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The binary Fe chalcogenides FeSe and FeS are two superconductors which were discovered in recent years and have attracted a lot of attention in physical, chemical and materials research fields. In this work, we have synthesized FeS1−xSex solid solution crystals with the whole x range (0 ≤x≤ 1), where the S-rich part (0.1 ≤x ＜ 0.5) is reported for the first time so far. A hydrothermal route was carried out by de-intercalating K from the K0.8Fe1.6(S1−xSex)2 precursor and FeS1−xSex crystal sheets were thus obtained. Powder X-ray diffraction shows that the tetragonal lattice is maintained from x = 0 to 1 in this solid solution, and the selected area electron diffraction indicates the S/Se mixed occupation without any superstructure. As the Se content x increases, the lattice parameters expand due to the larger radius of the Se anion. Magnetic susceptibility demonstrates that with x≤ 0.3, FeS1−xSex crystals superconduct with the critical temperature basically unchanged (∼4 K). On the other hand, the Se-rich part of FeS1−xSex crystals (x≥ 0.6) exhibits an antiferromagnetic transition below 50 K, which could be attributed to the oxygen incorporation during the synthesis. Resistance measurement shows that the nematic order transition which was reported for FeSe in previous studies is absent in FeS1−xSex (x≤ 0.3) superconductors. This suggests that the superconducting mechanism in FeS-based chalcogenides may differ from that of FeSe. [ABSTRACT FROM AUTHOR]

Understanding the effects of non-stoichiometry on the structure and physical properties of tetragonal Fe chalcogenides is of great importance, especially for developing fascinating superconductivity in this system, which might be very sensitive to the non-stoichiometry. In this study, a series of Fe1−xS single crystals were synthesized by a hydrothermal method, which show varying concentrations of Fe vacancies (0 ≤x≤ 0.1) in the structure. Based on the crystal samples, the effects of vacancies on the crystal structure and physical properties were studied. The vacancy-free sample (x = 0) showed a metallic state in resistance and superconductivity below 4.5 K, whereas for the samples with Fe vacancies (x≥ 0.05), the SC was degraded and the sample exhibited semiconducting behavior. Structural analysis showed that the Fe vacancy decreases the lattice parameter a, but elongates c, leading to enhanced tetragonality in Fe1−xS. Selected-area electron diffraction showed that the vacancy in Fe1−xS was disordered, which is different from the scenario in FeSe-based materials. On combining the abovementioned results with the first-principles calculations, it was speculated that the disappearance of SC in non-stoichiometric Fe1−xS resulted from the localization of the 3d electrons of Fe. Moreover, the accompanied metal–insulator transition induced by Fe vacancy mainly belonged to the Mott mechanism because the vacancy did not significantly alter the band structure. These results not only provide deep insight into the effect of Fe vacancy in Fe chalcogenides, but also provide a basis to effectively induce SC in Fe sulfides by decreasing the number of Fe vacancies. [ABSTRACT FROM AUTHOR]

A single crystal of a new layered telluride KFeCuTe2 has been successfully synthesized by the self-flux method, which is formed by intercalating K in the parent telluride Fe1+xCuTe2. This new compound crystallizes in the space group I4/mmm with the interstitial Fe in pristine Fe1+xCuTe2 completely removed after K intercalation. X-ray photoelectron spectroscopy (XPS) shows that after intercalation, the valence of Fe switched from a mixture of +2 and +3 to the single trivalent one. The KFeCuTe2 is a Mott semiconductor (Eg = 1.06 eV) with a larger resistivity than that of Fe1+xCuTe2 due to the absence of electron doping from interstitial Fe atoms. Most importantly, the magnetic susceptibility shows the antiferromagnetic transition in KFeCuTe2 at 60 K, instead of the spin-glass behavior in Fe1+xCuTe2, indicating the crucial role of interstitial Fe in breaking the long-range magnetic ordering. Our work provides a new compound to study the effect of interstitial Fe on the crystal and magnetic structure in layered tellurides. [ABSTRACT FROM AUTHOR]

