Stabilization Of Tetragonal Phase Research Articles

Computational investigation of the phase stability, electronic, optical, phonon spectrum, and elastic behavior of layered perovskites Ca2XO4 (X = Zr, Hf) for optoelectronic applications.

A significant class of solid-state materials, Ruddlesden-Popper (RP) perovskites are well-known for their rich chemical compositions that make them excellent electrocatalysts. Therefore, in this work, we conduct thorough analysis of RP perovskites, specifically Ca2XO4 (X = Zr, Hf). We delve into the structural, electronic, optical, and mechanical properties presenting their insights for the first time. Our investigations reveal that Ca2XO4 (X = Zr, Hf) exhibits stable tetragonal phase structures, with energies (E0) of - 10,522.93eV and - 33,520.14eV, respectively. The calculated in terms of the ground state determines to possess distinct values such as - 4.79 eV/atom for LiScTe2 and - 3.95 eV/atom for Ca2ZrO4 and Ca2HfO4. Notably, the semiconductor characteristics of Ca2ZrO4 and Ca2HfO4 are underscored by their respective wide direct band gap of 5.02eV and 5.30eV. Then, we discuss the optical parameters encompassing the dielectric function, absorption coefficient, optical conductivity, refractive index, and energy loss function. is described as ductile, whereas is defined as brittle. Our outcomes underscore remarkable ability of these materials to absorb ultraviolet radiation from the electromagnetic spectrum, positioning them as promising candidates for optoelectronic applications. We made these calculations by employing first-principles approach rooted in density functional theory (DFT) and utilizing the Perdew-Burke-Ernzerhof-Generalized Gradient Approximation (PBE-GGA) and Tran and Blaha-modified Becke-Johnson (TB-mBJ) functional within the WEIN2K framework. In this framework, Kramers-Kronig relations are used to obtain crucial optical parameters. Mechanical behavior is assessed by employing Voigt-Reuss-Hill approximation (VRH) fulfilling the Born's criteria which emphasizes that these materials are equally appropriate for a broad range of mechanical applications.

Stabilization of Tetragonal Phase in Hafnium Zirconium Oxide by Cation Doping for High-K Dielectric Insulators.

As electronic circuit integration intensifies, there is a rising demand for dielectric insulators that provide both superior insulation and high dielectric constants. This study focuses on developing high-k dielectric insulators by controlling the phase of the Hf0.5Zr0.5O2 (HZO) film with additional doping, utilizing yttrium (Y), tantalum (Ta), gallium (Ga), silicon (Si), and aluminum (Al) as dopants. Doping changes the ratio of tetragonal to monoclinic phases in doped HZO films, and Y-doped HZO (Y:HZO) films specifically exhibit a high tetragonal phase ratio and a dielectric constant of 40.9, indicating superior insulating properties compared to undoped HZO films. To clarify the fundamental mechanism driving the enhancement in dielectric properties, we have carried out various analyses combined with density functional theory (DFT) calculations. Through the optimization of the post-deposition annealing (PDA) process and the heterojunction structure with Al2O3, an Al2O3/Y:HZO heterojunction with a high dielectric constant and even lower leakage current compared to a single layer was developed. The thin-film transistor (TFT) with the Au/Ti/amorphous InGaZnO4 (a-IGZO)/Al2O3/YHZO/TiN heterojunction structure exhibits low subthreshold swing (SS) values within a narrow gate-source voltage (Vsg) range. This study advances knowledge on how the controlled-phase doped HZO films affect the dielectric constant and leakage current and will contribute to semiconductor technology advancements by overcoming the limitations of conventional high-k dielectric insulators.

