Thermal Study of A2O–(MoO3)2–P2O5 (A=Li, Na) Glasses

Alkali phosphomolybdate glasses have been prepared by quenching melted mixtures of P₂O₅, MoO₃ and A₂O(A=Li, Na). The composition dependence of the transition temperature of glasses belonging to ternary A₂O–(MoO₃)₂–P₂O₅ (A=Li, Na) systems is studied for several series of glasses corresponding to either a fixed A₂O rate or a constant Mo/P ratio. The interpretation of the results is based on the presence of different types of molybdenum and phosphorous structural groups and P–O–M (M=P, Mo) linkages in glasses. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrochemical Study of Glasses in the System Na2O-B2O3

The steady-state electrical conductivity and microhardness of glasses in the system Na₂O-B₂O₃ was studied. IR spectroscopy was applied to determine the content of impurity hydrogen in the glasses studied.     

Die Kristallstruktur eines neuen Alkalidigermanats,Na4K2Ge2O7

Na₄K₂Ge₂O₇ is monoclinic, space group P 2₁ (No. 4),a=6.010 (3),b=6.020 (3),c=29.26 (1) Å, γ=119.9 (1)° andZ=4. Its crystal structure has been determined from 1210 single crystal X-ray reflections and refined toR=0.114. The structure contains two independent Ge₂O₇ groups, the (GeOGe) angles of which are 128 and 132°.     

Über Na2PrO3 und Na2TbO3

On Na₂PrO₃ and Na₂TbO₃ Using an exchange reaction of Na₂O with Li₈TbO₆ (Na : Tb = 2.1 : 1; au-tube; 750°C, 30 d) yellow-orange colored single crystals of Na₂TbO₃ could be prepared for the first time. Na₂TbO₃ crystallizes monoclinic in C2/c (Z = 8; a = 576.92(6), b = 1001.27(9), c = 1117.91(14) pm, β = 99.98(1)°). According to four-circle data the Li₂SnO₃-type of structure is adopted (PW 1100, MoKα , 1935 I₀ (hkl), R = 4.86%, R_w = 3.63% for all 928 unique reflexions). By a similar exchange reaction of Na₂O with Li₈PrO₆ for the first time single crystals of Na₂PrO₃ could be prepared, too (Na : Pr = 2.2 : 1; au-tube; 700°C; 23 d). The structure determination reveils that there is a variant of the NaCl-type of structure, which ressembles to the Li₂SnO₃-type of structure (PW 1100, MoKα , 2199 I₀ (hkl)), R = 8.88%, R_w = 5.21% for all 947 unique reflexions; C2/c, Z = 8, a = 678.78(5), b = 977.47(7), c = 1080.38(9) pm, β = 108,4(1)°. In contrast to Na₂TbO₃ there are no layers according to NaO(Na_1/3Tb_2/3)O. All octahedral intersticies are occupied systematically with Pr⁴⁺ and Na⁺ : (Na_2/3Pr_1/3)O(Na_2/3Pr_1/3)O.     

Oxydation intermetallischer Phasen: Na3[AuO2] aus NaAu und Na2O2

Oxidation of Intermetallic Phases: Na₃[AuO₂] from NaAu and Na₂O₂ The hitherto unknown Na₃[AuO₂] was prepared in transparent, colourless single crystals from NaAu and Na₂O₂[1:1; sealed Ag-cylinder, 430°C, 6 d]. The crystal structure (P4₂/mnm); a = 970.5(1), c = 457.8(1) pm; Z = 4; four-circle diffractometer PW 1100, 333 out of 380 I₀(hkl), R = 7.0% and [R_w = 6.5%] was solved. Like KAgO-Type there are planar rings [Na₂Au₂O₄]^4?. Na(1) has the uncommon coordinations number 2 . The Effective Coordination Numbers, ECoN, the Mean Fictive Ionic Radii, MEFIR, and the Madelung Part of Lattice Energy, MAPLE, are calculated.     

