Pure Phase Research Articles

Sustainable Solutions for Industrial Wastewater Remediation by KBiFe2O5 Under Visible‐Light Irradiation

AbstractIndustrial wastewater poses a serious threat to human health and the environment. The rising demand for an easy, efficient, environment‐friendly, and cost‐effective method for wastewater treatment has paved the way for the photocatalytic degradation of wastewater. Organic dyes, which comprise a major portion of organic pollutants in industrial wastewater, are highly toxic and carcinogenic. The hydrothermal method, being economical, easily available, and environmentally friendly, is used to prepare the time‐varying KBiFe2O5 samples. KBiFe2O5 is a lead‐free (nonhazardous), low‐bandgap brownmillerite‐structured crystalline material that can use a wide range of solar spectrum. Their phase purity is also confirmed by powder X‐ray diffraction (XRD), UV–Vis diffuse reflectance spectrophotometer (UV–Vis DRS) is done to confirm the bandgap value and Fourier transform infrared (FTIR) spectroscopy is performed to identify the chemical bonds in the material. Degrading textile organic effluent methylene blue (MB) dye under visible light and comparing its photodegradation performance are conducted to investigate the synthesized samples’ photocatalytic properties. The photocatalytic activity is relatively enhanced by adding H2O2 in a precise amount. So, the synthesized samples effectively demonstrate photocatalytic behavior, which has been used for wastewater remediation purposes.

Discharging Performance Analysis of MXene Nano‐Enhanced Phase Change Material for Double and Triplex Tube Thermal Energy Storage

ABSTRACTThe present study numerically investigates the energy and exergy analysis of solidification of phase change materials within a double tube and triple tube latent heat storage unit using ANSYS Fluent. Double tube and triple tube thermal energy storage system's thermal characteristics are examined using MXene nano‐enhanced phase change material to determine system efficiency, discharged energy, heat transfer rate, exergy destruction, entropy generation number, exergetic efficiency, liquid fraction, solidification temperature contours. The result revealed that the double tube thermal energy storage with pure cetyl alcohol PCM has 14.76% lower discharge exergy than MXene‐based nano‐enhanced phase change material in pure solidification. In a triple tube thermal energy storage system, the solidification time for MXene‐based nano‐enhanced phase change material is impressively reduced by 54.76% compared to a double tube system using pure phase change material. At a Fourier number of 0.00672, MXene nano‐enhanced phase change material exhibits an 11.69% higher Stefan number (St) than cetyl alcohol phase change material in a double tube thermal energy storage system. At 2400 s, pure phase change material and MXene nano‐enhanced phase change material generated 3.14% and 4.88% less entropy than pure cetyl alcohol in the triple tube thermal energy storage system. During the pure solidification process in a double tube thermal energy storage system, pure cetyl alcohol experiences 7.60% higher exergy destruction compared to MXene nano‐enhanced phase change material at a solidification time of 2400 s. In a triple tube thermal energy storage system, the discharging temperature for pure cetyl alcohol phase change material is 2.92% lower than that in a double tube system. Double tube thermal energy storage with pure cetyl alcohol discharged more efficiently over 2400 s. The triple tube thermal energy storage system solidified cetyl alcohol PCM 20.83% faster than pure phase change material due to MXene nanoparticles' better thermophysical properties. Thus, MXene‐based nano‐enhanced cetyl alcohol phase change material solidifies faster per volume in a triple tube thermal energy storage latent heat system.

Aluminum and Iron Effects on the Electrical Conductivity of the Dense Hydrous Magnesium Silicate Phase E

AbstractThe electrical conductivity of pure and Al/Fe‐bearing phase E was measured up to 950 K at 15 GPa using a complex impedance spectroscopy. Pure phase E shows comparable conductivity to that of phase D, and a few orders of magnitude higher than that of phase A and super‐hydrous phase B. Al‐bearing phase E does not exhibit a conductivity difference, while a certain amount of incorporated Fe prominently increases its electrical conductivity by a factor of 4. Unlike the sole substitution 2Al3+→Mg2++Si4+ in phase D and H, H+ is likely involved in the substitution. Proton conduction is the dominant conduction mechanism, while small polaron conduction becomes dominant with increasing Fe content. Phase E in subducted slabs at depth of the upper transition zone cannot explain the high electrical conductivity anomalies beneath the Philippine Sea or Northeast China. Other mechanisms such as dehydration of hydrous minerals is needed to account for them.

