The Sr0.5Sn0.5V2O6–SnO2 composite was prepared by a solid-state route, and its crystal structure and physical properties were investigated. The X-ray diffraction confirmed the two-phase nature of the composite. One of the phases was assigned to a compound with a crystal structure related to that of foordite-type SnNb2O6. At room temperature, the dielectric constant ɛʹ of the composite (at 1 kHz) has a value of 2100, and the electrical conductivity σ has a small value ( 3.4 × 10–3 µS), which indicates the dominant role of the dielectric properties over the semiconductor ones. Impedance spectroscopy revealed that with increasing temperature, the capacitance of the grain interior increases due to thermal expansion. It exhibits two anomalies (at 270 °C and 420 °C) associated with the SnO₂ phase transition and oxygen vacancies. Meanwhile, the resistance of the grain interior, grain boundaries, and the Warburg element decreases with increasing temperature. TEM images revealed the variation of Sr0.5Sn0.5V2O6 crystallite size in the range from 100 to 150 nm. The study of the electrocatalytic properties of the composite revealed its moderate catalytic activity toward the water splitting reaction. Using the density functional theory (DFT), the thermodynamic stability of the composites was analyzed in the concentration range x = 0.0 – 1.0 with a step of x = 0.2 and it has been shown that all the compositions are thermodynamically metastable, even taking into account vibrational and configuration entropy terms, which explains the observed Sr0.5Sn0.5V2O6 phase as a composite or a kinetically stabilized compound.

Hexagonal layered Na2T2TeO6 (T = Co1/3Ni1/3Cu1/3) and Na2Z2TeO6 (Z = Co1/4Ni1/4Cu1/4Zn1/4) have been prepared by solid-state reactions. According to the X-ray Rietveld refinement, Na2Z2TeO6 is isostructural with its honeycomb-ordered constituents Na2M2TeO6 (M = Co, Zn), space group P6322. For Na2T2TeO6, however, only subcell (ignoring T/Te ordering) could be successfully refined despite presence of weak superstructure reflection. This is attributed to intergrowth of two packing modes with similar lattice parameters: P63/mcm (characteristic of Na2Ni2TeO6) and P6322. According to magnetic susceptibility and heat capacity measurements, both materials undergo antiferromagnetic ordering at low temperatures with negative Weiss temperatures of −38 and −26 K for the T- and Z-compositions, respectively. The Néel point of Na2T2TeO6, 16.9 K, is considerably lower than those of its Ni and Co constituents (both being about 27 K), in contrast to the sister system, monoclinic Na3T2SbO6, where TN is intermediate between those of Ni and Co constituents. Further lowering of the Néel point in Na2Z2TeO6, 8.6 K, is attributed to the diamagnetic dilution with Zn2+.

Monoclinic layered Li3(CoNiCuMgZn)0.4SbO6 and Na3(CoNiCuMgZn)0.4SbO6 (A3Q2SbO6 for short) were prepared by solid-state reactions. The X-ray Rietveld refinement of both materials confirms their structural analogy with their monocation counterparts (space group C2/m), random mixing of the five cations and their honeycomb ordering with Sb(5+). The Li compound shows considerable Li/Q site inversion, much larger than that in Li3Cu2SbO6. Static (DC) and dynamic (AC) magnetic susceptibility and specific heat measurements indicate the absence of any magnetic order down to 2 K in Na3Q2SbO6, while Li3Q2SbO6 demonstrates spin-cluster glass behaviour below 5 K. The Mydosh parameter (K) characterizing the frequency (f) shift of the freezing temperature amounts to 0.05. Within the critical slowing down model, a glassy freezing temperature (Tg) of 4.1 K (at f → 0), a microscopic spin flipping time (τ0) of 10-10 s and a critical exponent (zν) of 10 were obtained.

