Structural Phase Transition in 0D (3,5-DMP)2Bi1-xSbxCl5 Metal Halides: Expression of the Lone Pair Effect and Polyhedral Distortion.

Low-dimensional Bi/Sb-based organic-inorganic metal halides (OIMHs) have attracted immense attention from the research community because of their structural diversity and efficient luminescence properties. Further understanding of the relationship between the structure and luminescence properties of these materials is of utmost importance for tuning the luminescence properties for various practical applications. Herein, we have synthesized two lead-free Bi/Sb-based novel OIMHs, (3,5-DMP)2BiCl5 and (3,5-DMP)2SbCl5 [(3,5-DMP) = 3,5-dimethylpiperidine], with zero-dimensional (0D) structures and crystallizing in triclinic (P1¯ space group) and monoclinic (P21/c space group) crystal systems, respectively. Both the compounds behave as typical semiconductors with indirect optical band gaps of 3.34 and 3.36 eV for pristine Bi and Sb compounds. These compounds exhibit higher environmental and thermal stability at ambient conditions. Gradual substitution of Sb at the Bi site in (3,5-DMP)2Bi1-xSbxCl5 resulted in the introduction of structural strain due to the significant expression of the lone pair effect, thus leading to a structural transition from the triclinic to monoclinic phase. The effect of the structural phase transition on the optical properties is also studied in (3,5-DMP)2Bi1-xSbxCl5. This work may offer new direction and guidance for exploring various 0D hybrid metal halides and tuning the structures for improvement in the luminescence properties.

Structural Transition in (C2H5NH3)3Bi2-xSbxI9:[(Bi/Sb)2I9]3- Dimers to [(Bi/Sb)3I12]3- Trimers to (∞1)[(Bi/Sb)2I93-] 1D Infinite Chains.

Antimony/bismuth-based lead-free hybrid halide defect 2D perovskites have been generating enormous research interest due to their inherent excellent optical properties. Exploration of new phases and understanding of their structural and optoelectronic properties are of paramount importance in the process of developing materials for practical solar cell applications. In this article, we have reported a structural transition from the 0D hexagonal phase containing isolated [M2I9]3- (M = Bi/Sb) units to the 1D orthorhombic phase via a new monoclinic phase with novel isolated trimeric [M3I12]3- units in (C2H5NH3)3Bi2-2xSb2xI9. The hexagonal phase is stable up to 2x = 0.6 in (C2H5NH3)3Bi2-2xSb2xI9. With gradual substitution of Sb, the cation-cation repulsion increases, which destabilizes the [M2I9]3- unit, and hence, the hexagonal phase becomes unstable. At intermediate composition, 2x = 0.8-1.6, a new monoclinic phase (S.G.: C2/m) with the composition (C2H5NH3)2Bi2-2xSb2xI8 is formed, containing isolated [M3I12]3- units. The symmetry reduction resulted in larger distortion, which relaxes the strain and stabilizes the trimeric unit in the intermediate compositions. Finally, at higher Sb compositions (2x = 1.9-2.0), the compounds crystallize in the orthorhombic 1D phase. In all three phases of (C2H5NH3)3Bi2-2xSb2xI9, the cationic ethylammonium units are completely disordered over the whole unit cell. Raman study clearly shows the phase transition in (C2H5NH3)3Bi2-2xSb2xI9 and also the structural distortion in (C2H5NH3)2Bi2-2xSb2xI8. Optical property study shows that all the compounds are of indirect band gap type. Furthermore, PL study shows better emission properties of the 1D orthorhombic Sb compounds as compared to the 0D hexagonal and monoclinic phases.

Solvent-mediated crystallization of (TMS)2BiBr5·DMSO: a new 0D hybrid halide perovskite.

Lead-free hybrid halide perovskites have recently gained enormous research attention because of their excellent optical properties. Herein, we report a novel zero-dimensional (0D) hybrid halide perovskite, (TMS)2BiBr5·DMSO, stabilized by the dimethyl sulfoxide (DMSO) solvent. The structure contains isolated [BiBr5OS(CH3)2]2- anionic polyhedra and the cations [(CH3)3S]+ (trimethyl sulfonium ion, TMS) balance the charge, making it a 0D halide perovskite. Non-interaction of the trans Br atoms (with respect to the Bi-DMSO bond) with the cationic TMS resulted in shorter trans Bi-Br bonds as compared to other Bi-Br bonds in the isolated BiBr5·DMSO polyhedra. The optical properties study reveals that the compound is an indirect band gap type with a band gap of 2.79 eV. From the PL study it is observed that the compound shows emission in the blue region.