Temperature-concentration dependence of the electrical conductivity of glasses in the Zn(PO3)2-NaF system

Temperature-concentration dependence of the electrical conductivity in glasses of the Zn(PO₃)₂-NaF system was studied and compared with similar dependences for glasses of other systems. The extremal dependences log σ = f([Na⁺]) and {ie937-1} are interpreted from the standpoint of a macroscopically inhomogeneous structure of the glasses under study.     

X-ray diffraction study of ceramic samples of SrCu1/3Nb1/3O3

Ceramic samples of SrCu_1/3Nb_2/3O₃, obtained either by slow cooling or by quenching from 1200°C, were studied by X-ray diffraction using the Rietveld method. The slow-cooled SrCu_1/3Nb_2/3O₃ samples contain one phase with a perovskite structure (R _B = 4.14%, tetragonal crystal symmetry, space group P4/mmm, Z = 1, a = 3.935 ?, c = 4.124 ?), its diffraction peaks being considerably broadened. The samples quenched from 1200°C contain two SrCu_1/3Nb_2/3O₃ forms with a perovskite structure: one of them is oxygen deficient (R _B = 3.37%, tetragonal crystal symmetry, space group P4/mmm, Z = 1, a = 3.9687 ?, c = 4.0718 ?), and the other has no oxygen deficiency (R _B = 3.20%, tetragonal crystal symmetry, space group P4/mmm, Z = 1, a = 3.95307 ?, c = 4.08935 ?).     

The effects of La2O3 on the early stages of crystallization for MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramics

The early stages of crystallization for MgO-Al₂O₃-SiO₂-TiO₂-La₂O₃ glasses with different La₂O₃ concentrations were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The glass transition temperature (Tg) of the glass decreases at first and then increases again with increasing La₂O₃ concentration. This indicates that the structure of the glass becomes weaker at first and then stronger again. Lanthanum acts in glasses as network modifier and will usually decrease the network connectivity of the glass structure. Nevertheless, if the La₂O₃ concentration is high enough, the oxygen and other ions start to agglomerate around La, resulting in a more closely packed structure. Heat-treatment of the sample with x = 0.1 at 770–810 °C results in the precipitation of a droplet phase with higher mean atomic weight embedded in a matrix with lower mean atomic weight. The initial crystalline phase magnesium aluminum titanate (MAT) precipitates from the droplet phase. Nevertheless, for the sample with x = 0.4, dendrite-like structure could be observed after heat-treatment of the glass at 810 °C. Furthermore, the crystalline phase first precipitated is the lanthanum containing perrierite, which could be attributed to the rearrangement of the glass structure as an effect of La³⁺ incorporation.     

Novel 3D metal-organic framework with Prussian Blue topology: [Mn(HCOO)3]n·xnH2O

A novel complex, [Mn(HCOO)₃]_n·xnH₂O, has been synthesized and studied by X-ray crystallography. The structure is trigonal, space group R-3c, a = 8.327(1) Å, c = 22.890(6) Å, V = 1374.4(5) ų, Z = 6; final R = 0.045. The crystal structure reveals both O-atoms of the formic acid ligand coordinated to Mn(III) to form a three-dimensional porous framework with the topology of Prussian Blue.     

Effects of gamma irradiation on optical and structural properties of PbO–Bi2O3–B2O3 glasses

Optical and structural properties of xPbO·2xBi₂O₃(1−3x)B₂O₃ glasses of different composition have been studied using UV-VIS and FTIR spectroscopic techniques. Effects of gamma radiations on glass network and structural units have been studied by irradiating glass samples with a ⁶⁰Co radioisotope to the overall dose of 2.5 kGy. It is shown that irradiation causes compaction of the borate network by breaking the bonds between trigonal elements, which leads to a decrease in the optical band gap energy. Changes in the atomic structure before and after the irradiation are observed and explained.     