Layered Co-based chalcogenides ACo2Ch2 (A = Tl, K, Rb and Cs; Ch = Se, S) are believed to adopt the ThCr2Si2-type structure and they all share a similar [CoCh] functional layer. However, their interlayer magnetic interactions show significant differences, with the underlying mechanism still unclear. In this work, the chemical origin of the magnetic interactions in layered KCo2Se2−xSx (0 ≤x≤ 2) solid solution has been investigated by experiments and first-principles calculations. All the members of this solid solution are found to have the tetragonal ThCr2Si2-type structure with the space group I4/mmm. Both a and c lattice constants shrink monotonously with S doping. Ferromagnetic interactions are the same for all the members, even for a member with a similar layer distance to those of the antiferromagnetic TlCo2Se2−xSx. The calculated band structure and density of electronic states of KCo2Se2−xSx and TlCo2Se2−xSx show dramatically different scenarios, which is mainly due to the nature of Tl–Ch and K–Ch chemical bonding. Compared with the Tl chalcogenides, the K counterparts with ionic K–Ch bonds present more localized electronic states in terms of energy, which leads to positive interaction constants in the RKKY model. Our results give the quantitative explanation of the different interlayer couplings in the ACo2Ch2 family, as well as the influence of the intercalating layer on the properties of the functional layers in the ThCr2Si2-type structure. [ABSTRACT FROM AUTHOR]

Phase assemblages of the K-Fe-Se ternary system ( x < 33.3 %) were obtained by powder X-ray diffraction (PXRD). The superconducting phase KFeSe has not been detected in the phase assemblages. Based on the microscopic image and magnetic susceptibility of the samples with different annealing times, we demonstrate that KFeSe is the metastable phase, which only appeared at the beginning of annealing process, and converted to the non-superconducting phase after the long-time annealing. Graphical abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Organic–inorganic metal halides (OIMHs) possess low preparation costs and high photoluminescence quantum yield. Within a specific range, the temperature‐dependent nature of OIMHs' luminescent lifetime facilitates temperature sensing and thermal imaging functionalities. In this study, a non‐toxic (C10H22N)6SbBr9·H2O ([C10H22N]+ is 4‐(tert‐buty)cyclohexanamine cation) with a 0D structure crystallized in the Pbcn space group is obtained. Under blue light excitation at room temperature, it demonstrates intense broad emission centered at 635 nm. Further investigation into the correlation between temperature and photoluminescence lifetime has unveiled exceptional temperature sensing precision. The relative sensitivities within the range of power system temperature alert 30–70 °C lie between 2.5% and 4.5% K−1. This matches the typical high‐temperature warning threshold for power systems. Moreover, after immersion in water and alcohol, the compound maintains remarkable stability, with multiple heating/cooling cycles confirming its reliability under test temperatures. Additionally, a composite thin‐film device composed of (C10H22N)6SbBr9·H2O, showcasing its potential as a stable and durable thermal imaging temperature sensing device is fabricated. [ABSTRACT FROM AUTHOR]

This paper reports the results of the photocatalytic activity of hydrogen production from water reduction using a composite catalyst of SiC/CdS with two types of heterointerfaces. Type 1 consists of hexagonal SiC and hexagonal CdS, while type 2 consists of hexagonal SiC and cubic CdS. It was found that type 1 composite exhibited an H 2 evolution rate four times greater than type 2, despite the similar bandgaps and electropotentials of both cubic and hexagonal CdS. Meanwhile, increased BET surface area, good distribution of CdS, strong light absorption and low carrier recombination were observed in type 1 heterointerface. Lattice match is thought to be achieved between two hexagonal compounds with a lattice-constant-relationship of 3 a H-CdS = 4 a H-SiC . Further, the hexagonal SiC surface (006) was shown to have an affinity with the hexagonal CdS (002) facet due to their respective polar properties. The results of this paper demonstrate that lattice match plays an important role in forming efficient heterojunctions, which in turn enhance the photocatalytic performance of composite catalysts and will prove to be helpful in designing new composite photocatalytic systems. [ABSTRACT FROM AUTHOR]

