Search Results (101)

For the first time, the ternary Zintl phases RbCaBi and CsCaBi have been synthesized and structurally characterized via single-crystal X-ray diffraction methods. These two compounds, alongside KCaBi, are confirmed to crystallize in a tetragonal crystal system with the space group P4/nmm (no. 129) with two formula units per cell. The lattice constants increase monotonically from a = 5.3812(10) Å and c = 8.410(3) Å for KCaBi, to a = 5.4139(7) Å and c = 8.6180(17) Å for RbCaBi, and to a = 5.4709(11) Å and c = 8.914(3) Å for CsCaBi. The crystal structure can be visualized as an array of square prisms formed of Bi atoms, which are centered by alkali metal atoms, while the Ca atoms fill tetrahedra formed of Bi atoms. There are no direct Bi–Bi interactions in the crystal structure; therefore, with full cation ordering present, the chemical bonding in the ACaBi compounds can be rationalized within the fully ionic approximation as A⁺Ca²⁺Bi³⁻ (A = K, Rb, Cs). This suggests the opening of an (narrow) energy gap between the valence and conduction bands, i.e., semiconducting behavior. Full article

Reported are the synthesis and detailed analysis of the crystal and electronic structure of the novel Zintl phase Eu₉Zn_4.5As₉. This material was identified in the densely populated Eu–Zn–As compositional space. For structure determination and for property measurements, suitable single crystals of this compound were grown from either Sn- or Pb-flux. Single-crystal X-ray diffraction methods indicate that Eu₉Zn_4.5As₉ crystallizes in the orthorhombic crystal system with the space group Pnma (a = 12.1953(7) Å, b = 4.3730(2) Å, c = 42.674(2) Å) and is formally isostructural to Ca₉Mn_4+xSb₉, the less common “9–4–9” type. The structure is heavily disordered, with multiple partially occupied sites, yet, according to the Zintl-Klemm formalism, a charge-balanced composition (Eu²⁺)₉(Zn²⁺)_4.5(As³⁻)₉ is attained. Electronic structure calculations for a model, disorder-free structure indicate no energy gap between the valence and the conduction bands and suggest (semi)metallic behavior. Preliminary susceptibility measurements confirm the expected divalent nature of Eu²⁺ ([Xe] 4f⁷ ground state). Full article

Semiconducting clathrates are a distinct class of inclusion compounds with considerable interest for thermoelectric applications. We report here the synthesis, crystal structure and thermoelectric properties of Sn₃₈Sb₈I₈. The compound was synthesized via planetary ball milling of the corresponding elements for 6 h and then sintering of amorphous mixture at 620 K for 3 days. The crystal structure of the polycrystalline product was determined via X-ray powder diffraction and Rietveld refinement as a type-I clathrate (a = 12.0390(2), space group Pm-3n, No. 223) with mixed-occupied Sn/Sb framework sites and fully occupied I guest sites. Further analysis on the chemical composition, nanomorphology and vibrational modes of the material was carried out via Induced-Coupled-Plasma–Mass Spectrometry, SEM/EDX microscopy and Raman spectroscopy, respectively. Thermoelectric measurements were performed on hot-pressed samples with ca. 98% of the crystallographic density. The clathrate compound behaves as an n-type semiconductor with a band gap of 0.737 eV and exhibits a maximum ZT of 0.0016 at 473 K. Theoretical calculations on the formation enthalpy, electron density of states and transport properties provide insights into the experimentally observed physical behavior. Full article