It is now widely assumed that conductivity of solid electrolytes may be markedly enhanced by the "high-entropy" (HE) effect. However, HE electrolytes usually differ from their simpler isomorphs by other factors affecting conductivity: lattice expansion/contraction, mobile ion content, bond ionicity, quality of samples. To attribute enhanced conductivity to the HE effect, all other factors should be identical. This work compares "simple" and "HE" ceramic sodium-ion conductors of two related structure types: P2 Nax(MyTi1-y)O2 and honeycomb-ordered P2S Na2M2TeO6, with similar unit cell data, x values, density, and texture and does not reveal any considerable HE effect. In particular, new Na2M2TeO6 conductors combining three to five divalent M (from the list Mg, Co, Ni, Cu, Zn) show similar conductivities with their monocation analogs. Higher conductivity of the P2-type titanates (2-4 mS/cm at 373 K) is explained by the geometrical effect due to smaller size of octahedral cations and possibility of decreased x values.

This study investigates the development of composite ceramics for application in hard tissue augmentation, using GeO2 and germanium-strontium phosphates as base materials. Various pore-forming agents, including cetyltrimethylammonium bromide (CTB), polyethylene (PE), caffeine (CFF), and natural materials such as lemon peel (LMN), silk (SLK), loofah (LFH), and yam (YAM), were employed to introduce porosity into the scaffolds. The impact of these agents on phase composition, particle size, and surface properties was analyzed, revealing that some agents induced phase transformations, while others preserved a multi-phase structure. The incorporation of phosphorus and strontium into the scaffolds to enhance bioactivity was evaluated using XRF analysis. The scaffolds' porosity, particularly meso- and macroporosity, was significantly influenced by the pore-forming agents. Antimicrobial activity, demonstrated against both gram-negative and gram-positive bacteria, was also an important factor for scaffolds intended for medical implants and wound healing. Among the materials tested, SGP-SLK and SGP-CTB showed the most promising results, combining excellent bioactivity, enhanced bone regeneration potential, and superior antimicrobial performance. These findings suggest that composite scaffolds incorporating phosphorus, strontium, and suitable porosity are promising candidates for tissue engineering applications.

The concept of high-entropy oxides has triggered extensive research of this novel class of materials because their numerous functional properties are usually not mere linear combinations of those of the components. Here, we introduce the new series of compositionally complex honeycomb-layered magnets Na3-xLixT2SbO6 (T = Cu1/3Ni1/3Co1/3). An unusual feature of the system is its nonmonotonous dependences of the monoclinic lattice parameters b and beta on x. Rietveld refinement of the crystal structures of the Na and Li end members reveals apparent Sb-T site inversion in the former and considerable Li-Cu site inversion in the latter. The materials are characterized by measurements of specific heat C-p, magnetization M, and ac and dc magnetic susceptibility chi. Na3T2SbO6 exhibits sharp long-range antiferromagnetic order (T-N = 10.2 K) preceded by noticeable correlation effects at elevated temperatures. The magnetic phase diagram of Na3T2SbO6 is established. Introduction of Li, just at x = 0.8, destroys AFM order, resulting in spin-cluster glass behavior attributed to Li/Cu inversion, with T-G growing with x to 10.4 K at x = 3.

The concept of high-entropy oxides has triggered extensive research of this novel class of materials because their numerous functional properties are usually not mere linear combinations of those of the components. Here, we introduce the new series of compositionally complex honeycomb-layered magnets Na3-xLixT2SbO6 (T = Cu1/3Ni1/3Co1/3). An unusual feature of the system is its nonmonotonous dependences of the monoclinic lattice parameters b and β on x. Rietveld refinement of the crystal structures of the Na and Li end members reveals apparent Sb-T site inversion in the former and considerable Li-Cu site inversion in the latter. The materials are characterized by measurements of specific heat Cp, magnetization M, and ac and dc magnetic susceptibility χ. Na3T2SbO6 exhibits sharp long-range antiferromagnetic order (TN = 10.2 K) preceded by noticeable correlation effects at elevated temperatures. The magnetic phase diagram of Na3T2SbO6 is established. Introduction of Li, just at x = 0.8, destroys AFM order, resulting in spin-cluster glass behavior attributed to Li/Cu inversion, with TG growing with x to 10.4 K at x = 3.

