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1.
The crystal structure of the high-temperature modification of zinc pyrovanadate, namely, β′-Zn 2V 2O 7, is refined by the full-profile Rietveld method (GSAS) using the high-temperature X-ray diffraction data. The crystals are monoclinic (space group C2/ m, Z = 2); the unit cell parameters are as follows: a = 6.9324(2) Å, b = 8.4394(2) Å, c = 5.0326(1) Å, and β = 108.272(2)°. Comparative analysis of the crystal structures of β′-Zn 2V 2O 7, β-Mn 2V 2O 7, and Cd 2V 2O 7 is performed. 相似文献
2.
The crystallisation of CaO–ZrO 2–SiO 2 glasses doped with V 2O 5 (0.1–5 mol%) has been investigated in terms of microstructure and thermal parameters. Results indicate that crystallisation is predominantly controlled by a surface nucleation mechanism, even though a partial bulk nucleation has been encountered in compositions containing more than 2 mol% of doping oxide. As detected from differential thermal analysis curves, glass transition temperature and crystallisation temperature, are strongly dependent upon V 2O 5 content varying from 0.0 to 2.0 mol%, while the crystallisation activation energy values decrease with a parabolic trend from B-glass (0.0 mol% V 2O 5 content, 495±7) to V-0.7 (0.7 mol% V 2O 5 content, 420±6) composition, increasing again to 442±5 kJ/mol K with higher amount of V 2O 5. The microstructure of the glass-ceramic materials clearly showed a marked dependence upon the amount of V 2O 5, also due to the presence of phase separation for content higher than 0.7 mol%. Wollastonite, CaO·SiO 2, and a calcia–zirconia–silicate, 2CaO·4SiO 2·ZrO 2, are the main crystalline phases whose ratio slightly varies with vanadium oxide content. The glass ceramics obtained from the studied materials are greenish and bluish coloured, so it is possible to use the studied glasses as coloured frits for tile glazes. 相似文献
3.
The EPR and optical spectra of vanadium in glasses of ternary Al 2O 3P 2O 5SiO 2 and Al 2O 3P 2O 5B 2O 3 systems have been measured. The results were compared with earlier data for vanadium in binary phosphate, aluminophosphate and silicaphosphate glasses and with results of de-Biasi for V 4+ in crystalline powder α-crystobalite AlPO 4. The superpositions of two hyperfine spectra (ASB-I and ASB-II) were found for many glasses of ternary systems. Both spectra can be attributed to VO 2+ ions. The intensity ratio of the ASB-II spectrum to ASB-I depends on glass composition but is great (> 7) for all the glasses. Only the ASB-II spectrum was observed in glasses with low concentration of Al 2O 3. The spectral parameters of ASB-II spectrum are g| = 1.916–1.921; g⊥ 1.980–1.988; A| = (188?190) × 10 ?4cm?1 and A⊥ = (74–77) × 10 ?4cm?1. Three intense bands at 370, 455 and 700 ans 720 nm observed in these glasses can be attributed to V 3+ ions. The excellent agreement of the parameters of the EPR spectrum of V 4+ ions in crystalline α-crystobalite AIPO 4 and ASB-II spectra in the glasses under study suggest the identical electron structure of the paramagnetic species. This species is believed to be characterized by optical bands at 680 and 790 nm which have been observed by de Biasi. The orbital mixing coefficients indicate strong tetragonal distortion of vanadyl complexes responsible for the ASB-II spectrum. It is assumed that VO 2+ ions responsible for this spectrum act as modifiers fitting into the relatively small holes of the three-dimensional networks of phosphate glasses containing no cations of large radii. The microscopic basicity of oxygens in such holes must be about 0.48. 相似文献
4.
The electrical, thermal, optical, and morphological properties of CUO doped Bi 2O 3–B 2O 3–BaO–ZnO glasses were studied as a PbO-free, low firing transparent dielectric layer for plasma display panels (PDP). CuO improved the transmittance of Bi 2O 3–B 2O 3–BaO–ZnO by up to 84% in the visible region, eliminating a yellowish color typical of Bi 2O 3–B 2O 3–BaO–ZnO. A slight absorption within the near infrared (NIR) region was also observed. The glass transition temperature ( Tg), thermal coefficient of expansion (TCE), and root-mean square (rms) roughness of 0.005 wt% CuO doped Bi 2O 3–B 2O 3–BaO–ZnO were found to be 455 °C, 81.4 × 10 −7/K, respectively, and 162 ± 14 Å, which satisfied the requirements for a transparent dielectric layer for PDP application. 相似文献
5.
