Maxim Avdeev

Solid-state batteries require electrolytes with high Li-ion conductivity, together with good interfacial and chemical stability. Oxythiophosphate-type solid electrolytes appear to achieve such a balance, but their chemistry remains little investigated. Here, we report the low-temperature aqueous synthesis of lithium dithiophosphate undecahydrate, Li3PO2S2·11H2O, and its dehydration pathway to the monohydrate Li3PO2S2·H2O and to the anhydrous phase Li3PO2S2. Li3PO2S2·11H2O crystallizes in the P212121 space group, isostructural to the parent compound Na3PO2S2·11H2O. Upon annealing at 100 °C, a monohydrate forms with a C2cm structure solved ab initio from XRPD and PND data. Further dehydration at 200 °C yields anhydrous Li3PO2S2, which adopts a Pbca structure isostructural to the Na analog. Solid-state NMR spectroscopy confirms dominant (PO2S2) units in the hydrate and reveals partial transformation to (PO3S)/(PO4) units upon annealing. Li3PO2S2·11H2O exhibits a room-temperature ionic conductivity of ∼10–5 S cm–1. The ionic conductivities of Li3PO2S2·H2O and Li3PO2S2 are lower: σ = 8.7 × 10–8 S·cm–1 and 2.6 × 10–8 S·cm–1 (at 110 °C), with activation energies of ∼0.70 and ∼0.69 eV, respectively. These findings expand the oxythiophosphate structural family with new hydrated and anhydrous phases, providing a basis for tuning O/S composition and Li-ion transport through targeted cation substitution.

Alkali manganese oxynitridophosphates A1.1Mn2.9P3O8N2 (A = Na, Li) were prepared by one-step solid-state ammonolysis, where the lithium analogue is obtained directly rather than by alkali-ion exchange from the sodium compound. Both compositions crystallize in a previously unreported orthorhombic Pbcn framework, in which ordered O/N environments, unusual manganese coordination in MnO5N and MnO6N2 polyhedra, and alkali–manganese disorder are accommodated within the same structure. The proposed structural model is supported by complementary synchrotron X-ray and neutron powder diffraction, electron microscopy, solid-state NMR and XAS data, as well as density functional theory calculations. Magnetic susceptibility is consistent with predominantly Mn2+ and antiferromagnetic ordering below 35.1 K for the Li phase and 32.6 K for the Na phase. Although the Mn2+/Mn3+ redox couple lies within the accessible potential window of nonaqueous M-ion batteries, reversible alkali extraction is limited by the restricted migration pathways imposed by the framework. Overall, this work expands the compositional and structural landscape of oxynitridophosphates and highlights nitrogen incorporation in phosphate crystal chemistry as a route to unconventional coordination environments, new framework connectivities and functional properties.

We demonstrate rapid, scalable synthesis of solid-solution layered transition metal carbosulfides, TixNb2–xSC (0 ≤ x ≤ 2). Thermogravimetric analysis confirmed superior thermal stability of Ti2SC vs Nb2SC; oxidation of Nb2SC in air (750 °C) produced an accordion-like sulfur-bearing niobium oxide. Room-temperature X-ray diffraction and temperature-dependent neutron diffraction revealed linear contraction of lattice parameters with increasing Ti content. Strong anisotropic thermal expansion behavior arises from metallic basal planes vs nonmetallic M–S bonds, with Nb2SC showing larger volumetric expansion than Ti2SC. Specific heat measurments confirm that Ti2SC is stiffer than Nb2SC. In both thermal expansion and specific heat, nonmonotonic behaviors are linked to the critical role of Ti/Nb mixing. SQUID measurements show diamagnetic shielding in high-Nb samples, which, lacking an anomaly in specific heat, is ascribed to trace, percolating superconducting impurities rather than bulk superconductivity.

Recent studies have revealed metal-to-metal and intervalence-charge transfer transitions in cation ordered 6H perovskites with Cs3M+M2+M3+Cl9 stoichiometry. The structure and properties of two new members of this family, Cs3NaMnVCl9 and Cs3NaMnCrCl9, are reported here. In both compounds Na+ ions occupy sites in octahedra that share only corners, electronically isolating face-sharing M2Cl9 bioctahedral clusters. Analysis of synchrotron X-ray and neutron powder diffraction patterns reveals no sign of long-range ordering of the Mn2+ and V3+/Cr3+ ions, suggesting a random orientation of bimetallic Mn2+M3+Cl94– clusters. Magnetometry studies reveal paramagnetic behavior in both compounds, with negative Weiss temperatures and effective moments that closely align with expected values based on spin-only moments. No sign of long-range magnetic order is observed in either compound down to at least 2 K. The optical absorption spectra feature d-to-d transitions, ligand-to-metal charge transfer (LMCT), and metal-to-metal charge transfer (MMCT) transitions. Cs3NaMnVCl9 exhibits a Mn2+ to V3+ MMCT transition at ∼1390 nm (∼0.9 eV), whereas the comparable MMCT transition in Cs3NaMnCrCl9 falls at a much higher energy and cannot be resolved due to overlap with the LMCT transition. The striking difference in MMCT energy can be attributed to differences in the electron configuration of V3+ (t2g2eg0) and Cr3+ (t2g3eg0).

