB dye. The adsorption kinetics data of MB molecules on LaFeO3 nanoparticles are well fitted to the pseudo-first order model. Powder synthesized with chloride salts demonstrated high photodegradation efficiency of MB dye compared to that prepared by nitrate salts, which can be attributed to its relatively small band gap and high porosity. These two factors ensure a greater number of photogenerated electrons and more sites for photocatalytic reactions.

Preparation and chemical stability evaluation of Ln2Zr2O7‐SrZrO3 novel composite ceramics cured simultaneously with An and 90Sr

AbstractIn response to the low separation efficiency of actinide nuclide (An) and fission product (FP) in the separation process of high‐level radioactive waste, as well as the large amount of secondary waste. A novel Ln(1‐x)SrxZrO(3.5‐0.5x) (0 ≤ x ≤1) multiphase ceramic waste form (Nd3+ simulating An3+), which can cure both An and Sr simultaneously, was in‐situ synthesized by sol‐gel spray pyrolysis method. The series of multiphase ceramics are composed of cubic pyrochlore phase Nd2Zr2O7 (NZO) and orthorhombic perovskite phase SrZrO3 (SZO), without any accompanying impurities. The two phases exhibit excellent compatibility, and their content can change regularly with the change of x. Nd and Sr occupy their most stable crystal lattice positions, with low transposition doping levels. The density of the composite ceramics is high, and the measured density is as high as 88 % of the theoretical density. The above experimental results confirm that the new multiphase ceramics can cure An and Sr simultaneously and separately, showing strong adaptability to waste components and high chemical stability.

Characterization of Bismuth Titanate by Line Profile Analysis

Bismuth Titanate (BIT), Bi4Ti3O12, was synthesized using the solid-state reaction process from the oxide mixture of Bi2O3CO3 and TiO2. The characterization analysis of the prepared sample was done by X-ray diffraction technique. The X-ray diffraction data revealed an orthorhombic perovskite phase that was clearly explained. The Scherrer method, modified W-H analysis, and the SSP studies were conducted to figure out the crystallite size and micro strain in Bi4Ti3O12. Morphological studies included SEM and TEM analysis. FTIR spectral investigation supports the M-O coordination of the synthesized Bi4Ti3O12 sample. The phase formation patterns of Bi4Ti3O12 determined by different methods are highly connected.

A new (La0.2Nd0.2Gd0.2Sr0.2Ba0.2)Co0.2Fe0.8O3-δ high-entropy oxide cathode for intermediate temperature solid oxide fuel cell

The main degradation mechanism of La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes is Sr segregation on the surface. In this paper, the high-entropy (La0.2Nd0.2Gd0.2Sr0.2Ba0.2)Co0.2Fe0.8O3-δ(HE-LSCF) oxide with perovskite-type is designed to improve the cathode stability. The orthorhombic perovskite phase with the space group of Pbnm(62) is obtained when the HE-LSCF oxide precursor powders are calcined at 800 °C for 2 h. The orthorhombic perovskite phase is still stable when the HE-LSCF oxide precursor powders are calcined at 1250 °C for 2 h. At 700 °C，the specific polarization resistance (Rasp) of the pristine HE-LSCF and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathodes is 0.71Ωcm2 and 0.57Ωcm2, respectively. The electrode process related to the oxygen dissociation and the interfacial charge transfer involving atomic oxygen is the rate-determining step of the oxygen reduction reaction in HE-LSCF cathodes. After being aged for 200 h at 800 °C, Rasp at 700 °C of the LSCF and HE-LSCF electrodes increases by 122.8% and 5.6%，respectively. The SEM, EDS and XPS results show that Sr segregates on the LSCF cathode surface after being aged, but Sr segregation on the HE-LSCF cathode surface is hindered. The research results show that HE- LSCF will be a potential cathode material for the intermediate temperature solid oxide fuel cells.

