The structure of Ba3W2O9; an example of face-shared octahedra with tungsten (VI)

The structure of Ba₃W₂O₉ has been determined from powder x-ray diffraction data and found to be the same as in Cs₃Tl₂Cl₉. Two-thirds of the octahedral sites between hexagonal closest-packed BaO₃ layers (ABAB…) are filled by the tungsten atoms. The enneaoxo W₂O₉^6? group represents the first crystal chemistry example of tungsten (VI) in a face-sharing arrangement. Infrared and Raman data are consistent with overall 32 (D₃) site symmetry. Crystallographic and spectroscopic evidence supports a covalent bonding model with oxygen pπ → metal dπ stabilization of this tungsten (VI) phase.     

Crystal growth and luminescence of Sb3+-Doped Cs2NaMCl6 (M = Sc,Y, La)

Crystal growth and the luminescence properties of Cs₂NaMCl₆-Sb³⁺ (M = Sc, Y, La) are described. The emission consists of one band which shifts to lower energies for an increasing ionic radius of M³⁺ (i.e. from Sc via Y to La). The excitation bands of the luminescence of all three compounds are at the same energy and show a structure which can be explained by assuming a dynamical Jahn-Teller effect to be operative in the excited state of the Sb³⁺-ion.     

Electrical conductivity of the systems (Rb4−xMx)Cu16I7Cl13 (M=K,Cs), Rb4Cu16(I7−xBrx)Cl13 and Rb4Cu16I7(Cl13−xBrx)

The solid solution ranges in the systems (Rb_4?xK_x)Cu₁₆I₇Cl₁₃, (Rb_4?xCs_x)Cu₁₆I₇Cl₁₃, Rb₄Cu₁₆(I_7?xBr_x)Cl₁₃, and Rb₄Cu₁₆I₇(Cl_13?xBr_x), have been examined and the electrical conductivity has been measured as a function of temperature and composition. In the system (Rb_4?xK_x)Cu₁₆I₇Cl₁₃, room temperature conductivities increase from 0.32Scm^?1 for x=0 to 0.47Scm^?1 for x=0.40. On the other hand, the conductivities of the systems (Rb_4?xCs_x)Cu₁₆I₇Cl₁₃ and Rb₄Cu₁₆I₇(Cl_13?xBr_x) decrease with increasing x. The system Rb₄Cu₁₆(I_7?xBr_x)Cl₁₃ shows no significant change of the conductivity on x.     

Preparation and crystal chemistry of some rare earth vanadium (IV) pyrochlores (RE)2V2O7; RE = Lu,Yb, Tm,Lu1−xYx, Lu1−xScx

The preparation of the phases (RE)₂V₂O₇ where RE = Lu, Yb, Tm, and the solid solutions Sc_xLu_1?x (x = .10 → .50) and Y_xLu_1?x (x = .20 and .40), using a $\text{CO}\text{CO}{}_2$ buffer system are described. Precision lattice constants were determined and compared with previous work, finding good agreement with (1) but not with (2). The solid solution (Sc_xLu_1?x)₂V₂O₇ exists as a pyrochlore to x = .30, compared with x = .55 for the similar (Sc_xLu_1?x)₂ Ti₂O₇ system. Chemical analysis on the members x = .40 and x = .50 indicate significant amounts of V(III) and X-ray data show a diminishing intensity for the “ordering” reflections (h, k, l all odd). These results suggest that Lu(III), Sc(III), V(III) and V(IV) are partially disordered over both cation sites tending toward a C-type (RE)₂O₃ structure or a defect fluorite structure with increasing x.     

Cs2Si2Te6, ein polypertelluridosilikat (IV)

The new compound Cs₂Si₂Te₆ crystallizes in the monoclinic system (space group: Cc, No. 9) with the lattice constants a = 828.5(4) pm, b = 1393.5(6) pm, c = 1340.4(6) pm, ß = 100.35(12)°.Fivefold Si₂Te₃-rings, each formed by two SiTe₄ tetrahedra, connected by common Te atoms and Te-Te groups, are linked by Te bridges to infinite strings.     

K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9) perovskite compounds

We systematize available experimental data on the crystal structure of the ternary halides K₂(Rb₂,Cs₂,Tl₂)TeBr₆(I₆) and Rb₃(Cs₃)Sb₂(Bi₂)Br₉(I₉), analyze the general trends in the properties of their single crystals, and examine the key features of the physicochemical interaction in related systems.     