Homogeneity regions of double molybdates in the Na2MoO4-MgMoO4 system and structures of triclinic Na1.51Mg2.245(MoO4)3 and Na1.66Mn2.17(MoO4)3

In the samples of the Na₂MoO₄-MgMoO₄ system quenched in the air at above 600°C, by powder X-ray diffraction two double molybdates of variable composition are detected: monoclinic alluaudite-like Na_4?2x Mg_1+x (MoO₄)₃ (0.05 ≤ x ≤ 0.35) and triclinic Na_2?2y Mg_2+y (MoO₄)₃ (0.10 ≤ y ≤ 0.40) isostructural to previously studied Na₂Mg₅(MoO₄)₆. Sodium-magnesium molybdate of the Li₃Fe(MoO₄)₃ structure type is not revealed in this system. By spontaneous flux crystallization, the crystals are obtained and the structures of two triclinic double molybdates of the Na₂Mg₅(MoO₄)₆ structure type (space group $P\bar 1$ , Z = 1) containing magnesium and manganese are determined. The results of the refinement of site occupancies made it possible to determine the composition of the studied crystals: for the compound with magnesium (Na)_0.5(Na_0.255□_0.745)(Na_0.755Mg_0.245)Mg₂(MoO₄)₃ or Na_1.51Mg_2.245(MoO₄)₃ (a = 6.9577(1) Å, b = 8.6330(2) Å, c = 10.2571(2) Å, α = 106.933(1)°, β = 104.864(1)°, γ = 103.453(1)°, R = 0.0188); for the compound with manganese (Na)_0.5(Na_0.33□_0.67)(Na_0.83Mn_0.17)Mn₂(MoO₄)₃ or Na_1.64Mn_2.17(MoO₄)₃ (a = 7.0778(2) Å, b = 8.8115(2) Å, c = 10.4256(2) Å, α = 106.521(1)°, β = 105.639(3)°, Γ = 103.233(1)°, R = 0.0175). The Na₂Mg₅(MoO₄)₆ structure is redetermined and it is shown that actually it corresponds to the composition Na_1.40Mg_2.30(MoO₄)₃.     

Electrical properties of LiBBaTe glass doped with Nd2O3

The dc and ac electrical conductivity of barium tellurite borate glass doped with Nd₂O₃ in the composition 50 B₂O₃- (20-X) BaO- 20TeO₂ 10 LiF or Li₂O where x = 0.5, 1, 1.5 and 2 Nd₂O₃ were measured in the temperature range 303–648 K and in the frequency range 0.1–100 kHz. The dc and ac conductivities values increase, whereas the activation energy of conductivities decreases with increasing Nd₂O₃ content in the glasses containing LiF and by the replacement of LiF by Li₂O the conductivity was found to decrease with addition of Nd₂O₃. The electrical conduction has been observed to be due to small polaron hopping at high temperatures. The frequency dependence of the ac conductivity follows the power law σ_AC (ω) = A ω^s. The frequency exponent (s) values (in the range 0.94 and 0.33) decreases with increasing temperature. The dielectric constant and dielectric loss increased with increasing temperature and decreased with increase in frequency for all glasses studied. In LiF glasses, it is observed that, the values of ?^\ and tan δ are observed to increase with the addition of Nd₂O₃ whereas they decrease in the glasses containing Li₂O. The electrical modulus formalism has been used for studying electrical relaxation behavior in studied glasses. It is for first time that the Nd₂O₃ doped barium tellurite borate glasses have been investigated for dc and ac conductivities and dielectric properties over a wide range of frequency and temperature.     

Structure determination of low-dimensional conductor sodium molybdenum purple bronze Na0.9Mo6O17

Structure determination of the molybdenum purple bronze Na_0.9Mo₆O₁₇ is carried out by single-crystal X-ray diffraction. The crystal is monoclinic with space group A2 and the lattice constants are a = 12.983(2), b = 5.518(1), c = 9.591(2) Å, β = 89.94(1)°, Z = 2. Full-matrix least-squares refinement gives the final values of R(F) = 0.028 and R_w(F) = 0.040 for 1484 independent reflections, in which the occupancy factor of the sodium atom becomes 0.899(12). The present structure is built up of the linkage of the MoO₄ and MoO₆ polyhedra. There are slabs which consist of four layers of distorted MoO₆ octahedra sharing corners. Both the structure and the molybdenum valence distribution estimated from the MoO bond lengths are considered to lead to the two-dimensional electronic transport. This structure is compared with those of other members of molybdenum purple bronzes, K_0.9Mo₆O₁₇ and Li_0.9Mo₆O₁₇. The difference of the electronic properties among these compounds can be well understood on the basis of their structural characteristics.     