Anaplasma phagocytophilum causes tick-borne fever (TBF) in ruminants and is considered the most widespread tick-borne pathogen in sheep in Europe. This study aimed to determine the contribution of TBF to lamb mortality in Ireland and to identify factors associated with the risk of co-infection with A. phagocytophilum. Samples from dead lambs submitted to 3 Irish Regional Veterinary Laboratories (RVLs) in 2021 and 2022 were screened for the presence of A. phagocytophilum using real-time PCR. In total, 864 animals were sampled, of which 57 (6.6%) tested positive. The majority of the positive results originated in the northwest of the country; a region generally associated with high rainfall and a high prevalence of ticks and tick-borne infections in sheep. The most common causes of death reported in all lambs (including both TBF-positive and TBF-negative animals) were pneumonia, clostridial infection, and bacteraemia. Pneumonia accounted for 14.5% of deaths including 22.8 and 13.0% of TBF-positive and TBF-negative lambs, respectively. Bacteria from the family Pasteurellaceae were identified in 33.3 and 17.7% of TBF-positive and TBF-negative lambs, respectively. It was concluded that A. phagocytophilum is a possible concomitant infection and contributor to other infectious diseases in sheep, particularly those caused by bacteria in the Pasteurellaceae family. Understanding the prevalence and co-morbid associations of TBF is essential for improving disease surveillance and control strategies in endemic regions. Full article

The incorporation of transition metal atoms into [Ge₉] clusters is a widely studied area of Zintl-cluster chemistry. Recently, it was shown that clusters comprising single transition metal atoms in the cluster surface show catalytic properties. Here, we present a synthetic approach to four new compounds comprising silylated Ge₉ clusters with organometallic ruthenium complexes. [η⁵-Ge₉Hyp₃]RuCp* (1), [η¹-Ge₉(Si^tBu₂H)₃]RuCp(PPh₃)₂ (2), and [Hyp₃Ge₉][RuCp(PPh₃)₂(MeCN)] (3b) (Cp = cyclopentadienyl, Cp* = pentamethylcyclopentadienyl, Hyp = Si(SiMe₃)₃, Ph = C₆H₅, ^tBu = tert-butyl) were characterized by means of NMR spectroscopy and single-crystal structure determination. In the case of 2, a new isomer with an approximated C_4v symmetric monocapped square antiprism of nine Ge atoms with an unexpected ligand arrangement comprising three ditertbutylsilane ligands attached to the open square was obtained. [Hyp₃Ge₉][RuCp(PPh₃)₂] (3a) was characterized via NMR spectroscopy and LIFDI mass spectrometry. Overall, we were able to show that the steric demand of the ligands Cp vs. Cp* and hypersilylchloride vs. ditertbutylsilane strongly influence the arrangement of the atoms and ligands on the cluster. In addition, the solvent also affects the cluster, as it appears that the ruthenium atom in 3a dissociates from the cluster surface upon acetonitrile coordination to form 3b. These results show that choosing the right synthetic tools and ligands makes a big difference in the outcome of the metalation reaction. Full article

Four quaternary Zintl phase thermoelectric (TE) materials belonging to the Ba_1-xEu_xZn₂Sb₂ (x = 0.02(1), 0.04(1), 0.08(1), 0.15(1)) system were successfully synthesized using the molten Pb-flux or the conventional high-temperature reaction methods. Their crystal structures were characterized by both powder and single-crystal X-ray diffraction analyses, and all four isotypic title compounds adopted the orthorhombic BaCu₂S₂-type (Pnma, Z = 4, Pearson code oP20) structure. The radius ratio criterion, based on the cationic and anionic elements (i.e., r₊/r₋), was successfully verified in the title system, as in our previous reports, where r₊/r₋ > 1 for the BaCu₂S₂-type structure. A series of density functional theory calculations were performed using a hypothetical model with the idealized compositions of Ba_0.75Eu_0.25Zn₂Sb₂, and the results were compared with the ternary parental compound BaZn₂Sb₂ to understand the influence of Eu substituents in the Ba_1-xEu_xZn₂Sb₂ system. A similar overall shape of the density of states (DOS) curves and the near-constant DOS values at E_F before and after the cationic substitution suggest only marginal changes in the carrier concentration. Therefore, carrier mobility has a dominant role in rationalizing the observed variations in the electrical transport properties of the title system. Temperature-dependent TE property measurements proved that an increase in the Seebeck coefficient S and a decrease in electrical conductivity σ were observed as the Eu substituents gradually increased in the Ba_1-xEu_xZn₂Sb₂ system, although the overall S and σ values were lower than those in the parental compound BaZn₂Sb₂. The thermal conductivities of these title compounds were successfully lowered by phonon scattering, but due to the overall smaller electrical transport properties, the observed maximum ZT was 0.49 at 773 K for Ba_0.98(1)Eu_0.02Zn₂Sb₂. Full article

