ABSTRACT The novel sodium tetrachlorido‐/azidoaurate(III) dihydrates Na[AuCl 4– x (N 3 ) x ]·2H 2 O ( x = 0, 1, 2, 3, 4) provide the first example of a complete series of gradual substitution on square planar complex anions to be described. Transparent yellow to dark orange single crystals of these phases were synthesized by reaction of NaN 3 and AuCl 3 or HAuCl 4 in different molar ratios from aqueous solution. Controlled dehydration of Na[Au(N 3 ) 4 ]·2H 2 O led to Na[Au(N 3 ) 4 ]·H 2 O and Na[Au(N 3 ) 4 ] in form of orange microcrystalline powders, the latter being a highly explosive material. Predominant structural features of all phases are discrete anions [AuCl 4– x (N 3 ) x ] – with gold in an ordered square planar coordination of azide/chloride anions. Vibrational spectra show good agreement with other known azidoaurates(III).

Double hydroxide perovskites with magnetic transition-metal ions were recently identified as a unique class of materials that combine magnetic frustration with correlated proton disorder-a prerequisite for quantum-disordered fluctuating magnetic ground states resembling spin liquids. Here we present the results of muon spin relaxation (μSR) measurements carried out on fully deuterated samples of the double hydroxyperovskites CuSn(OH)6 (S = 1/2) and MnSn(OH)6 (S = 5/2) over the temperature range 0.053-50 K. The absence of any long-range magnetic order is confirmed down to 0.053 K. We observe no oscillations of the muon asymmetry down to the lowest temperature. The muon relaxation rates show a continuous increase with decreasing temperature, indicating persistent spin fluctuations in both compounds. Spin correlations are consistent with homogeneous spin dynamics. These observations reinforce the assertion that both compounds have a quantum-dynamic magnetic ground state that is consistent with a spin-liquid-like phase stabilized by proton disorder.

An understanding of the thermal properties of materials is integral to any fundamental investigation and is of interest for technologically significant applications. Furthermore, an understanding of low thermal conductivity materials continues to be of fundamental importance. In this work, phase-pure dense polycrystalline Cs2AgBiBr6 was prepared following extensive investigations into preventing the formation of impurity phases upon densification. This allowed for an investigation of the low temperature thermal properties of Cs2AgBiBr6, which revealed a low Debye temperature of 80 K and an Einstein temperature of 21 K, associated with low-frequency soft modes, that result in low thermal conductivity. This work enhances the ongoing research on inorganic perovskites and elucidates the low temperature thermal properties that will aid investigations of this and similar perovskites.

The magnetic properties of Gdin polycrystalline GdTewere investigated by magnetization, heat capacity, magnetoresistance, and electron spin resonance (ESR) which all reveal clear indications of a magnetic phase transition atK in their temperature dependencies. The transition displays characters of competing ferromagnetic and antiferromagnetic interactions which is particularly supported by distinct anomalies in the ESR linewidth and intensity, providing a local picture of magnetism at the transition. A pronounced negative magnetoresistance documents a strong coupling between magnetic order and charge transport in the puckered GdTe double layers that form the GdTecrystal structure.

Realizing topological phases in strongly correlated materials has become a major impetus in condensed matter physics. Although many compounds are now classified as topological insulators, f-electron systems provide an especially fertile platform for emergent heavy-fermion phenomena driven by the interplay of topology and many-body effects. In this study, we examine the crystalline topology of a new RAsS series (R = Y, La, Sm), revealing a structural variant from previous reports. We demonstrate that YAsS and SmAsS host hourglass fermions protected by glide symmetry. SmAsS notably exhibits a strong effective-mass enhancement, placing it alongside SmB6 and YbB12 as a material that exemplifies how the Kondo effects pin the correlated f-electron states near the Fermi energy and, consequently, renormalize the energy and mass scales of topological surface states without destroying their crystalline protection. This tunability establishes SmAsS as a bridge between weakly correlated topological materials and Kondo insulators. To capture these features, we construct a minimal model incorporating f-electron degrees of freedom, which reproduces the observed topological properties and predicts that the surface states survive in the correlated regime, albeit shifted in energy. Our work thus introduces a new family of correlated topological materials and forecasts the robustness of their surface states under Kondo correlations.

