Crystal structure and physical properties of quaternary clathrates Ba8ZnxGe46−x−ySiy, Ba8(Zn,Cu)xGe46−x and Ba8(Zn,Pd)xGe46−x

Three series of vacancy-free quaternary clathrates of type I, Ba₈Zn_xGe_46−x−ySi_y, Ba₈(Zn,Cu)_xGe_46−x, and Ba₈(Zn,Pd)_xGe_46−x, have been prepared by reactions of elemental ingots in vacuum sealed quartz at 800 °C. In all cases cubic primitive symmetry (space group Pm3?n, a∼1.1 nm) was confirmed for the clathrate phase by X-ray powder diffraction and X-ray single crystal analyses. The lattice parameters show a linear increase with increase in Ge for Ba₈Zn_xGe_46−x−ySi_y. M atoms (Zn, Pd, Cu) preferably occupy the 6d site in random mixtures. No defects were observed for the 6d site. Site preference of Ge and Si in Ba₈Zn_xGe_46−x−ySi_y has been elucidated from X-ray refinement: Ge atoms linearly substitute Si in the 24k site whilst a significant deviation from linearity is observed for occupation of the 16i site. A connectivity scheme for the phase equilibria in the “Ba₈Ge₄₆” corner at 800 °C has been derived and a three-dimensional isothermal section at 800 °C is presented for the Ba-Pd-Zn-Ge system. Studies of transport properties carried out for Ba₈{Cu,Pd,Zn}_xGe_46−x and Ba₈Zn_xSi_yGe_46−x−y evidenced predominantly electrons as charge carriers and the closeness of the systems to a metal-to-insulator transition, fine-tuned by substitution and mechanical processing of starting material Ba₈Ge₄₃. A promising figure of merit, ZT ∼0.45 at 750 K, has been derived for Ba₈Zn_7.4Ge_19.8Si_18.8, where pricey germanium is exchanged by reasonably cheap silicon.     

Etude systématique des relations entre les structures wadéite et tétragermanate

Systematic study of solid solutions with general formula A_2?xA_x′(B_1?zB_z′)Ge_3?ySi_yO₉ (A, A′ = K, Rb, Cs, Tl; B, B′ = Ge, Ti, Sn) has been carried out. These results allow us to propose a tridimensional diagram of existence of wadeite and tetragermanate structures, as a function of the sizes of A, B, Ge, and Si elements. Condition of stability based upon differences of sizes between A and M elements and B and M elements (M = Ge, Si) were found. The variation of compactness of wadeite and tetragermanate structures shows up the particular role of M element (Ge, Si).     

Homoatomic Clustering in the Intermediate Valence Compounds Yb1−yAl3−xSix and Yb1−yAl3−xGex

Two new phases, Yb_1−xAl_3−xSi_x and Yb_1−yAl_3−xGe_x, were found by systematic investigations of the according ternary systems. The crystal structures of Yb_1−yAl_2.8Si_0.2 and Yb_1−yAl_2.8Ge_0.2 (defect HT-PuAl₃ type) were studied by X-ray powder methods (CuKα₁ radiation, λ=1.54056 Å, hexagonal system, space group P6₃/mmc (No. 194), a=6.009(1) and 6.015(1) Å, c=14.199(2) and 14.241(5) Å, V=444.0(2) and 446.2(3) ų, 93 and 92 reflections, and 8200 and 8000 profile points for silicide and germanide, respectively). Full profile refinements with 11 and 13 structural parameters resulted in R_I=0.049 and 0.054, and R_p=0.088 and 0.104, respectively. The ternary structures are distorted closest packings in comparison with the binary YbAl₃ compound with AuCu₃-type structure. They are characterized by the formation of Al₃-, Si₃-, and Ge₃-homoatomic clusters and aluminum networks. Magnetization measurements show that both the silicide and germanide are valence fluctuation compounds with enhanced electronic density of states at the Fermi level similar to the binary YbAl₃. The characteristic maximum of the magnetic susceptibility increases from ≈120 K for YbAl₃ to ≈140 K for Yb_1−yAl_2.8Si_0.2or Yb_1−yAl_2.8Ge_0.2 and further to ≈150 K for Yb_1−yAl_2.75Si_0.25. The S-shape of the electrical resistivity curves is also characteristic of valence fluctuations.     