Manifestation of dissimilar types of magnetism in iron- and chromium-substituted Mn2SnS4.

Mn2SnS4 belongs to the MII2AIVQ4 (M = transition metal; A = Si, Ge and Sn; Q = S, Se and Te) class of compounds that crystallizes in the orthorhombic space group Cmmm and shows complex magnetic properties. Here we report the synthesis and magnetic properties of Fe- and Cr-substituted Mn2SnS4 quaternary chalcogenides. All these compounds have been synthesized using a high-temperature solid-state route. Room temperature neutron diffraction studies on the specific compositions of chromium- and iron-substituted compounds were performed to obtain the site occupancy of different elements in the unit cell. The neutron diffraction analysis by employing the Rietveld refinement shows that for the Fe-substituted compound, most of the Fe goes to the Mn site with a small amount at the Sn site, while in the Cr-substituted sample, all the Cr occupy the Mn site. However, the Sn site almost remains intact in the case of the Fe-substituted compound, while it is significantly disordered for the Cr-substituted sample as a fraction of Mn occupies the Sn site and an equivalent amount of Sn occupies the Mn site. XPS study shows that both Cr and Fe exist in the +3 oxidation state, while Mn exists in the +2 state and Sn exists in a mixture of +2 and +4 oxidation states. Magnetic property study of these substituted compounds shows different types of magnetism, which is attributed to the variation of d-electrons of the substituent atom. The chromium-doped compounds show ferrimagnetic character along with two transitions: one transition at ∼37 K and another at ∼152 K. However, in Fe-substituted Mn2SnS4 samples, the low-temperature transition disappears and an increase in the high-temperature antiferromagnetic ordering temperature i.e. from 152 K (Mn2SnS4) to 174 K (Mn1.82Fe0.18SnS4) is observed. The increase in the antiferromagnetic ordering temperature in Mn2-xFexSnS4 may be attributed to the increase in the covalence of Mn/Fe-S-Mn/Fe bonds (shorter) with iron substitution.

Nominal Effect of Mg Intercalation on the Superconducting Properties of 2H-NbSe2.

2H-NbSe2 is a phonon-mediated, Fermi-surface topology-dependent multiband superconductor with an incommensurate charge-density wave (CDW) that coexists at a local level with superconductivity. Usually, the intercalation in 2H-NbSe2 enriches the CDW, enhances the c-axis lattice parameter, and distorts the Fermi surface, which result in a decrease in the superconducting transition temperature (Tc). The rate of decrease of Tc depends on the electronic structure, size, valence, magnetic nature, and electronegativity of the intercalating species. Herein, we report an unusual effect of Mg intercalation on the superconductivity of 2H-MgxNbSe2 (x = 0.0, 0.02, 0.06, 0.08, 0.10, and 0.12) synthesized by a high-temperature solid-state reaction method. Unlike other s- and p-block elements/species as intercalants (Rb, Sn, Ga, and Al) that have a sharp detrimental effect on the Tc of 2H-NbSe2 within 1-5% of intercalation, Mg is found to be an exception. Upon Mg intercalation up to x = 0.06, no remarkable changes in Tc as compared to the parent 2H-NbSe2 (Tc ∼ 6.7 K) are observed, and further intercalation results in a small decrease in Tc (for x = 0.12, Tc = 6.2 K). From heat-capacity measurements, it is inferred that superconducting Mg-intercalated 2H-NbSe2 exhibits strong electron-phonon coupling. Electronic structure calculations on two s-block element intercalated compounds of formula M0.125NbSe2 (M = Mg, Rb) show that Rb s-, p-, and d-states completely overlap with the Nb d states, while the Mg s states lie in a low-energy region as compared to Nb d states, indicating a weak interaction between the intercalant and the Nb sublattice in Mg0.125NbSe2 as compared to Rb0.125NbSe2. These results suggest that the electronic states of the Nb network in 2H-NbSe2 are least altered with Mg intercalation, which could be one of the reasons for the minimal effect on the Tc with intercalation.

Mixed-valent antimony-induced disorder in substituted antiferromagnetic Mn2SnS4.