Gradient refractive index tellurite glass-ceramics for miniaturized and lightweight MWIR imaging

Tellurite glasses are highly anticipated for creating gradient refractive index (GRIN) lenses, which have the potential to be applied in the lightweight and miniaturization of optical imaging systems to improve their performance. However, it is still challenging to precipitate pure crystalline phases in tellurite glasses after heat treatment to control the refractive index via spatial variation of nanocrystal distribution. Here, we present a novel method for fabricating axial telluride GRIN glass via a gradient heat-treatment technique. Through the selection of glass composition and control of the heat treatment process, pure phase Bi4TeO8 nanocrystals with a high refractive index (n) can be precipitated in telluride glass with a lower refractive index. This allows the axial telluride GRIN structure of maximum refractive index difference Δn ∼ 0.1 to be obtained by modulating the spatial distribution and concentration of Bi4TeO8 nanocrystals. This work not only demonstrates the feasibility of producing GRIN lenses from tellurite glass but also lays the foundation for the future development of medium wave infrared (MWIR) imaging.

Synthesis of high purity Ti2AlC MAX phase by combustion method through thermal explosion mode: Optimization of process parameters & evaluation of microstructure

Obtaining high-purity MAX-phase powders is a challenging issue. Therefore, in this article, the effects of two key parameters, including mechanical activation time (1, 2, and 3 h), and preheating temperature (800 and 1000 °C) were investigated on the formation mechanism of Ti2AlC MAX phase using mechanically activated (assisted) self-propagating high-temperature synthesis (MA-SHS) combustion method through thermal explosion mode. For this aim, a powder mixture of titanium, aluminum, and carbon with a stoichiometry ratio of (2:1:1) was used. Differential thermal analysis (DTA) was carried out to evaluate the effect of mechanical activation and preheating temperature of the formation temperature of the target MAX phase. Subsequently, the microstructural, phase analysis, chemical composition, and determination of surface chemical states studies were carried out through scanning electron microscopy (SEM), X-ray energy distribution spectroscopy (EDS) transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectric spectroscopy (XPS), respectively. DTA results illustrated that applying mechanical activation alters the formation temperature, which leads to an increase in the purity of the MAX phase. The quantitative measurements were carried out using the Rietveld method to determine the purity of the achieved MAX phase. The results indicated that samples subjected to 2 h of mechanical activation at a preheat temperature of 1000 °C exhibited to contain 96.1 % of Ti2AlC MAX phase, which is the highest value among other specimens and the lowest amount of secondary and oxide phases (3.9 % of TiC) during the combustion synthesis process compared to other samples.

A novel method for strengthening C/C composite joint with high entropy alloy/Ni composite interlayers by spark plasma sintering: In-situ synthesis of high entropy cermet joint structure