Exploring semiconductors with a large band gap and a small hole effective mass are of great importance for the development of outstanding p-type transparent conducting materials. In this work, we report the single crystal growth of two Zn-based chalcogenides K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4. Single crystal X-ray diffraction revealed that K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4 crystallize in P 2/ c and Ibam space group, respectively. Both compounds show layered structure, and the layers are formed by edge-sharing tetragonal [Zn 3 Q 4 ]2- units and alkali-metal cations are distributed between the layers. To our surprise, compared to the previously reported structure obtained by powder X-ray diffraction, K 2 Zn 3 S 4 crystallized in a new type of structure in which adjacent layers were displaced. Both experiments and theoretical calculations indicate that K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4 are direct semiconductors with large band gaps, and the experimental values are 3.6 eV for K 2 Zn 3 S 4 and 3.1 eV for Rb 2 Zn 3 Se 4. Based on first-principles calculations, the hole effective masses of K 2 Zn 3 S 4 are calculated to be as small as 0.425 me, revealing the potential remarkable transparent conductivity in this Zn-based chalcogenide. [Display omitted] • The single-crystal growth of two Zn-based chalcogenides K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4. • K 2 Zn 3 S 4 is unexpectedly found to crystallize in a new structure. • Rb 2 Zn 3 Se 4 as a new compound adopts the same structure with known Cs 2 Zn 3 Se 4. • K 2 Zn 3 S 4 exhibits both a large band gap and a small calculated hole effective mass. • Indicate the potential p-type transport conducting behavior of K 2 Zn 3 S 4. [ABSTRACT FROM AUTHOR]

Hybrid metal halides display a range of optical properties and hold promise for various applications such as solid-state lighting, anti-counterfeiting measures, backlight displays, and X-ray detection. The incorporation of zinc into (C 13 H 26 N) 2 MnBr 4 aims to enhance its structural rigidity and improve its narrow band green light emission properties. The resulting (C 13 H 26 N) 2 ZnBr 4 compound exhibits an identical crystal structure to (C 13 H 26 N) 2 MnBr 4 , indicating the potential for a solid solution of varying Zn and Mn ratios within this structural framework. (C 13 H 26 N) 2 Zn 0.2 Mn 0.8 Br 4 exhibits significantly enhanced properties, including a photoluminescence quantum yield of 92%, a minimum full width at half maximum of 43 nm, and 85% retention of room temperature emission at 420 K. Additionally, crystals of (C 13 H 26 N) 2 ZnCl 4 and (C 7 H 18 N) 2 ZnX 4 (X = Br, I) are synthesized, with (C 7 H 18 N) 2 ZnBr 4 displaying luminescent color changes dependent on excitation. (C 7 H 18 N) 2 Zn 0.2 Mn 0.8 Br 4 demonstrates reversible phase transitions and alterations in optical properties. A white light-emitting diode utilizing (C 13 H 26 N) 2 Zn 0.2 Mn 0.8 Br 4 and commercial phosphors exhibited a color gamut of 112.2% of the National Television Standards Committee 1931 Standard. This investigation introduces a stable and highly efficient narrow-band green phosphor suitable for displays., (© 2024 Wiley‐VCH GmbH.)

Developing efficient electrocatalyst in sulfides for hydrogen evolution reaction (HER) still poses challenges due to the lack of understanding the role of sulfide heterointerface. Here, we report a sulfide heterostructure RuS x /NbS 2 , which is composed of 3R-type NbS 2 loaded by amorphous RuS x nanoparticles with S-S bonds formed at the interface. As HER electrocatalyst, the RuS x /NbS 2 shows remarkable low overpotential of 38 mV to drive a current density of 10 mA cm -2 in acid, and also low Tafel slope of 51.05 mV dec -1 . The intrinsic activity of RuS x /NbS 2 is much higher than that of Ru/NbS 2 reference as well as the commercial Pt/C. Both experiments and theoretical calculations unveil a reversed charge transfer at the interface from NbS 2 to RuS x that driven by the formation of S-S bonds, resulting in electron-rich Ru configuration for strong hydrogen adsorption. Meanwhile, electronic redistribution induced by the sulfide heterostructure facilitates hydrogen spillover (HSo) effect in this system, leading to accelerated hydrogen desorption at the basal plane of NbS 2 . This study provides an effective S-S bond strategy in sulfide heterostructure to synergistically modulate the charge transfer and adsorption thermodynamics, which is very valuable for the development of efficient electrocatalysts in practical applications., (© 2024 Wiley-VCH GmbH.)