Among MII2AIVQ4 (M = transition metal; A = Si, Ge, and Sn; Q = S, Se, and Te)-type compounds, most of which crystallize in an olivine or spinel structure, Mn2SnS4 is a unique compound that crystallizes in the orthorhombic space group Cmmm and exhibits complex magnetic properties. In this article, we report synthesis and study of the effect of Sb substitution (up to 20%) on the magnetic properties of Mn2SnS4. All the compounds were found to be in a single phase and indexed with the orthorhombic parent structure. Rietveld refinement of the room-temperature neutron diffraction data of Mn2Sn0.85Sb0.15S4 sample shows that Sb occupies the Mn site by replacing an equivalent amount of Mn. Subsequently, the replaced Mn occupies the Sn site causing disorder at both the Mn and the Sn sites, and the refined composition (Mn1.85(1)Sb0.15(1))(Sn0.85(1)Mn0.15(1))S4 is obtained. Although the purpose of incorporation of Sb(iii) was to create a mixed valence state at the Mn site, XPS study shows contrasting results. Sb exists in a mixed valence state, Sb(iii) and Sb(v), which balances the charge at the Sn(iv) site. Magnetic study of the compounds shows a very interesting trend. Pure Mn2SnS4 shows two magnetic transitions: one at 152 K that corresponds to antiferromagnetic ordering and other at 53 K corresponding to weak ferromagnetic ordering possibly due to spin canting. With antimony substitution, the temperature (152 K) of antiferromagnetic ordering remains unchanged, whereas the temperature of weak ferromagnetic ordering gradually increases with an increase in the Sb content from 53 K for the undoped compound to 88 K for 20% Sb-doped Mn2SnS4. The increase in the temperature of weak ferromagnetic ordering could be attributed to the incorporation of Sb, which induces more disorder at the Mn site, thereby making the magnetic lattice dilute with reduced frustration.

Synthesis of CuSbS2 Nanoplates and CuSbS2-Cu3SbS4 Nanocomposite: Effect of Sulfur Source on Different Phase Formation.

Layered CuSbS2 and related ternary metal chalcogenides have attracted huge research interest due to their potential applications in sustainable energy storage, photovoltaics, and related area. Here, we report facile synthesis of CuSbS2 nanoplates and CuSbS2-Cu3SbS4 nanocomposite using hot injection method with varying sulfur precursors. Elemental sulfur (S8) as sulfur precursor results in nanoplates of pure CuSbS2, while thioacetamide (TA) as sulfur source gives nanocomposite with Cu3SbS4 nanoparticle decorated on the surface of CuSbS2 nanoplates. The ease of reduction of TA as compared to sulfur at high temperature, in the presence of oleylamine, promotes the oxidation of antimony from (III) to (V) state and the formation of Cu3SbS4 phase containing Sb(V). Raman scattering study confirms the presence of Cu3SbS4 phase in CuSbS2-Cu3SbS4 nanocomposite. X-ray photoemission spectroscopy study on CuSbS2 nanoplates and CuSbS2-Cu3SbS4 nanocomposite confirms the desired valence state of the constituent elements. Electrochemical properties measurement shows better specific capacitance for CuSbS2-Cu3SbS4 nanocomposite (151 F/g) as compared to CuSbS2 nanoplates along with long-term cyclic stability with 68.2% capacitance retention.

CsMn4As3: A Layered Tetragonal Transition-Metal Pnictide Compound with an Antiferromagnetic Ground State.

We report the synthesis and properties of a new layered tetragonal ternary compound CsMn4As3 (structure type, KCu4S3; space group, P4/ mmm, no. 123; and Z = 2). The material is a small band gap semiconductor and exhibits an antiferromagnetic ground state associated with Mn spins. The compound exhibits a signature of a distinct magnetic moment canting event at 150(5) K with a canting angle ≈ 0.3°. Although some features of the magnetic characteristics of this new compound are qualitatively similar to those of the related BaMn2As2, the underlying Mn sublattices of the two materials are quite different. While the Mn square-lattice layers in BaMn2As2 are equally spaced along the c-direction with the interlayer distance dL Ba = 6.7341(4) Å, the Mn sublattice forms bilayers in CsMn4As3 with the interlayer distance within a bilayer being dL Cs = 3.1661(6) Å; the distance between the two adjacent bilayers is dB = 7.290(6) Å. This difference in the Mn sublattice is bound to significantly alter the energy balance among the J1, J2, and J c exchange interactions within the J1- J2- J c model compared to those in BaMn2As2 and the other related 122 compounds, including the well-known iron-arsenide superconductor parent compound BaFe2As2. Owing to the novelty of its transition-metal sublattice, this new addition to the family of tetragonal materials related to the iron-based superconductors brings prospects for doping and pressure studies in the search of new superconducting phases as well as other exciting correlated electron properties.