Realizing near-full density monophasic tetragonal 1.5-mol% yttria-stabilized zirconia ceramics via current-ramp flash sintering

This study demonstrates the successful fabrication of near-full density monophasic tetragonal 1.5-mol% yttria-stabilized zirconia (1.5YSZ) ceramics using current-ramp flash (CRF) sintering technique. The process involved regulating Joule heating in the samples by fine-tuning the input power through an alternating current field (nominal current density: 50 mA·mm−2) within a 3-min timeframe at a furnace temperature of 1100°C. This approach effectively enhanced grain size uniformity, which is crucial for preventing sample cracking associated with spontaneous tetragonal-to-monoclinic (T→M) phase transformation, thereby promoting densification with average relative densities exceeding 99%. The highest average fracture toughness of the 1.5YSZ samples was measured at 9.2 MPa·m0.5 using the standardized single-edge pre-cracked beam method. This toughness is approximately double that of commonly used 3YSZ samples produced by CRF sintering, all of which exhibited comparable average grain sizes and relative densities. Additionally, the 1.5YSZ samples demonstrated nearly identical resistance to low-temperature degradation (LTD) compared to the 3YSZ samples after accelerated hydrothermal aging at 140°C for 15 h, roughly equivalent to 60 years at 37°C. The reduced yttria concentration in 1.5YSZ facilitates T→M phase transformation at lower stress thresholds, enhancing toughness through increased crack shielding from a larger volume fraction of transformed grains. Furthermore, the uniform yttria distribution in 1.5YSZ, revealed by scanning transmission electron microscopy, compensates for the reduced tetragonal phase stability and contributes to improved LTD resistance. Notably, these exceptional properties were achieved at a furnace temperature 300°C lower and with a sintering duration several hours shorter than those of conventionally-sintered counterparts.

Effect of cadmium content on the stabilization of tetragonal phase of zirconium dioxide nanostructure prepared by Sol-Gel method

Effect of cadmium content on the stabilization of tetragonal phase of zirconium dioxide nanostructure prepared by Sol-Gel method

Role of magnesium ions in modifying oxide growth rate on Zircaloy under breakaway corrosion regimes

General corrosion of nuclear reactor in core material like Zircaloy-2 and breakaway corrosion in particular are of great importance in ensuring its smooth long term operation. Metal ions like Mg2+ added to the coolant, to mitigate corrosion of other structural materials like Carbon steel, can get incorporated in the corrosion product oxide on Zircaloy-2 and alter its corrosion behavior. Plasma Electrolytic Oxidation (PEO) method was employed to investigate the effect of Mg2+ ions during breakaway corrosion of Zircaloy-2. The main objective was to understand the morphology, protectiveness, semiconducting properties of the Mg modified oxide films on Zircaloy-2 surface. DC potentials 300, 400 and 500 V were used to accelerate corrosion kinetics and form oxide mimicking the breakaway corrosion regime. Borate buffer (pH 9.8) was used as the electrolyte, and Mg acetate was added as Mg source for probing the effect of Mg2+ ions. Oxide morphology depended largely on the formation potentials. The presence of magnesium resulted in thinner oxides with lower defect densities. GIXRD of the oxide showed stabilization of tetragonal phase in presence of Mg at 300 and 400 V. Oxide resistance and charge transfer resistances measured by EIS were observed to be higher due to Mg incorporation at these potentials. Mg addition facilitated formation of t-ZrO2. The electrochemical measurements suggested that the presence of Mg in ZrO2 could reduce the connected porosity in the oxide thereby stifling the diffusion paths. These factors lead to improved corrosion protectiveness of the oxide formed in the presence of Mg.

Prediction of the structural and magnetic properties of the all-d-metal Heusler alloys Ni–Mn–Cr

In this work, all-d metal Heusler alloys Ni–Mn–Cr were predicted by first principles. Their structure, magnetism, tetragonal distortion and electronic properties were studied. The cubic groud state structures of Ni2MnCr and NiMnCr2 are XA type, and that of NiMn2Cr is L21 type. All of them have magnetism. The change of their lattice constants is closely related to the covalent radius of atoms. Ni2MnCr has a stable tetragonal phase and may undergo martensitic transition. NiMn2Cr has a lower energy tetragonal phase, but is dynamically unstable. The equilibrium volumes of the two compounds expand through tetragonal distortion. NiMnCr2 does not have a lower energy tetragonal phase. In the tetragonal distortion, the atomic magnetic moments are influnced by the interatomic distance and the magnetic moments of neighboring atoms. The origin of the tetragonal distortion and magnetic properties was discussed in terms of the electronic density of states.