Low-dimensional organic-inorganic metal halides (OIMHs) have been explored as single-component white light emitters for applications in solid-state lighting. Herein, we report a zero-dimensional (0D) In-based OIMH (TMPDA)[InCl 5 (H 2 O)] (TMPDA = N,N,N',N' -tetramethyl-1,4-phenylenediamine), which crystallizes in the noncentrosymmetric P 2 1 2 1 2 1 space group and contains hydrogen bonds between the adjacent [InCl 5 (H 2 O)] 2- octahedra in structure. It exhibits a large optical band gap (4.10 eV) and dual-band emission under UV light. Spectroscopic analysis and theoretical calculation indicate that the high (404 nm)- and low (513 nm)-energy emissions are attributed to the bound excitons in organic ligands and self-trapped excitons in [InCl 5 (H 2 O)] 2- units, respectively. It is found that Sb doping in this 0D hybrid provides additional orange (590 nm) emission assigned to the 3 P 1 → 1 S 0 triplet radiative recombination. By adjusting the doping level, the emission color can be turned from turquoise to orange, and interestingly, a single-component white-light emission is realized by balancing the high-energy emission from organic ligand, the turquoise emission from [InCl 5 (H 2 O)] 2- , and the orange one from [SbCl 5 (H 2 O)] 2- . This work not only provides a new OIMH showing the single-component white light emission but also demonstrates the potential of In-based hybrids with hydrogen bonds for solid-state luminescence.

Organic-inorganic metal halides (OIMHs) have drawn considerable attention due to their remarkable optoelectronic properties and substantial promise for nonlinear optical applications. In this research, phenazine has been selected as the organic cation because of its π-conjugated feature. Three compounds, (C 12 H 9 N 2 )PbCl 3 , (C 12 H 9 N 2 )SbCl 4 , and (C 12 H 9 N 2 ) 2 InBr 4 ·Br, were synthesized. Initial space group assignments were centrosymmetric for (C 12 H 9 N 2 )PbCl 3 and (C 12 H 9 N 2 )SbCl 4 . However, under 1550 nm laser excitation, (C 12 H 9 N 2 )PbCl 3 and (C 12 H 9 N 2 )SbCl 4 exhibited second harmonic generation intensities ∼1.7 times greater than that of the benchmark KH 2 PO 4 . Structural reevaluation ultimately confirmed non-centrosymmetric P 1 and P 2 1 space groups for (C 12 H 9 N 2 )PbCl 3 and (C 12 H 9 N 2 )SbCl 4 , respectively. Upon excitation at 335 nm and 470 nm, (C 12 H 9 N 2 )PbCl 3 , (C 12 H 9 N 2 )SbCl 4 , and (C 12 H 9 N 2 ) 2 InBr 4 ·Br emit fluorescence at room temperature. (C 12 H 9 N 2 ) 2 InBr 4 ·Br exhibits reversible phase transitions, showing potential for phase change energy storage. Our research underscores the critical role of comprehensive experimental validation in determining the precise crystallographic space groups and reveals the extensive potential of OIMHs as versatile candidates for advanced optoelectronic applications.