Darstellung und Kristallstruktur von Na2Mn3O7

Synthesis and Crystal-Structure of Na₂Mn₃O₇ Single crystals of Na₂Mn₃O₇ have been grown hydrothermally applying high oxygen pressure (p = 2 kbar). The new compound cystallizes triclinic; space group P1 ; a = 6.636(6) Å, b = 6.854(6) Å, c = 7.548(6) Å, α = 105.76(6)°, β = 106.86(6)°, γ = 111.60(6)°; Z = 2. The crystal structure has been solved and refined to R = 7.9% and R_w = 6.2% (diffractometer data, 1044 independent reflexions). The crystal structure consists of Mn₃O₇^2? anions with manganese coordinated octahedrally by oxygen. These layered anions are hold together by Na⁺ ions (coordination numbers 5 and 6).     

Structural correlations in BaO–PbO–B2O3 glasses as inferred from FTIR spectra

Infrared spectra of xBaO·(30-x)PbO·70B₂O₃, xBaO·(40-x)PbO·60B₂O₃ and xBaO·(50-x)PbO·50B₂O₃ glasses have been quantitatively analyzed. The fraction of four coordinated boron atoms varies linearly, for each group, between the values of the corresponding binary borate glasses. The data could be used to calculate and follow the composition dependence of the concentration of structural units in all glasses. The results show a linear increase in the ratio of PbO forming BO₄ units to the total content of PbO, with increasing B₂O₃ in binary PbO–B₂O₃ glasses. Similar behavior has been observed for the ratio of BaO forming BO₄ units to the total content of BaO in binary BaO–B₂O₃ glasses. The ratio of PbO forming PbO₄ units to the total PbO content, and that of BaO forming asymmetric BO₃ units to the total BaO content, shows a reversed dependence. The linear change in fraction of four coordinated boron atoms and in density and molar volume suggests that the studied glasses can be treated as mixtures of binary PbO–B₂O₃ and BaO–B₂O₃ matrices.     

Oxydation intermetallischer Phasen: K4{Na2[Tl2O6]} aus NaTl und K2O2

Oxidation of Intermetallic Phases: K₄{Na₂[Tl₂O₆]} from NaTl and K₂O₂ The hitherto unknown K₄{Na₂[Tl₂O₆]} was prepared in form of transparent, yellow single crystals from NaTl and KO_1,08 (molar ratio 1:1.3; sealed Ag-cylinder; 450°C, 30 d). The structure determination (four-circle diffractometer, MoKα, 1 280 out of 1 523 I_o(hkl), R = 5.75%, R_w = 4.58%) confirms the space group P2₁/c with a = 641.3 pm, b = 691.1 pm, c = 1188.5 pm, β = 95.69° and Z = 2. As characteristic building units of the structure there are doubles of tetrahedra of [Tl₂O₆] and [Na₂O₆]. The compound is isotypic with Cs₆[In₂O₆] and Rb₆[Tl₂O₆]. The Madelung Part of Lattice Energy, MAPLE, the Mean Fictive Ionic Radii, MEFIR, Effective Coordination Numbers, ECoN, and Charge Distribution, CHARDI, are calculated.     

