Electrical Conductivity Measurements Research Articles

Effect of irradiation on Co0.72Sr0.07Ni0.21Fe2O4 ferrite nanoparticles and their catalytic efficiency in water treatment

This study investigates the magnetic, thermal, and electrical properties of Co0.72Sr0.07Ni0.21Fe2O4 ferrite nanoparticles under different conditions, including as-prepared, irradiated (at a dose of 100 kGy in CO2 atmosphere), and aged (at 1000°C). The magnetic properties are analyzed using M-H loops, revealing that the aged sample exhibits the highest magnetization values. The observed decrease in magnetization after irradiation and increase after aging is consistent due to the presence of a new phase (γ-FeOOH) in the irradiated sample that XRD confirms. Electrical conductivity measurements demonstrate that the aging sample exhibits the highest electrical conductivity due to increased grain boundaries, while the irradiated sample shows increased conductivity attributed to oxygen vacancies. As well as the nanocomposite of PVP and Co0.72Sr0.07Ni0.21Fe2O4 nanoparticles aged (at 1000°C) is found to be effective in degrading the Toluidine Blue (TB) dye through catalytic oxidation and photodegradation mechanisms. The catalytic degradation of TB dye provides valuable insights into the potential application of these ferrite nanoparticles in environmental remediation and wastewater treatment. Also, nanocomposite demonstrated significant antimicrobial activity against five pathogenic bacterial strains commonly found in contaminated water, with superior effectiveness against Gram-negative bacteria, particularly Salmonella enterica and Pseudomonas aeruginosa, suggesting its potential as an effective water treatment agent. The novelty and the aims are to analyze the changes in magnetization and conductivity of the nanoparticles under different conditions, including as-prepared, irradiated, and aged samples. Additionally, the catalytic efficiency of the aged nanoparticles in degrading Toluidine Blue (TB) dye is examined, providing insights into their potential application in environmental remediation and wastewater treatment.

Additive Manufacturing and Precipitation Hardening of Low-Alloyed Copper Alloys Containing Chromium and Hafnium

Copper alloys with chromium and hafnium offer the possibility of precipitation hardening and combine enhanced strength with high electrical and thermal conductivities. The production process, which starts with raw materials, involves powder production by gas atomization and leads to additive manufacturing by laser powder bed fusion with different parameter sets. The aim is to utilize precipitation reactions afterwards in CuHf0.7Cr0.35 during temperature exposure for further property optimization. This research focuses on the low-alloyed copper alloy with hafnium and chromium, compares this with conventionally manufactured specimens, and relates the alloy to additively manufactured specimens of other benchmark alloys such as CuCr1Zr. Measurements of hardness and electrical conductivity are accompanied by metallographic investigations to understand the behavior of CuHf0.7Cr0.35 manufactured by generative methods. In the as-built condition, melting traces remain visible in the microstructure, and hardness values of 101 HV and an electrical conductivity of 17.5 MS/m are reached. Solution annealing completely recrystallizes the microstructure, and the following quenching holds further alloying elements in supersaturated solid solution, resulting in 73 HV and 16.5 MS/m. Subsequent target-oriented precipitation reactions enable peak values of about 190 HV and 42 MS/m. Future research will assess mechanical and physical properties at elevated temperatures and evaluate possible applications.

Cooperative Use of N-Heterocyclic Carbenes and Thiols on a Silver Surface: A Synergetic Approach to Surface Modification.

Surface modification through the formation of a self-assembled monolayer (SAM) can effectively engineer the physicochemical properties of the surface/material. However, the precise design of multifunctional SAMs at the molecular level is still a major challenge. Here, we jointly use N-heterocyclic carbenes (NHCs) and thiols to form multifunctional hetero-SAM systems that demonstrate excellent chemical stability, electrical conductivity, and, in silico, catalytic activity. This synergistic effect is facilitated by the high surface mobility and electron-rich nature of NHCs, combined with the strong binding strength of thiols. Scanning tunneling microscopy, electrical conductivity, and scanning electron microscope measurements, as well as density functional theory calculations, were employed to explore the synergistic interactions in the supramolecular SAMs. The van der Waals integration of ballbot-type NHCs and thiols enables the SAMs to exhibit both superior surface anticorrosion properties (attributing to the shift in the d-band center) and low surface resistance originating from the band alignment. Moreover, we find that the deposition sequence of flat-lying NHCs and thiols results in SAMs with different configurations, which can further tune the mechanistic pathway in silico in the acetylene hydrogenation process. Our results provide essential molecular insights into the local electronic control of the new SAM/metal interface and the high stability of the emergent multifunctionality (NHC/thiol)-SAMs forming self-assembled lamellae structures in the nanometer regime.