Ferroelectric and Magnetic Optimization of A-Site La-Substitution in Bismuth Ferrite

La-substituted Bismuth ferrite, with the chemical composition Bi1-xLaxFeO3 (with x = 0.0, 0.05, 0.10 and 0.15), were synthesized using Sol-gel technique and sintered at a relatively low temperature of 600 °C. XRD-spectra confirmed the formation of rhombohedrally distorted perovskite phase up to x = 0.10 and the presence of peaks corresponding to orthorhombic perovskite phase of LaFeO3 at x = 0.15. PE loop shows the polarization behavior of the prepared samples. Studies of dielectric constants and dielectric loss factors were also carried out. La-substitution of x = 0.05 shows optimum saturation and remanent magnetization. Possible mechanisms explaining the various trends of the different properties are being discussed.

Preparation of a nano-size (La0.2Nd0.2Sm0.2Sr0.2Ba0.2)Co0.2Fe0.8O3-δ/SDC high-entropy oxide composite cathode

The nano-size (La0.2Nd0.2Sm0.2Sr0.2Ba0.2)Co0.2Fe0.8O3/Ce0.8Sm0.2O1.9（SDC)composite cathodes were prepared by impregnating high entropy (La0.2Nd0.2Sm0.2Sr0.2Ba0.2)Co0.2Fe0.8O3 (HE-LNSSB) catalytic phase into the SDC electrode skeleton. The catalytic activity and the stability of the nano-size LNSSB phase are investigated. The XRD results show that the orthorhombic perovskite phase was obtained when the HE-LNSSB precursor was calcined at 800 °C. At 700 °C, the pristine nano-size HE-LNSSB/SDC composite cathode shows a specific polar resistance (Rasp) of 0.30 Ω·cm2. The Rasp of the pristine nano-size HE-LNSSB composite cathode was reduced by 50.8 % compared with that of the sintered HE-LNSSB cathode. The Rasp of the aged nano-size HE-LNSSB composite cathode was 0.31 Ω·cm2 at 700 °C and the catalytic activity did not decay. The SEM and the XPS results show that the particle micrograph of the nano-size HE-LNSSB catalytic phase hardly changes and Sr elements do not segregate on the HE-LNSSB phase surface after being aged. The research results show that the nano-size HE-LNSSB/SDC composite cathode will be a potential cathode material for the intermediate temperature solid oxide fuel cells.

Electrochemical Performance of SrFeO3−δ for Application as a Symmetric Electrode in Solid Oxide Fuel Cells

SrFeO3−δ has been earlier reported to exhibit a large area-specific resistance even though it possesses high mixed ionic–electronic conductivity both in oxidizing and reducing conditions. The present study clarifies this aspect and investigates the defect chemistry and electrochemical performance correlations in SrFeO3−δ for the possible use as a symmetric electrode in solid oxide fuel cells. A conventional solid-state reaction method is adopted for powder synthesis. Structural characterization indicates an orthorhombic perovskite phase formation with a δ of 0.21. High dc electrical conductivities of ∼114.9 and 0.26 S·cm–1 are observed at 800 °C in air and reducing conditions, respectively. The area-specific resistance (ASR) for the SrFeO3−δ electrode is measured in a symmetrical half-cell configuration under various gas environments. At 800 °C, SrFeO3−δ offered low ASRs of 0.082, 0.055, and 0.122 Ω·cm2 in air, oxygen, and 3% H2O/H2, respectively. Although the ASR possesses excellent temporal stability in an oxidizing atmosphere, it increases to 0.42 Ω·cm2 after 100 h in reducing conditions owing to the brownmillerite phase formation. The redox cycling performance is also affected with the ASR rising from 0.13 to 0.24 Ω·cm2 at 800 °C in 3% H2O/H2 after 20 cycles. A maximum power density of 202 mW·cm−2 is achieved from the electrolyte-supported symmetric single cell based on the SrFeO3−δ electrodes at 800 °C. The results demonstrate the viability of using a SrFeO3−δ-based electrode for symmetrical solid oxide fuel cells.