Substantial Cd-Cd bonding in Ca6PtCd11: a condensed intermetallic phase built of pentagonal Cd7 and rectangular Cd4/2Pt pyramids.

The novel intermetallic Ca6PtCd11 is orthorhombic, Pnma, Z = 4, with a = 18.799(2) Å, b = 5.986(1) Å, c = 15.585(3) Å. The heavily condensed network contains three types of parallel cadmium chains: apically strongly interbonded Cd7 pentagonal bipyramids, linear Cd arrays, and rectangular Cd4/2Pt pyramids. All of the atoms have 11-13 neighbors. Calculations by means of the linear muffin-tin orbitals method in the atomic spheres approximation indicate that some Cd-Cd interactions correspond to notably high Hamilton populations (1.07 eV per average bond) whereas the Ca-Ca covalent interactions (integrated crystal orbital Hamiltonian population) are particularly small (0.17 eV/bond). (Pt-Cd interactions are individually greater but much less in aggregate.) The Ca-Ca separations are small, appreciably less than the single bond metallic diameters, and unusually uniform (Δ = 0.14 Å). The Cd atoms make major contributions to the stability of the phase via substantial 5s and 5p bonding, which include back-donation of Cd 5s, 5p and Pt 5d into Ca 3d states in the principal bonding modes for Ca-Cd and Ca-Pt. Bonding Ca-Ca, Ca-Cd, and Cd-Cd states remain above EF, and some relative oxidation of Ca in this structure seems probable. Ca6PtCd11 joins a small group of other phases in which Cd clustering and Cd-Cd bonding are important.

Cluster chemistry in electron-poor Ae-Pt-Cd systems (Ae = Ca, Sr, Ba): (Sr,Ba)Pt2Cd4, Ca6Pt8Cd16, and its known antitype Er6Pd16Sb8.

Three new ternary polar intermetallic compounds, cubic Ca6Pt8Cd16, and tetragonal (Sr, Ba)Pt2Cd4 have been discovered during explorations of the Ae-Pt-Cd systems. Cubic Ca6Pt8Cd16 (Fm-3m, Z = 4, a = 13.513(1) Å) contains a 3D array of separate Cd8 tetrahedral stars (TS) that are both face capped along the axes and diagonally bridged by Pt atoms to generate the 3D anionic network Cd8[Pt(1)]6/2[Pt(2)]4/8. The complementary cationic surface of the cell consists of a face-centered cube of Pt(3)@Ca6 octahedra. This structure is an ordered ternary variant of Sc11Ir4 (Sc6Ir8Sc16), a stuffed version of the close relative Na6Au7Cd16, and a network inverse of the recent Er6Sb8Pd16 (compare Ca6Pt8Cd16). The three groups of elements each occur in only one structural version. The new AePt2Cd4, Ae = Sr, Ba, are tetragonal (P42/mnm,Z = 2, a ≈ 8.30 Å, c ≈ 4.47 Å) and contain chains of edge-sharing Cd4 tetrahedra along c that are bridged by four-bonded Ba/Sr. LMTO-ASA and ICOHP calculation results and comparisons show that the major bonding (Hamilton) populations in Ca6Pt8Cd16 and Er6Sb8Pd16 come from polar Pt-Cd and Pd-Sb interactions, that Pt exhibits larger relativistic contributions than Pd, that characteristic size and orbital differences are most evident for Sb 5s, Pt8, and Pd16, and that some terms remain incomparable, Ca-Cd versus Er-Pd.

Y3MnAu5: three distinctive d-metal functions in an intergrown cluster phase.

The new Y(3)MnAu(5) intermetallic phase is obtained from the arc-melted elements in virtually quantitative yields after annealing at 1000 °C for ~3 d. Its remarkable structure [rhombohedral, R3, Z = 6; a = 8.489(1) Å, c = 18.144(2) Å] consists of a 2:1 cubic-close-packed intergrowth between edge-shared Mn-centered Au rhombohedra (Mn@Au(8)) with gold-centered antiprismatic (Au@Y(6)) clusters via a common gold network. Magnetic susceptibility (χ) data for Y(3)MnAu(5) were fitted by a Curie-Weiss law. The Curie constant indicates a large effective moment corresponding to nearly localized Mn spins S = 5/2, and the Weiss temperature demonstrates the dominance of ferromagnetic (FM) interactions. An antiferromagnetic (AFM) transition at T(N) = 75 K and a possible spin reorientation transition at 65 K were observed. Analysis of the χ data for T < T(N) suggests a planar noncollinear helical AFM structure that arises from competing AFM interactions between FM-aligned layers of spins in the ab-plane with a turn angle of 69° between the spins along the helix c-axis. A magnetic field-induced spin flop transition is observed below T(N). Spin-polarized LMTO-LSDA calculations indicate an ~2 eV splitting of the Mn 3d states and a metallic ground state, and their COHP analyses demonstrate that ~81% of the total Hamilton populations originate from heteroatomic polar Y-Au and Mn-Au bonding. The Mn 3d, Y 4d, and Au 5d characteristics are remarkably diverse: localized and magnetically polarized for Mn; reducing and cationic for Y; and relativistically strongly bonded and oxidizing for Au, bonding of the latter two being broadly delocalized.