Stabilization of durable tetragonal phase and barrier regions in y-123 ceramic systems with partial substitution mechanism

This study examines the impact of Tb and Zn doping on the Y-123 superconducting system by analyzing crack propagation mechanisms through Vickers microhardness measurements. The measurements are conducted at various application forces ranging from 0.245 N to 2.940 N. The microhardness measurements are used to determine the role of impurity addition on Vickers hardness, modulus of elasticity, brittleness index, fracture toughness, and yield strengths. It is found that impurity ions serving as strong barrier regions improve the surface residual compressive stress sites and interactivity between the adjacent layers. Similarly, the sensitivity to the external forces reduce significantly with the substitution mechanism due to the induced new slip systems and ionic bond formations. Accordingly, all the mechanical performance properties are recorded to increase significantly with the impurity ions. Especially, the replacement of Zn by Cu ions in the Y-123 matrix exhibits higher resistance to failure, mechanical strength, and stabilization of the durable tetragonal phase. Accordingly, Zn/Cu substitution in Y-123 ceramics paves the way for the applications of ceramic compounds in the fields of heavy-industrial technology and industrial power systems. All the ceramic materials also exhibit indentation size effect feature based on the recovery mechanism. Additionally, load-independent microhardness parameters are semi-empirically modeled by Meyer's law, Hays-Kendall, indentation-induced cracking, elastic–plastic deformation, and proportional sample resistance model for the first time. According to the comparisons, the IIC model is identified as the most suitable for interpreting the real microhardness results of newly produced Y-123 ceramic matrices.

Effects of amorphous phase and yttrium on flash sintering and microstructures of ZrO2–SiO2 ceramic nanocomposites

AbstractFlash sintering has been used to consolidate a wide range of ceramics and ceramic composites. However, flash sintering of ceramic nanocomposite with a substantial amorphous phase is rarely studied. Meanwhile, the effects of yttrium addition on the flash sintering behaviors and microstructures of ZrO2‐based ceramic nanocomposite remain unknown. Herein, ZrO2‐SiO2 crystalline‐amorphous ceramic nanocomposites (CACNs) with different contents of amorphous phase and two types of yttrium dopants were sintered by flash sintering. Results showed that the content of amorphous phase (SiO2) had significant effects on the flash sintering behavior. The CACN with 65 mol% SiO2 was nonflash sinterable due to the high electric resistivity of SiO2, whereas, the CACN with 45 mol% SiO2 can be flash sintered to high densification within 35 seconds. The flash‐sintered CACNs consisted of ZrO2 nanocrystallites distributed in an amorphous SiO2 matrix. Flash sintering enhanced the tetragonal‐to‐monoclinic phase transformation of ZrO2. In addition, influences of yttrium dopant on CACNs were also investigated. Yttrium dopants can rapidly dissolve in ZrO2 lattices and show a tetragonal phase stabilization effect during flash sintering. Firework‐like ZrO2 microcrystallites formed by dendritic growth were observed close to the cathode region, which was attributed to athermal electric field effects and the formation and aggregation of oxygen vacancies at the cathode region. The results would provide guidance for fabricating CACNs via flash sintering.