C/C composite was successfully brazed with TiZrHfTa/Ni or ZrHfNbTa/Ni composite interlayers using spark plasma sintering. The influence of different interlayers and joining parameters on the joint morphology, shear strength at room temperature and 1000 °C was investigated. For both composite interlayers, the C/C joints obtained at 1800 °C for 30 min consisted of a single high entropy cermet structure, with a near equimolar high entropy carbide hard phase and a near pure Ni binder phase. However, the use of different composite interlayers resulted in differences in the elastic modulus and hardness of the formed high entropy carbide phase. The maximum shear strengths of the obtained C/C composite joints using TiZrHfTa/Ni and ZrHfNbTa/Ni interlayers at room temperature were close, with value of 37.49 ± 1.44 MPa and 38.95 ± 1.26 MPa, respectively. Because (Zr-Hf-Nb-Ta)C had better high-temperature stability than (Ti-Zr-Hf-Ta)C, the obtained C/C-ZrHfNbTa/Ni-C/C joint exhibited a higher shear strength of 28.54 ± 1.71 MPa at 1000 °C. After shear testing at both room temperature and 1000 °C, fractures in all joints predominantly occurred within the C/C composite near the reaction layer, indicating a substrate failure mode. The use of composite interlayers resulted in C/C composite joints with excellent shear strength, primarily due to the in-situ synthesized high entropy cermet reaction layer, which provided superior strength and toughness. Additionally, the laser-textured pattern on the C/C composite surface formed numerous interlocking structures at the joint interface, further enhancing the joints' shear strength.

Biosynthesis of NiO nanoparticles using Senna occidentalis leaves extract: Effects of annealing temperature and antibacterial activity

In this work a cost effective and ecofriendly green method for the preparation of NiO nanostructures employing Senna occidentalis (S. occidentalis) leaves extract has been reported. XRD studies show that the 400 °C and 500 °C annealed nanostructures were authenticated as pure face centered cubic phase with an average crystallite size are about 27 nm and 15 nm, respectively. The SEM results show that both the annealed samples were nearly spherical with grain sizes ranging between 40 and 700 nm. The band gap of 400 °C and 500 °C annealed NiO nanoparticles (NPs) was estimated to be 5.28 eV and 5.40 eV, respectively from UV-visible studies while the occurrence of Ni-O stretching in the FTIR spectra validates the formation of NiO. Further this work witnesses that the NiO NPs synthesized from the green route offer better antibacterial activity. The observed maximum zone of inhibition of 500 °C annealed NiO NPs was found to be 20 mm and 19 mm for Serratia marcescens and Bacillus cereus strains and indicates that this material can serve as a prospective drug for biomedical application.

Photocatalytic and thermoelectric properties of Cu2SrSnS4 nanoparticles by solvothermal method

In the present work, flower-like Cu2SrSnS4 (CSTS) sample is successfully prepared by solvothermal method. The XRD and Raman analysis confirm that pure CSTS phase with trigonal structure is obtained. The band gap of as-obtained CSTS naocrystals is estimated to be 1.49eV. The removal of methylene blue (MB) within 100min under simulated solar light irradiation is around 90%, depicting that CSTS is a potential material for effective solar light photocatalytic application. Meanwhile, The Seebeck coefficient and electrical conductivity of CSTS material can reach to 128.57μV•K-1 and 20.35S·m-1 at 675K, respectively, indicating its potential for thermoelectric application.

H2S gas sensing behavior of 2-D V2O5 nanowire network structure

In this study, a nanowire network-based V2O5 nanostructure, designed as the active surface in H2S gas sensors, was produced using an environmentally friendly method known as hydrothermal synthesis. The morphological, structural, and electrical properties of the produced nanostructure were characterized using various measurement techniques. XRD, SEM, and EDX analyses confirmed that the nanostructure was in a pure monoclinic phase, had a two-dimensional (2-D) nanowire network morphology, and was deposited stoichiometrically. From UV–Vis analysis, the energy band gap value of the nanostructure was calculated to be 2.65 eV. In gas sensing measurements conducted between 27 °C and 102 °C, the optimal operating temperature of the fabricated sensor was determined to be 42 °C. At this temperature, which is close to room temperature, the sensor exhibited a high sensitivity of 21.16 % for 50 ppm H2S gas, along with good selectivity, stable repeatability, and baseline stability. Moreover, for 2 ppm H2S gas, the response and recovery times were 39 s and 58 s, respectively. A comprehensive electrical analysis of the sensor was carried out through impedance spectroscopy measurements over a wide temperature range. Our findings indicate that the 2-D V2O5 nanowire network structure (NNS) results in several notable effects, including low operating temperature, high selectivity, and stability for H2S gas, demonstrating considerable potential for industrial applications.

