Zr Sites Research Articles

Vibrational sum frequency generation (VSFG) spectroscopy of water adsorption on surfaces of yttria-stabilized cubic zirconia (YSZ).

Yttria-stabilized zirconia (YSZ) is found in a wide range of applications, from solid-oxide fuel cells to medical devices and implants. A molecular-level understanding of the hydration of YSZ surfaces is essential for optimizing its performance and durability in these applications. Nevertheless, only a limited amount of literature is available about the surface hydration of YSZ single crystals. In this study, we employ surface-sensitive non-linear vibrational sum frequency generation spectroscopy to investigate the hydration of YSZ(100), (110), and (111) single crystal substrates under ambient laboratory conditions. Three types of hydroxyl groups were identified at all three YSZ-D2O interfaces: (i) hydroxyls on the metal sites of Zr or Y resulting from the dissociative chemisorption of water, (ii) hydroxyls from proton adsorption to O sites formed from water dissociation, and (iii) hydroxyl groups as part of the physisorbed water at the interface.

Production of Branched Alkanes by Upcycling of Waste Polyethylene over Controlled Acid Sites of SO4/ZrO2-Al2O3 Catalyst.

Branched alkanes, which enhance the octane number of gasoline, can be produced from waste polyethylene. However, achieving highly selective production of branched alkanes presents a significant challenge in the upcycling of waste polyethylene, and the maximum selectivity for branched alkanes reported up to date is about 70%. Here, we report a one-pot process to convert polyethylene into gasoline-range hydrocarbons (C4-C13) with yield of 73.3% over SO42-ZrO2-Al2O3 catalyst at 280 °C. The proportion of branched alkanes reaches 90.1% within the C4-C13 fraction. Incorporation of sulfate group endows the catalyst with strong Lewis acid sites and weak and moderate Brønsted acid sites. In situ X-ray absorption, in situ infrared spectroscopy, in situ small angle neutron scattering, and DFT calculations reveal that polyethylene activation occurs through the synergy between sulfate groups and strong Lewis acid sites (Zr sites). The weak and moderate Brønsted acid sites preferentially catalyze the isomerization and type A β-scission processes, which favors the formation of branched alkanes, while suppressing competing reactions that produce straight-chain alkanes.

Production of Branched Alkanes by Upcycling of Waste Polyethylene over Controlled Acid Sites of SO4/ZrO2‐Al2O3 Catalyst

Branched alkanes, which enhance the octane number of gasoline, can be produced from waste polyethylene. However, achieving highly selective production of branched alkanes presents a significant challenge in the upcycling of waste polyethylene, and the maximum selectivity for branched alkanes reported up to date is about 70%. Here, we report a one‐pot process to convert polyethylene into gasoline‐range hydrocarbons (C4‐C13) with yield of 73.3% over SO42‐ZrO2‐Al2O3 catalyst at 280 °C. The proportion of branched alkanes reaches 90.1% within the C4‐C13 fraction. Incorporation of sulfate group endows the catalyst with strong Lewis acid sites and weak and moderate Brønsted acid sites. In situ X‐ray absorption, in situ infrared spectroscopy, in situ small angle neutron scattering, and DFT calculations reveal that polyethylene activation occurs through the synergy between sulfate groups and strong Lewis acid sites (Zr sites). The weak and moderate Brønsted acid sites preferentially catalyze the isomerization and type A β‐scission processes, which favors the formation of branched alkanes, while suppressing competing reactions that produce straight‐chain alkanes.

