Structural Transition in (C₂H₅NH₃)₃Bi_2–<i>x</i>Sb_<i>x</i>I₉:[(Bi/Sb)₂I₉]^3– Dimers to [(Bi/Sb)₃I₁₂]^3– Trimers to (∞^<b>1</b>)[(Bi/Sb)₂I₉^3–] 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

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)Au₂Zn₄ (<b>I</b>) and Na_0.72(4)Au₂Zn₂ (<b>II</b>) that are commensurately and incommensurately modulated derivatives of K_0.37Cd₂, respectively. Compound <b>I</b> crystallizes in tetragonal space group <i>P</i>4/<i>mbm</i> (No. 127), <i>a</i> = 7.986(1) Å, <i>c</i> = 7.971(1) Å, <i>Z</i> = 4, as a 1 × 1 × 3 superstructure derivative of K_0.37Cd₂ (<i>I</i>4/<i>mcm</i>). Compound <b>II</b> is a weakly incommensurate derivative of K_0.37Cd₂ with a modulation vector <i>q</i> = 0.189(1) along <i>c</i>. Its structure was solved in superspace group <i>P</i>4/<i>mbm</i>(00<i>g</i>)­00ss, <i>a</i> = 7.8799(6) Å, <i>c</i> = 2.7326(4) Å, <i>Z</i> = 2, as well as its average structure in <i>P</i>4/<i>mbm</i> with the same lattice parameters.. The Au–Zn networks in both consist of layers of gold or zinc squares that are condensed antiprismatically along <i>c</i> ([Au_4/2Zn₄Zn₄Au_4/2] for <b>I</b> and [Au_4/2Zn₄Au_4/2] for <b>II</b>) 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 (<b>I</b>) (shown) or between (<b>II</b>) 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

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 (<i>Fm-</i>3<i>m</i>, <i>Z</i> = 4, <i>a</i> = 13.513(1) Å) contains a 3D array of separate Cd₈ tetrahedral stars (<i>TS</i>) 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 (<i>P</i>4₂/<i>mnm,</i> <i>Z</i> = 2, <i>a</i> ≈ 8.30 Å, <i>c</i> ≈ 4.47 Å) and contain chains of edge-sharing Cd₄ tetrahedra along <i>c</i> 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

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)Au₂Zn₄ (<b>I</b>) and Na_0.72(4)Au₂Zn₂ (<b>II</b>) that are commensurately and incommensurately modulated derivatives of K_0.37Cd₂, respectively. Compound <b>I</b> crystallizes in tetragonal space group <i>P</i>4/<i>mbm</i> (No. 127), <i>a</i> = 7.986(1) Å, <i>c</i> = 7.971(1) Å, <i>Z</i> = 4, as a 1 × 1 × 3 superstructure derivative of K_0.37Cd₂ (<i>I</i>4/<i>mcm</i>). Compound <b>II</b> is a weakly incommensurate derivative of K_0.37Cd₂ with a modulation vector <i>q</i> = 0.189(1) along <i>c</i>. Its structure was solved in superspace group <i>P</i>4/<i>mbm</i>(00<i>g</i>)­00ss, <i>a</i> = 7.8799(6) Å, <i>c</i> = 2.7326(4) Å, <i>Z</i> = 2, as well as its average structure in <i>P</i>4/<i>mbm</i> with the same lattice parameters.. The Au–Zn networks in both consist of layers of gold or zinc squares that are condensed antiprismatically along <i>c</i> ([Au_4/2Zn₄Zn₄Au_4/2] for <b>I</b> and [Au_4/2Zn₄Au_4/2] for <b>II</b>) 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 (<b>I</b>) (shown) or between (<b>II</b>) 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

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)Au₂Zn₄ (<b>I</b>) and Na_0.72(4)Au₂Zn₂ (<b>II</b>) that are commensurately and incommensurately modulated derivatives of K_0.37Cd₂, respectively. Compound <b>I</b> crystallizes in tetragonal space group <i>P</i>4/<i>mbm</i> (No. 127), <i>a</i> = 7.986(1) Å, <i>c</i> = 7.971(1) Å, <i>Z</i> = 4, as a 1 × 1 × 3 superstructure derivative of K_0.37Cd₂ (<i>I</i>4/<i>mcm</i>). Compound <b>II</b> is a weakly incommensurate derivative of K_0.37Cd₂ with a modulation vector <i>q</i> = 0.189(1) along <i>c</i>. Its structure was solved in superspace group <i>P</i>4/<i>mbm</i>(00<i>g</i>)­00ss, <i>a</i> = 7.8799(6) Å, <i>c</i> = 2.7326(4) Å, <i>Z</i> = 2, as well as its average structure in <i>P</i>4/<i>mbm</i> with the same lattice parameters.. The Au–Zn networks in both consist of layers of gold or zinc squares that are condensed antiprismatically along <i>c</i> ([Au_4/2Zn₄Zn₄Au_4/2] for <b>I</b> and [Au_4/2Zn₄Au_4/2] for <b>II</b>) 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 (<b>I</b>) (shown) or between (<b>II</b>) 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

Substantial Cd–Cd Bonding in Ca₆PtCd₁₁: A Condensed Intermetallic Phase Built of Pentagonal Cd₇ and Rectangular Cd_4/2Pt Pyramids

The novel intermetallic Ca₆PtCd₁₁ is orthorhombic, <i>Pnma</i>, <i>Z</i> = 4, with <i>a</i> = 18.799(2) Å, <i>b</i> = 5.986(1) Å, <i>c</i> = 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 Cd_4/2Pt 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 <i>E</i>_F, 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

Microwave dielectric properties of new complex perovskites: (Ba_1/3Ln_2/3)(Zn_1/3Ti_2/3)O₃ (Ln=La, Pr, and Nd) and (Ba_(1+x)/3La_(2-x)/3)(Zn_1/3Ti_(2-x)/3Nb_x/3)O₃

Complex perovskites of the formula (Ba_1/3Ln_2/3)(Zn_1/3Ti_2/3)O₃ (Ln=La, Pr, and Nd) and (Ba_(1+x)/3La_(2-x)/3)(Zn_1/3Ti_(2-x)/3Nb_x/3)O₃ (x=0.5,0.75,1.0,1.25) have been synthesized by solid state reactions and are found to crystallize in the cubic structure (space group Pm3m) from Rietveld refinement of powder X-ray data. The lattice parameter and the grain size increases with Nb substitution. Among the above oxides, (Ba_1/3La_2/3)(Zn_1/3Ti_2/3)O₃ shows the best dielectric properties with quality factor (Q) of 3139 at 6.67 GHz and a temperature coefficient of resonant frequency (τf) of -10.8 ppm/°C. Further, the temperature coefficient of resonant frequency (τf) shows a large and systematic variation (with a continued decrease and a change of sign from positive to negative) with increase in Nb content