The long-term performance of batteries depends strongly on the 3D morphology of electrode materials. Morphological changes, i.e., particle fracture and surface deterioration, are among the most prominent sources of electrode degradation. A profound understanding of the fracture mechanics of electrode materials in micro- and nanoscale dimensions requires the use of advanced in situ and operando techniques. In this paper, we demonstrate the capabilities of laboratory X-ray microscopy and nano X-ray computed tomography (nano-XCT) for the non-destructive study of the electrode material’s 3D morphology and defects, such as microcracks, at sub-micron resolution. We investigate the morphology of Na0.9Fe0.45Ti1.55O4 sodium iron titanate (NFTO) cathode material in Li-ion batteries using laboratory-based in situ and operando X-ray microscopy. The impact of the morphology on the degradation of battery materials, particularly the size- and density-dependence of the fracture behavior of the particles, is revealed based on a semi-quantitative analysis of the formation and propagation of microcracks in particles. Finally, we discuss design concepts of the operando cells for the study of electrochemical processes.

A set of sodium iron titanite samples with general formula Na x Fe +2x/2 Ti 2 – x/2 O 4 was prepared using solid-state synthesis in an inert atmosphere to test for application as cathode materials for Na-ion batteries. These materials have several advantages over analogues with Fe 3+ , demonstrating better sodium ion conductivity and higher Na+ ions capacity without phase transition or destruction of the structure. [1] In the course of the investigation, several compositions of a new compound were obtained with NSIT-like structure type similar to Na 0.9 Fe 3+0.9 Ti 1.1 O 4 . Among them, composition with x = 0.9 was selected due to its electrochemical performance and structural peculiarity. From the crystallographic point of view, formation of phases in Na x Fe +2x/2 Ti 2 – x/2 O 4 system with Na 0.9 Fe 3+0.9 Ti 1.1 O 4 structure (having Fe 3+ ions mixed with Ti 4+ ions) is rather unusual due to different radii of mixing ions (Fe 2+ = 0.92 Å, Fe 3+ = 0.785 Å, Ti +4 = 0.745 Å (CN=6) [2]). The Na 0.9 Fe 3+0.9 Ti 1.1 O 4 was further studied by operando XANES spectroscopy. The sample was placed as a cathode inside custom electrochemical cell with glassy carbon X-Ray transparent windows. Li foil was used as anode and 1M LiPF6 in 1:1 EC:DMC commercial solution (Sigma) was used as electrolyte. The cell was cycled in 1.6 to 4.5

Electrochemical characterization of the novel sodium iron titanate Na0.9Fe0.45Ti1.55O4 was performed upon cycling in the Li-ion half-cell. The material exhibited stable cycling in the voltage range 2–4.5 V, and the number of alkali ions extracted per formula unit was approximately half of the Na stoichiometry value. Using laboratory X-ray absorption spectrometry, we measured operando Fe K-edge X-ray absorption spectra in the first 10 charge–discharge cycles and quantified the portion of charge associated with the transition metal redox reaction. Although 3d metals are commonly accepted redox-active centers in the intercalation process, we found that in all cycles the amount of oxidized and reduced Fe ions was almost 20% less than the total number of transferred electrons. Using density functional theory (DFT) simulations, we show that part of the reversible capacity is related to the redox reaction on oxygen ions.