The bismuth‐rich subiodides Bi[IrBi 6 I 12 ], Ag 3 [IrBi 6 I 12 ], and Bi x Cu 3–3 x [IrBi 6 I 12 ] were synthesized by high‐temperature reactions in sealed silica ampules and characterized by powder and single‐crystal X‐ray diffraction, differential scanning calorimetry, energy‐dispersive X‐ray spectroscopy, and density functional theory (DFT) calculations. All three compounds contain cuboctahedral [IrBi 6 I 12 ] 3− cluster anions composed of an iridium‐centered bismuth octahedron with iodide‐bridged edges, but differ markedly in the occupation of the octahedral voids of the underlying rock‐salt‐related packing. In Bi[IrBi 6 I 12 ], the clusters are linked by Bi 3+ cations into infinite chains. Ag 3 [IrBi 6 I 12 ] adopts a rock‐salt‐related superstructure with a high degree of occupation of octahedral voids by Ag + and thus represents the most densely interconnected member of this cluster family known so far. At room temperature, the silver substructure is strongly disordered and gives rise to an ionic conductivity of 1.05 × 10 − 4 S cm −1 , whereas at 100 K a commensurately modulated fivefold superstructure reveals long‐range silver ordering. Attempts to prepare the corresponding copper compound “Cu 3 [IrBi 6 I 12 ]” were unsuccessful; instead, a phase with a homogeneity range, Bi x Cu 3–3 x [IrBi 6 I 12 ] with x ≥ 0.5, was obtained, in which Bi 3+ is replaced by Cu+ distributed over trigonal‐planar and tetrahedral sites in and around the corresponding octahedral voids. Electron‐counting considerations and DFT‐based bonding analyses consistently support an electron‐precise 18‐electron configuration for iridium in [IrBi 6 I 12 ] 3− . DFT calculations identify Bi[IrBi 6 I 12 ] and Ag 3 [IrBi 6 I 12 ] as narrow‐gap semiconductors.

We report the synthesis, structure, and magnetic properties of two 1:3 ordered quadruple perovskites Sr4MRu3O12 (M = Li and Na). Sr4NaRu3O12 crystallizes in the centrosymmetric space group R3̅, and Sr4LiRu3O12 appears to be isostructural to the Na compound based on the PXRD data. In Sr4NaRu3O12, both Na and Ru are predominantly ordered at the B sites (here Na/Li and Ru), and the structure contains only corner-connected RuO6 and NaO6 octahedra. This atomic ordering also leads to a rather large unit cell with a = 11.25 Å and c = 27.6 Å compared to the basic 12R structure (a ∼ 5.5 Å and c ∼ 27 Å). Magnetic measurements reveal that Sr4NaRu3O12 undergoes a magnetic transition to an antiferromagnetic state below TN ∼ 265 K, confirmed by DSC and neutron diffraction. The Ru moments show a collinear antiferromagnetic spin alignment along the hexagonal c-axis with a propagation vector k = (0, 0, 1.5). Interestingly, those Ru moments lying on the 3-fold roto-inversion do not significantly contribute to the magnetic order, since they are located between antiferromagnetically coupled Ru atoms and are therefore highly frustrated. Sr4LiRu3O12 shows a magnetic anomaly around 110 K, possibly associated with competing ferromagnetic and antiferromagnetic interactions.