Optimizing the structural, optical, dielectric, and electrical properties of polyvinyl alcohol/polyvinyl pyrrolidone/zinc manganite nanocomposites for optical and energy storage applications

This study investigates the structural, dielectric, optical, and electrical properties of eco-friendly polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) matrices embedded with zinc manganite nanoparticles (ZnMn2O4NPs). The nanocomposites films were prepared using a casting method for potential applications in flexible electrochemical devices. FTIR spectroscopy confirmed the successful incorporation of ZnMn2O4NPs into the polymeric matrix. UV–Vis absorption analysis revealed an increase in absorbance with increasing ZnMn2O4 nanoparticle content. Among the various blend nanocomposites, the lowest bandgap energy was observed for the sample containing 2.5 %ZnMn2O4 NPs. Measurements of electrical conductivity, dielectric characteristics, and complex impedance were made for all prepared films. The findings showed that as frequency and nanofiller concentration increased, so did AC conductivity and dielectric characteristics. Overall, the PVA/PVP-2.5 % ZnMn2O4 nanocomposite exhibited superior properties compared to the pure polymer blend. This sample demonstrated optimal electrical conductivity and dielectric constant. These findings suggest that by carefully adjusting the ZnMn2O4 concentration, it is possible to fine-tune the dielectric, optical, and electrical properties of these nanocomposite films. This versatility offers promising potential for applications in optoelectronic devices, energy storage devices, and nanodielectric materials.

Evaluation of Different Blending Methods to Obtain Copper Composites with Graphene Oxide

This study evaluated mixing methods for producing graphene oxide-reinforced copper matrix composites aiming for a better dispersion of graphene oxide in the composite, using powder metallurgy techniques. The compacted specimens were prepared by four different mixing processes that employed either a mechanical stirrer, rotary evaporator, tip ultrasound, or ultrasound process followed by mechanical stirring. Characterizations were performed using optical microscopy, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, compression tests, Vickers microhardness, and electrical conductivity measurements. The results indicate that the combined method yields a more homogeneous microstructure and superior mechanical properties, while electrical conductivity was maintained at a level higher than that achieved by the other methods.

Recovery and Size-Tuning of Amorphous Silica from Geothermal Scales in Batangas, Philippines

Scale deposits in geothermal power plants are well-known potential sources of minerals. Extensive research in mineral recovery is crucial due to the considerable variability in scale composition and geochemistry based on location. Geothermal scales from Batangas, Philippines, were used to synthesize size-modified amorphous silica (SiO2) via sol-gel method. Initial analyses employing x-ray fluorescence spectroscopy (XRF), total dissolved solids (TDS), electrical conductivity (EC), and pH measurements confirmed that the scale is rich in silica and salts at neutral pH. Then, the effect of varying scale concentration, precipitation pH, and aging time on the particle size distribution of recovered amorphous silica were investigated. Dynamic light scattering (DLS) for particle size analysis (PSA) revealed that the sample with 2.5% (w/v) scale precursor in NaOH and precipitated until pH 10 had the lowest average cumulant diameter (1.66 μm). Moreover, the synergy of precipitation pH and aging time was found to significantly affect the polydispersity index and cumulative diameter of precipitated SiO2 based on 23 factorial ANOVA at 0.05 significance level. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) confirmed that the precipitates were amorphous SiO2 with spherical morphology. This study proves the viability of utilizing geothermal scales from Batangas, Philippines for the synthesis of amorphous SiO2 with controlled particle size, which is a potential filler for composite materials.

Improved Pyroelectric Nanogenerator Performance of P(VDF-TrFE)/rGO Thin Film by Optimized rGO Reduction.