Low-dimensional tin-based halide perovskites are considered as eco-friendly substitutions of the iconic lead-based perovskites to host the potential as optoelectronic materials. However, a fundamental understanding of the structure-property relationship of these Sn(II)-based hybrids is still inadequate due to the limited members of this material family. To our knowledge, there is still lack of reports on a series of Sn(II)-based halide perovskites with the same organic cation but covering chloride, bromide, and iodide. In this work, three new halide perovskites TMPDASnX 4 (X = Cl, Br, I) (TMPDA = N,N, N ', N '-tetramethyl-1,4-phenylenediamine) are successfully synthesized, which provide the ideal paradigm to study the halogen-dependent evolution of the structure and properties of Sn(II)-based hybrid perovskites. Despite sharing the same monoclinic lattice ( P 2 1 / m space group), it is demonstrated that TMPDASnCl 4 adopts a one-dimensional structure composed of a five-coordinated pyramid configuration due to an extremely long Sn···Cl distance, while the typical two-dimensional motif is still maintained in TMPDASnBr 4 and TMPDASnI 4 . The ambient stability is declined in the order from chloride to bromide and then to iodide. TMPDASnCl 4 exhibits a broad-band bluish-white-light emission (centered at 515 nm, full width at half-maximum (fwhm) = 193 nm) with the Commission Internationale de l' Elairage (CIE) coordinates as (0.29, 0.34). Further, the correlated color temperature and color-rendering index were determined as 7617 K and 80.5, respectively. Based on the synthesis of new crystals, our work sheds light on the composition-structure-property relationship of hybrid Sn(II)-based halide perovskites., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Transition metal subchalcogenides involve electron-rich metals and can facilitate an in-depth understanding of the relationships among quantum properties such as superconductivity, charge density wave, and topological band structures. However, effective experimental routes toward synthesizing transition metal subchalcogenides are still lacking, hindering the development of new quantum materials. Herein, we propose a eutectic polytelluride flux strategy as an excellent solution to address phase discovery and crystal growth in transition metal subtelluride systems. We report new phases easily and selectively synthesized using a eutectic "K 3 Te 4 " polytelluride flux upon adjusting the ratio of Nb metal to flux in the starting materials (K/Nb/Te = 3: x :4). Using a high Nb content in the solvent ( x = 2 and 1), crystals of KNb 3 Te 3 O 0.38 and K 0.9 Nb 3 Te 4 are obtained. Both subtellurides exhibit diverse Nb clusters, including face-sharing and edge-sharing Nb 6 octahedral columns and zig-zag Nb chains. Reducing the Nb content to x = 0.33 leads to the formation of a layered compound, K 1.06 NbTe 2 . This compound comprises a NbTe 6 trigonal prism with K intercalated between the layers. Single crystals of known binary Nb tellurides can also be grown using another eutectic flux "KTe 3.2 ", and the obtained NbTe 2 exhibits a new polymorphism with extra trimerization along the b -axis in the Nb-Nb bonded double zig-zag cluster. Precise control over the structural dimensionality and oxidation state, combined with the facile crystal growth process, makes our synthetic strategy an efficient route to explore quantum materials in transition metal subchalcogenides.

Organic-inorganic metal halides (OIMHs) have various crystal structures and offer excellent semiconducting properties. Here, we report three novel OIMHs, (PPA) 6 InBr 9 (PPA = [C 6 H 5 (CH 2 ) 3 NH 3 ] + ), (PBA) 2 SbBr 5 , and (PBA) 2 SbI 6 (PBA = [C 6 H 5 (CH 2 ) 4 NH 3 ] + ), showing typical zero-dimensional (0D) structure, octahedra dimers, and corner-sharing one-dimensional chains and crystallized in the monoclinic system with P 2 1 , P 2 1 / c , and C 2/ c space groups, respectively. (PPA) 6 InBr 9 , (PBA) 2 SbBr 5 , and (PBA) 2 SbI 6 have experimental optical band gaps of ∼3.16, ∼2.24, and 1.48 eV, respectively. (PPA) 6 InBr 9 exhibits bright-orange light emission centered at 642 nm with a full-width at half-maximum of 179 nm (0.51 eV) and a Stokes shift of 277 nm (1.46 eV). After Sb 3+ doping, the peak position did not change, and the photoluminescence quantum yield increased significantly from 9.2 to 53.0%. The efficient emission of Sb:(PPA) 6 InBr 9 stems from the isolated ns 2 luminescent center and strong electron-phonon coupling, making the spin-forbidden 3 P 1 - 1 S 0 observable. By combining commercial blue and green phosphors with orange-red-light-emitting (PPA) 6 In 0.99 Sb 0.01 Br 9 , a white-light-emitting diode was constructed, with the color-rendering index reaching up to 92.3. Our work highlights three novel 0D OIMHs, with chemical doping of Sb 3+ shown to significantly enhance the luminescence properties, demonstrating their potential applications in solid-state lighting.

A new series of compounds, ANi 5 Bi 5.6+δ (where A = K, Rb, and Cs) are discovered with a quasi-one-dimensional (Q1D) [Ni 5 Bi 5.6+δ ] - double-walled column and a coaxial inner one-dimensional Bi atomic chain. The columns are linked to each other by intercolumn Bi-Bi bonds and separated by an A + cation. Typical metallic behaviors with strong correlation of itinerant electrons and the Sommerfeld coefficient enhanced with the increasing cationic radius were experimentally observed and supported by first-principles calculations. Compared to AMn 6 Bi 5 (where A = K, Rb, and Cs), the enhanced intercolumn distances and the substitution of Ni for Mn give rise to strong diamagnetic susceptibilities in ANi 5 Bi 5.6+δ . First-principles calculations reveal possible uncharged Ni atoms with even number of electrons in ANi 5 Bi 5.6+δ , which may explain the emergence of diamagnetism. ANi 5 Bi 5.6+δ , as Q1D diamagnetic metals with strong electron correlation, provide a unique platform to understand exotic magnetism and explore novel quantum effects.