Synthesized by coprecipitation method for controlled phase structures of 5YSZ

Yttria-stabilized zirconia (YSZ), which exhibits a tetragonal phase, finds widespread application in the realm of high-temperature solid electrolytes. In the context of this research endeavor, a concerted effort was undertaken to procure a stable and controlled tetragonal phase structure within 5 mol% yttria-stabilized zirconia (5 YSZ) by modulating the precipitation rate of YSZ sols in three distinct precipitation environments, namely acidic (AC), near to neutral (NE), and alkaline (AL) conditions. Through the characterization of 5 YSZ compounds synthesized in these various environments, encompassing an assessment of their elemental composition, phase structure, local structure, and microscale morphology, it was discerned that under acidic conditions, the product exhibited non-uniform elemental distribution, pronounced agglomeration, and an abundance of hydroxyl groups, all of which proved detrimental to the stability of the tetragonal phase, resulting in the presence of 40.63% monoclinic phase. Conversely, under alkaline conditions, substantial agglomeration and hydroxyl group presence were also noted, with 34.7% monoclinic phase in the product. In stark contrast, under the condition which is near to neutral, the product demonstrated uniform elemental distribution, excellent dispersion characteristics, and a virtual absence of hydroxyl groups. The tetragonal phase structure remained stable and homogeneous, with almost negligible monoclinic phase content. Subsequent ceramic processing resulted in the highest attainable density (99.7%), coupled with the highest ionic conductivity at 850 °C (35.2 mS/cm). This study underscores that pH control during coprecipitation reactions stands as a robust and effective methodology for achieving a stable tetragonal phase structure.

Preparation of Solid Superacid SO42-/ZrO2 and SO42-/ZrO2-MxOy (M=Ce, Co, Mn, and Zn) and Its Application in Toluene Nitration.

The nitration reaction of aromatic compounds is one of the extensively studied chemical reactions that result in the manufacturing of various industrial products applied in pharmaceuticals, dyes, perfumes, and explosives. A series of modified sulfated zirconia (SZ) catalysts SO42-/ZrO2-MxOy (M=Ce, Co, Mn, Zn, and M/SZ) doped with different metal elements by a coprecipitation method were investigated in the toluene nitration reaction. Various characterization techniques (X-ray diffraction, Brunauer-Emmett-Teller, thermogravimetric analysis, X-ray photoelectron spectroscopy, and temperature-programmed desorption of ammonia) indicated that doping metal elements in SZ led to excellent catalytic properties, increasing the specific surface area of the catalyst and facilitating the formation of a stable tetragonal zirconia phase. Doping zinc and cobalt in SZ enhanced the acidity of the catalyst and formed stronger acidic sites, promoting the generation of nitronium ions and providing more active sites for the toluene nitration reaction. Additionally, it reduced the loss of sulfate ions in the catalytic system that helped in improving the stability of the catalyst. Under the same conditions, the catalytic activity of toluene nitration reaction demonstrated the following order: Zn/SZ > Ce/SZ > Co/SZ > Mn/SZ > SZ, with the zinc-doped SZ catalyst exhibiting the best catalytic performance, achieving a toluene conversion rate of 78.58% and a para/ortho nitrotoluene ratio of 0.67.

Continuous supercritical hydrothermal synthesis of stabilized ZrO2 nanocomposites: Doping mechanism of typical metals and transition elements

In this study, Mg, Ce, Y and La-doped nano-zirconia particles were successfully obtained by continuous supercritical hydrothermal synthesis combined with nanotechnology and crystal stabilization technology. Through detailed characterization and analysis of the structure, crystal form, grain size of the particles and by-products, the doping amount of different element dopants was optimized, and the stable pathway of tetragonal and cubic phases was proposed. Moreover, the doping mechanisms of different elements and phase diagram of doped nano-zirconia were revealed. The results show that the crystal form is determined by the doping amount, ionic radius and intrinsic properties of ions. Y and Ce doping can completely stabilize the tetragonal or cubic phase without the formation of by-products. Mg and La doping produce by-products of Mg(OH)2 and La2O2CO3. As the ionic radius increases, the radius mismatch with Zr4+ leads to a stronger ability to stabilize the tetragonal or cubic phase. At the same time, minimum dopant for stable tetragonal or cubic phases will decrease.