Glasses in the system MgO/Al 2O 3/TiO 2/ZrO 2/SiO 2 with and without the addition of As 2O 3 and Sb 2O 3 were thermally treated. Up to a temperature of 950 °C, this resulted in the formation of ZrTiO 4, sapphirine and high quartz solid solution. Annealing at higher temperatures led to the formation of low quartz solid solutions, ZrTiO 4 and sapphirine. This resulted in a continuous increase of density, hardness, fracture toughness and thermal expansivity. In the glass doped with As 2O 5 and Sb 2O 5 annealing temperatures >1000 °C resulted in the formation of cristobalite instead of quartz. Then the density, hardness and strength decreased again, while the fracture toughness (up to 2.8 MPa m 1/2) and the thermal expansion coefficient increased strongly. In the dilatometric curves, a steep increase in expansion is observed in the temperature range from 100 to 200 °C, which is attributed to the transformation of low cristobalite to high cristobalite. The mean linear thermal expansion coefficient (25–200 °C) is 20 × 10 ?6 K ?1 and the largest up to now reported in the literature for alkali-free silicate glass–ceramics. 相似文献
6.
This study explores a series of optical, thermal, and structural properties based on 60P 2O 5–30ZnO–10Al 2O 3 (60P) glasses that doped with varied rare earth (RE) elements Yb 2O 3 and P 2O 5 components replaced by SiO 2. It was found that the glasses density decrease with SiO 2 concentration added to replace P 2O 5, whereas they increase with increased concentration of Yb 3+-doped. Moreover, the glasses transition temperature, softening temperature, and refractive index increase with Yb 3+ concentrations added, whereas the thermal expansion coefficient decreases. For the 60P glasses, 7 mol% Yb 2O 3 doped has the maximum fluorescence which is suppressed when Yb 2O 3 is doped up to 9 mol%. In addition, maximum lifetime was found to be 2.68 ms at an optimal Yb 3+-doping at 1 mol% for 53P 2O 5–7SiO 2–30ZnO–10Al 2O 3 glass. 相似文献
7.
The heliangolide-class sesquiterpene lactone 8β-angeloyloxy-9α-acetoxycalyculatolide, C 22H 26O 8, 1, crystallizes in orthorhombic space group P2 12 12 1 with a=12.455(3), b=12.601(3), c=14.023(5) Å, V=2200(1)Å, 3 Z=4. R=0.059 for 1735 observed data. The 11,13-dihydro-11α, 13-epoxyatripliciolide-8β-angelate, C 20H 22O 7. 1/2 H 2O, 2, crystallizes as the hemihydrate with two molecules in the asymmetric unit in triclinic space group P1 with a=9.422(1), b=9.559(1), c=12.358(3) Å, α=101.62(2)°, β=91.30(2)°, γ=117.80(1)°, V=955.6(7)Å 3, Z=2. R=0.046 for 3607 observed data. In both, the 10-membered rings adopt approximate chair-boat conformations. Their conformations are typical for heliangolides. The methyl group C14 is α, while the C-15 has a β-orientation. The α-methylene-γ-lactone is trans-fused at C6 and C7 with H6 β and H7 α. In compound 2, the epoxide at C11–C13 has an α orientation. 相似文献
8.