Low-temperature sintered Li2BaP2O7 ceramic: structural insights, bond characteristics, and microwave dielectric properties

The Li2BaP2O7 ceramics, synthesized through the solid-state reaction method, exhibit a pure monoclinic phase. Upon sintering at 750 °C, the ceramic achieves a high relative density of 97.3%, which is indicative of an optimal microstructure conducive to the superior microwave dielectric properties: a εr of 9.9, a Q × f of 86200 GHz, and a τf of -95.4 ppm/°C. The variation in relative density is identified as the principal driver of changes in both the εr and Q × f values for the Li2BaP2O7 ceramics. The molecular polarizability is pivotal in determining the εr of Li2BaP2O7 ceramics. The P-V-L theory analysis elucidates that the P-O bond significantly surpasses other chemical bonds in contributing to the ionicity, lattice energy, and bond energy, thereby underscoring its dominance over the three principal microwave dielectric characteristics. Furthermore, Raman spectroscopy data demonstrate that the P-O bond vibration predominantly governs the overall vibrational spectrum.

Quantitative pre-lithiation modulation of aluminum foil anode kinetics enables high rate and stable cycling of high-loading all-solid-state batteries

Aluminum (Al) foil holds great promise as a pure alloy anode for all-solid-state batteries (ASSBs) due to its suitable potential, high theoretical capacity, and excellent electronic conductivity. However, it remains challenging to achieve high reversibility and stability of the Al foil anode for ASSBs. Herein, we investigate the morphological and lithium (Li) kinetics evolutions of the Al foil anode paired with sulfide solid-state electrolyte (SSE). We identify that the significant reversible capacity loss stems from diminished Li kinetics at low Li contents (LixAl, 0 < x < 0.5), where the accumulation of pores and pure delithiated Al phase obstructs Li diffusion, increasing interfacial resistance and overpotential. Conversely, the Al foil anode with high Li contents (LixAl, 0.5 < x < 1) demonstrates reversible structures and rapid Li kinetics. Through precise pre-lithiation control, ASSBs with LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes exhibit outstanding rate capabilities and cycling stability, achieving over 4,000 cycles with 82.1 % capacity retention at 5C and demonstrating long-term cycling over 1,000 cycles with nearly 100 % capacity retention at ultra-high loadings. This work offers a viable strategy for advancing practical-level ASSBs with enhanced performance and longevity, contributing valuable insights to future battery technology.

Luminescent yttrium organic frameworks: Cell imaging, gas adsorption and nitro sensing applications

The flexibility of ligand (L) yield, two different yttrium organic frameworks, denoted as {[Y(L)2(H2O)4]·Cl3·DMF·(H2O)3·(S)}n (MOF-1) and {[Y(L)3/2(H2O)2]·(NO3)3·(S)}n (MOF-2), where L denotes 9,10-bis((4-carboxylatopyridinium-1-methylene)anthracene and S denotes the disordered solvent molecules. Detailed single crystal X-ray study established a one dimensional (1D) chain for MOF-1 and a three dimensional (3D) frameworks with one channel voids structure for MOF-2, respectively, due to different conformation of the ligand. In both MOFs, Y(III) have bicapped trigonal prismatic geometry. The phase purity of both MOFs has been confirmed by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and IR spectroscopic studies. MOF-1, with its particle size in nano range, good fluorescence property and solubility in water, is a suitable candidate for cell imaging study. In contrast, three dimensional framework of MOF-2, with small voids, makes it well suited for gas adsorption and sensing of nitro aromatics compounds.