Limits of critical grain size for the tetragonal phase stabilization in CaO‐doped ZrO2 ceramic and associated benefits

AbstractRecently, CaO‐doped (≤4 mol.%) tetragonal zirconia (CaSZ) ceramic was recommended as a potential alternative to yttria‐stabilized ZrO2 (YSZ). Here, we investigate the limits of starting particle sizes on the stability of tetragonal (t) phase and other associated benefits on measured properties. Synthesized CaSZ powders calcined with different temperatures were used as a mono‐sized or mixed (i.e., two different calcination temperatures) batch fraction for making dense CaSZ ceramic. The mixed‐batch powders were found to be far more efficient in stabilizing the t‐phase in ceramic. Compared to YSZ, CaSZ recorded remarkable enhancement in toughness (up to 8.3 MPa ). Contrary to YSZ, CaSZ ceramic demonstrated outstanding thermal stability.

Highly efficient ZrO2 photocatalysts in the presence of UV radiation synthesized in a very short time by plasma electrolytic oxidation of zirconium

We demonstrated in this paper that plasma electrolytic oxidation of zirconium in an alkaline electrolyte (10 g/L trisodium phosphate decahydrate) with the addition of NaAlO2 is a highly efficient method for obtaining ZrO2 coatings that are effective photocatalysts for the decomposition of organic pollutants under UV irradiation. ZrO2 coatings were formed by varying the PEO time from 60 s to 600 s, the NaAlO2 concentration up to 4 g/L, and characterized by SEM/EDS, XRD, XPS, DRS, and photoluminescence spectroscopy. Methyl orange decomposition was used to examine the photocatalytic activity (PA) of ZrO2 coatings. The PA of the formed PEO coatings is determined by the ratio of monoclinic and tetragonal ZrO2 phases, as well as the content of incorporated Al3+ in the crystal structure of ZrO2. Al3+ incorporated into ZrO2 coatings improves tetragonal phase stability by causing the formation of oxygen vacancies, which is crucial for enhancing their PA. Furthermore, the Al3+ dopant serves as a capture site for photo-induced electrons, inhibiting electron/hole recombination. The best PA was demonstrated by the ZrO2 coating formed after 60 s in an alkaline electrolyte with 4 g/L NaAlO2 addition, which contains the most tetragonal ZrO2 phases (around 51.3 %) and Al (around 3.14 at. %) of all formed ZrO2 coatings. After 8 h of irradiation, the PA of this coating was approximately 95 %.

Study on the properties of 8YSZ thermal barrier coatings by atmospheric plasma spraying

The 8 wt.% yttrium oxide partially stabilized zirconia (8YSZ) coatings were prepared by atmospheric plasma spraying (APS). The microstructure and properties of the coating were analyzed. The results show that the overall morphology of 8YSZ coating is smooth. The XRD pattern shows that the 8YSZ coating don’t undergo phase transformation and has a stable tetragonal phase. 8YSZ thermal barrier coating (TBC) remains intact after 70 thermal cycle tests. The finite element results show that the 8YSZ TBC has good thermal insulation. Potentiodynamic polarization and electrochemical impedance spectroscopy show that the coating has good corrosion resistance.

Role of promoters over yttria‐zirconia supported Ni catalyst for dry reforming of methane

AbstractDry reforming of methane (DRM) bears great hope for the catalytic community as well as environmentalists for its potential to convert two greenhouse gases, CH4 and CO2, together into synthetic feedstock “syngas”. The stable tetragonal zirconium yttrium oxide phase over the “Yttria‐zirconia supported Ni” catalyst (Ni/YZr) brings >70% CH4 conversion against 50% CH4 conversion over zirconia supported Ni catalyst) in 7 h time‐on‐stream (TOS). The use of the second metal oxide (MOx; M = Ho, Ga, Gd, Ba, Cs) in a small amount (4 wt%) over Ni/YZ catalyst is found to promote the catalytic activity further. Herein, we have prepared such metal‐promoted yttria‐zirconia supported Ni catalyst, employed them for DRM and characterized them with surface area porosity, X‐ray diffraction, spectroscopic techniques, temperature programmed techniques and transmission electron microscopy. A fine correlation of characterization results with catalytic activity brings out various useful information that would be useful for establishing yttria‐zirconia supported Ni catalyst for DRM. Ni stabilized over cubic zirconium holmium oxide phase in 5Ni4Ho/YZr catalyst, cubic zirconium gadolinium oxide phase in 5Ni4Gd/YZr catalyst and cubic zirconium barium oxide phase in 5Ni4Ba/YZr catalyst perform excellent toward DRM. Catalytically, 5Ni4Ho/YZr catalyst achieves CH4 conversion as high as ~85% whereas 5Ni4Ba/YZr and 5Ni4Gd/YZr show CH4 conversions of about ~80%. Even in 30 h TOS study, 5Ni4Ho/YZr catalyst showed >81% CH4 conversion with retaining highest H2/CO (0.97).