Evolution structurale de nouveaux germanates et silicates de type wadéïte et de structure apparentée

The crystal structure of 12 new silicates and germanates with the general formulas: A₂BSi₃O₉ (A = K, Rb; B = Ti, Sn) and A₂BGe₃O₉ (A = K, Rb, Cs, Tl; B = Ti, Sn) were determined. Silicates and germanates Cs₂BGe₃O₉ (B = Ti, Sn) and Tl₂TiGe₃O₉ belong to wadéïte type structure. Nonplanar cyclic Ge₃O₉ rings are present in germanates A₂BGe₃O₉ (A = K, Rb; B = Ti, Sn) and Tl₂SnGe₃O₉. Structural evolution of these compounds is discussed.     

Superconductivity and crystal structure of the solid solutions of Ba8−δSi46−xGex (0?x?23) with Type I clathrate structure

The solid solutions of barium containing Type I clathrate, Ba_8−δSi_46−xGe_x (0?x?23) were prepared under high-pressure and high-temperature conditions of 3 GPa at 800°C. All the solid solutions showed superconductivity, and the transition temperature (T_c) decreased from 8.0 to 2.0 K as the germanium content increased from x=0 to 23 in Ba_8−δSi_46−xGe_x. The single crystals with five different compositions were obtained and the structures, compositions, and site occupancies were determined from X-ray single-crystal analysis. A slight barium deficiency was observed at Ba1 (2a) sites for all the clathrates. The Ge atoms replaced the Si atoms at the Si3 (24k) site in the composition range of x<8, and then at the Si2 (16i) site. The crystals had a slight deficiency in the covalent (Si, Ge) network and the deficiency increased with the increase of the Ge content.     

On the distribution of tetrelide atoms (Si, Ge) in Gd5(SixGe1−x)4

A crystallographic study of the Si/Ge site preferences in the Si-rich regime of Gd₅(Si_xGe_1−x)₄ and a crystal chemical analysis of these site preferences for the entire range is presented. The room temperature crystal structure of Gd₅Si₄ as well as four pseudobinary phases, Gd₅(Si_xGe_1−x)₄ for x?0.6, is reported. All structures are orthorhombic (space group Pnma), Gd₅Si₄-type and show decreasing volume as the Si concentration increases. Refinements of the site occupancies for the three crystallographic sites for Si/Ge atoms in the asymmetric unit reveal a nonrandom, but still incompletely ordered arrangement of Si and Ge atoms. The distribution of Si and Ge atoms at each site impacts the fractions of possible homonuclear and heteronuclear Si-Si, Si-Ge and Ge-Ge dimers in the various structures. This distribution correlates with the observed room temperature crystal structures for the entire series of Gd₅(Si_xGe_1−x)₄.     

La4(Si5.2Ge2.8O18)(TeO3)4 and La2(Si6O13)(TeO3)2: Intergrowth of the lanthanum(III) tellurite layer with the XO4 (X=Si/Ge) tetrahedral layer