Doping La into the Ba-sites of Ba ₇ Nb ₄ MoO ₂₀ enhances oxide ion conduction by regulating occupancy in oxygen sites, leading to a high bulk oxide ion conductivity of 0.01 S cm ⁻¹ at 500 °C for the Ba _6.90 La _0.10 Nb ₄ MoO _20.05 composition.

This study focuses on the binary δ-Co2.5Zn17.5 and pseudobinary δ-Co2.5–xMnxZn17.5 (x = 0–1.2) intermetallic phases, prepared via a high-temperature synthetic route. The crystal structure and atomic distribution of δ-Co2Mn0.5Zn17.5 were established using X-ray and neutron diffraction experiments. The pseudobinary δ-Co2Mn0.5Zn17.5 adopts a chiral crystal structure (P64), consistent with the binary δ-Co2.5Zn17.5. Theoretical calculations were employed to understand the site preferences of Co and Zn, as well as the overall phase stability of the binary compound. Interestingly, the substitution of Mn for Co occurs through Zn mediation (an indirect substitution). In the crystal structure, Mn occupies Zn sites at the 6c position; the displaced Zn then occupies the 3a site, ultimately maintaining the stoichiometry of Co2Mn0.5Zn17.5. The binary δ-Co2.5Zn17.5 exhibits diamagnetism, whereas Mn incorporation into the binary δ-Co2.5Zn17.5 induces cluster-glass magnetism in the pseudobinary δ-Co2Mn0.5Zn17.5, with a spin-freezing temperature of 10 K. While both compounds are structurally chiral, this chirality does not appear to influence their magnetic behavior. Instead, the cluster-glass state in the Mn-substituted phase is driven by the atomic randomness of the Mn atoms in the structural lattice. This out-of-equilibrium behavior below 10 K is further supported by the alternating-current (ac) magnetic susceptibility, thermoremanent magnetization, and the thermal memory effect.

This investigation focuses on the solid-state synthesis and a detailed structural and phase analytical investigation of the CoxNi3–xGa4 series along a constant Ga compositional line within Co–Ni–Ga phase space. Combined analysis of single crystal X-ray diffraction and neutron powder diffraction of CoxNi3–xGa4, x = 1.5 reveals a random distribution of Co and Ni over a single Wyckoff site, which contrasts with previous report suggesting atomic ordering. Phase analyses via X-ray powder diffraction indicates a vacancy order–disorder transition as the Co concentration increases beyond a critical limit. DFT calculation predicted a semimetallic and nonmagnetic ground state, supported by the absence of magnetic peaks or intensity enhancement at 10 K neutron data compared to 300 K. Interestingly, Peierls-like distortions are observed within the Ga substructure in the vacancy-ordered phase, whereas such distortions are absent in the vacancy-disordered phase. These distortions result in periodic charge localization and exhibit subtle alterations between room temperature and 180 K. Magnetic measurements further reveal cluster spin-glass behavior with a high coercivity. The nontrivial spin dynamics, coupled with large coercivity, makes this phase a compelling candidate for multifunctional applications.

Al-containing perovskite oxynitrides, SrAl0.2M0.8O2.4N0.6 (M = Nb, Ta), were synthesized by ammonolysis of layered Sr5M4O15 precursors with α-Al2O3. This reaction demonstrates that the cation-insertion chemistry of layered-perovskite-derived oxynitrides can be extended to trivalent Al3+, beyond the mono- and divalent cations explored in previous systems. Neutron Rietveld refinements revealed tetragonal perovskite frameworks with strongly anisotropic O/N distributions, where nitrogen preferentially occupies the axial anion site. Solid-state 27Al MAS NMR confirmed octahedral, largely O-rich Al coordination, whereas 93Nb MAS NMR revealed highly disordered and low-symmetry Nb-centered local environments in SrAl0.2Nb0.8O2.4N0.6 despite its well-defined average structure. Diffuse-reflectance spectroscopy showed discernible band gap widening and marked suppression of subgap absorption relative to SrNbO2N and SrTaO2N, indicating that Al incorporation modifies both the anion composition and defect-related electronic structure. Impedance analysis indicated an appreciable dielectric response for SrAl0.2Nb0.8O2.4N0.6, with the high-frequency bulk-related component giving effective dielectric constants of approximately 350–360 over the temperature range of 290–350 K. This result suggests that Nb-centered local disorder can contribute substantially to dielectric polarizability when defect-related electronic conduction is sufficiently suppressed. Trivalent-cation insertion therefore offers a useful route to tune anion chemistry, defect states, local structure, and dielectric behavior in mixed-anion perovskites.

We report a crown-ether-assisted topotactic ion-exchange reaction in the β-pyrochlore oxide KOs ₂ O ₆ , enabling complete extraction of K ⁺ ions under mild aqueous conditions without degradation of the rigid Os–O cage framework.