Pre-existing mobile Zn2+ ions in ZnZr4(PO4)6 for capacitive- and battery- type energy storage systems

Zinc-ion based energy storage systems with a pure intrinsic Zn2+ ion conductor, ZnZr4(PO4)6 (ZnZrP), and consisting of variable valence Zr sites, are fabricated for the first time. Zn2+ ions are loosely held within the voids of the Zr-phosphate framework enabling ionic conduction in the solid matrix. By combining with activated carbon (AC), the resulting ZnZrP-AC composite exhibits a high mixed ionic-electronic conductivity of 1.25 mS cm−1. Benefitting from the high conductivity, fast charge transfer and transport across the ZnZrP-AC cross-section are enabled through short diffusion pathways in the resulting hybrid supercapacitor (HSC) or Zn-ion battery (ZIB). The HSC (ZnZrP-AC/ZnCl2-γ-butyrolactone/Zn-AC) delivers a specific capacitance of 275F g−1, energy and power density maxima of 153 Wh kg−1 and 7.2 kW kg−1 and a cycling life of 10,000 cycles, with 87.2 % capacitance retention. In the ZIB configuration of ZnZrP-AC/Zn(CF3SO3)2-acetonitrile/Zn-AC, a capacity of 136 mAh/g (at 50 mA g−1), with capacity retention of 95 % after 100 cycles is achieved, with a mixed diffusive and surface-confined fast charge storage mechanism. The active materials remain largely intact after cycling confirming the durability of the cell architecture with potential for scale-up and practical applications.

CO2 Fixation via epoxide cycloaddition with a highly active and stable MOF-808/GO composite catalyst

The CO2 cycloaddition reaction effectively mitigates the greenhouse effect while producing high-value cyclic carbonates. Metal-organic frameworks (MOFs) have shown promise for CO2 cycloaddition with epoxides; however, the aggregation of MOFs due to high surface energy hinders mass transfer and catalytic performance. By pre-coordinating graphene oxide (GO) to regulate the dispersion of MOF-808, the resulting MOF-808/GO-100 composite catalyst exhibits twice the activity of pristine MOF-808, achieving 92.6% conversion of epichlorohydrin (ECH) with 98.2% selectivity to ECH carbonate without adding any co-catalysts. The incorporation of GO introduces numerous hydroxyl groups on the catalyst surface, serving as hydrogen bonding donors. The oxygen-containing groups on GO can compete with ligands for Zr coordination, generating defective Zr sites. The synergistic effect between defective Zr sites and hydrogen bonding donors collectively promotes epoxide opening. Notably, GO correspondingly enhances the dispersion of MOF-808 and induces mesopore formation through its stacking effect at the interface with MOF-808. Across various epoxide cycloaddition reactions, MOF-808/GO-100 consistently demonstrated optimal performance and maintained high stability over multiple reaction cycles.

Regulating zeolite acid-base sites for selective hydrogenation of 5-hydroxymethylfurfural

The hydrogenation of biomass-derived 5-hydroxymethylfurfural (HMF) to the value-added chemicals plays a vital role in the development of renewable resources, while the precisely chemical regulation of products selectivity remains a great challenge. Herein, Zr-Beta based catalysts were fabricated with the controllable acid-base sites for the selective hydrogenation of HMF. Importantly, the products selectivity could be facilely switched over Zr-Beta based catalysts: 100 % of 2,5-bis(isopropoxymethyl)furan (BPMF) selectivity was acquired over Zr-Beta, whereas 99.4 % of 2,5-bis(hydroxymethyl)furan (BHMF) selectivity was achieved over K-Zr-Beta. The characterization analysis revealed that more Lewis acid sites in Zr-Beta facilitated Meerwein-Ponndorf-Verley (MPV) reduction of HMF and the further etherification of BHMF to acquire BPMF. However, the incorporation of K+ into Zr-Beta could exchange with silanol protons and Zr(IV) sites, which resulted in the decrease of Lewis acid amount accompanied with the generation of base sites. Notably, the regulated acid and base sites in K-Zr-Beta catalyst synergistically acted in the selective hydrogenation of HMF to BHMF. This work provides a feasible strategy for adjusting selectivity of HMF hydrogenation products by tuning the catalysts acid-base sites.