The non-stoichiometric system Li0.8Ni0.6Sb0.4O2 is a Li-deficient derivative of the zigzag honeycomb antiferromagnet Li3Ni2SbO6. Structural and magnetic properties of Li0.8Ni0.6Sb0.4O2 were studied by means of X-ray diffraction, magnetic susceptibility, specific heat, and nuclear magnetic resonance measurements. Powder X-ray diffraction data shows the formation of a new phase, which is Sb-enriched and Li-deficient with respect to the structurally honeycomb-ordered Li3Ni2SbO6. This structural modification manifests in a drastic change of the magnetic properties in comparison to the stoichiometric partner. Bulk static (dc) magnetic susceptibility measurements show an overall antiferromagnetic interaction (Θ = −4 K) between Ni2+ spins (S = 1), while dynamic (ac) susceptibility reveals a transition into a spin glass state at a freezing temperature TSG ~ 8 K. These results were supported by the absence of the λ-anomaly in the specific heat Cp(T) down to 2 K. Moreover, combination of the bulk static susceptibility, heat capacity and 7Li NMR studies indicates a complicated temperature transformation of the magnetic system. We observe a development of a cluster spin glass, where the Ising-like Ni2+ magnetic moments demonstrate a 2D correlated slow short-range dynamics already at 12 K, whereas the formation of 3D short range static ordered clusters occurs far below the spin-glass freezing temperature at T ~ 4 K as it can be seen from the 7Li NMR spectrum.

The set of compositions with Fe2+ in the system NaxFex/2Ti2-x/2O4 has been prepared by solid-state reactions in the inert atmosphere at 1050 degrees C. The oxidation state of iron was confirmed using the XANES method. Na0.88Fe0.44Ti1.56O4 is the new four-element compound in Na2O-"FeO"-TiO2 system. According to the X-ray powder data, it is orthorhombic, Pnma, a = 9.3624(1), b = 2.96718(4), c = 11.3435(1) angstrom and has the same structure as Na0.9Fe0.9Ti1.1O4 with Fe3+. The structure was refined by the Rietveld method. The 3D-framework of (Fe, Ti)O-6 octahedra contains quadruple rutile-like chains and sodium ions in double tunnels. Fe/Ti partial ordering in the framework and sodium distribution in the tunnels were studied additionally using the method of bond valence sums and Voronoi tessellation. The structure and composition of Na0.88Fe0.44Ti1.56O4 make it a promising material for cathode application.

An orthorhombic compound, NaMnSbO4, represents a square net of magnetic Mn2+ ions residing in vertex-shared oxygen octahedra. Its static and dynamic magnetic properties were studied using magnetic susceptibility, specific heat, magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and density functional calculations. Thermodynamic data indicate an establishment of the long-range magnetic order with TN about 44 K, which is preceded by a short-range one at about 55 K. In addition, a non-trivial wasp-waisted hysteresis loop of the magnetization was observed, indicating that the ground state is most probably canted antiferromagnetic. Temperature dependence of the magnetic susceptibility is described reasonably well in the framework of 2D square lattice model with the main exchange parameter J = -5.3 K, which is in good agreement with density functional analysis, NMR and ESR data.

Crystallographic and magnetic properties of new layered honeycomb-lattice Li3Co2SbO6 antimonate were studied and compared with its sodium precursor Na3Co2SbO6.

We report the first four magnetic representatives of the trigonal layered A2M(4+)TeO6 (here, M = Mn) family. Na2MnTeO6 was synthesized from NaMnO2, NaNO3, and TeO2 at 650-720 °C, but analogues for which A = Li and K could not be obtained by direct synthesis. However, those for which A = Li, Ag, and Tl (but not K) were prepared by exchange reactions between Na2MnTeO6 and the corresponding molten nitrates. The oxygen content was verified by redox titration. According to the X-ray diffraction Rietveld analysis, the four new compounds are isostructural with Na2GeTeO6, trigonal ( P3̅1 c), based on ilmenite-like layers of edge-shared oxygen octahedra occupied by Mn(4+) and Te(6+) in an ordered manner. These layers are separated by cations A, also in a distorted octahedral coordination. However, off-center displacement of Tl+ is so strong, due to the lone-pair effect, that its coordination is better described as trigonal pyramid. Each MnO6 octahedron shares two opposite faces with AO6 octahedra, whereas TeO6 octahedra avoid sharing faces. Besides this double-layered structure, Na2MnTeO6 was often accompanied by a transient triple-layered rhombohedral polytype. However, it could not be prepared as a single phase and disappeared on annealing at 700-720 °C. All A2MnTeO6 samples (A = Ag, Li, Na, or Tl) revealed the unusual phenomenon of hidden magnetic order. Low-field magnetic susceptibility data exhibit a Curie-Weiss type behavior for all samples under study and do not show any sign of the establishment of long-range magnetic order down to 2 K. In contrast, both the magnetic susceptibility in sufficiently high external magnetic fields and the zero-field specific heat unambiguously revealed an onset of antiferromagnetic order at low temperatures. The frustration index f = Θ/ TN takes values larger than the classical values for three-dimensional antiferromagnets and implies moderate frustration on the triangular lattice.