Ternary diagrams of phase, stability, and optical properties of cesium lead mixed-halide perovskites

Cesium lead halides have been intensively studied as promising light absorption and emission materials. However, the complexity and instability of their phases has prevented a comprehensive investigation of the structural and optical properties of Cs-based mixed halides over a broad range of mixing ratios. Herein, we derive the ternary diagrams of phase, optical bandgap, and photoluminescence intensity of cesium lead halide perovskites (CsPbX3), with three vertices of CsPbI3, CsPbBr3 and CsPbCl3. For material property tests, mixed halide perovskite powders are synthesized using a facile solid-state reaction method. The orthorhombic perovskite (γ) phase, which is desired for photovoltaic and optoelectronic applications, is successfully obtained by quenching the powders from 350 °C to room temperature. By comparing the phase diagrams of as-ball-milled and heat-treated powders, we report a single-phase region (γ-phase) and a multi-phase region (I-rich and Cl-rich γ-phases). In aged powders having single-phase compositions, Cl-rich compositions presented considerably higher phase stability than I-rich ones. In the single-phase region, the lattice constant increases and optical bandgap decreases almost linearly with increase in average size of X-site ions, as per Vegard's law with extremely small bowing parameters (< 0.1 Å). Therefore, one can easily design an infinite number of composition combinations in the single-phase boundary to achieve a desired bandgap in the range of 1.73–2.96 eV. Ternary maps of photoluminescence intensity demonstrate potential compositions for high-performance optoelectronics. Our results provide a valuable database for developing desirable perovskite compositions for various optoelectronic applications.

Synthesis–dependent morphological, structural and photophysical properties of semicrystalline KNbO3:SiO2 hybrid silicates

Polycrystalline ceramics of KNbO3 (KNO) were prepared via sol–gel (by acrylamide polymerization), hydrothermal, and solid–state chemistry reactions. Pure orthorhombic perovskite phases crystallized in the Cm2m (38) space group were attained in all cases. Average crystallite sizes ranging 33–44 ​nm and grain structures varying from 350 to 580 ​nm were obtained depending on the implemented synthetic route. Prepared KNO compounds were embedded in porous a–SiO2 sonogel networks at different dopant rates to conform semicrystalline KNbO3:SiO2 hybrid silicates. Results evidence a clear dependence of the structural and optoelectronic properties of the composite glasses on the employed synthesis methodology. The massive porosity of the sonogel matrix and related defective bonding environment promoted strong intermolecular host–guest interactions influencing the electronic states, structural phase transitions, and Raman and luminescent features of the hybrid glasses via surface–assisted mechanisms and chemical charge–transfers. NLO/SHG activity was observed in all hybrid sonogels (HSG) due to the ferroelectric nature of KNO and the average macroscopic crystallite alignment attained along the polycondensation stage of the solid–solutions; where bulk NLO susceptibilities up to 9.10×10−11 ​esu and molecular hyperpolarizabilities in the 10−23 ​esu range, were estimated. Depending on the synthetic method and hybridized in–gap levels, bandgap energy narrowing was observed for the KNO/HSG systems, showing Eg values ranging 2.45–3.30 eV. A synergistic study comprising morphological, structural, spectroscopic, and quadratic NLO/SHG characterizations was performed to explore these novel composites’ structural and photophysical properties for Pb–free ferroelectric/optoelectronic composite applications.

Discovery of high-pressure post-perovskite phase in HoCrO3

By employing both experimental and theoretical methods, we investigated the high-pressure structural aspects of HoCrO3 up to 100 GPa. We found by the first-time evidence of a perovskite-to-post-perovskite transformation in an orthochromite. X-ray diffraction measurements showed that the ambient orthorhombic perovskite phase starts transforming to the post-perovskite phase at ∼20 GPa. However, the ambient phase does not completely transform to perovskite even at 75 GPa. The large coexistence between both phases is assigned to the effect of kinetic barriers. The conclusions extracted from x-ray diffraction agree well with density-functional theory. Raman spectroscopy also supports the observed phase transition. Discontinuities in mode frequencies, changes in the slope of the pressure dependency of frequencies, and changes in mode intensities were observed near ∼20 GPa, i.e. at the transition pressure. Our studies also demonstrated that even at 100 GPa Cr–O–Cr distortions are not sufficient to raise the Néel temperature of HoCrO3 to 300 K. Our analysis showed that the bulk modulus of the perovskite phase is B0 = 269(15) – 298(15) GPa with a pressure derivative, B0′ = 4.2(9) – 4.7(9) being HoCrO3 one of the less compressible known perovskites. Our work suggests that the post-perovskite phase could be stabilized in other orthochromites also by high-pressure treatment.