Simultaneous construction of Zr-β zeolite with high content and high accessibility of framework Zr sites in the conversion of ethanol to 1,3-butadiene: Mechanisms and synergistic effects

Metallosilicate zeolites, represented by Zr-β zeolite, possess unique porosity and tunable acidity, showing great potential in the conversion of ethanol to 1,3-butadiene. However, there still remains potential for further improvement of catalytic activity and stability by breaking the bottleneck framework metal site content and microporosity diffusion. In this paper, a novel Zr-β zeolite with both high content and high accessibility of framework Zr sites was successfully synthesized via the combination strategy of “Improved Decomposition Reconstruction” and “Silanization.” Based on the activity evaluation experiments of key reaction steps and in situ DRIFTS in the conversion of ethanol to 1,3-butadiene, the enhanced activity and stability are due to the synergistic effects of the content and accessibility of framework Zr sites, which both facilitate reactant conversion and inhibit the covering of active sites or the plugging of pore channels by polymerized heavy compounds. The prepared zeolite demonstrates excellent performance with a total conversion of 66 % and a 1,3-butadiene selectivity above 67 % in 100 h, along with good regenerability.

Weakening O-Intermediates Adsorption Strength Over the Pd Metallene via Lewis-Acidic Site Modulation for Enhanced Oxygen Reduction.

The reasonable design and modulation of the electronic properties of Pd metallene are acknowledged as a promising avenue for enhancing the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs), yet they remain a formidable challenge. Herein, a thin-sheet structure of Zr-doped Pd metallene (PdZr metallene) with abundant defects is proposed using a facile wet-chemical approach for efficient and highly durable ORR electrocatalysis. Multiple microstructural analyses uncover that orchestrated electronic and oxophilic regulation of PdZr metallene via Lewis-acidic Zr site modulation could concurrently optimize the electronic configuration of Pd, downshift the d-band center of Pd, and, thus, promote the intrinsic activity. Benefiting from the unique two-dimensional morphology and electronic structure optimization facilitated by the Zr coupling effect, the resultant PdZr metallene demonstrates significantly enhanced ORR electrocatalytic performance in basic solutions, with a high half-wave potential (E1/2) of 0.87 V and commendable stability for 30 000 s, surpassing those of Pd metallene and various advanced Pd-based catalysts reported in the literature. Encouragingly, the PdZr metallene-based AEMFC achieves an increased maximum power density (90.4 mW cm-2) and impressive robustness over 12 h in an alkaline environment, manifesting the practical application of PdZr metallene in AEMFCs. This study showcases the applicability of PdZr metallene via Lewis acid site regulation for fabricating highly active electrocatalysts for high-performance AEMFCs.

Advanced Numerical Modeling of BaZrS3 Chalcogenide Perovskite Cells: Titanium Alloying and Back Surface Field Effects

Chalcogenide perovskites are emerging as superior alternatives to hybrid halide perovskites for photovoltaic applications due to their non-carcinogenic composition and enhanced environmental resilience, including superior resistance to moisture. This study focuses on the computational modeling of BaZrS3 (Barium Zirconium Sulfide) based solar cells, featuring a native bandgap of ∼1.71 eV. Through precise bandgap engineering via Ti alloying at the Zr site, the study aims to optimize the bandgap to the ideal range for photovoltaic efficiency. The device architecture is further refined by adjusting parameters such as layer thickness, doping densities, trap densities and metal contacts. The optimum device efficiencies at this stage were found to be 22.45 % for BaZrS3; 23.91 % for Ba(Zr0.99Ti0.01)S3; 26.64 % for Ba(Zr0.98Ti0.02)S3; and 27.74 % for Ba(Zr0.97Ti0.03)S3. Additionally, the incorporation of various back surface fields (BSFs) (CdTe, CIGS, CZTSe, Cu2Te, FeSi2, GeSe, PbS, µc-Si, SnTe, SnS, Sn2S3, and WSe2) is investigated to enhance photo-absorption. The findings indicate that a Ti alloying concentration of 3 % at the Zr site, coupled with a Cu2Te BSF, achieves the highest efficiency, approximately 30 %. These optimized structures present a robust framework for developing efficient, stable, and non-toxic photovoltaic devices utilizing chalcogenide perovskites.