0D Cs3Cu2X5 (X = I,Br, and Cl) Nanocrystals: Colloidal Syntheses and Optical Properties

0D lead‐free metal halide nanocrystals (NCs) are an emerging class of materials with intriguing optical properties. Herein, colloidal synthetic routes are presented for the production of 0D Cs₃Cu₂X₅ (X = I, Br, and Cl) NCs with orthorhombic structure and well‐defined morphologies. All these Cs₃Cu₂X₅ NCs exhibit broadband blue‐green photoluminescence (PL) emissions in the range of 445–527 nm with large Stokes shifts, which are attributed to their intrinsic self‐trapped exciton (STE) emission characteristics. The high PL quantum yield of 48.7% is obtained from Cs₃Cu₂Cl₅ NCs, while Cs₃Cu₂I₅ NCs exhibit considerable air stability over 45 days. Intriguingly, as X is changed from I to Br and Cl, Cs₃Cu₂X₅ NCs exhibit a continuous redshift of emission peaks, which is contrary to the blueshift in CsPbX₃ perovskite NCs.     

Crystal structures of two cesium phosphate-tellurates : Te(OH)6.Cs2HPO4 and Te(OH)6.Cs2HPO4.2CsH2PO4

Te(OH)₆.Cs₂HPO₄ and Te(OH)₆.Cs₂HPO₄.2CsH₂PO₄ are monoclinic, the first one with a = 8.204(5), b = 18.416(9), $\text{c}\text{= 6.995(5)}\text{A}\text{?}$, β = 89.89(5)°, Z = 4, space group P2₁/n, the second one with a = 9.591(6), b = 13.163(9), $\text{c}\text{= 8.367(5)}\text{A}\text{?}$, β = 106.27(5)°, Z = 2, space group P2₁/m. As already observed in previously described phosphate-tellurates the main feature of these atomic arrangements is the coexistence of two independent and different types of anions (PO₄ and TeO₆ groups) in the unit cell.     

The new pyrochlores Pb2(M0 · 5Sb1 · 5)O6 · 5 (M = Al,Sc, Cr,Fe, Ga,Rh)

From mixtures of PbO, M₂O₃ (M = Al, Sc, Cr, Fe, Ga, Rh), and Sb₂O₃, the new oxides Pb₂(M_{0 · 5}Sb_{1 · 5})O_{6 · 5} have been obtained as coloured powders giving X-ray diffraction patterns typical of cubic pyrochlores, S.G. Fd3?m (No. 227), and $\text{a}\text{A}\text{?}$ values from 10.3964(1) (M = Al) to 10.5558(1) (M = Sc). The best R factors were obtained for Pb in 16(c) positions, M and Sb (1:3) randomly distributed in 16(d), oxygen in 48(f) and one half of the 8(a) sites, and $\text{x}$ values for the oxygen positional parameter (origin at center, 3?m) from 0.430 (M = Sc) to 0.436 (M = Al). Apparent interatomic distances compare with those calculated. The angles of the coordination polyhedra around the metals are reported for the compounds of Al and Sc. Seven-coordination of Pb(II) is accounted for by the non-bonded electron pair effect.     

The preparation and characterization of Ba3Te2O9; a new oxide structure

The structure of Ba₃Te₂O₉ has been determined from x-ray powder diffraction data and by profile refinement of neutron diffraction data. We find tellurium octahedrally coordinated as expected and the same face-shared [B₂O₉]^6? unit as observed in Ba₃W₂O₉. The phase Ba₃Te₂O₉ has, however, a Cs₃Fe₂F₉ type structure ($\text{P}\text{6}{}_3\text{mmc}$, $\text{a}\text{=}\text{5}\text{.8603(1)}\text{A}\text{?}$, $\text{c}\text{=14.3037(6)}\text{A}\text{?}$) rather than the Cs₃Tl₂Cl₉ structure (R3c) found for the tungsten analogue. The two oxide structures have the same BaO₃ layer sequence but differ only in the spatial arrangement of the [B₂O₉] groups in the lattice. Infrared and Raman spectra confirm the different site symmetries associated with the different packing of the tungstate and tellurate anions in their respective structures.     