Two novel lanthanum(III) silicate tellurites, namely, La₄(Si_5.2Ge_2.8O₁₈)(TeO₃)₄ and La₂(Si₆O₁₃)(TeO₃)₂, have been synthesized by the solid state reactions and their structures determined by single crystal X-ray diffraction. The structure of La₄(Si_5.2Ge_2.8O₁₈)(TeO₃)₄ features a three-dimensional (3D) network composed of the [(Ge_2.82Si_5.18)O₁₈]⁴⁻ tetrahedral layers and the [La₄(TeO₃)₄]⁴⁺ layers that alternate along the b-axis. The germanate-silicate layer consists of corner-sharing XO₄ (X=Si/Ge) tetrahedra, forming four- and six-member rings. The structure of La₂(Si₆O₁₃)(TeO₃)₂ is a 3D network composed of the [Si₆O₁₃]²⁻ double layers and the [La₂(TeO₃)₂]²⁺ layers that alternate along the a-axis. The [Si₆O₁₃]²⁻ double layer is built by corner-sharing silicate tetrahedra, forming four-, five- and eight-member rings. The TeO₃²⁻ anions in both compounds are only involved in the coordination with La³⁺ ions to form a lanthanum(III) tellurite layer. La₄(Si_5.2Ge_2.8O₁₈)(TeO₃)₄ is a wide band-gap semiconductor.     

Mixed conductivity and Mössbauer spectra of (La0.5Sr0.5)1−xFe1−yAlyO3−δ (x=0-0.05, y=0-0.30)

Aluminum incorporation in the rhombohedrally distorted perovskite lattice of (La_0.5Sr_0.5)_1−xFe_1−yAl_yO_3−δ (x=0-0.05, y=0-0.30) decreases the unit cell volume and partial ionic and p-type electronic conductivities, while the oxygen nonstoichiometry and thermal expansion at 900-1200 K increase on doping. The creation of A-site cation vacancies has an opposite effect on the transport properties of Al-substituted ceramics. The maximum A-site deficiency tolerated by the (La,Sr)(Fe,Al)O_3−δ structure is however limited, close to 3-4%. The Mössbauer spectroscopy revealed progressive localization of electron holes and a mixed charge-compensation mechanism, which results in higher average oxidation state of iron when Al³⁺ concentration increases. The average thermal expansion coefficients of (La_0.5Sr_0.5)_1−xFe_1−yAl_yO_3−δ are (12.2-13.0)×10⁻⁶ K⁻¹ at 300-900 K and (20.1-30.0)×10⁻⁶ K⁻¹ at 900-1200 K in air. The steady-state oxygen permeability (OP) of dense Al-containing membranes is determined mainly by the bulk ionic conductivity. The ion transference numbers at 973-1223 K in air, calculated from the oxygen permeation and faradaic efficiency (FE) data, vary in the range 1×10⁻⁴-3×10⁻³, increasing with temperature.     

Crystal structure and electrical conductivity of lanthanum-calcium chromites-titanates La1−xCaxCr1−yTiyO3−δ (x=0-1, y=0-1)