Simultaneous structure and surface engineering of metal-organic framework derived LiNi0.5-xFe2xMn1.5-xO4 cathode material for improving high voltage performance of lithium-ion batteries

This study presents a novel material synthesis approach utilizing a terephthalic acid-based metal-organic framework as a precursor and employing an ethanol-assisted hydrothermal treatment to produce high-performance Fe-doped LiNi0.5Mn1.5O4 (LNMO) cathode material. This strategy yields a well-crystallized spinel structure with uniformly distributed transition metal ions. Additionally, the appropriate quantity of Fe dopant can achieve the desired Mn3+/Mn4+ ratio, level of structural disordering, and crystal phase purity for Fe-doped LNMO. The synthesis process also aids in forming an amorphous Li2CO3 surface layer, approximately 1 nm thick, which protects the active material from excessive reaction with electrolyte. The typical Fe-doped LNMO cathode (S-05) exhibits superior performance compared to a commercialized LNMO counterpart. It delivers an initial discharge capacity of 135 mAh g-1 at 1 C with exceptional cycling stability over 500 cycles (capacity retention of 90%) under high voltage (5.0 V vs. Li+/Li). Furthermore, its rate capability significantly improves, with a capacity retention of 85% (5 C/0.2 C). This enhanced performance aligns with evidence of activated Ni2+/Ni3+/Ni4+ redox reactions and suppressed cathode electrolyte interphase resistance, leading to promoted Li+ diffusion. Moreover, it is found the cathode helps alleviate electrolyte degradation at high voltages by inhibiting the formation of singlet oxygen in the electrolyte.

Bismorpholin-4-ium tetrabromo-cadmium metal-organic single crystal delivering Crystal structure, physicochemical properties and Characterizations for Optoelectronic Applications

For the development of nonlinear optical (NLO) materials, compositions of cadmium chloride (CC) and Morpholinium bromide (MB) molecules were utilized to form metal-organic materials. Morpholinium bromide was incorporated with cadmium metal to have electron charge transfer by constructing acentric structures that take advantage of strong third-order nonlinear optical properties. Bis Morpholinium cadmium bromide (BMCB) crystals were synthesized by a slow evaporation method (SEST). The BMCB crystal belongs to monoclinic P21/c space group with four molecules in the unit cell (a=6.7607(4) Å, b=16.5811(2) Å, c=14.9744(2) Å, β=94.136(3) ° and Z=4). The grown BMCB crystal phase purity and crystallinity were further investigated using powder X-ray diffraction (PXRD) analysis. Using Fourier transform infrared (FTIR) spectroscopy, the functional groups and their vibrational states were evaluated. From the results obtained from UV-vis-NIR spectral analysis, it is clear that the title compound is transparent in the visible range with the lower cut-off wavelength of 254 nm. The TG-DTA measurement has been used to evaluate thermal stability. Microhardness measurements were carried out to evaluate the mechanical stability of the grown crystal. The third-order nonlinear optical (NLO) characteristics were studied using Z-scan technique. The grown crystal exhibits outstanding third-order NLO response and wide laser damage threshold (LDT), which are crucial characteristics for developing practical NLO devices. The findings consequently open a novel path for the logical design of enormous, thermally stable and NLO-active metal-organic complexes for NLO applications.

Synthesis of Ternary Layered Double Hydroxides and Application for Wastewater Treatment

AbstractThis study systematically investigates the optimization of synthesis parameters for ternary layered double hydroxide (LDH) to achieve a pure phase and high crystallinity. The , LDH is synthesized using the coprecipitation method and applied for wastewater treatment. The ternary LDH is synthesized at 60 °C for 24 h and exhibited maximum crystallinity with a crystallite size of 4 nm. The crystallinity index (CI) is a quantitative indicator of crystallinity, which is calculated using the X‐ray diffraction (XRD) method. The influence of reaction time on the structural characteristics of this LDH was thoroughly investigated, mainly focusing on achieving well‐crystalline LDH. Experimental results revealed a direct correlation between reaction time and crystallinity. This study highlights the significant influence of controlled synthesis and reaction time on producing high crystalline ternary LDH. The role of different parameters, such as solution pH, adsorbent dosage, contact time, and dye concentration, has been investigated. The adsorption isotherm data is analyzed using different isotherm models, which shows this material having a significant adsorption capacity of 82.92 mg/g for Congo Red dye.