Structure and polymorphism of complex phosphates prepared from fluxes of the Na2O-P2O5-Fe2O3-Nb2O5 system

The phase formation of complex phosphates in the Na₂O-P₂O₅-Fe₂O₃-Nb₂O₅ flux system was studied in the ranges of sodium-to-phosphorus ratios of 0.7–1.2 and iron-to-niobium ratios of 0.9–2.7. The crystallization region and crystallization conditions for the compounds of composition Na_3?2x Fe_2-x Nb_x(PO₄)₃ (0.8 ≤ x < 1.2) were found. These compounds can be prepared in two (hexagonal and monoclinic) polymorphs. Single-crystal X-ray diffraction experiments were carried out for hexagonal NaFeNb(PO₄)₃ (space group $R\bar 3$ c, a = 8.590 Å, c = 22.013 Å). The polymorphism in Na_3-2x Fe_2-x Nb_x(PO₄)₃ complex phosphates is considered as dependent on the preparation parameters.     

Preparation,Structure and Properties of the One-Dimensional Polymeric Complex Na2[AlW3O4(O2CEt)8]2

Abstract

The heterometallic polymeric cluster Na₂[AlW₃O₄ (O₂CEt)₈]₂ (1) has been prepared by reaction of W(CO)₆ and NaWO₄·2H₂O with AlCl₃ at 120°C in propionic anhydride and characterized by X-ray crystallography, with the following crystal data: triclinic, space group P1, a = 12.205(5), b = 13.032(4), c = 13.925(3) Å, α = 90.21(3)°, β = 109.53(5)°, γ = 117.26(6)°, V = 1822.8(1)ų, Z = 1, R = 0.038 and R_w = 0.101. The structure consists of two triangular [W₃O₄(O₂CEt)₈]^4? cluster unit, which act as polydenate ligands to link Al³⁺ and Na⁺ ions forming a one–dimensional chain structure. IR spectra show characteristic [W₃O₄]⁴⁺ bands at 746–815 cm^?1. Thermal analysis reveals that the complex is air stable up to 250°C. Cluster 1 decomposes in hot aqueous 2 M HCl solution to produce discrete [W₃O₄]⁴⁺ units.     

Crystal structure of a new vanadate variety in the lomonosovite group: Na5Ti2O2[Si2O7](VO4)

The title compound has been prepared by a flux crystallisation method and its crystal structure was determined by single crystal X-ray diffraction: space group P, a=5.309(1), b=7.133(1), c=14.746(2) Å, α=99.05(1), β=95.97(1), γ=90.08(1)°, wR₂=0.073, R=0.028. The structure may be described as built by seidozerite modules of composition Na₂Ti₂O₂Si₂O₇ — brucite-type layers of [TiO₆] and [NaO₆] octahedra embedded between layers of [TiO₆] octahedra, [Si₂O₇] groups and [NaO₈] polyhedra. These almost centrosymmetrical triple-layers alternate along the c-axis with polar double-layer-modules of composition Na₃VO₄ formed by isolated [VO₄]³⁻ anions and six- and four-coordinate Na cations. The crystal structure is discussed in context with minerals of the lomonosovite group. The thermal decomposition behaviour suggests a decay to the single modular components Na₂Ti₂O₂Si₂O₇ and Na₃VO₄.     

The effect of Er3+ and Sm3+ on phase separation and crystallization in Na2O/K2O/BaF2/BaO/Al2O3/SiO2 glasses

Thermal annealing of Sm⁺³ or Er⁺³ doped Na₂O/K₂O/BaF₂/BaO/Al₂O₃/SiO₂ glasses led to the precipitation of nanocrystalline BaF₂. The mean crystallite sizes were in the range from 9 to 15 nm as shown by XRD line broadening. Whereas glasses without rare earth oxides showed crystallites homogenously dispersed in the amorphous matrix, those doped with 0.05 mol% ErF₃ or SmF₃ showed highly agglomerated crystals. The latter was due to droplet phase separation in the rare earth doped glasses as proved by transmission electron microscopy while in the undoped glasses phase separation did not occur. Furthermore, the size of the droplets depended on the BaO-concentration. Fluorescence emission spectra of a samarium doped sample showed higher intensities than in the glasses they were prepared from.