Five series of perovskite-type compounds in the system La_1−xCa_xCr_1−yTi_yO₃ with the nominal compositions y=0, x=0-0.5; y=0.2, x=0.2-0.8; y=0.5, x=0.5-1.0; y=0.8, x=0.6-1.0 and y=1, x=0.8-1 were synthesized by a ceramic technique in air (final heating 1350 °C). On the basis of the X-ray analysis of the samples with (Ca/Ti)?1, the phase diagram of the CaTiO₃-LaCr^IIIO₃-CaCr^IVO₃ quasi-ternary system was constructed. Extended solid solution with a wide homogeneity range is formed in the quasi-ternary system CaCr^IVO₃-CaTiO₃-LaCr^IIIO₃. The solid solution La_{(1−x′−y)}Ca_(x′+y)Cr^IV_x′Cr^III_{(1−x′−y)}Ti_yO₃ exists by up to 0.6-0.7 mol fractions of CaCr^IVO₃ (x^′<0.6-0.7) at the experimental conditions. The crystal structure of the compounds is orthorhombic in the space group Pbnm at room temperature. The lattice parameters and the average interatomic distances of the samples within the solid solution ranges decrease uniformly with increasing Ca content. Outside the quasi-ternary system, the nominal compositions La_0.1Ca_0.9TiO₃, La_0.2Ca_0.8TiO₃, La_0.4Ca_0.6Cr_0.2Ti_0.8O₃ and La_0.3Ca_0.7Cr_0.2Ti_0.8O₃ in the system La_1−xCa_xCr_1−yTi_yO₃ were found as single phases with an orthorhombic structure. In the temperature range between 850 and 1000 °C, the synthesized single-phase compositions are stable at pO₂=6×10⁻¹⁶-0.21×10⁵ Pa. Oxygen stoichiometry and electrical conductivity of the separate compounds were investigated as functions of temperature and oxygen partial pressure. The chemical stability of these oxides with respect to oxygen release during thermal dissociation decreases with increasing Ca-content. At 900 °C and oxygen partial pressure 1×10⁻¹⁵-0.21×10⁵ Pa, the compounds with x>y (acceptor doped) are p-type semiconductors and those with x<y (donor doped) and x=y are n-type semiconductors. The type and level of electrical conductivity are functions of the concentration ratios of cations occupying the B-sites of the perovskite structures: [Cr³⁺]/[Cr⁴⁺] and [Ti⁴⁺]/[Ti³⁺]. The maximum electrical conductivity at 900 °C and pO₂=10⁻¹⁵ Pa was found for the composition La_0.1Ca_0.9TiO₃ (near 50 S/cm) and in air at 900 °C for La_0.5Ca_0.5CrO₃ (close to 100 S/cm).     

Synthesis, Crystal Structure and Physical Properties of LixMg0.857−xCu2.143O3−y

Solid solutions of Li-doped Mg_0.857Cu_2.143O₃ (Li_xMg_0.857−xCu_2.143O_3−y) were prepared at 950°C for 12 h in air by the solid-state method using Li₂CO₃, MgO and CuO powders. The solid solutions were obtained as the single α phase with the güggenite structure in 0≦x≦0.06 region. With the increasing of the Li content x, the lattice parameters a, b and unit cell volume V decreased, while c increased. On the basis of the charge neutrality, hole carrier estimated by the oxygen content increased with the Li substitution. The Seebeck coefficient at room temperature of x = 0.03 sample was +400 μV/K. The electrical resistivity ρ at room temperature drastically decreased with the increasing x. Temperature dependences of ρ for x = 0.01, 0.03 and 0.06 samples were semi-conductive behavior from room temperature to about 12 K. Interaction between Cu²⁺ and Cu²⁺ through O²⁻ seems to be somewhat large antiferromagnetic one. Sperconducting transition was not detected in the temperature range.     

Oxygen ionic and electronic transport in apatite-type La10−x(Si,Al)6O26±δ

The main factor governing the oxygen ionic conductivity in apatite-type La_10−xSi_6−yAl_yO_{27−3x/2−y/2} (x=0-0.33; y=0.5-1.5) is the concentration of mobile interstitials determined by the total oxygen content. The ion transference numbers, measured by modified faradaic efficiency technique, vary in the range 0.9949-0.9997 in air and increase on reducing oxygen partial pressure due to decreasing p-type electronic conduction. The activation energies for ionic and hole transport are (56-67)±3 kJ/mol and (57-100)±8 kJ/mol, respectively. Increasing oxygen content leads to higher hole conduction in oxidizing atmospheres and promotes minor oxygen losses from the lattice when the oxygen pressure decreases, although the overall level of ionic conductivity is almost constant in the p(O₂) range from 50 kPa down to 10⁻¹⁶ Pa. Under reducing conditions at temperatures above 1100 K, silicon oxide volatilization from the surface layers of apatite ceramics results in a moderate decrease of the conductivity with time. This suggests that the operation of electrochemical cells with silicate-based solid electrolytes should be limited to the intermediate-temperature range, such as 800-1000 K, where the ionic transport in most-conductive apatite phases containing 26.50-26.75 oxygen atoms per unit formula is higher than that in stabilized zirconia. The average thermal expansion coefficients of apatite ceramics, calculated from dilatometric data in air, are (8.7-10.8)×10⁻⁶ K⁻¹ at 300-1300 K.     