The pyroelectric nanogenerator (PyNG) has gained increasing attention due to its capability of converting ambient or waste thermal energy into electrical energy. In recent years, nanocomposite films of poly(vinylidene fluoride-co-trifluoro ethylene) (P(VDF-TrFE)) and nanofillers such as reduced graphene oxide (rGO) have been employed due to their high flexibility, good dielectric properties, and high charge mobility for the application of wearable devices. This work investigated the effect of rGO reduction on pyroelectric nanogenerator performance. To prepare rGO, GO was reduced with different reducing agents at various conditions. The resulting rGO samples were characterized by XPS, FT-IR, XRD, and electrical conductivity measurements to obtain quantitative and qualitative information on the change in surface functionalities. Molecularly thin nanocomposite films of P(VDF-TrFE)/rGO were deposited on an ITO-glass substrate by the Langmuir-Schaefer (LS) technique. A PyNG sandwich-like structure was fabricated by arranging the thin films facing each other, and it was subjected to the pyroelectric current test. For various PyNGs of the thin films containing rGO prepared by different methods, the average pyroelectric peak-to-peak current (APC) and the pyroelectric coefficient (p) values were measured. It was found that a more reduced rGO resulted in higher electrical conductivity, and the thin films containing rGO of higher conductivity yielded higher APC and p values and, thus, better energy-harvesting performance. However, the thin films having rGO of too high conductivity produced slightly reduced performance. The Maxwell-Wagner effect in the two-phase system successfully explained these optimization results. In addition, the APC and p values for the thin film with the best performance increased with increasing temperature range. The current PyNG's performance with an energy density of 3.85 mW/cm2 and a p value of 334 μC/(m2∙K) for ΔT = 20 °C was found to be superior to that reported in other studies in the literature. Since the present PyNG showed excellent performance, it is expected to be promising for the application to microelectronics including wearable devices.

DES/O microemulsion for solubilizing and delivering curcumin via the nasal administration to treat acute asthma

As a natural small molecule drug derived from turmeric, curcumin is known for its good biosafety and a range of beneficial effects, including anti-inflammatory, anti-spasmodic, antioxidant, antibacterial, anti-tumor, and neuroprotective effects. Even though, its insolubility in water and instability severely limit its bioavailability and clinical applications. The present study developed a deep eutectic solvent (DES) in oil microemulsion (DES/O-ME) system loaded with Cur for intranasal administration, aiming to enhance both the solubility and permeability of Cur to significantly increase its bioavailability. The project first constructed and screened the optimal choline chloride-based DES. Subsequently, the DES/O-ME system was prepared and optimized to achieve uniform particle size and stability using a pseudo-ternary phase diagram and electrical conductivity measurements. The resulting DES/O-ME system was thoroughly evaluated for its solubilization efficacy, permeability, mucosal cytotoxicity, and stability. Additionally, the therapeutic efficacy of the Cur-DES/O-ME was assessed in vivo using a murine model of allergic asthma. This comprehensive evaluation highlights the potential of the DES/O-ME system as a promising intranasal drug delivery platform to overcome the limitations of curcumin’s bioavailability and clinical application.

КІНЕТИКА ВЗАЄМОДІЇ КАЛІЙСУПЕРОКСИДУ З 18-КРАУН-6

The dissolution processes of KO2 in the presence of 18-crown-6 in dimethylsulfoxide (DMSO) were studied, and the properties of the complexes formed were compared with the properties of complexes with KCl, KBr, KI, and KOH (in the general case, KX). Using the electrical conductivity measurement method, the change in the electrical conductivity of the КО2 -18-crown-6 - solvent, КOH - 18-crown-6 - solvent and KBr - 18-crown-6 - solvent systems during the formation of the corresponding ions during the interaction of the crown ether with КХ was studied in solid form. Complex formation in the systems KO2-18-crown-6-solvent, KOH-18-crown-6-solvent and KBr-18-crown-6-solvent in dimethyl sulfoxide was studied. It is shown that the dependences of the specific electrical conductivity of the solution on time during the interaction of KO2, KOH and KBr c 18-crown-6 in DMSO are typical kinetic curves with asymptotes. The limiting stage is the interaction of the dissolved reagent with the surface of the solid substance. Possible kinetic mechanisms of the process were analyzed. It is shown that the change in electrical conductivity over time under these conditions is described by an exponential equation. The coefficients of this equation are determined for different systems. It is proved that the value of the parameter that characterizes the content of ions at t®¥ depends on the concentration of each of the reactants and is determined by the concentration of the one of them that is present in the mixture in the smallest amount. The resulting kinetic equations make it possible to estimate the time required to reach equilibrium. It is shown that the time to reach the asymptotic values ​​depends on the nature of the anion. The dependence of the electrical conductivity of solutions of salts and KOH in the presence of 18-crown-6 in the equilibrium state on the concentration of the components was established. It has been proved that the kinetics of the formation of the crown ether - salt complex dissociated into ions is described by an exponential equation, the parameters of which depend on the concentration of the component taken in shortage and the nature of the anion. The dependence of electrical conductivity on the composition of binary mixtures KBr - KO2, KCl - KO2, KI - KO2 was established for the first time. The resulting kinetic equations make it possible to estimate the time required to reach equilibrium. It is shown that the equilibrium solutions retain their properties for 150 hours and can be further used to study reactions involving active oxygen.