Adsorption dynamics of gaseous toluene with and without formaldehyde and water vapors on composites of UiO-66-NH2 and microporous carbon

To improve the adsorption capacity/selectivity of activated carbon (AC) against diverse volatile organic compounds (VOCs), a series of AC-based composites have been prepared with UiO-66-NH2 (U6N) and coded as AC-U6Nx (x = 1–20 wt/wt%). The adsorption potential of AC-U6Nx is evaluated against toluene in relation to the effects of composite compositions and the presence of competing feed gases/vapors (e.g., formaldehyde (FA) and water vapor). Although AC-U6N(1%) adsorbs toluene preferentially over FA, the selectivity factor of the former decreases from 6.4 to 2.63 as the x value increases from 1 to 20 wt%. This indicates the crucial role of U6N-NH2 groups in active capturing of FA over toluene through Schiff-base adsorption mechanism. Interestingly, the partition coefficient (PC100%: 0.045 ± 0.004 mol kg−1 Pa−1) of AC-U6N(1%) for 100 ppm FA remains nearly constant across varying toluene levels (1–100 ppm), suggesting the preferential occupation of active sites by FA (pore-filling). The contrasting role of relative humidity (RH) is also evidenced, as AC-U6N(1%), exhibits the highest capacity for toluene and FA under dry (0 % RH) and humid (20 % RH) conditions, respectively. The adsorption behavior of VOC on AC-U6N(1%) surface active sites (e.g., graphitic basal planes, NH2, COO–, and Zr sites) is predictable with a good fit of experimental data to the Freundlich isotherm and pseudo-second-order (PSOM) kinetic models. A density functional theory (DFT) simulation supports the enhancement of toluene adsorption on the interface of AC and U6N-based systems. Overall, this work offers practical guidelines for the construction of advanced functional adsorbents against diverse VOCs under both competitive and non-competitive conditions.

Brightening dark excitons in inorganic halide perovskites by local symmetry breaking

Thermally activated delayed fluorescence (TADF) phenomenon, defined as thermal activation of triplet dark-state excitons into singlet state excitons through reverse intersystem crossing (RISC), has become a prevalent principle for designing organic-based electro-/photo-luminescent molecules. However, activating dark excitons in inorganic metal halide perovskites (MHPs) still remains challenging. Herein, we report an efficient strategy of doping-induced local symmetry breaking to brighten dark excitons in inorganic halide perovskite Cs2ZrCl6, which result in a 500 % enhancement of low-temperature luminescence emission. Lattice symmetry breaking confirmed by the X-ray absorption spectroscopy measurements could disturb the local coordination environment at the Zr site. The singlet-triplet energy gap (ΔEST) fitted from temperature-dependent photoluminescence decay curves decreases from 0.087 to 0.071 eV, thus reducing up-conversion barrier of dark excitons. Theoretical calculation indicates large spatial separation of charge density favorable for enhanced TADF emission. Furthermore, a flexible X-ray scintillator screen with poly (dimethylsiloxane) as the matrix could obtain high-quality X-ray imaging with a 14 lp mm−1 resolution. This work gives insights into improving photoemission of inorganic MHPs via brightening dark excitons.

Efficient control of automotive emission by Pt-based and Rh-based three-way catalysts: The critical role of phase structure of ceria-zirconia support

Rationally design efficient supports material is essential for heterogeneous catalysts with enhanced activity in many industrial catalytic processes, accordingly a clear understanding of the support effect is necessary. Herein, two ceria-zirconia materials without/with partial κ-Ce2Zr2O8(CZ/κCZ) structure were achieved and then employed as supports for Rh-based and Pt-based three-way catalysts (TWCs), respectively. According to the results of systematic characterizations, it has been manifested that the surface conditions of supports significantly affected the activity and stability of Rh-based and Pt-based catalysts. As κCZ exhibits an intrinsic Zr-rich surface with more oxygen vacancies with respect to CZ, Rh species supported on κCZ mainly occupy the Zr sites over the surface, thus exhibit a more electronic-rich and active state due to the decreased Rh-Ce interfaces, which weakened the undesirable electron transfer from Rh to Ce. As a result, κCZ delivered as an ideal support for improving the performance of Rh-based TWCs effectively. On contrary, comparing with Pt/CZ, more serious sintering of Pt nanoparticles and inferior activity as well as stability have been detected in Pt/κCZ due to the decreased Pt-Ce interfaces, which weakened the anchor effects of the support through Pt-O-Ce bonds. This finding enhances the understanding of support effects for the development of advanced TWCs.