The novel sodium tetrachlorido-/azidoaurate(III) dihydrates Na[AuCl4- x(N3)x]·2H2O (x = 0, 1, 2, 3, 4) provide the first example of a complete series of gradual substitution on square planar complex anions to be described. Transparent yellow to dark orange single crystals of these phases were synthesized by reaction of NaN3 and AuCl3 or HAuCl4 in different molar ratios from aqueous solution. Controlled dehydration of Na[Au(N3)4]·2H2O led to Na[Au(N3)4]·H2O and Na[Au(N3)4] in form of orange microcrystalline powders, the latter being a highly explosive material. Predominant structural features of all phases are discrete anions [AuCl4- x(N3)x]- with gold in an ordered square planar coordination of azide/chloride anions. Vibrational spectra show good agreement with other known azidoaurates(III).

Synergistic liquid-liquid extraction (LLE) of Li+ commonly relies on β-diketonates in combination with neutral phosphine oxides such as tri-n-octylphosphine oxide (TOPO), yet the co-ligand is typically treated as an empirical additive rather than a design element. Here we show that commercially available diphosphine dioxides, featuring a preorganised PO⋯PO donor set and a spacer-defined bite, act as powerful co-ligands for Li+ extraction with 3-benzoyl-1,1,1-trifluoroacetone (HBTA) under mild pH conditions. Compared to TOPO, the best-performing PO⋯PO co-ligand enhances Li+ transfer while suppressing Na+/K+ co-extraction, consistent with altered solution speciation and stoichiometry. These results establish a chelating co-ligand (PO⋯PO) as a simple, modular strategy to control synergy in Li+ extraction systems based on classical CO⋯CO extractants such as HBTA.

Disorder in frustrated quantum systems can critically influence their magnetic ground states and drive exotic correlated behavior. In the S = 12 system ktenasite, Cu2.7Zn2.3(SO4)2(OH)6 & centerdot;6H2O, we show that structural disorder drives an unexpected dimensional crossover and stabilizes a rare coexistence of distinct magnetic states. Neutron diffraction reveals significant Cu/Zn mixing at the Cu2 site, which tunes the Cu2+ sublattice from a two-dimensional scalene-distorted triangular lattice into a one-dimensional spin-chain network. Magnetic susceptibility, neutron diffraction, ac susceptibility, and specific heat measurements collectively indicate magnetic duality: a coexistence of incommensurate long-range magnetic order below TN = 4 K and a cluster spin-glass state with Tf = 3.28 K at nu = 10 Hz. Our findings highlight ktenasite as a rare platform where structural disorder tunes the effective dimensionality and stabilizes coexisting ordered and glassy magnetic phases, offering a unique opportunity to explore the interplay of frustration, disorder, and dimensional crossover in quantum magnets.

Delafossite compounds containing rare-earth ions have been proven to be an ideal platform to investigate frustrated magnetic ground states. Here, we discuss two triangular-lattice antiferromagnets, TlErSe_2 and TlTmSe_2, as potential candidates for hosting exotic quantum states. Powder X-ray diffraction data analysis of the black-color polycrystalline TlRESe_2 (RE: Er and Tm) samples confirms the phase purity. Both materials crystallize in the trigonal α-NaFeO_2 structure (R3m) with lattice parameters a = 4.1070(4) Å and c = 23.1472(1) Å for the erbium compound and a = 4.0916(1) Å and c = 23.1483(2) Å for the thulium compound. Magnetic susceptibility measurements show an effective moment of μ_eff = 9.6(2) μ_B/f.u. (7.5(1) μ_B/f.u.) for TlErSe_2 (TlTmSe_2) for temperatures above 200 K. While ^3He specific-heat measurements reveal long-range magnetic order below T_N = 0.42K for TlErSe_2, no sign of long-range magnetic order was observed for TlTmSe_2. Based on our results, we map out the T-H phase diagram for polycrystalline TlErSe_2 and discuss the striking difference in the magnetic behavior of TlTmSe_2 based on our ab initio quantum chemical calculations.