Non-ionic surfactants are an important solvent in the field of green chemistry with tremendous application potential. Understanding their phase properties in bulk or in confined environments is of high commercial value. In recent years, the combination of molecular dynamics (MD) simulations with multinuclear solid-state NMR spectroscopy and calorimetric techniques has evolved into the most powerful tool for their investigation. Showing recent examples from our groups, the present review demonstrates the power and versatility of this approach, which can handle both small model-surfactants like octanol and large technical surfactants like technical polyethylene glycol (PEG) mixtures and reveals otherwise unobtainable knowledge about their phase behavior and the underlying molecular arrangements. Full article

The La-doped ternary Zintl phase Ca_10.43(3)La_0.57Sb_9.69(1) was successfully synthesized by arc melting, and the title compound adopted the Ho₁₁Ge₁₀-type structure with a tetragonal I4/mmm space group (Z = 4, Pearson code tI84). The complex crystal structure is composed of (1) the four different kinds of cationic Ca or Ca/La mixed sites surrounded by seven or nine Sb atoms and (2) the 3-dimensional cage-shaped anionic frameworks built by the other two types of Sb atoms. In particular, the La dopants preferred to occupy the Ca4 and Ca1 sites, and this specific cationic-site preference can be rationalized by both electronic and size-factor criteria. Moreover, the ca. 16% occupational deficiency observed at the Sb3 site was attributed to the energetically unfavorable antibonding character of the Sb3–Sb3 bond in the [Sb3]₄ tetramers, according to a series of DFT calculations. A crystal Hamilton overlap population curve analysis also proved that the title compound Ca_10.43(3)La_0.57Sb_9.69(1) tried to keep the valence electron count below 71.02 to remain energetically stable in the Ho₁₁Ge₁₀-type phase. Measurements of temperature-dependent electrical transport properties revealed that the La doping indeed enhanced the electrical conductivity of Ca_10.43(3)La_0.57Sb_9.69(1) compared to the un-doped Ca₁₁Sb₁₀. However, unlike other rare earth metal (RE)-doped compounds in the Ca_11−xRE_xSb₁₀ (RE = Nd and Sm) system that display semiconducting behavior, the La-doped title compound showed poor metallic electrical properties. The positive values of Seebeck coefficients indicated the p-type character of the title compound despite the successful n-type La doping, and this should be attributed to Sb deficiency. Full article

Assessing handling qualities is crucial for ensuring the safety and operational efficiency of aircraft control characteristics. The growing interest in Urban Air Mobility (UAM) has increased the focus on electric Vertical Takeoff and Landing (eVTOL) aircraft; however, a comprehensive assessment of eVTOL handling qualities remains a challenge. This paper proposed a handling qualities framework to assess eVTOL handling qualities, integrating pilot compensation, task performance, and qualitative comments. An experiment was conducted, where eye-tracking data and subjective ratings from 16 participants as they performed various Mission Task Elements (MTEs) in an eVTOL simulator were analyzed. The relationship between pilot compensation and task workload was investigated based on eye metrics. Data mining results revealed that pilots’ eye movement patterns and workload perception change when performing Mission Task Elements (MTEs) that involve aircraft deficiencies. Additionally, pupil size, pupil diameter, iris diameter, interpupillary distance, iris-to-pupil ratio, and gaze entropy are found to be correlated with both handling qualities and task workload. Furthermore, a handling qualities and pilot workload recognition model is developed based on Long-Short Term Memory (LSTM), which is subsequently trained and evaluated with experimental data, achieving an accuracy of 97%. A case study was conducted to validate the effectiveness of the proposed framework. Overall, the proposed framework addresses the limitations of the existing Handling Qualities Rating Method (HQRM), offering a more comprehensive approach to handling qualities assessment. Full article