Microwave-assisted hydrothermal synthesis of αβ-Ni(OH)2 nanoflowers on nickel foam for ultra-stable electrodes of supercapacitors

Transition metal hydroxides (TMHs) are considered promising materials for supercapacitors because of their high theoretical capacitance and tunable morphology. Among TMHs, nickel hydroxide stands out for its multiple oxidation states, facilitating charge storage. This paper reports on a novel microwave-assisted hydrothermal technique employed to synthesize mixed-phase nickel hydroxide nanoflowers directly at the surface of nickel foam substrates with improved electrochemical stability compared to pure phases of nickel hydroxide. The analysis of nickel hydroxide in different phases alpha, beta and mixed-phase materials using physiochemical techniques like XRD, SEM, EDX, RAMAN, FT-IR and TGA is explained. The areal capacitance calculated from GCD tests for α-Ni(OH)2, β-Ni(OH)2 and αβ-Ni(OH)2 is estimated 7.35 F/cm2, 2.66 F/cm2 and 5.12 F/cm2 at a current density of 10 mAcm−2. The mass-specific capacitance calculated from GCD tests for α-Ni(OH)2, β-Ni(OH)2 and αβ-Ni(OH)2 is estimated 2311 Fg−1, 688 Fg−1 and 1511 Fg−1 at a current density of 10 mAcm−2. The cyclic stability test revealed the superior cycling performance of nickel hydroxide in mixed-phase as the cathode of an ultralong supercapacitor with nearly 100% capacitance retention after 5000 cycles at 50 mAcm−2. The proposed synthesis technique advances the efficiency and control of nanostructure geometry, providing insights into the design for electrodes of extreme-performance supercapacitors. However, conventional synthesis methods are time-consuming and energy-intensive. These findings underscore the potential of mixed-phase nickel hydroxide as an outstanding electrode material with extended cyclic performance for supercapacitors, contributing to the improvement of energy storage technologies in the renewable energy landscape.

Regulating novel tunable green to red upconversion luminescence in Er3+/Yb3+ co-doped SrBi2Nb2O9 ferroelectric ceramic

A series of SrBi2-x-yNb2ErxYbyO9 (SBN) ferroelectric ceramics co-doped with Erbium and Ytterbium have been fabricated through solid-state approach, the formation of pure phase SrBi2Nb2O9 has been confirmed by XRD spectra corresponding to orthorhombic geometry having phase group A21am. The lattice parameters and volume of the unit cell increase with the content of Yb3+. SEM study revealed the randomly oriented plate-like structure of SBN having average particle sizes ranging from 0.9 μm to 2.23 μm. The FTIR characteristic bands are found at wavenumber 602 cm−1 and 812 cm−1. In Photoluminescence (PL) spectra, two green emission bands (524 nm and 549 nm) and one weak red band (660 nm) are acquired using a 488 nm excitation wavelength. The diffuse reflectance spectra (DRS) of ceramic compounds reveal that the values of band gap ranges from values 2.7–3.1eV. Two UCL bands are seen at wavelength 533 nm, and at wavelength 554 nm in the green part of the upconversion photoluminescence (UCL) spectra, and a single band observed at a wavelength of 672 nm in the red region upon excited by 980 nm laser. The green band dominates for initial concentration up to x = 0.03, y = 0.03 after which red emission dominates with increasing concentration of Yb3+. The dependence study of pump power on UCL emission intensity reveals that there are two photons are involved in UC emissions of green and red. The time decay analysis of SBN composition showed that the average decay time of Er3+ is 70μs and that of the co-doped system (Er3+/Yb3+) is 37 μs

Investigations on optical properties of synthesized covellite CuS hollow nano cubic structures