Insight of BaCe0.5Fe0.5O3- δ twin perovskite oxide composite for solid oxide electrochemical cells.

One-pot synthesized twin perovskite oxide composite of BaCe0.5Fe0.5O3- δ (BCF), comprising cubic and orthorhombic perovskite phases, shows triple-conducting properties for promising solid oxide electrochemical cells. Phase composition evolution of BCF under various conditions was systematically investigated, revealing that the cubic perovskite phase could be fully/partially reduced into the orthorhombic phase under certain conditions. The reduction happened between the two phases at the interface, leading to the microstructure change. As a result, the corresponding apparent conducting properties also changed due to the difference between predominant conduction properties for each phase. Based on the revealed phase composition, microstructure, and electrochemical properties changes, a deep understanding of BCF's application in different conditions (oxidizing atmospheres, reducing/oxidizing gradients, cathodic conditions, and anodic conditions) was achieved. Triple-conducting property (H+/O2-/e-), fast open-circuit voltage response (∼16-∼470mV) for gradients change, and improved single-cell performance (∼31% lower polarization resistance at 600°C) were comprehensively demonstrated. Besides, the performance was analyzed under anodic conditions, which showed that the microstructure and phase change significantly affected the anodic behavior.

Sub-switching domain effect for analysis the non-linear dielectric behavior of (K0.49 Na0.49Li0.02) (Nb0.98Sb0.02)O3 ceramic based on Rayleigh model

The solid-state sintering technique has been implemented to synthesize (K0.5Na0.5NbO3)-0.02(LiSbO3) (KNN-LS) Pb-free ceramic. The crystal structure, dielectric and ferroelectric properties of the prepared material were investigated. Pure orthorhombic perovskite phase [I(220)/I(002) = 1.68] with Amm2 space group has been detected at room temperature for sintered ceramic. Two anomalous permittivity peaks corresponding to orthorhombic–tetragonal (O–T) phase transition at T = 175 °C and tetragonal–cubic (T–C) phase transition at T = 355 °C have been observed. At polymorphic phase transition, the Rayleigh model shown the extrinsic contributions caused by domain wall motion is about 80%, while the intrinsic contribution attributed to the lattice distortion is about 20%. Ferroelectric properties were investigated in a wide range of temperatures (RT-225)°C. The results shown a conductive material at high temperature due to the higher cation disorder and leakage current above PPT. The present results are interested for understanding the mechanism of t permittivity–temperature behavior of KNN-doped LS ions based on Rayleigh model. The large remnant polarization and low coercive field below PPT make the material a suitable candidate for energy storage application.

Glycine-nitrate auto-combustion synthesis and magnetic properties of nanocrystalline NdAlxFe1–xO3 perovskites

The effect of substitution of Fe3+ by Al3+ on the structure and magnetic properties of NdAlxFe1–xO3 perovskite nano-powders (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) prepared by the glycine-nitrate auto-combustion method was studied. All samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and energy dispersive X-ray spectroscopy (EDX). The magnetic properties of the samples were investigated using a vibrating sample magnetometer (VSM). The X-ray results for all samples reveal the formation of an orthorhombic perovskite phase (space group Pbnm) with no secondary phase. The crystallite sizes of the nanoparticles are found to decrease with increasing Al content, and are in the range of 53–38 nm. SEM images show spherical nanoparticles with agglomeration. The FT-IR spectra confirm the presence of metal oxygen bonds. The M–H loop of the pristine NdFeO3 sample is antiferromagnetic in the a/b plane with weak ferromagnetism in the c-axis. Introducing Al inclusions in the pristine polycrystal thereby creating magnetic vacancies is seen to influence the magnetic properties. The magnetic dilution results in enhanced magnetisation at low Al content; x = 0.1, 0.2 (saturation magnetisation being 2.08 and 2.05 emu/g, respectively) compared to the pristine sample with a saturation magnetisation of 1.43 emu/g due to increased exchange interaction. Also dilution with nonmagnetic dopant induces the phase transition from weak ferromagnetic to paramagnetic depending on the impurity concentration. The coercive field for NdFeO3 is found to be equal to 1950 Oe and decreases with Al-substitution. These findings lay a ground work for research in tuning magnetic properties and in spintronics with potential applications in data storage, switches and electronic devices.