The temperature dependent structural phase transition from the tetragonal chalcopyrite like structure to the cubic sphalerite like structure in CuInSe 2 was investigated by in‐situ high temperature synchrotron radiation X‐ray diffraction. The data were collected in 1K steps during heating and cooling cycles (rate 38 K/h). The Rietveld analysis of the diffractograms led us to determine the temperature dependence of the lattice parameters, including the tetragonal deformation, |1‐η|, and distortion |u‐¼| (η=c/2a, a and c are the tetragonal lattice constant; u is the anion x‐coordinate). The thermal expansion coefficients α a and α c of the tetragonal lattice constant which are related to the linear thermal expansion coefficient α L were obtained, as were α a of the cubic lattice constant, also α u and α η. The transition temperature is clearly identified via a strong anomaly in α L. The temperature dependence of the anion position parameter was found to be rather weak, nearly α u∼0, whereas α η increases slightly. However, both increase strongly when approaching to within 10 K of the transition temperature (the critical region) and |1‐η| as well as |u‐¼| go to zero with |T‐T trans| 0.2 approaching the phase transition. The cation occupancy values, derived from the Rietveld analysis, remain constant below the critical region. Close to the transition temperature, the number of electrons at the Cu site increases with a dercrease in the number of electrons at the In site with increasing temperature, indicating a Cu‐In anti site occupancy, which is assumed to be the driving force of the phase transition. At the transition temperature 67% of Cu + were found to occupy the Me1 site with a corresponding 67% of In 3+ at the Me2 site. Although full disorder is reached with 50%, this level seems to be high enough that the phase transition takes place. The order parameter of the phase transition, goes with |T‐T trans| β to zero with the critical exponent β=0.35(7) which is in good agreement to the critical exponent β=0.332 calculated for order‐disorder transitions according to the Ising model. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
Researches were conducted for glasses in the systems BeO–Al 2O 3–B 2O 3 and MgO–Al 2O 3–B 2O. The following characteristics have been determined: thermal expansion coefficient within 20–300 °C, structural thermal expansion coefficient (STEC) and glass transition temperature. The discussed properties of Be-aluminoborate and Mg-aluminoborate glasses have been compared with those of Ca-, Sr- and Ba-aluminoborate glasses. TEC of studied glasses gets higher going from Be-aluminoborate glasses to Ba-aluminoborate ones, but Tg decreases under the same succession. The dependence of STEC on the nature of a given cation is more complicated. The pattern of dependence of the properties on composition is due to changing the boron coordination number with respect to oxygen, which is the main network-former, and to competition between the aluminium and boron for the oxygen brought by an ion-modifier. The difference between the effect of one ion-modifier and that of another is determined by decreasing the radius of an ion and increasing its electric field strength in the succession from Ba 2+ to Be 2+. The ions of Be and Mg can also act as network-former to some extent. 相似文献
10.
The atomic structures of two V 2O 5–P 2O 5 glasses and vitreous (v-) V 2O 5 were investigated by X-ray and neutron diffraction. The V=O double bond is a common characteristic of the VO n units that constitute the structures of the glasses. VO 5 square pyramids with elongated bonds of ~ 0.190 nm to the pyramidal base are found for the 50V 2O 5–50P 2O 5 glass. These weaker V–O bonds are balanced in V–O–P bridges by overbonded P–O bonds. The V (IV) sites, which account for 19.7% and 35.2% of the total V sites in the 73V 2O 5–27P 2O 5 and 50V 2O 5–50P 2O 5 glasses, respectively, form similar pyramids in agreement with the structure of crystalline (VO) 2P 2O 7. The short-range structure of v-V 2O 5 and the 73V 2O 5-27P 2O 5 glass is formed of mixtures of VO 5 and VO 4 pyramids. A significant amount of V···O distances > 0.22 nm found for all glasses belong either to linkages V=O···V or to three-coordinated O sites. 相似文献
11.
The crystal structure of β‐CsB 5O 8 has been determined from X‐ray powder diffraction data using synchrotron radiation: Pbca, a = 7.8131(3) Å, b = 12.0652(4) Å, c = 14.9582(4) Å, Z = 8, ρ calc = 2.967 g/cm 3, R‐p = 0.076, R‐wp = 0.094. β‐CsB 5O 8 was found to be isostructural with β‐KB 5O 8 and β‐RbB 5O 8. The crystal structure consists of a double interlocking framework built up from B‐O pentaborate groups. The crystal structure exhibits a highly anisotropic thermal expansion: α a = 53, α b = 16, α c = 14 · 10 ‐6/K; the anisotropy may be caused by partial straightening of the screw chains of the pentaborate groups. The similarity of the thermal and compositional (Cs‐Rb‐K substitution) deformations of CsB 5O 8 is revealed: increasing the radius of the metal by 0.01 Å leads to the same deformations of the crystal structure as increasing the temperature by 35°C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
A series of Bi 2O 3–BaO–SiO 2–R xO y (designated BiBaSi glass) glass sealants doped with different contents of α-Al 2O 3 have been investigated. Al 2O 3 was added as a modifier to affect the structure and the behavior of the glass. The thermal properties such as glass transition temperature (Tg), softening temperature (Tf) and coefficient of thermal expansion (CTE) were measured by a dilatometer. The sealing performance was investigated by sealing a SOFC single cell stack and measuring its open circuit voltage (OCV). Tg, Tf and suitable usage temperature of the sealants increased with increasing Al 2O 3 content in the glass, while CTE decreased. When the Al 2O 3 content was lower than 10 wt.%, excellent sealing performance was observed. 相似文献
13.