Design and preparation of a sensitive electrochemical aptasensor based on hierarchical porous UiO-66 for detecting ampicillin

Hierarchical porous UiO-66 (HP-UiO-66) was rationally prepared using sodium acetate and polyvinylpyrrolidone as auxiliaries. The defective structure of HP-UiO-66 was confirmed by various characterization methods. Compared with the pristine UiO-66, HP-UiO-66 possessed more accessible Zr sites to load aptamers. The electrochemical aptasensor based on HP-UiO-66 was used to detect ampicillin (AMP) as an analytical model with a low limit of detection (3.0 fg mL−1) by differential pulse voltammetry. This fabricated aptasensor exhibited good reproducibility, stability, and specificity toward AMP. The sensor could be used to quantitatively detect AMP even in real samples (tap water and milk).

Porous Frustrated Lewis Pairs Catalyst Constructed on Defective Zirconium-Based Metal-Organic Frameworks for Hydrogenation Reactions with H2.

A porous metal-organic framework (MOF)-based frustrated Lewis pairs (FLPs) were prepared via a ligand replacement strategy to generate organic linker defects in zirconium-based MOF (MOF-808), thereby exposing Zr sites as Lewis acid. Due to the rigid features of the MOF skeleton, the unsaturated metal cluster and the adjacent lattice oxygen (Lewis bases) are in sterically hindered positions, which formed FLP sites with efficient H2 activation ability. This porous heterogeneous FLP catalyst [MOF-808-OH (15%)] exhibits high performance styrene hydrogenation to ethylbenzene with 99% yield. The high structural stability and reusability enabled the catalyst to maintain an over 98% activity after five cycles. This work provides a defect modulation strategy to prepare MOF-based solid FLP catalysts.

Formation Mechanism of Eutectic Microstructure for Ca(Zr,Hf)O3/(Zr,Hf)O2 by Rapid Solidification Process at High Temperature

Abstract: Ca(Zr1-x,Hfx)O3/(Zr1-xHfx)O2 (x=0, 1/3, 0.5) eutectic film was prepared by rapid solidification process using high power laser irradiation method. The coating process was performed in an electric furnace at 1300°C. Solidified film with fine lamellar structure were obtained. When the Zr site was substituted with Hf, the lamellar spacing increased with the amount of the substitution. Separate from the solidification film prepared by laser irradiation, rapidly solidifying sample with x=0.1 composition was prepared using optical floating zone apparatus. The melt of the sample was free-fallen onto a copper dish. No film-like rapidly solidified sample was obtained. Hf ion was homogeneously solid-soluble in both phases of CaZrO3 and phase ZrO2.

Peri-Implant Microbial Signature Shifts in Titanium, Zirconia and Ceria-Stabilized Zirconia Reinforced with Alumina Sites Subjected to Experimental Peri-Implantitis: A Preclinical Study in Dogs.