Disorder in frustrated quantum systems can critically influence their magnetic ground states and drive exotic correlated behavior. In the S = 1/2 system ktenasite, Cu_2.7Zn_2.3(SO_4)_2(OH)_6·6H_2O, we show that structural disorder drives an unexpected dimensional crossover and stabilizes a rare coexistence of distinct magnetic states. Neutron diffraction reveals significant Cu/Zn mixing at the Cu2 site, which tunes the Cu^2+ sublattice from a two-dimensional scalene-distorted triangular lattice into a one-dimensional spin-chain network. Magnetic susceptibility, neutron diffraction, ac susceptibility, and specific heat measurements collectively indicate magnetic duality: a coexistence of incommensurate long-range magnetic order below T_N = 4K and a cluster spin-glass state with T_f = 3.28K at ν= 10Hz. Our findings highlight ktenasite as a rare platform where structural disorder tunes the effective dimensionality and stabilizes coexisting ordered and glassy magnetic phases, offering a unique opportunity to explore the interplay of frustration, disorder, and dimensional crossover in quantum magnets.

Semiconductors with one-dimensional (1D) substructures are promising for next-generation optical and electronic devices due to their directional transport and flexibility. Representatives of this class include HgPbP14-type materials. This study investigates the related semiconductors Ag1.7(1)Ge1.0(1)P14 and Ag1.4(1)Sn1.0(1)P14. Single-crystal X-ray diffraction indicates that their structure is unconventional due to its incommensurate modulation. Both compounds crystallize orthorhombically in the (3 + 1)D superspace group Pnma(0β0)s00 (No. 62.1.9.4). Ag1.7(1)Ge1.0(1)P14 (refined composition Ag2.2(1)Ge1.3(1)P18.7(1)) with the cell parameters a = 12.986(1) Å, b = 3.2648(4) Å, c = 10.841(1) Å, and a modulation wave vector q = (0, 0.39(1), 0), and Ag1.4(1)Sn1.0(1)P14 (refined as Ag1.9(1)Sn1.3(1)P18.7(1)) with a = 13.014(1) Å, b = 3.2602(4) Å, c = 10.905(1) Å, and q = (0, 0.42(1), 0) were investigated. Three structural models were generated, differing in modulation functions, site occupancies, and the split of one atomic position. Depending on the occupancy, the structure can be derived from Cu2P20, AgP15, or HgPbP14 -type materials. 119Sn Mössbauer spectroscopy confirms the +II oxidation state of tin in Ag1.4(1)Sn1.0(1)P14. Additional characterization was performed by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, angle-dependent Raman spectroscopy, and photoluminescence measurements. Single-crystal conductivity measurements revealed semiconducting behavior of Ag1.7(1)Ge1.0(1)P14 (0.2 S/cm).

Frustrated magnetism in face-centered-cubic (fcc) magnetic sublattices remains underexplored but holds considerable potential for exotic magnetic behavior. Here we report on the crystal structure and the magnetic and thermodynamic properties of the A-site-vacant hydroxide double perovskite MnSn(OH)6. Despite dominant antiferromagnetic interactions among Mn2+ moments, evidenced by a negative Curie-Weiss temperature, the lack of a sharp thermodynamic transition down to 350 mK implies the absence of long-range magnetic order. However, a broad hump in the specific heat at 1.6 K suggests short-range correlations. Neutron diffraction at low temperatures confirms the presence of three-dimensional antiferromagnetic correlations, manifested as diffuse magnetic scattering with a correlation length xi = 24.66 & Aring; and magnetic propagation vectors k = ( 1 1 2 ) and 1 2 2 (00.6250) at 20 mK.