Mg₃Sb₂-based materials, part of the Zintl compound family, are known for their low thermal conductivity but face challenges in thermoelectric applications due to their low energy conversion efficiency. This study addressed these limitations through first-principles calculations using the CASTEP module in Materials Studio 8.0, aiming to enhance the thermoelectric performance of Mg₃Sb₂ via strategic doping. Density functional theory (DFT) calculations were performed to analyze electronic properties, including band structure and density of states (D.O.S.), providing insights into the influence of various dopants. The semiclassical Boltzmann transport theory, implemented in BoltzTrap (version 1.2.5), was used to evaluate key thermoelectric properties such as the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and electronic figure of merit (eZT). The results indicate that doping significantly improved the thermoelectric properties of Mg₃Sb₂, facilitating a transition from p-type to n-type behavior. Bi doping reduced the band gap from 0.401 eV to 0.144 eV, increasing carrier concentration and mobility, resulting in an electrical conductivity of 1.66 × 10⁶ S/m and an eZT of 0.757. Ge doping increased the Seebeck coefficient to −392.1 μV/K at 300 K and reduced the band gap to 0.09 eV, achieving an electronic ZT of 0.859 with low thermal conductivity (11 W/mK). Si doping enhanced stability and achieved an electrical conductivity of 1.627 × 10⁶ S/m with an electronic thermal conductivity of 11.3 W/mK, improving thermoelectric performance. These findings established the potential of doped Mg₃Sb₂ as a highly efficient thermoelectric material, paving the way for future research and applications in sustainable energy solutions. Full article

The ternary Zintl phase, Yb₂CdSb₂, was discovered to exist in two different polymorphic forms. In addition to the orthorhombic α-Yb₂CdSb₂ (space group Cmc2₁) known for its excellent thermoelectric properties, we present the synthesis and characterization of the crystal and electronic structure of its monoclinic variant, β-Yb₂CdSb₂. Structural characterization was performed with the single-crystal X-ray diffraction method. β-Yb₂CdSb₂ crystallizes in a monoclinic crystal system with the non-centrosymmetric space group Cm (Z = 33, a = 81.801(5) Å, b = 4.6186(3) Å, c = 12.6742(7) Å, β = 93.0610(10)°) and constitutes a new structure type. The complex crystal structure of β-Yb₂CdSb₂ contrasts with the previously studied β-Ca₂CdPn₂ (Pn = P, As, Sb) polymorphs, although it shares similar structural features. It consists of three different layers, made of corner-sharing [CdSb₄] tetrahedra and stacked in the ABC sequence. The layers are interconnected via [CdSb₃] trigonal planar units. Multiple Yb and Cd atomic sites exhibit partial occupancy, resulting in extensive structural disorder. Valence electron partitioning within the Zintl–Klemm formalism yields the formulation (Yb²⁺)_1.98(Cd²⁺)_1.01(Sb³⁻)₂(h⁺)_0.02, highlighting the nearly charge-balanced composition. Detailed electronic structure calculations reveal the closed band gap and presumably semimetallic nature of β-Yb₂CdSb₂ with the band structure features hinting at potential topological properties. Full article

Semiconducting clathrates have attracted considerable interest in the field of thermoelectric materials. We report here a computational study on the crystal structure, the enthalpy of formation, and the physical properties of the following type-I clathrates: (a) experimentally studied Cs₈Sn₄₄ and hypothetical Cs₈Sn₄₆ and (b) hypothetical (NH₄)₈Sn_46−x (x = 0 or 2). The ab initio VASP calculations for the nominal stoichiometries include the geometry optimization of the initial structural models, enthalpies of formation, and the electronic and phonon density of states. Comparison of the chemical bonding of the structural models is performed via the electron localization function. The results show that the presence and distribution of defects in the Sn framework for both Cs₈Sn_46−x and (NH₄)₈Sn_46−x systems significantly alters the formation energy and its electrical properties, ranging from metallic to semiconducting behavior. In particular, one defect per six-membered Sn ring in a 3D spiro-network is the thermodynamically preferred configuration that results in the Cs₈Sn₄₄ and (NH₄)₈Sn₄₄ stoichiometries with narrow-band gap semiconducting behavior. Moreover, the rotation of the ammonium cation in the polyhedral cavities is an interesting feature that may promote the use of ammonium or other small molecular cations as guests in clathrates for thermoelectric applications; this is due to the decrease in the lattice thermal conductivity. Full article