MSb2O6 compounds (M = Mg, Co, Ni, Cu, Zn) are known in the tetragonal trirutile forms, slightly distorted monoclinically with M = Cu due to the Jahn-Teller effect. In this study, using a low-temperature exchange reaction between ilmenite-type NaSbO3 and molten MSO4-KCl (or MgCl2-KCl) mixtures, these five compositions were prepared for the first time as trigonal layered rosiaite (PbSb2O6)-type phases. Upon heating, they irreversibly transform to the known phases via amorphous intermediates, in contrast to previously studied isostructural MnSb2O6, where the stable phase is structurally related to the metastable phase. The same method was found to be applicable for preparing stable rosiaite-type CdSb2O6. The formula volumes of the new phases show an excellent correlation with the ionic radii (except for M = Cu, for which a Jahn-Teller distortion is suspected) and are 2-3% larger than those for the known forms although all coordination numbers are the same. The crystal structure of CoSb2O6 was refined via the Rietveld method: P3[combining macron]1m, a = 5.1318(3) Å, and c = 4.5520(3) Å. Compounds with M = Co and Ni antiferromagnetically order at 11 and 15 K, respectively, whereas the copper compound does not show long-range magnetic order down to 1.5 K. A comparison between the magnetic behavior of the metastable and stable polymorphs was carried out. FeSb2O6 could not be prepared because of the 2Fe2+ + Sb5+ = 2Fe3+ + Sb3+ redox reaction. This electron transfer produces an additional 5s2 shell for Sb and results in a volume increase. A comparison of the formula volume for the stable mixture FeSbO4 + 0.5Sb2O4 with that extrapolated for FeSb2O6 predicted that the trirutile-type FeSb2O6 can be stabilized at high pressures.

Four new manganese germanates and silicates, A2MnGeO4 (A = Li, Na) and A2MnSiO4 (A = Na, Ag), were prepared, and their crystal structures were determined using the X-ray Rietveld method. All of them contain all components in tetrahedral coordination. Li2MnGeO4 is orthorhombic (Pmn21) layered, isostructural with Li2CdGeO4, and the three other compounds are monoclinic (Pn) cristobalite-related frameworks. As in other stuffed cristobalites of various symmetry (Pn A2MXO4, Pna21 and Pbca AMO2), average bond angles on bridging oxygens (here, Mn-O-X) increase with increasing A/X and/or A/M radius ratios, indicating the trend to the ideal cubic (Fd3̅m) structure typified by CsAlO2. The sublattices of the magnetic Mn2+ ions in both structure types under study (Pmn21 and Pn) are essentially the same; namely, they are pseudocubic eutaxy with 12 nearest neighbors. The magnetic properties of the four new phases plus Li2MnSiO4 were characterized by carrying out magnetic susceptibility, specific heat, magnetization, and electron spin resonance measurements and also by performing energy-mapping analysis to evaluate their spin exchange constants. Ag2MnSiO4 remains paramagnetic down to 2 K, but A2MnXO4 (A = Li, Na; X = Si, Ge) undergo a three-dimensional antiferromagnetic ordering. All five phases exhibit short-range AFM ordering correlations, hence showing them to be low-dimensional magnets and a magnetic field induced spin-reorientation transition at T < TN for all AFM phases. We constructed the magnetic phase diagrams for A2MnXO4 (A = Li, Na; X = Si, Ge) on the basis of the thermodynamic data in magnetic fields up to 9 T. The magnetic properties of all five phases experimentally determined are well explained by their spin exchange constants evaluated by performing energy-mapping analysis.