Two homologous intermetallic phases in the Na-Au-Zn system with sodium bound in unusual paired sites within 1D tunnels.

The Na-Au-Zn system contains the two intermetallic phases Na(0.97(4))Au(2)Zn(4) (I) and Na(0.72(4))Au(2)Zn(2) (II) that are commensurately and incommensurately modulated derivatives of K(0.37)Cd(2), respectively. Compound I crystallizes in tetragonal space group P4/mbm (No. 127), a = 7.986(1) Å, c = 7.971(1) Å, Z = 4, as a 1 × 1 × 3 superstructure derivative of K(0.37)Cd(2) (I4/mcm). Compound II is a weakly incommensurate derivative of K(0.37)Cd(2) with a modulation vector q = 0.189(1) along c. Its structure was solved in superspace group P4/mbm(00g)00ss, a = 7.8799(6) Å, c = 2.7326(4) Å, Z = 2, as well as its average structure in P4/mbm with the same lattice parameters.. The Au-Zn networks in both consist of layers of gold or zinc squares that are condensed antiprismatically along c ([Au(4/2)Zn(4)Zn(4)Au(4/2)] for I and [Au(4/2)Zn(4)Au(4/2)] for II) to define fairly uniform tunnels. The long-range cation dispositions in the tunnels are all clearly and rationally defined by electron density (Fourier) mapping. These show only close, somewhat diffuse, pairs of opposed, ≤50% occupied Na sites that are centered on (I) (shown) or between (II) the gold squares. Tight-binding electronic structure calculations via linear muffin-tin-orbital (LMTO) methods, assuming random occupancy of ≤ ∼100% of nonpaired Na sites, again show that the major Hamilton bonding populations in both compounds arise from the polar heteroatomic Au-Zn interactions. Clear Na-Au (and lesser Na-Zn) bonding is also evident in the COHP functions. These two compounds are the only stable ternary phases in the (Cs,Rb,K,Na)-Au-Zn systems, emphasizing the special bonding and packing requirements in these sodium structures.

Relativistic effects and gold site distributions: synthesis, structure, and bonding in a polar intermetallic Na6Cd16Au7.

Na(6)Cd(16)Au(7) has been synthesized via typical high-temperature reactions, and its structure refined by single crystal X-ray diffraction as cubic, Fm ̅3m, a = 13.589(1) Å, Z = 4. The structure consists of Cd(8) tetrahedral star (TS) building blocks that are face capped by six shared gold (Au2) vertexes and further diagonally bridged via Au1 to generate an orthogonal, three-dimensional framework [Cd(8)(Au2)(6/2)(Au1)(4/8)], an ordered ternary derivative of Mn(6)Th(23). Linear muffin-tin-orbital (LMTO)-atomic sphere approximation (ASA) electronic structure calculations indicate that Na(6)Cd(16)Au(7) is metallic and that ∼76% of the total crystal orbital Hamilton populations (-ICOHP) originate from polar Cd-Au bonding with 18% more from fewer Cd-Cd contacts. Na(6)Cd(16)Au(7) (45 valence electron count (vec)) is isotypic with the older electron-richer Mg(6)Cu(16)Si(7) (56 vec) in which the atom types are switched and bonding characteristics among the network elements are altered considerably (Si for Au, Cu for Cd, Mg for Na). The earlier and more electronegative element Au now occupies the Si site, in accord with the larger relativistic bonding contributions from polar Cd-Au versus Cu-Si bonds with the neighboring Cd in the former Cu positions. Substantial electronic differences in partial densities-of-states (PDOS) and COHP data for all atoms emphasize these. Strong contributions of nearby Au 5d(10) to bonding states without altering the formal vec are the likely origin of these effects.