Due to the high impact of semiconductors with respect to many applications for electronics and energy transformation, the search for new compounds and a deep understanding of the structure–property relationship in such materials has a high priority. Electron-precise Zintl compounds of the composition A₃TrPn₂ (A = Li − Cs, Tr = Al − In, Pn = P, As) have been reported for 22 possible element combinations and show a large variety of different crystal structures comprising zero-, one-, two- and three-dimensional polyanionic substructures. From Li to Cs, the compounds systematically lower the complexity of the anionic structure. For an insight into possible crystal–structure band–structure relations for all compounds (experimentally known or predicted), their band structures, density of states and crystal orbital Hamilton populations were calculated on a basis of DFT/PBE0 and SVP/TZVP basis sets. All but three (Na₃AlP₂, Na₃GaP₂ and Na₃AlAs₂) compounds show direct or pseudo-direct band gaps. Indirect band gaps seem to be linked to one specific structure type, but only for Al and Ga compounds. Arsenides show smaller band gaps than phosphides due to weaker Tr-As bonds. The bonding situation was confirmed by a Mullikan analysis, and most states close to the Fermi level were assigned to non-bonding orbitals. Full article

Three novel binary barium arsenides, Ba₃As₄, Ba₅As₄, and Ba₁₆As₁₁, were synthesized and their crystal and electronic structures were investigated. Structural data collected via the single-crystal X-ray diffraction method indicate that the anionic substructures of all three novel compounds are composed of structural motifs based on the homoatomic As–As contacts, with [As₂]⁴⁻ dimers found in Ba₅As₄ and Ba₁₆As₁₁, and an [As₄]⁶⁻ tetramer found in Ba₃As₄. Ba₃As₄ and Ba₅As₄ crystallize in the orthorhombic crystal system—with the non-centrosymmetric space group Fdd2 (a = 15.3680(20) Å, b = 18.7550(30) Å, c = 6.2816(10) Å) for the former, and the centrosymmetric space group Cmce (a = 16.8820(30) Å, b = 8.5391(16) Å, and c = 8.6127(16) Å) for the latter—adopting Eu₃As₄ and Eu₅As₄ structure types, respectively. The heavily disordered Ba₁₆As₁₁ structure was solved in the tetragonal crystal system with the space group $P\overline{4}{2}_{1}m$ (a = 12.8944(12) Å and c = 11.8141(17) Å). The Zintl concept can be applied to each of these materials as follows: Ba₃As₄ = (Ba²⁺)₃[As₄]⁶⁻, Ba₅As₄ = (Ba²⁺)₅(As³⁻)₂[As₂]⁴⁻, and 2 × Ba₁₆As₁₁ = (Ba²⁺)₃₂(As³⁻) ≈ ₂₀[As₂]⁴⁻ ≈ 1, pointing to the charge-balanced nature of these compounds. Electronic structure calculations indicate narrow bandgap semiconducting behavior, with calculated bandgaps of 0.47 eV for Ba₃As₄, 0.34 eV for Ba₅As₄, and 0.33 eV for Ba₁₆As₁₁. Full article

This review gives an overview of current trends in the investigation of confined molecules such as water, small and higher alcohols, carbonic acids, ethylene glycol, and non-ionic surfactants, such as polyethylene glycol or Triton-X, as guest molecules in neat and functionalized mesoporous silica materials employing solid-state NMR spectroscopy, supported by calorimetry and molecular dynamics simulations. The combination of steric interactions, hydrogen bonds, and hydrophobic and hydrophilic interactions results in a fascinating phase behavior in the confinement. Combining solid-state NMR and relaxometry, DNP hyperpolarization, molecular dynamics simulations, and general physicochemical techniques, it is possible to monitor these confined molecules and gain deep insights into this phase behavior and the underlying molecular arrangements. In many cases, the competition between hydrogen bonding and electrostatic interactions between polar and non-polar moieties of the guests and the host leads to the formation of ordered structures, despite the cramped surroundings inside the pores. Full article