Phase Formation and Stabilization Behavior of Ca-PSZ by Post-Heat Treatment II: CaOx-ZrO2(1 − x) (x = 5–10 mol%)

The effects of CaO content and post-heat treatment were investigated on the phase stability and mechanical and thermal properties of Ca-PSZ. ZrO2 specimens with 5–10 mol% CaO were sintered, and post-heat treatment was performed at 1200 °C for 100 h. Subsequently, to test and analyze the crystal structure and the microstructure, the mechanical and thermal properties of the specimens were evaluated. All specimens were partially stabilized by 5–10 mol% CaO (5CSZ–10CSZ) in a mixed monoclinic and tetragonal phase; however, peaks of the secondary phase of CaZrO3 were observed in 10CSZ. The ratio of the monoclinic phase decreased from 62.50% (5CSZ) to 21.02% (10CSZ) as the CaO content increased. Additionally, the monoclinic phase ratio decreased from 59.38% (5CSZ) to 19.57% (9CSZ) after the post-heat treatment; an increase to 24.84% was observed for 10CSZ. An increase in Vickers hardness from 676.02 to 1256.25 HV and flexural strength from 437.7 to 842.7 MPa was observed with increasing CaO content. The post-heat treatment resulted in further increases in these values as the CaO content increased from 5CSZ to 9CSZ; however, the Vickers hardness and flexural strength of 10CSZ decreased by approximately 8% and 9%, respectively. The thermal expansion coefficient exhibited the same tendency as the mechanical properties. This coefficient increased from 8.229 × 10−6 to 9.448 × 10−6 K−1 with increasing CaO content and was enhanced after the post-heat treatment in 5CSZ to 9CSZ; however, the thermal expansion coefficient of 10CSZ decreased by approximately 4% after the post-heat treatment. The mechanically and thermally stable tetragonal phase increased, and the monoclinic phase decreased as the doped Ca replaced the Zr sites, as was confirmed by the X-ray diffraction (XRD) analysis. The post-heat treatment and the increased Ca addition further facilitated the replacement of Zr sites by Ca. However, at high Ca concentrations of 10CSZ, an equilibrium phase of CaZrO3 was formed as a secondary phase at the post-heat treatment temperature, resulting in low performance.

Tetragonal phase stabilization and densification in AC flash-sintered 1.5 mol% yttria-stabilized zirconia polycrystals with high toughness

For the first time, isothermal pressureless flash sintering of 1.5 mol% yttria-stabilized zirconia (1.5YSZ) polycrystals designed for high toughness was performed in a 1-kHz alternating current field (120 V·cm−1). The parameters governing tetragonal phase stability and densification needed to maximize the toughness of 1.5YSZ were investigated by varying the applied current density limit and holding time. A sample with relative density exceeding 98% and indentation toughness of about 13 MPa·m0.5 was sintered at 1100°C by applying 40 mA·mm−2 to the green body for 2 min, where the average steady-state temperature during flash reached 1330°C. Unlike flash sintering of conventional oxide ceramics, the applied current density and densification were not positively correlated despite pore closure. While Joule heating intensified when applying higher current densities, sample densification was hindered as the accelerated grain growth resulted in intergranular cracks which were generated by spontaneous tetragonal-to-monoclinic martensitic phase transformation during cooling.