The magnetic semiconductor in a two-dimensional system is a major subject for both theoretical and experimental investigations. Here we report the synthesis of a new quaternary manganese chalcogenide KMnCuTe 2 , which shows layered structure and antiferromagnetic (AFM) semiconducting features. Single crystals of KMnCuTe 2 were obtained using a self-flux method and based on single-crystal X-ray diffraction, KMnCuTe 2 adopts the ThCr 2 Si 2 -type structure composed of edge-sharing tetrahedral layers separated by K + cations. The Mn and Cu atoms randomly distribute in the centre of tetrahedral units. Attributed to the large radius of Te, KMnCuTe 2 has large lattice parameters ( a = 4.3115(3) Å and c = 14.9360(20) Å), leading to a long metal-metal distance (3.049 Å) in the tetrahedral layers. Based on the experiments and theoretical calculations, KMnCuTe 2 exhibits a G-type AFM interaction with the transition temperature at around 225 K and an indirect semiconducting nature with the band gap of 0.95 eV. The magnetic semiconducting property of KMnCuTe 2 is unique in AMnMCh 2 systems (A = Li, Na, K, M = Cu, Ag and Ch = S, Se, Te), which could be associated with the large metal-metal distance. Our work not only highlights the role of metal-metal interactions on regulating the properties of ThCr 2 Si 2 -type compounds, but also provides a feasible strategy to obtain the layered magnetic semiconductor., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Three new lead-free organic-inorganic metal halides (OIMHs) (C 7 H 8 N 3 ) 3 InX 6 ·H 2 O (X = Cl, Br) and (C 7 H 8 N 3 ) 2 SbBr 5 were synthesized. First-principles calculations indicate that the highest occupied molecular orbitals (HOMOs) of the two In-based OIMHs are constituted of π orbitals from [C 7 H 8 N 3 ] + spacers. (C 7 H 8 N 3 ) 3 InX 6 ·H 2 O (X = Cl, Br) shows an indirect optical gap, which may result from this organic-contributed band edge. Despite the indirect-gap nature with extra phonon process during absorption, the photoluminescence of (C 7 H 8 N 3 ) 3 InBr 6 ·H 2 O can still be significantly enhanced through Sb doping, with the internal photoluminescence quantum yields (PLQY) increased 10-fold from 5% to 52%. A white light-emitting diode (WLED) was fabricated based on (C 7 H 8 N 3 ) 3 InBr 6 ·H 2 O:Sb 3+ , exhibiting a high color-rendering index of 90. Our work provides new systems to deeply understand the principles for organic spacer choice to obtain the 0D metal OIMHs with specific band structure and also the significant enhancement of luminescence performance by chemical doping.

The Pb-free hybrid-layered-double perovskites (HLDPs) have been proposed as green and stable semiconducting materials for optoelectronic devices, but the synthesized members are still limited. Here, we report the synthesis of three new HLDPs, (C 8 H 20 N 2 ) 2 AgMBr 8 (M = In, Sb, and Bi), by a solution method using 1,4-bis(ammoniomethyl)cyclohexane (C 8 H 20 N 2 2+ ) as the organic spacing cation. All three of these HLDPs show ⟨100⟩-oriented layered structures with Ag and In/Sb/Bi order arranged in corner-sharing octahedral layers. The first-principle calculations indicate the indirect-gap nature of (C 8 H 20 N 2 ) 2 AgInBr 8 and (C 8 H 20 N 2 ) 2 AgSbBr 8 , while their Bi counterpart shows a direct band gap after considering spin-orbit coupling. The band gaps obtained by diffuse-reflectance spectroscopy are 3.11, 2.60, and 2.70 eV for M = In, Sb, and Bi, respectively. (C 8 H 20 N 2 ) 2 AgInBr 8 shows a broadband red emission centered at 690 nm, and it is mainly attributed to the self-trapped-excitons mechanism. Our results not only provide a series of new "Pb-free" HLDPs with chemical diversity but also help us to further understand the structure-property relationships of HLDP materials.