In this work, hollow nanocubes of CuS were synthesized by employing a chemical route via Kirkendall effect. The influence of sulphur concentration on the optical and structural properties of CuS by varying the amount of sulphur during synthesis was investigated. The synthesized hollow cubes were characterized by using Scanning Electron microscope (SEM), X-Ray Diffraction (XRD) Analysis, Ultra Violet -Visible (UV-Vis.) Spectroscopy, Photoluminescence (PL) Spectroscopy, Raman Spectroscopy and X-ray photoelectron Spectroscopy (XPS). The formation of cubic morphology was affirmed by SEM analysis in all three samples. The length of the sidesthe of the cube lies in the range of 500-600 nm. XRD studies confirmed the formation of the pure phase of covellite CuS. Also, XPS analysis validated the presence of excess sulphur in the sample with Cu:S as 1:150 along with variation in the stoichiometric ratio of 1: 0.5. Since, this was not the case for Cu:S as 1:100, as it showed the desired stoichiometry of 1.1: 0.9 that supports the pure phase of CuS. Raman spectra further confirmed the purity of the sample. Absorption analysis revealed a well-defined bandgap with the absence of an intermediate defect state with a bandgap of 1.4 eV in the optimized sample. PL spectra displayed a decent recombination rate and minimum non-radiative losses in the 1:100 sample. These outcomes assurances the sample with Cu:S as 1:100 could be used as a potential material for solar cell applications.

Effects of Sintering Temperature on the Electrical Performance of Ce0.8Sm0.2O1.9–Pr2NiO4 Composite Electrolyte for SOFCs

Abstract Novel composite electrolyte Sm0.2Ce0.8O1.9–Pr2NiO4 (SDC–PNO) for solid oxide fuel cells (SOFCs) was prepared. The effects of sintering temperature on the performance of SDC–PNO composite electrolyte were studied. X-ray diffraction (XRD) analysis confirms that the composite samples sintering at different temperatures contain two pure phases corresponding to SDC and PNO, respectively. It indicates that there is no interfacial reaction between Sm0.2Ce0.8O1.9 and Pr2NiO4, and the composite electrolyte keeps regular grain boundaries after long-term operation. The results of scanning electron microscopy (SEM) show that a dense structure can be formed after sintering at 1250 °C. The electrical properties were tested in air by electrochemical impedance spectroscopy technique in the temperature range of 400–800 °C. Results show that an appropriate increase of the sintering temperature can effectively increase the conductivity of SDC–PNO composite electrolyte, and the maximum conductivity of 0.102 S/cm can be obtained in the sample sintered at 1250 °C and tested at 800 °C. In summary, the electrical conductivity of Sm0.2Ce0.8O1.9 can be significantly increased by adding Pr2NiO4, and SDC–PNO composite electrolyte is a promising electrolyte for solid oxide fuel cells.

The origin of ferroelectricity in HfO2 from orbital hybridization and covalency

Fluorite-structured HfO2 ferroelectrics exhibit remarkable ferroelectricity owing to the robust thickness scalability, rendering them promising for next-generation ferroelectric memories. Unlike the well-understood perovskite structured ferroelectrics, such as Pb(Zr,Ti)O3, the origin of ferroelectricity in HfO2 remains elusive, which impedes the experimental fabrication of pure and stable ferroelectric orthorhombic phase in films. This study seeks to elucidate its origin by analyzing the covalent nature of local chemical bonding and changes in orbital hybridization and by catching the typical feather of the half-unit-cell spacer/polar layer in the orthorhombic phase. Notably, we find that the differences in the hybridization intensity of the 2s orbitals of two types of O atoms (OI and OII) and 5d orbitals of Hf atoms play a crucial role in inducing ferroelectric distortion. Furthermore, we demonstrate that the intrinsic mechanisms of stress in enhancing the ferroelectricity of HfO2 originate from the modulation of orbital hybridization intensity of the Hf–O bonds. These insights provide a vital theoretical foundation for further exploration of ferroelectric phase transitions and property modulation in HfO2 and similar fluorite-structured ferroelectrics.