This study evaluates the dynamic shift in the microbiota at the peri-implant site of titanium (Ti) and zirconia (Zr) implants subjected to experimental peri-implantitis (PI) and, for the first time, of implants made of ceria-stabilized alumina-reinforced zirconia (Ce-TZP/Al), a revolutionary zirconia that is set to play a key role in modern implant dentistry. One- and two-piece (TP) implants, including Ce-TZP/AL TP/G3 glass, were placed bilaterally (six implants/side) in five beagle dogs to mimic a natural vs. ligature-induced PI following a split-mouth design. The experiment spanned 30 weeks from tooth extraction. Both PI models promoted plaque deposition at peri-implant sites. Comparatively, the PI induced by ligatures favored the deposition of anaerobes (p = 0.047 vs. natural). Regardless of the model, the plaque deposition pattern was entirely dependent on the implanted material. Ligated Ti and Zr implant sites accumulated up to 2.14 log CFU/mL unit anaerobic load (p ≤ 0.033 vs. non-ligated implant sites), predominantly comprising obligate anaerobes. Naturally occurring PI induced the deposition of co-occurring networks of obligate anaerobes and less oxygen-dependent bacteria. PI induction favored the enrichment of Ti and Zr sites with bacterial taxa belonging to the orange and red complexes (up to 28% increase naturally and up to 71% in the ligated hemiarch). Anaerobic deposition was significantly lower in ligated Ce-TZP/Al implant sites (p ≤ 0.014 vs. TI and Zr) and independent of the induction model (0.63-1 log units of increase). Facultative bacteria prevailed at Ce-TZP/AL sites. The abundance was lower in the Ce-TZP/AL TP implant. Unlike Ti and Zr sites, taxa from the orange and red complexes were negligible. Biofilms configured at the Ti and Zr sites after ligation-induced PI resemble those found in severe IP. We hypothesize that, although surface properties (surface energy and surface roughness) and physicochemical properties of the substrate play an important role in bacterial adhesion and subsequent plaque formation, Ce-TZP/Al modulates several biological activities that preserve the integrity of the gingival seal by limiting PI progression. In conclusion, biofilm progression differs in peri-implant sites according to the specific properties of the material. Ce-TZP/A, unlike titanium or zirconia, prevents dysbiosis in sites subjected to experimental PI and preserves the microbial signature of emergent obligate anaerobes related to PI development.

The isomerization of glucose to fructose in ethanol over ZrO2 on mesoporous silica prepared through in-situ and post-impregnation methods

Fructose is a vital ketose in the production of 5-hydroxymethylfurfural platform molecules. Herein, Zr-doped hexagonal mesoporous silica was prepared over in situ co-assembly (Zr-x-HMS, x is the mole ratio of Si to Zr, x = 20, 50) and post-impregnation (Zr-Imx-HMS, x = 20, 50, 100) processes to regulate its catalytic performance against the isomerization of glucose to fructose in ethanol. The post-impregnation process did not significantly change the original pore structure and morphology of HMS, Zr-Im50-HMS with medium Zr loading possessed the most Lewis acid sites with medium strength among Zr-Imx-HMS catalysts. The in situ process changed the physical properties of HMS and enhanced the interaction of Zr sites and silica framework, facilitating the formation of Lewis acid sites with medium strength. Zr-Im50-HMS possessed the most suitable acidity for fructose production, and an optimal yield of 31.2% was achieved at 160 °C and 20 min. Moreover, the recyclability of Zr-Im50-HMS was acceptable.

Zeolite-catalyzed one-pot sucrose-to-HMF transformation: Ge outperforms Sn, Zr, and Al sites

The conversion of renewable compounds to versatile platform molecules over environmentally friendly heterogeneous catalysts is a major challenge. Zeolites stand as active, selective, and reusable solid catalysts for various acid-catalyzed reactions involved in the one-pot cascade transformation of polysaccharides to 5-hydroxymethylfurfural (HMF), a platform molecule opening the way to various valuable chemicals. However, the acidity-performance relationships of zeolite catalysts in HMF synthesis have not been fully elucidated. Here, we have addressed the effect of acid site nature in zeolite catalysts for sucrose-to-HMF transformation by comparing the performance of conventional Al-substituted IWW zeolite with that of Sn-, Zr-, and Ge-containing zeolite catalysts of the same structure. Ge-associated acid sites were found to exhibit superior HMF selectivity compared to Sn, Zr, and Al acid centers, while experiencing evolution into Brønsted acid centers during the catalytic run. The conversion of sucrose over germanosilicate zeolites enhances with increasing catalyst pore diameter or decreasing crystal size. Specifically, the extra-large pore Ge-UTL catalyst, featuring intersecting 14- and 12-ring pores (crystal size 10 × 20 × <1 μm), and large-pore Ge-IWW with 12-, 10- and 8-ring pores (crystal sizes of 1 μm) showed a yield of targeted HMF comparable to or even exceeding the values previously reported for homogeneous or heterogeneous catalysis (54 % after 3 h at 120 °C). Ge-IWW catalyst demonstrated reusability across a minimum of 3 catalytic runs, while in situ structural transformation precluded stable performance of Ge-UTL catalyst in the repetitive catalytic cycles. The results of this study highlight zeolites with uncharacteristic chemical compositions as active, selective, and reusable catalysts for highly demanding applications in biomass valorization.