Comprehensive evaluation of TiO2 nanofluid stability: Insights from pH, EC measurements, and UV-Vis spectroscopy

This study delves into assessing the stability of different nanofluids containing TiO2 nanoparticles, employing either ethylene glycol (EG) or water as the base fluid. The results obtained will be applied to photovoltaic panels in future work, in particular to solve the cooling problems facing these systems, in order to improve their efficiency and durability. The nanoparticles, approximately 75 nm in size as determined by the Debye-Scherrer equation and X-ray diffraction (XRD), were utilized to formulate nanofluids at concentrations of 0.1 %, 0.3 %, and 0.5 % using a two-step method. To gauge the stability of these prepared nanofluids, practical investigations were conducted involving pH and electrical conductivity (EC) measurements, along with UV-Vis spectroscopy spanning the wavelength range of 200–800 nm. The findings reveal that nanofluids with 0.1 % and 0.5 % TiO2 in water demonstrated promising stability. Moreover, the absorbance levels of nanofluids containing 0.1 %, 0.3 %, and 0.5 % TiO2 in EG, as well as 0.3 % TiO2 in water, decreased with increasing settling time, as observed through UV-Vis spectroscopy analysis, consistent with prior research. Additionally, the study of pH and EC stability for 0.5 % TiO2 in water indicated satisfactory results.

High temperature thermoelectric properties of BaxSr2−xFeCoO6 double perovskites

Abstract In this study, environmentally benign BaxSr2-xFeCoO6 (BSFC) double perovskites are synthesized via solid-state reaction route for high-temperature thermoelectric applications. The crystal structure and morphology of the ceramic samples are analyzed using XRD and SEM, respectively. Rietveld refinement of XRD data confirms a cubic structure with Pm3̅m space-group. High-temperature thermoelectric measurements exhibits that substituting Ba for Sr in Sr2FeCoO6 increases the Seebeck coefficient (S) but at the expense of the electrical conductivity (σ). The highest Seebeck coefficient of 117 μV/K has been observed in Ba0.5Sr1.5FeCoO6 at 910 K. Temperature-dependent electrical conductivity measurements indicates a semiconductor-to-metal like transition in all samples, with BSFC (x = 0.1) achieving the highest conductivity of 4 × 104 S m−1 at ∼623 K. The thermoelectric power factor has been enhanced by over 50% with Ba substitution in Sr2FeCoO6. Electron transport in these double perovskites is found to follow the small polaron hopping conduction mechanism.

Preparation and Electrical Properties of Nanocomposite Based on Epoxy Resin and Core-Shell Polyaniline/Multi-Walled Carbon Nanotubes

Nanocomposites of epoxy resin containing various concentrations of carboxylated multiwalled carbon nanotubes (C-MWCNTs) and surface modified C-MWCNTs various concentration of both C-MWCNTs and core-shell nanoparticles were prepared. The physical, mechanical and electrical properties of prepared epoxy nanocomposites were investigated using experimental evaluations such as dynamic mechanical thermal analysis (DMTA), differential scanning calorimeter (DSC), and tensile strength measurements. The results of DSC tests revealed that the introduction of nanoparticles into the epoxy resin did not have much effect on the curing system, and by adding these nanoparticles to the epoxy resin, there is no need to change the curing system. However, the released energy during of epoxy curing show a 24% increase with the introduction of nanofiller into the epoxy matrix. The results of electrical conductivity measurements indicated a higher elastic dielectric constant for nanocomposites up to 200% incomparison with neat epoxy resin. The use of these epoxy nanocomposites in modern electrical and electro-optical industries is of great practical importance.