A+1Nb5+O3 (A = Li, Na, K) Perovskites with Different Fine Structures for Oxidative Coupling of Methane: Tracing the Crystalline Phase Effect on the Surface Active Sites

Targeting to unravel the catalytic sites of some specific perovskites for OCM reaction, and elucidate the influences of crystal phase changes on the active sites, three A+1Nb5+O3 (A = Li, Na, K) complex oxides were synthesized in the pure phase. The reaction performance is ranked as NaNbO3 > KNbO3 > LiNbO3 for the catalysts. It is revealed that LiNbO3 possesses a hexagonal ilmenite-type phase, and NaNbO3 and KNbO3 possess orthorhombic and tetragonal perovskite phases, respectively. Due to the fine structure difference, NaNbO3 and KNbO3 have higher oxygen mobility than LiNbO3, as testified by the electric conductivity measurements. Moreover, the Nb–O bond strength of NaNbO3 and KNbO3 is much weaker than that of LiNbO3, which promotes also the oxygen mobility and phase transformation of the two samples, especially in the high temperature OCM process. As a result, more oxygen vacancies/defects are generated on NaNbO3 and KNbO3, which facilitates the efficient formation of OCM active and selective surface O2– species and basic sites. Subsequently, the OCM performance of NaNbO3 and KNbO3 can be evidently improved. Combining the above advantages, NaNbO3 exhibits the optimal OCM performance in all the samples.

Ce0.9Pr0.1O2‐δ‐Pr0.6Ca0.4MnO3‐δ dual‐phase membranes: oxygen permeability and stability

AbstractPreviously unreported Ce0.9Pr0.1O2‐δ‐Pr0.6Ca0.4MnO3‐δ (CPO‐PCMO) dual‐phase membrane is designed and successfully fabricated. The crystal structure, surface morphology, stability, and oxygen permeability is systematically investigated. The XRD results reveal that CPO‐PCMO dual‐phase membranes are made up of cubic fluorite phase and orthorhombic perovskite phase, which exhibit excellent stability at elevated temperature under air atmospheres as well as various low oxygen conditions such as Ar or CO2 atmospheres. In addition, no obvious holes, cracks, and impurities are observed. The obtained CPO‐PCMO membrane with 0.8 mm thickness exhibits comparable oxygen permeability with a flux of 0.23 mL min−1cm−2 under air/He gradient at 1000 °C and stably works over 300 min without obvious deterioration under air/CO2 gradient, suggesting it has good CO2 stability.

Synthesis and characterization of Ho-doped SmFeO3 nanofibers with enhanced glycol sensing properties

A facile electrospinning route was exploited to prepare Sm1-xHoxFeO3 (0 ≤ x ≤ 0.07) nanofibers with orthorhombic perovskite phase. The XRD refinement technique was employed to obtain the lattice parameters of all samples. The characterization results show that the Ho partial substitution on A site ions of SmFeO3 leads to the decrease of crystallite size and increase of porosity, which is beneficial to enhance gas sensing properties of sensors. The Sm0.95Ho0.05FeO3 sensor exhibits the best response (26.12) to 100 ppm glycol at 200 °C among Sm1-xHoxFeO3 sensors. Especially, the as-prepared Sm0.95Ho0.05FeO3 oxides have an ultra-high response value of 10.20 to 5 ppm glycol. Hence the as-prepared Sm0.95Ho0.05FeO3 nanofibers can be regarded as an ultra-sensitive glycol candidate material.

Effectively Promoting Activity and Stability of a MnCo2O4-Based Cathode by In Situ Constructed Heterointerfaces for Solid Oxide Fuel Cells.