Effect of sintering additives on the properties of alumina toughened zirconia (ATZ)

The effect of small amounts of copper oxide, manganese oxide, and stainless steel as sintering additives on the sintering behavior and mechanical properties of Alumina Toughened Zirconia (ATZ, 3Y-TZP with 20 wt% Al2O3) ceramic composites were evaluated and contrasted with that of undoped ATZ by using microwave sintering (MW) method. Green bodies were sintered at 1250°C, 1350°C, and 1500°C using a holding time of 5 min., with a heating rate of 30°C /min. In general, all ATZ samples exhibited a similar trend, as the results showed that the relative density and mechanical properties increased with increasing sintering temperature regardless of the addition of dopants. It was found that the addition of 0.2 wt% CuO, 0.5 wt% MnO2, and 0.2 wt% SS were beneficial in enhancing the densification and improving the mechanical properties of ATZ without inducing grain coarsening. The ATZ composite samples' relative density, tetragonal phase stability, microstructural evolution, Vickers hardness, and fracture toughness were revealed. The addition of 0.2 wt% CuO was the most beneficial in improving the properties of ATZ at a low sintering temperature of 1250°C since the sample obtained the highest relative density of 97%, Vickers hardness of 13.2GPa and fracture toughness of 6.5 MPa m1/2. In contrast, the undoped ATZ required a high sintering temperature to achieve comparable results to the doped samples. The ANOVA analysis revealed that the CuO-doped ATZ sample exhibited the highest significance and was the most suitable in improving both hardness (H) and fracture toughness (KIc) across all temperature conditions. This study also proved that the microwave sintering technique promotes the densification and mechanical properties of ceramic composites compared to the conventional sintering technique.Graphical abstract

Copper Ferrite Nanoparticles Synthesized Using Anion-Exchange Resin: Influence of Synthesis Parameters on the Cubic Phase Stability

Copper ferrite is of great interest to researchers as a material with unique magnetic, optical, catalytic, and structural properties. In particular, the magnetic properties of this material are structurally sensitive and can be tuned by changing the distribution of Cu and Fe cations in octahedral and tetrahedral positions by controlling the synthesis parameters. In this study, we propose a new, simple, and convenient method for the synthesis of copper ferrite nanoparticles using a strongly basic anion-exchange resin in the OH form. The effect and possible mechanism of polysaccharide addition on the elemental composition, yield, and particle size of CuFe2O4 are investigated and discussed. It is shown that anion-exchange resin precipitation leads to a mixture of unstable cubic (c-CuFe2O4) phases at standard temperature and stable tetragonal (t-CuFe2O4) phases. The effect of reaction conditions on the stability of c-CuFe2O4 is studied by temperature-dependent XRD measurements and discussed in terms of cation distribution, cooperative Jahn-Teller distortion, and Cu2+ and oxygen vacancies in the copper ferrite lattice. The observed differences in the values of the saturation magnetization and coercivity of the prepared samples are explained in terms of variations in the particle size and structural properties of copper ferrite.

Iridium oxide nanoribbons with metastable monoclinic phase for highly efficient electrocatalytic oxygen evolution

Metastable metal oxides with ribbon morphologies have promising applications for energy conversion catalysis, however they are largely restricted by their limited synthesis methods. In this study, a monoclinic phase iridium oxide nanoribbon with a space group of C2/m is successfully obtained, which is distinct from rutile iridium oxide with a stable tetragonal phase (P42/mnm). A molten-alkali mechanochemical method provides a unique strategy for achieving this layered nanoribbon structure via a conversion from a monoclinic phase K0.25IrO2 (I2/m (12)) precursor. The formation mechanism of IrO2 nanoribbon is clearly revealed, with its further conversion to IrO2 nanosheet with a trigonal phase. When applied as an electrocatalyst for the oxygen evolution reaction in acidic condition, the intrinsic catalytic activity of IrO2 nanoribbon is higher than that of tetragonal phase IrO2 due to the low d band centre of Ir in this special monoclinic phase structure, as confirmed by density functional theory calculations.