LiI–AgI–B 2O 3 glasses mixed with different concentrations of V 2O 5 (ranging from 0 to 1.0 mol%) were prepared. Electrical and dielectric properties over wide ranges of frequency (10 ?2–10 7 Hz) and temperature (173–523 K) have been studied. Additionally spectroscopic properties viz., optical absorption and ESR spectra have been investigated. The optical absorption and ESR studies have revealed that vanadium ions do exist in both V 4+ and V 5+ states and the redox ratio is the highest in the glasses containing 0.8 mol% of V 2O 5. The results of conductivity measurements have indicated that there is a mixed conduction (both ionic and electronic). The ionic conduction seems to be dominant over polaron hopping only in the glasses containing V 2O 5 more than 0.8 mol% of V 2O 5. The impedance spectra have also indicated that the conduction is predominantly polaronic in nature. The frequency and temperature dependence of the electrical moduli as well as dielectric loss parameters have exhibited relaxation character attributed to the vanadyl complexes. The relaxation effects have been analyzed by the graphical method and from this analysis it has been established that there is a spreading of relaxation times. The results have been further discussed quantitatively in the light of different valance states of vanadium ions with the aid of the data on spectroscopic properties. 相似文献
14.
Thermal expansion of the monoclinic nonlinear optical crystal BiB 3O 6 (bismuth triborate) was measured by dilatometry within the temperature range from 173 K to 573 K using single crystal samples of dimensions ∼7 x 7 x 8 mm 3. The four independent tensor coefficients are given and the calculated loci of zero thermal expansion of BiB 3O 6 are related to the loci of phase matching for second harmonic generation. Characteristic features of the crystal structure are taken to discuss the marked anisotropy of thermal expansion of BiB 3O 6. 相似文献
15.
Crystallization of splat-cooled V 2O 5 under high pressure was examined. By X-ray diffraction and thermal analysis, it is shown that the non-crystalline V 2O 5 crystallizes dramatically up to about 6 kb. Crystallization temperature increases with increasing pressure under this pressure range.At higher pressure (20–60 kbar), crystallization occurs gradually and the crystallization temperature has a slight tendency to decrease with increasing pressure. 相似文献
16.
A complex study of the (001) cleavage surface of a V 2O 5 single crystal annealed in vacuum at 450 and 550°C has been performed. Tunnel microscopy of the sample surface annealed in vacuum at 550°C showed the formation of a plane with a corundum structure, reconstructed according to the V 2O 3 (0001)-(1/√3 × 1/√3) R30° type, on the surface. X-ray photoelectron spectroscopy revealed a significant modification of interatomic bonds in the surface layers of V 2O 5 single crystal after vacuum annealing at 550°C, which is related to the partial reduction of V 5+ ions and formation of lower vanadium oxides. These modifications lead to a decrease in the electrical resistivity of V 2O 5 and the occurrence of bending at a temperature of 61.5°С in the temperature dependence of the sample resistance, which is indicative of phase transition. 相似文献
17.