Synthesis of new molybdenum-tungsten, vanadium-tungsten and vanadium-molybdenum-tungsten oxynitrides from freeze-dried precursors

Interstitial molybdenum-tungsten, vanadium-tungsten and vanadium-molybdenum-tungsten oxynitrides in the solid solution series Mo_1−zW_z(O_xN_y) and V_1−zW_z(O_xN_y) (z=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1), and V_1−u−zMo_uW_z(O_xN_y) (u, z=0.2, 0.33, 0.4, 0.6; u+z<1), have been obtained by ammonolysis of precursors resulting from the freeze-drying of aqueous solutions of the metal salts (NH₄VO₃, (NH₄)₆Mo₇O₂₄·4H₂O and (NH₄)₆W₁₂O₃₉·18H₂O). A study of the influence of the preparative variables on the outcomes of this procedure is presented. Compounds in the Mo_1−zW_z(O_xN_y) series are prepared as single phases by ammonolysis of the respective freeze-dried precursors (during 2 h) at different temperatures between 973 and 1023 K, optimised for each composition, followed by slow cooling of the samples (except for the Mo-only containing phase, in which fast cooling has been used). Compounds in the V_1−zW_z(O_xN_y) and V_1−u−zMo_uW_z(O_xN_y) series are prepared as single phases by ammonolysis (during 2 h) of crystalline precursors (as resulting from thermal treatment in air at 873 K, during 12 h, of the freeze-dried precursors) at 1073 K, followed by slow cooling of the samples. All the compounds in these series have the rock-salt crystal structure, in which the metal atoms are in an fcc arrangement, with non-metal atoms occupying octahedral interstitial positions. The materials have been characterized by X-ray powder diffraction, elemental analysis, scanning electron microscopy and magnetic measurements.     

Crystal structures of RPt3−xSi1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) studied by single crystal X-ray diffraction

The crystal structures of ternary compounds RPt_3−xSi_1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) have been elucidated from X-ray single crystal CCD data. All compounds are isotypic and crystallize in the tetragonal space group P4/mbm. The general formula RPt_3−xSi_1−y arises from defects: x≈0.20, y≈0.14. The crystal structure of RPt_3−xSi_1−y can be considered as a packing of four types of building blocks which derive from the CePt₃B-type unit cell by various degrees of distortion and Pt, Si-defects.     

Structure and photoluminescence properties of Ce-doped novel silicon-oxynitride Ba4−zMzSi8O20−3xN2x (M=Mg, Ca, Sr)

Structural and photoluminescence properties of undoped and Ce³⁺-doped novel silicon-oxynitride phosphors of Ba_4−zM_zSi₈O_20−3xN_2x (M=Mg, Sr, Ca) are reported. Single-phase solid solutions of Ba_4−zM_zSi₈O_20−3xN_2x oxynitride were synthesized by partial substitutions of 3O²⁻→2N³⁻ and Ba→M (M=Mg, Ca, Sr) in orthorhombic Ba₂Si₄O₁₀. The influences of the type of alkaline earth ions of M, the Ce³⁺ concentration on the photoluminescence properties and thermal quenching behaviors of Ba₃MSi₈O_20−3xN_2x (M=Mg, Ca, Sr, x=0.5) were investigated. Under excitation at about 330 nm, Ba₃MSi₈O_20−3xN_2x:Ce³⁺ (x=0.5) exhibits efficient blue emission centered at 400-450 nm in the range of 350-650 nm owing to the 5d→4f transition of Ce³⁺. The emission band of Ce³⁺ shifts to long wavelength by increasing the ionic size of M due to the modification of the crystal field, as well as the Ce³⁺ concentrations due to the Stokes shift and energy transfer or reabsorption of Ce³⁺ ions. Among the silicon-oxynitride phosphors of Ba₃MSi₈O_18.5N:Ce³⁺, M=Sr_0.6Ca_0.4 possesses the best thermal stability probably related to its high onset of the absorption edge of Ce³⁺.     