KTiOPO4 and Cs2WO2Cl4: Two exceptional cases of do ion luminescence

The compound KTiOPO₄ shows an extremely short wavelength titanate emission (390 nm) which is quenched at about 100 K. This luminescence is discussed in terms of a self-trapped excition which becomes mobile at higher temperatures. Comparison with other titanates is made. The linear titanate chain in KTiOPO₄ must be rather covalent. In Cs₂WO₂Cl₄ we observed an extremely long wavelength tungstate emission. Comparison with related tungstates is made. In Cs₂WO₂Cl₄ the chlorotungstate group is completely isolated. The low quenching temperature of this luminescence has a different origin from that of KTiOPO₄.     

Citrate gel synthesis and characterization of (ZrO2)0.85(REO1.5)0.15 (RE = Y, Sc) solid solutions

By the citrate gel method, (ZrO₂)_0.85(REO_1.5)_0.15 (RE = Y, Sc) solid solutions in pure cubic fluorite structure were prepared at relatively low calcination temperatures. The existence of the strong coordination interaction between the COO⁻ groups of the ligands and metal ions could effectively prevent the segregation of metal ions during the gel formation. Upon heat treatment within 110-500 °C, the gel decomposed by multi-steps, with the formation of well-defined intermediate decomposition products, while, the bonding nature between COO⁻ groups and metal ions changed with temperature: unidentate (110-250 °C) → bridging (300-350 °C) → ionic (400-500 °C). The oxide powder resulted from the calcination of the gel at 800 °C is an assembly of mesoporous nanoparticles with uniform sizes, but agglomerated in lumps. It was confirmed that the chemical homogeneity, nanoparticle size uniformity and crystallinity, sinterability and electrical conductivity of (ZrO₂)_0.85(REO_1.5)_0.15 can be remarkably improved by avoiding the phase separation (solid/liquid) phenomenon during the preparation of the gels.     

Structures cristallines des phases M2Ga2Fe2O9 (M = In,Sc) nouveaux exemples de coordinence 5 du fer

New quaternary oxides are reported : M₂Ga₂Fe₂O₉ (M = In,Sc). In₂Ga₂Fe₂O₉ has been studied by single-crystal X-ray diffraction analysis. Its structure is a new type with space group Pba2 and $\text{z}\text{=}\text{8}\text{3}\text{:}\text{a}\text{= 19.253(3)}$, b = 7.2176(2), $\text{c}\text{= 3.2581(1)}\text{A}\text{?}$, D_x = 6.05 g.cm^?3, μ(AgK_α) = 9mm^?1, F(000) = 757.1, R = 0.037 for 420 independant reflexions (R_w = 0.037). The indium are heptahedrally coordinated by seven oxygen atoms and the iron and gallium atoms by five oxygen atoms at the apices of a trigonal bipyramid.     

Synthesis and transformation of zero-dimensional Cs3BiX6 (X = Cl,Br) perovskite-analogue nanocrystals

The unique structure of zero-dimensional (0D) perovskite-analogues has attracted a great amount of research interest in recent years. To date, the current compositional library of 0D perovskites is largely limited to the lead-based Cs₄PbX₆ (X = Cl, Br, and I) systems. In this work, we report a new synthesis of lead-free 0D Cs₃BiX₆ (X = Cl, Br) perovskite-analogue nanocrystals (NCs) with a uniform cubic shape. We observe a broad photoluminescence peak centered at 390 nm for the 0D Cs₃BiCl₆ NCs at low temperatures. This feature originates from a self-trapped exciton mechanism. In situ thermal stability studies show that Cs₃BiX₆ NCs remain stable upon heating up to 200 °C without crystal structural degradation. Moreover, we demonstrate that the Cs₃BiX₆ NCs can transform into other bismuth-based perovskite-analogues via facile anion exchange or metal ion insertion reactions. Our study presented here offers the opportunity for further understanding of the structure-property relationship of 0D perovskite-analogue materials, leading toward their future optoelectronic applications.

     

The thallous chalcogenides Tl6X4Y (X = Cl,Br, I; Y = S,Se)

Single crystals of Tl₆X₄Y(X = Cl, Br, I; Y = S, Se) were prepared by the Bridgman technique. The compounds were characterized by complete X-ray structural analyses. All are isotypic, space group $\text{P}\text{4}\text{mnc}$, with a = 843.3(2) pm, c = 917.2(2) pm for Tl₆Cl₄S, a = 872.1(2) pm, c = 932.8(1) pm for Tl₆Br₄S, a = 917.6(3) pm, c = 960.8(1) pm for Tl₆I₄S and a = 917.8(3) pm, c = 967.5(1) pm for Tl₆I₄Se. FIR spectra as well as photoacoustic spectra are given.     