Temperature dependent conductivity, dielectric relaxation, electrical modulus and impedance spectroscopy of Ni substituted Na[formula omitted]Zr[formula omitted]Ni[formula omitted]Si[formula omitted]PO[formula omitted]

We investigate the structural, dielectric relaxation, electric modulus and impedance behavior of Ni-doped NASICON ceramic Na3+2xZr2−xNixSi2PO12 (x=0.05–0.2) prepared using the solid-state reaction method. The increase in dielectric constant with temperature and decrease with frequency is explained on the basis of space charge polarization using the two-layer model of Maxwell–Wagner relaxation. The dielectric loss peak at lower temperatures follows the Arrhenius-type behavior with frequency having activation energy of 0.27 ± 0.01 eV of dipolar relaxation, suggests similar type of defects are responsible for all the doped samples. The real (ϵ′) and imaginary (ϵ′′) permittivity variation with frequency shows the broad relaxation behavior indicates the non-Debye type of relaxation in the measured temperature range. The permittivity values decrease with the amount of doping due to the increased number of charge carriers upon Ni doping at the Zr site. The impedance variation with frequency at various temperatures shows two types of relaxation for all the samples correspond to grain and grain boundary contribution in total impedance. The grain contributions are observed at higher frequencies, while grain-boundary contributions occur at the lower side of frequencies. The imaginary part of the electric modulus also shows two types of relaxation peaks for all the samples indicating similar activation energy at low temperatures and variable activation energy at higher temperatures. The fitting of the imaginary modulus using KWW function shows the non-Debye type of relaxation. We find that all modulus curves merge with each other at low temperatures showing a similar type of relaxation, while curves at high temperatures show the dispersed behavior above the peak frequency. The a.c. conductivity data are fitted using the double power law confirming the grain and grain boundary contributions in total conductivity. The double power law exponent variation with temperature shows the small polaron hopping conduction over the measured temperature range for all the doped samples.

Preparation and electrochemical properties of Li6La3Zr0.7Ti0.3Ta0.5Sb0.5O12 high-entropy Li-garnet solid electrolyte

Garnet-type solid electrolytes stand out as promising Li-ion conductors for the next-generation batteries. It has been demonstrated that the inherent properties of garnets can be tailored by introducing various dopants into their crystal structures. Recently, there has been a growing interest in the concept of high entropy stabilization for materials design. In this study, we synthesized high-entropy garnets denoted as Li6La3Zr0.7Ti0.3Ta0.5Sb0.5O12 (LLZTTSO), wherein Ti, Sb, and Ta occupy the Zr site. The formation of the cubic garnet phase in LLZTTSO was confirmed through X-ray diffraction (XRD), and the resulting lattice parameter agreed with predictions made using computational methods. Despite the substantial porosity (relative density 80.6%) attributed to the low sintering temperature, LLZTTSO exhibits a bulk ionic conductivity of 0.099 mS cm−1 at 25°C, and a total ionic conductivity of 0.088 mS cm−1, accompanied by an activation energy of 0.497 eV. Furthermore, LLZTTSO demonstrates a critical current density of 0.275 mA cm−2 at 25°C, showcasing its potential even without any interfacial modification.