The development of multiphase composite electrocatalysts plays a key role in achieving the efficient and durable operation of intermediate-temperature solid oxide fuel cells (IT-SOFCs). Herein, a self-assembled nanocomposite is developed as the oxygen reduction reaction (ORR) catalyst for IT-SOFCs through a coprecipitation method. The nanocomposite is composed of a doped (Mn0.6Mg0.4)0.8Sc0.2Co2O4 (MMSCO) spinel oxide (84 wt %), an orthorhombic perovskite phase (11.3 wt %, the spontaneous combination of PrO2 additives and spinel), and a minor Sc2O3 phase (4.7 wt %). The surface of the (Mn0.6Mg0.4)0.8Sc0.2Co2O4 phase is activated by the self-assembled nanocoating with many heterogeneous interfaces. Thence, the ORR kinetics is obviously accelerated and an area-specific resistance (ASR) of ∼0.11 Ω cm2 is obtained at 750 °C. Moreover, a single cell with the cathode shows a peak power density (PPD) of 1144.1 mW cm-2 at 750 °C, much higher than that of the cell with the MnCo2O4 cathode (456.2 mW cm-2). An enhanced stability of ∼120 h (0.8 A cm-2, 750 °C) is also achieved, related to the reduced thermal expansion coefficient (13.9 × 10-6 K-1). The improvement in ORR kinetics and stability can be attributed to the refinement of grains, the formation of heterointerfaces, and the enhancement of mechanical compatibility.

Synthesis of Ba-doped porous LaFeO3 microspheres with perovskite structure for rapid detection of ethanol gas

In this work, porous La1−xBaxFeO3 (x = 0.01, 0.02, 0.03, 0.04 and 0.05) microspheres of the orthorhombic perovskite phase were prepared by an environment-friendly one-step hydrothermal method with a series of characterization of the six sensing nanomaterials. Characterization results show that their grain size is between 21.2 and 23.2 nm, and the grain growth is inhibited with the increase in Ba-doping concentration. The samples are all spherical with a diameter of about 10 μm, and the surface is very rough. By the gas sensing study of the samples, the results show that the La1−xBaxFeO3 sensor exhibits a fairly high response to the ethanol gas. In particular, the La1−xBaxFeO3 microspheres with a Ba-doping concentration of 2 mol% showed not only a significant improvement in sensitivity but also a rather rapid response recovery time compared to the undoped samples, demonstrating the superiority as an ethanol sensing nanomaterial. More importantly, the optimum operating temperature of La0.98Ba0.02FeO3 is only 200 °C, while that of the pure LaFeO3 is 260 °C. The Ba-doped porous microspheres prepared are a high-performance sensing material capable of rapid and accurate detection of ethanol.

Physical properties of the (K0·44Na0·52Li0.04)0.97La0·01Nb0·9Ta0·1O3 ceramic with coexisting tetragonal and orthorhombic monocrystalline grains at room temperature

A structural and physical properties study on ferroelectric (K0·44Na0·52Li0.04)0.97La0·01Nb0·9Ta0·1O3 ceramics with monocrystalline grains of orthorhombic (O) and tetragonal (T) perovskite phases coexisting at room temperature (RT) is presented. Different sintering temperatures were evaluated. XRD analysis demonstrates high crystalline quality of both phases with volume fractions depending of the sintering temperature. SEM shows grain facets and morphologies of both phases in all samples. Raman analysis confirms the dopant incorporation and the coexistence of both phases. The contributions of each phase in the dielectric response are deconvoluted using the frequency-temperature dielectric analysis. The orthorhombic-to-tetragonal (TO-T) and tetragonal-to-cubic (TT-C) phase transition temperatures shift ~100 °C below those reported for pure-KNN in all samples, as consequence of the Li, La, and Ta doping combination. Li doping promotes T-phase grain growth and decreases TO-T below RT. La incorporation promotes the O-phase grain growth and decreases TO-T and TT-C. The optimal sintering temperature is 1180 °C with 50-50 volume fractions of T-O phases. Piezoresponse studies show a complex 180°-domain structure.