Crystals of CeFeSb3 were synthesised using a Bi-flux. The compound crystallises in the CePdSb3 structure type and contains alternating slabs of Fe-centered Sb octahedra pairs and Sb square layers separated by layers of Ce atoms. Short Fe-Fe distances of 2.682 Å in the octahedra pairs suggest a covalent bond, which was confirmed by quantum chemical calculations. Magnetisation measurements indicate a complex antiferromagnetic ordering at TN = 4.7 K, attributed to localised Ce 4f moments, likely mediated by RKKY interactions. Mößbauer spectroscopy confirms the non-magnetic behaviour of the Fe atoms. Electrical transport data corroborate CeFeSb3 as a metal with Kondo-like interactions competing with the magnetic ordering.

CuSn(OH)6 is a quantum spin system from the family of magnetic double perovskite hydroxides, having a frustrated magnetic sublattice. It is also known as the natural mineral mushistonite, whose crystal structure has remained elusive for decades. Here we employ x-ray and neutron powder diffraction to solve the crystal structure of CuSn(OH)6 and propose a structure model in the orthorhombic space group Pnnn with correlated proton disorder. The occupation of the hydrogen sites in the structure is constrained by "ice rules" similar to those known for water ice, albeit with only local correlations. The resulting frustration of the hydrogen bonding network is likely to have a complex and interesting interplay with the strong magnetic frustration expected in the face-centered magnetic sublattice. Structural distortions, which are quite pronounced in Cu2+ compounds due to the Jahn-Teller effect, partially alleviate both types of frustration. We also show that hydrostatic pressure tends to suppress proton disorder through a sequence of proton-ordering transitions, as some of the split hydrogen sites merge already at 1.75 GPa while others show a tendency toward possible merging at higher pressures.

The face-centered-cubic lattice is composed of edge-sharing tetrahedra, making it a leading candidate host for strongly frustrated magnetism, but relatively few face-centered frustrated materials have been investigated. In the hydroxide double perovskite CuSn(OH)6, magnetic frustration of the Cu2+ quantum spins is partially relieved by strong Jahn-Teller distortions. Nevertheless, the system shows no signs of long-range magnetic order down to 45 mK and instead exhibits broad thermodynamic anomalies in specific heat and magnetization, indicating short-range dynamical spin correlations-a behavior typical of quantum spin liquids. We propose that such an unusual robustness of the spin-liquid-like state is a combined effect of quantum fluctuations of the S = 12 quantum spins, residual frustration on the highly distorted face-centered Cu2+ sublattice, and correlated proton disorder. Similar to the disorder-induced spin-liquid mimicry in YbMgGaO4 and herbertsmithite, proton disorder destabilizes the long-range magnetic order by introducing randomness into the magnetic exchange interaction network. However, unlike the quenched substitutional disorder on the magnetic sublattice, which is difficult to control, proton disorder can, in principle, be tuned through pressure-driven proton ordering transitions. This opens up the prospect of tuning the degree of disorder in a magnetic system to better understand its influence on the magnetic ground state.

In this comprehensive study, we present results of bulk measurements (magnetization, specific heat, ac susceptibility, thermal expansion, and magnetostriction) combined with local methods such as nuclear magnetic resonance (23Na NMR) and electron spin resonance (ESR) and simulations (McPhase) on polycrystalline and single-crystalline NaGdS2 samples. The rare-earth delafossite NaGdS2 is a triangular-lattice magnet with S = 7/2 spin-only Gd3+ moments with suppressed single-ion anisotropy. In our study, we estimate that NaGdS2 has a weak antiferromagnetic exchange (JH/kB approximate to 52 mK) and signs of long-range magnetic order are absent down to lowest temperature. However, indications of short range magnetic order are found below 180 mK in the ac susceptibility and thermal expansion. Our results indicate an interplay of Heisenberg-type and dipolar exchange. Due to the large moment of the Gd3+ ions, one expects a strong impact of the dipolar coupling in NaGdS2, in contrast to the related NaYbS2. ESR and 23Na NMR measurements, indeed, indicate the formation of short-range ferromagnetic correlations. NaGdS2 appears to be a rare system, in which magnetic order is suppressed by a competition between Heisenberg and dipolar interactions.