Sustainable biomass derived natural surfactant of soybean seeds in fly ash industrial waste utilization for carbon storage: Evaluation of environmental impact

The rising carbon emissions challenge global environmental sustainability and climate stability. This study aims to advance climate change mitigation by integrating fly ash and natural surfactant into CO2 sequestration strategies. Fly ash, a by-product of industrial processes, presents an opportunity for innovative reuse. By combining fly ash with a natural surfactant extracted from soybean seeds, both industrial waste management and greenhouse gas reduction can be addressed. The surfactant was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, surface tension, and electrical conductivity measurements, confirming saponin presence with a critical micelle concentration of 0.3 wt%. Pressure decay studies revealed that a (5 wt% fly ash + NS) demonstrated the highest CO2 absorption, supported by microscopic analysis. Further research on optimizing reaction conditions and kinetics of mineralization could enhance this method’s efficiency and scalability for broader application.

An increase of the oncogenesis frequency is associated with the DAMPs accumulation and the killer cell subpopulations ratio change in patients with long-term post-COVID-19 syndrome

In patients with malignant lesions of the lungs and pancreas, the development of which was facilitated by the long-term post-COVID-19 syndrome (PCS), presence a significant increase (on average by 80%) in the serum content of the cytotoxic oligonucleotide fraction DAMP was found. High antigenic load due to the increase of DAMP contributed to the absorptive function growth and insufficient digestive function of neutrophils; decrease in the NADPH-catalase activity reserve in oxygen-dependent phagocytosis. An increase of CD16+ NK cells of innate immunity and an overexpression of CD8+ killer/suppressor T lymphocyte receptors of adaptive immunity in response to the suppressor coreceptors competitive action were revealed. These changes in cellular immunity were more pronounced in patients with malignant lung lesions and correlated with low serum conductivity. To predict the individual course of the disease, it is advisable to carry out screening measurements of electrical conductivity of blood serum and to determine the control points of innate and adaptive immunity changes in patients with comorbid pathology: PCS and an oncological process. In further studies, attention should be paid to the algorithm development of immunological and screening tests for the oncological diseases course prognosis and the treatment tactics effectiveness.

Effect of solvent and temperature on the micellization and thermophysical properties of cetyltrimethylammonium bromide

The Micellization is the fundamental phenomenon in colloid and surface chemistry which plays a pivotal role in a multitude of industrial processes, biological systems, and everyday applications. In this study, we investigate the micellization behavior of the cationic surfactant, cetyltrimethylammonium bromide (CTAB) within aqueous and ethanol–water mixtures across a temperature range. The electrical conductivity measurements unveil insights into the critical micelle concentration (CMC) and the degree of counterion dissociation (β) at each temperature. Notably, as ethanol content increases in the solvent, both CMC and β values exhibit a corresponding uptick. These findings enable the assessment of standard Gibbs free energy (ΔGmic0). Furthermore, our investigation extends to find out the thermophysical properties (viz., density, dynamic viscosity, and kinematic viscosity) assessments across varying ethanol compositions and temperatures. These metrics facilitate the calculation of activation energy for mixed systems. The implications of these results (data) could be useful for both the fundamental as well applied research, and promise valuable insights for future endeavors.

Advanced Nuclear Magnetic Resonance, Fourier Transform–Infrared, Visible-NearInfrared and X-ray Diffraction Methods Used for Characterization of Organo-Mineral Fertilizers Based on Biosolids