Dependence of the mixed alkali effect on temperature and total alkali oxide content in y[xLi2O·(1−x)Na2O]·(1−y)B2O3 glasses

The complex conductivity spectra of mixed alkali borate glasses of compositions y [xLi₂O·(1−x)Na₂O]·(1−y)B₂O₃ (with x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0; y=0.1, 0.2, 0.3) in a frequency range between 10⁻² Hz and 3 MHz and at temperatures ranging from 298 to 573 K have been studied. For each glass composition the conductivities show a transition from the dc values into a dispersive regime where the conductivity is found to increase continuously with frequency, tending towards a linear frequency dependence at sufficiently low temperatures. Mixed alkali effects (MAEs) in the dc conductivity and activation energy are identified and discussed. It has been for the first time found that the strength of the MAE in the logarithm of the dc conductivity linearly increases with the total alkali oxide content, y, and the reciprocal temperature, 1/T.     

Stability and oxide ion conductivity in rare-earth aluminium cuspidines

RE₄(Al_2−xGe_xO_7+x/2□_1−x/2)O₂ (RE=Gd³⁺ and Nd³⁺) oxy-cuspidine series have been prepared by ceramic method (RE=Gd³⁺) and freeze-dried precursor method (RE=Nd³⁺). The compositional ranges and the high temperature stability have been determined for both series. Gadolinium aluminium cuspidines are stable at very high temperatures but the analogous neodymium compounds are only stable below 1273 K. Joint Rietveld analyses of neutron powder diffraction (NPD) and laboratory X-ray powder diffraction (LXRPD) have been carried out for Nd₄(Al₂O₇□₁)O₂ and Nd₄(Al_1.5Ge_0.5O_7.25□_0.75)O₂ compositions. Furthermore, Rietveld refinement of synchrotron X-ray powder diffraction (SXRPD) data were carried out for Gd₄(Al_1.0Ge_1.0O_7.5□_0.5)O₂ composition. The refinements have confirmed the known structural features of the cuspidine framework. These cuspidines series are oxide ion conductors with negligible electronic contribution as determined from impedance spectroscopy at variable oxygen partial pressures. The enhancement in the overall oxide conductivity along the two oxy-cuspidine series is two orders of magnitude. Typical ionic conductivity values for doped samples are around 4×10⁻⁵ S cm⁻¹ at 973 K.     

Crystal structure, thermal expansion and conductivity of anisotropic La1−xSrxGa1−2xMg2xO3−y (x=0.05, 0.1) single crystals

Crystal structure and anisotropy of the thermal expansion of single crystals of La_1−xSr_xGa_1−2xMg_2xO_3−y (x=0.05 and 0.1) were measured in the temperature range 300-1270 K. High-resolution X-ray powder diffraction data obtained by synchrotron experiments have been used to determine the crystal structure and thermal expansion. The room temperature structure of the crystal with x=0.05 was found to be orthorhombic (Imma, Z=4, a=7.79423(3) Å, b=5.49896(2) Å, c=5.53806(2) Å), whereas the symmetry of the x=0.1 crystal is monoclinic (I2/a, Z=4, a=7.82129(5) Å, b=5.54361(3) Å, c=5.51654(4) Å, β=90.040(1)°). The conductivity in two orthogonal directions of the crystals has been studied. Both, the conductivity and the structural data indicate three phase transitions in La_0.95Sr_0.05Ga_0.9Mg_0.1O_2.92 at 520-570 K (Imma-I2/a), 770 K (I2/a-R3c) and at 870 K (R3c-R-3c), respectively. Two transitions at 770 K (I2/a-R3c) and in the range 870-970 K (R3c-R-3c) occur in La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85.     