LuMnGe2, un nouveau type structural apparente a ceux de TiMn(Fe)Si2, ZrMnSi2 et ZrFeSi2; ScMnGe2, un nouvel isotype de TiMn(Fe)Si2

LuMnGe₂ has been studied by single - crystal X-ray diffraction analysis. The structure is of a new type with space group Cmmm and Z = 12: a = 5.466(2), b = 18.519(7), $\text{c}\text{= 8.173(3)}\text{A}\text{?}$, D_x = 9.03 Mg m^?3, μ(AgKα) = 31 mm^?1, F(000) = 1919, R = 0.030 for 593 independant reflexions (R_w = 0.034). The LuMnGe₂ structure type had been predicted and completes a large structural family TT′Si(Ge)₂ where T = Nb, Ti, Zr, Hf, Sc, Lu and T′ = Cr, Mn, Re, Fe, Co, where ScMnGe₂ is another new member, isostructural with TiMn(Fe)Si₂     

Cs4GeTe6, ein o-Pertelluridogermanat (IV)

The new compound Cs₄GeTe₆ crystallizes in the monoclinic system, space group P2₁/n (No. 14) with the lattice constants a = 1784.5(8) pm, b = 1398.1(6) pm, c = 786.7(4) pm, β = 101.6(1)°. The Ge-atoms are tetrahedrally coordinated by two single Te-atoms and two “end on” bonded Te₂-dumbbells, forming hitherto unknown discrete GeTe₆^4?-anions.     

Etude du systeme KPO3-LaP3O9. Donnees cristal lographiques sur K2La(PO3)5 et (NH4)2La(PO3)5

The system KPO₃-LaP₃O₉ has been studied for the first time by differential thermal analysis and X ray diffraction. The system shows two compounds KLa(PO₃)₄ and K₂La(PO₃)₅ which melt in a peritectic decomposition at 880°C and 770°C respectively. An eutectic point appears at 705°C; The eutectic point corresponds to a concentration of 10% molar LaP₃O₉.Infra Red absorption spectra are typical of chain phosphates.The new compound K₂La(PO₃₅ is isotypic whith (NH₄)₂La(PO₃)₅ which has been synthetized for the first time. They belong to the triclinic system whith space group P1 and Z = 2. The parameters of the unit cell are: $\text{a = 7.309(4)}\text{A}\text{?}$$\text{b = 13.35(2)}\text{A}\text{?}$$\text{c = 7.155(7)}\text{A}\text{?}$α = 90°3(1) β = 109°17(7) γ = 89°90(4) for K₂La(PO₃)₅ and: $\text{a = 7.174(8)}\text{A}\text{?}$$\text{b = 13.38(2)}\text{A}\text{?}$$\text{c = 7.35(2)}\text{A}\text{?}$α = 90°6(2) β = 107°4(1) γ = 89°82(7) for (NH₄)₂La(PO₃)₅.     

New tetrahedrally coordinated A2CdBr4 compounds (A = Cs,CH3NH3)

(CH₃NH₃)₂CdBr₄ and Cs₂CdBr₄ are two compounds with a tetrahedral CdBr₄-coordination. Their room temperature structures are determined. (CH₃NH₃)₂CdBr₄: monoclinic, $\text{P}\text{2}{}_1\text{c}$, $\text{a}\text{= 8.1227(13)}\text{A}\text{?}$, $\text{b}\text{= 13.4355(16)}\text{A}\text{?}$, $\text{c}\text{= 11.4194(13)}\text{A}\text{?}$, β = 96.194(11) °, z = 4. Cs₂CdBr₄: orthorhombic, Pnma, $\text{a}\text{= 10.235(5)}\text{A}\text{?}$, $\text{b}\text{= 7.946(3)}\text{A}\text{?}$, $\text{c}\text{= 13.977(5)}\text{A}\text{?}$, z = 4.     

The resistivity of mixed valence compound Cs2Au2Cl6 at high pressure and low temperatures

Resistivity measurements of the mixed valence compound Cs₂Au^IAu^IIICl₆ at quasihydrostatic pressures up to ～120 kbar and temperatures down to ～10 K show a resistivity drop of about 9 decades and a semiconductor to metal transition at ～60 kbar. The results will be discussed, especially with respect to a possible continuous transition from the tetragonal distorted to the cubic perovskite structure.