The reaction of MnTe with AgSbTe 2 in an equimolar ratio (ATMS) provides a new semiconductor, AgMnSbTe 3 . AgMnSbTe 3 crystallizes in an average rock-salt NaCl structure with Ag, Mn, and Sb cations statistically occupying the Na sites. AgMnSbTe 3 is a p-type semiconductor with a narrow optical band gap of ∼0.36 eV. A pair distribution function analysis indicates that local distortions are associated with the location of the Ag atoms in the lattice. Density functional theory calculations suggest a specific electronic band structure with multi-peak valence band maxima prone to energy convergence. In addition, Ag 2 Te nanograins precipitate at grain boundaries of AgMnSbTe 3 . The energy offset of the valence band edge between AgMnSbTe 3 and Ag 2 Te is ∼0.05 eV, which implies that Ag 2 Te precipitates exhibit a negligible effect on the hole transmission. As a result, ATMS exhibits a high power factor of ∼12.2 μW cm -1 K -2 at 823 K, ultralow lattice thermal conductivity of ∼0.34 W m -1 K -1 (823 K), high peak ZT of ∼1.46 at 823 K, and high average ZT of ∼0.87 in the temperature range of 400-823 K.

It is known that as the FeAs 4 tetrahedron in the Fe-based superconductor is close to the regular tetrahedron, critical temperature ( T c ) can be greatly increased. Recently, a Co-based superconductor of LaCoSi (4 K) with "111" structure was found. In this work, we improve the T c of LaCoSi through structural regulation. T c can be increased by the chemical substitution of Co by Fe, while the superconductivity is suppressed by the Ni substitution. The combined analysis of neutron and synchrotron X-ray powder diffractions reveals that the change of the Si-Co-Si bond angles of the CoSi 4 tetrahedron is possibly responsible for the determination of superconducting properties. The Fe chemical substitution is favorable for the formation of the regular tetrahedron of CoSi 4 . The present new Co-based superconductor of LaCoSi provides a possible method to enhance the superconductivity performance of the Co-based superconductors via controlling Co-based tetrahedra similar to those well established in the Fe-based superconductors.

Low-dimensional organic-inorganic metal halides (OIMHs), as emerging light-emitting materials, have aroused widespread attention owing to their unique structural tunability and photoelectric characteristics. OIMHs are also promising materials for optoelectronic equipment, light-emitting diodes, and photodetectors. In this study, (C 3 H 12 N 2 ) 2 Sb 2 Cl 10 (C 3 H 12 N 2 2+ is an N -methylethylenediamine cation), a new zero-dimensional OIMH, has been reported, and (C 3 H 12 N 2 ) 2 Sb 2 Cl 10 possesses a P 2 1 / n space group. The (C 3 H 12 N 2 ) 2 Sb 2 Cl 10 structure contains [Sb 2 Cl 10 ] 4- dimers (composed of two edge-sharing [SbCl 6 ] 3- octahedra) that are surrounded by C 3 H 12 N 2 2+ cations. The experimental band gap of (C 3 H 12 N 2 ) 2 Sb 2 Cl 10 is 3.80 eV, and density functional theory calculation demonstrates that (C 3 H 12 N 2 ) 2 Sb 2 Cl 10 possesses a direct band gap, with the edge of the band gap mainly contributed from the inorganic units. (C 3 H 12 N 2 ) 2 Sb 2 Cl 10 exhibits good ambient and thermal stability. Under 395 nm excitation at room temperature, (C 3 H 12 N 2 ) 2 Sb 2 Cl 10 exhibits a broad emission with a full width at half-maximum of ∼114 nm, peaking at 480 nm, and the broad emission was ascribed to self-trapped exciton emission.