The dc conductivity of semiconducting vanadium tellurite glasses of compositions in the range 50 to 80 mol% V 2O 5 has been measured in the temperature region 77 to 400 K. Measurements have been made on annealed samples at different annealing temperatures. Annealing the samples at temperature of about 250°C causes the appearance of a complex crystalline phase resulting in an increase of conductivity. Results are reported for amorphous samples of different compositions. The conductivity of tellurite glasses is slightly higher than the corresponding composition of phosphate glasses, but the general trend of the increase of conductivity and decrease of high temperature activation energy with increasing V 2O 5 content is similar in the two systems. The data have been analysed in the light of existing models of polaronic hopping conduction. A definite conclusion about the mechanics of conduction (adiabatic or nonadiabatic) is difficult in the absence of a precise knowledge of the characteristic phonon frequency v0. Adiabatic hopping is indicated for v0~10 11 Hz, however this value leads to unreasonably low value for the Debye temperature θ D, and higher values for v0~10 13 hz satifiies the conditions for nonadiabatic hopping which appears to be the likely mechanism of conduction in V 2O 5TeO 2 glasses. The low temperature data (< 100 K) can be fitted to Mott's variable range hopping, which when combined with ac conductivity data gives reasonable values of α, but a high value for the disorder energy. 相似文献
18.
Glasses in the system BaO/Al 2O 3/B 2O 3 with and without the addition of platinum were melted. In one sample series, the BaO-concentration was varied while the ratio [Al 2O 3]/[B 2O 3] was kept constant. In another sample series, the [BaO]/[Al 2O 3]-ratio (= 0.9) was kept constant and the B 2O 3 concentration was varied. The samples were thermally treated at 720 °C for 24 h and subsequently at 780 °C for 4 h. In most thermally treated samples, the crystalline phase BaO · Al 2O 3 · B 2O 3 occurred. At some compositions, the platinum-doped samples showed larger concentrations of the crystalline phases. The most remarkable property of the obtained glass–ceramics is their zero or negative thermal expansion coefficient. Here, notable differences were observed: samples with fine grained microstructures showed thermal expansion coefficients approximately zero up to temperatures of around 80 °C. By contrast, samples with coarser microstructures and large spheroidal crystals exhibit negative expansion coefficients up to temperatures of around 280–375 °C. The thermal expansions of these samples were close to those of the mean thermal expansion of the unit cell of the BaO · Al 2O 3 · B 2O 3 phase. The thermal expansion of the fine grained samples was approximately equal to that of the crystallographic a-axis of the BaO · Al 2O 3 · B 2O 3 phase. 相似文献
19.
A novel structure type has been established as a result of studying a non-merohedral microtwin of polyoxovanadate (K 2ZnV 5O 14) by X-ray diffractometry ( R = 0.0595). The new compound, synthesized under hydrothermal conditions in the ZnCl 2–K 2CO 3–V 2O 5–H 2O system, is characterized as follows: a = 8.066(5) Å, b = 8.117(5) Å, c = 9.236(5) Å, β = 105.287(5)°, sp. P2 1/ m, Z = 2, ρ calcd = 3.54 g/cm 3. Edge-shared five-core “clusters” consisting of vanadium octahedra, between which ZnO 4 tetrahedra (sharing vertices with octahedra) are located, form two-dimensional two-layer anion packets of the (ZnV 5O 14) 2– composition, alternating along the c axis with layers of potassium atoms. Structural peculiarities determine the morphology and color of new-phase crystals. 相似文献
20.
The influence of the substrate temperature T
sub (20–360°C) and the oxygen pressure P(O2) (5 × 10−3−0.13 Pa) in an evaporation chamber on the structure and phase composition of films prepared through laser sputtering of a vanadium target is investigated by electron diffraction and in situ transmission electron microscopy (with the use of the bend extinction contour technique for determining the bending of the crystal lattice). It is demonstrated that the oxygen content in the films increases with an increase in the oxygen pressure P(O2) at a fixed substrate temperature T
sub and decreases with an increase in the substrate temperature T
sub at a fixed oxygen pressure P(O2). The conditions responsible for the formation and composition of the crystalline (VO0.9) and amorphous (V2O3) phases in the films are determined. It is established that the phase composition of the film depends on the angle of condensation of the vapor-plasma flow. The crystallization of the V2O3 amorphous phase is accompanied by an increase in the density by 9.2%. It is revealed that the V2O3 spherulites growing in the amorphous film have a bent crystal lattice. The bending of the crystal lattice can be as large as ∼42 deg/μm. 相似文献
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