A novel boron-rich quaternary scandium borocarbosilicide Sc3.67−xB41.4−y−zC0.67+zSi0.33−w

A novel quaternary scandium borocarbosilicide Sc_3.67−xB_41.4−y−zC_0.67+zSi_0.33−w was found. Single crystallites were obtained as an intergrowth phase in the float-zoned single crystal of Sc_0.83−xB_10.0−yC_0.17+ySi_0.083−z that has a face-centered cubic crystal structure. Single crystal structure analysis revealed that the compound has a hexagonal structure with lattice constants a = b = 1.43055(8) nm and c = 2.37477(13) nm and space group (No. 187). The crystal composition calculated from the structure analysis for the crystal with x = 0.52, y = 1.42, z = 1.17, and w = 0.02 was ScB_12.3C_0.58Si_0.10 and that agreed rather well with the composition of ScB_11.5C_0.61Si_0.04 measured by EPMA. In the crystal structure that is a new structure type of boron-rich borides, there are 79 structurally independent atomic sites, 69 boron and/or carbon sites, two silicon sites and eight scandium sites. Boron and carbon form seven structurally independent B₁₂ icosahedra, one B₉ polyhedron, one B₁₀ polyhedron, one irregularly shaped B₁₆ polyhedron in which only 10.7 boron atoms are available because of partial occupancies and 10 bridging sites. All polyhedron units and bridging site atoms interconnect each other forming a three-dimensional boron framework structure. Sc atoms reside in the open spaces in the boron framework structure.     

Sol–gel preparation and characterization of Bi4(Si1−xGex)3O12 solid solutions

Micro-crystals of Bi₄(Ge_xSi_1?x)₃O₁₂ (x = 0, 0.25, 0.5, 0.75, 1) solid solution series were synthesized by a sol–gel method, using stoichiometric Si(OC₂H₅)₄, GeO₂, Bi(NO₃)₃·5H₂O as the starting materials. The as-prepared series were studied by X-ray diffraction, Raman spectra, differential thermal analysis, and fluorescence spectra. Experiments showed that single phase of Bi₄(Si_1?xGe_x)₃O₁₂ was obtained by the sol–gel method. For all the composition, Bi₄Si₃O₁₂ and Bi₄Ge₃O₁₂ can completely dissolve into each other. The refined cell parameters were in proportion to the composition. Bi₄Ge₃O₁₂ showed the strongest fluorescence emission while Bi₄Si₃O₁₂ showed the weakest fluorescence emission.     

Über die Silbergermanate Ag4Ge9O20 und Ag2Ge4O9

Zusammenfassung Der Germanat-Zeolith Ag₃HGe₇O₁₆·4 H₂O wird durch Ionenaustausch aus dem isotypen Ammonium-Zeolith hergestellt. Nach Dehydratation des Ag-Zeoliths bildet sich bei 460°C das zuMe ₄Ge₉O₂₀ (Me=Na, K) isotype Ag₄Ge₉O₂₀. Durch Erhitzen auf 650°C entsteht das zuMe ₂Ge₄O₉ (Me=Na, K, Rb, Tl) isotype Ag₂Ge₄O₉. Oberhalb 760°C erfolgt unter Dissoziation die Bildung von metallischem Silber und GeO₂ (Rutilform).

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The zeolithic germanate Ag₃HGe₇O₁₆·4 H₂O has been prepared by ion-exchange from the analogous ammonium compound. After dehydration at 460°C Ag₄Ge₉O₂₀ is formed, which is isostructural withMe ₄Ge₉O₂₀ (Me=Na, K). By heating up to 650°C Ag₂Ge₄O₉ is obtained, having the structure ofMe ₂Ge₄O₉ (Me=Na, K, Rb, Tl). Above 760°C the compound decomposes into silver, oxygen and GeO₂ (rutile).

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