Layered sulfides with high selectivity for binding heavy metal ions and radionuclide ions are promising materials in effluent treatment and water purification. Here we present a rationally designed layered sulfide K x [Bi 4- x Mn x S 6 ] ( x = 1.28) deriving from the Bi 2 Se 3 -structure type by targeted substitution to generate quintuple [Bi 4- x Mn x S 6 ] x - layers and K + cations between them. The material has dual functionality: it is an attractive semiconductor with a bandgap of 1.40 eV and also an environmental remediation ion-exchange material. The compound is paramagnetic, and optical adsorption spectroscopy and DFT electronic structure calculations reveal that it possesses a direct band gap and a work function of 5.26 eV. The K + ions exchange readily with alkali or alkaline-earth ions (Rb + , Cs + , and Sr 2+ ) or soft ions (Pb 2+ , Cd 2+ , Cr 3+ , and Zn 2+ ). Furthermore, when the K + ions are depleted the Mn 2+ ions in the Bi 2 Se 3 -type slabs can also be replaced by soft ions, achieving large adsorption capacities. The ion exchange reactions of K x [Bi 4- x Mn x S 6 ] can be used to create new materials of the type M x [Bi 4- x Mn x S 6 ] in a low temperature kinetically controlled manner with significantly different electronic structures. The K x [Bi 4- x Mn x S 6 ] ( x = 1.28) exhibits efficient capture of Cd 2+ and Pb 2+ ions with high distribution coefficient, K d (10 7 mL/g), and exchange capacities of 221.2 and 342.4 mg/g, respectively. The material exhibits excellent capacities even in high concentration of competitive ions and over a broad pH range (2.5-11.0). The results highlight the promise of the K x [Bi 4- x Mn x S 6 ] ( x = 1.28) phase to serve not only as a highly selective adsorbent for industrial and nuclear wastewater but also as a magnetic 2D semiconductor for optoelectronic applications.

In this work, we report the discovery of a new Ni-based quasi-one-dimensional selenide: Cs 0.9 Ni 3.1 Se 3 . This compound adopts the TlFe 3 Te 3 -type structure with space group P6 3 / m, which consists of infinite [Ni 3 Se 3 ] chains with face-sharing Ni 6 octahedra along the c direction. The lattice parameters are calculated as a = 9.26301(4) Å and c = 4.34272(2) Å, with the Ni-Ni distance in the ab plane as 2.582(3) Å, suggesting the formation of a Ni-Ni metallic bond in this compound. Interestingly, it has been found that Cs 0.9 Ni 3.1 Se 3 is nonstoichiometric, which is different from the other TlFe 3 Te 3 -type phases reported so far. Structure refinement shows that the extra Ni atom in the structure may occupy the 2c site, together with Cs atoms. Cs 0.9 Ni 3.1 Se 3 shows metallic behavior with monotonously decreased resistivity with temperatures from 300 to 0.5 K. Measurements on the magnetic susceptibility display a spin-glass state below 7 K. The specific heat curve gives a Sommerfeld coefficient of 14.6 mJ·K -2 ·mol -1 and a Debye temperature of 143.6 K. The discovery of this new compound enriches the diversity of low-dimensional materials in a transition-metal-based family and also sheds light on the structure-property relationship of this system.

Understanding the effects of non-stoichiometry on the structure and physical properties of tetragonal Fe chalcogenides is of great importance, especially for developing fascinating superconductivity in this system, which might be very sensitive to the non-stoichiometry. In this study, a series of Fe 1-x S single crystals were synthesized by a hydrothermal method, which show varying concentrations of Fe vacancies (0 ≤ x ≤ 0.1) in the structure. Based on the crystal samples, the effects of vacancies on the crystal structure and physical properties were studied. The vacancy-free sample (x = 0) showed a metallic state in resistance and superconductivity below 4.5 K, whereas for the samples with Fe vacancies (x ≥ 0.05), the SC was degraded and the sample exhibited semiconducting behavior. Structural analysis showed that the Fe vacancy decreases the lattice parameter a, but elongates c, leading to enhanced tetragonality in Fe 1-x S. Selected-area electron diffraction showed that the vacancy in Fe 1-x S was disordered, which is different from the scenario in FeSe-based materials. On combining the abovementioned results with the first-principles calculations, it was speculated that the disappearance of SC in non-stoichiometric Fe 1-x S resulted from the localization of the 3d electrons of Fe. Moreover, the accompanied metal-insulator transition induced by Fe vacancy mainly belonged to the Mott mechanism because the vacancy did not significantly alter the band structure. These results not only provide deep insight into the effect of Fe vacancy in Fe chalcogenides, but also provide a basis to effectively induce SC in Fe sulfides by decreasing the number of Fe vacancies.