Biosolids from stabilized sludge present a high fertilization potential, due to their rich content of nutrients and organic matter. The intrinsic and subtle properties of such fertilizers may greatly influence the fertilization efficiency. In this sense, the utility, advantages and limitations of advanced characterization methods, for the investigation of structural and dynamic properties at the microscopic scale of slightly different formulations of fertilizers were assessed. For that, three formulas of organo-mineral fertilizers based on biosolids (V1, V2 and V3), having at least 2% N, 2% P2O5, and 2% K2O, were characterized by advanced methods, such as 1H NMR relaxometry, 1H MAS and 13C CP-MAS NMR spectroscopy, 1H double-quantum NMR and FT-IR spectroscopy. Advanced structural characterization was performed using SEM, EDX and X-ray diffraction. Four dynamical components were identified in the NMR T2 distribution showing that the rigid component has a percentage larger than 90%, which explains the broad band of NMR spectra confirmed by the distributions of many components in residual dipolar coupling as were revealed by 1H DQ-NMR measurements. SEM and EDX measurements helped the identification of components from crystalline-like X-ray diffraction patterns. To evaluate the release properties of organo-mineral fertilizers, dynamic measurements of classical electric conductivity and pH were performed by placing 0.25 g of the formulas (V1, V2 and V3) in 200 mL of distilled water. The content of N and P were quantified using specific reactants, combined with VIS-nearIR spectroscopy. Two release mechanisms were observed and characterized. It was found that V3 presents the smallest release velocity but releases the largest number of fertilizers.

Hot zone electrical resistance measurement for health monitoring of SiC and Si-based materials

SiC-based materials are good candidates for structural applications at high temperature. However, due to their limited damage tolerance, in-service health monitoring using electrical conductivity measurements would be beneficial. Still, electrical measurements in hot zones on these materials remain a major challenge and require the design of a specific contact material that ensure adhesion of the measurement wires to the material while limiting chemical reactivity with the substrate. TiSi2-Si eutectic compound was found to be a good candidate for this application. An electrical conductivity (EC) measurement was carried out up successfully to 1300 °C in vacuum on a sintered SiC sample using this contact material. Post-measurement analysis of the contact was carried out, and cracks and SiC growth were observed, but without any impact on the electrical resistance measurement.

Electrical Conductivity Measurements in Ternary SiO2–PbO–CaO Slags

Electrical Conductivity Measurements in Ternary SiO2–PbO–CaO Slags

Aliovalent Doping of Niobium and Tantalum Pentoxide as Potential Alternative Support Material for Fuel Cell Catalysts

AbstractAs the usually used Carbon Blacks (CB) as support materials in fuel cell catalysts are thermodynamically unstable, alternative supports with high chemical stability and electrical conductivity are to be found. After the investigation of Nb and Ta‐doped SnO2 in an earlier publication, which revealed interesting conductivity properties, we expanded our portfolio of mutual doping of elements of stable oxides into the oxides of the others by reporting here on the Sn, Hf and W‐doping as guests into the base oxides Nb2O5 and Ta2O5. The changes in unit cell parameters as indicators for the doping success were investigated in the doping range of x=0–10 mol % guest fraction. From a complete solubility of the guest ions in case of Hf and W‐doping in the base oxides to a limited solubility in case of Sn‐doping, a whole spectrum of different results was obtained. Additional insight came from UV/vis spectroscopic investigations in diffuse reflectance as well as electrical conductivity measurements.

Effects of lattice instability on the thermoelectric behavior of kagome metal ScV6Sn6

Kagome metal ScV6Sn6 has been a subject of interest due to the emergence of a first-order structural phase transition with intriguing charge density wave behavior below the transition temperature Tc ∼ 92 K. To explore the thermoelectric properties and provide experimental insights into the nature of the phase transition, we have carried out a combined study by means of the electrical resistivity, Seebeck coefficient, and thermal conductivity measurements on single crystalline ScV6Sn6. Pronounced features near Tc have been characterized by all measured physical quantities. In particular, the Seebeck coefficient exhibits a marked reduction as lowering temperature across Tc, attributed to an imbalance of the contribution from different type of carriers induced by the structural phase transition. From the examination of the electronic and lattice thermal conductivities, we obtained a confirmation that the observed enhancement at Tc is essentially caused by the change of the lattice thermal conductivity, demonstrating the primary importance of lattice distortions for the heat transport of ScV6Sn6. In addition, the lattice thermal conductivity above Tc was found to increase monotonically with temperature. We associated the peculiar phenomenon with lattice fluctuations, highlighting the essence of structural instability in the kagome lattice ScV6Sn6. These results add to the knowledge about the thermal transport properties in kagome materials with a hexagonal HfFe6Ge6-type structure.