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1.
The Eu2Sn2O7 compound has been prepared by solid-state reaction (by sequentially firing a stoichiometric mixture of Eu2O3 and SnO2 in air at 1273 and 1473 K) and its heat capacity has been determined by differential scanning calorimetry in the temperature range 370–1000 K. The heat capacity data have been used to evaluate the thermodynamic properties of europium stannate: enthalpy increment H°(T)–H°(370 K), entropy change S°(T)–S°(370 K), and reduced Gibbs energy Ф°(T). Raman spectra of Eu2Sn2O7 polycrystals with the pyrochlore structure have been measured in the range 200–1200 cm–1.  相似文献   

2.
Gd2Sn2O7 gadolinium stannate with the pyrochlore structure has been prepared by solid-state reaction and its high-temperature heat capacity has been determined by differential scanning calorimetry in the temperature range 350–1020 K. The Cp(T) data are shown to be well represented by the classic Maier–Kelley equation. The experimental Cp(T) data have been used to evaluate the thermodynamic functions of gadolinium stannate: enthalpy increment H°(T)–H°(339 K), entropy change S°(T)–S°(339 K), and reduced Gibbs energy Ф°(Т).  相似文献   

3.
Tb2Sn2O7 has been prepared by solid-state reaction in air at 1473 K over a period of 200 h and its isobaric heat capacity has been studied experimentally in the range 350–1073 K. The C p(T) data for this compound have no extrema and are well represented by the classic Maier–Kelley equation. The experimental C p(T) data have been used to evaluate the thermodynamic properties of terbium stannate (pyrochlore structure): enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(Т).  相似文献   

4.
The Dy2Ge2O7 and Ho2Ge2O7 pyrogermanates have been prepared by solid-state reactions in several sequential firing steps in the temperature range 1237–1473 K using stoichiometric mixtures of Dy2O3 (or Ho2O3) and GeO2. The heat capacity of the synthesized germanates has been determined as a function of temperature by differential scanning calorimetry in the range 350–1000 K. The experimentally determined C p (T) curves of the dysprosium and holmium germanates have no anomalies and are well represented by the Maier–Kelley equation. The experimental C p (T) data have been used to evaluate the thermodynamic functions of the Dy2Ge2O7 and Ho2Ge2O7 pyrogermanates: enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(T).  相似文献   

5.
The Sm2Ge2O7 and Eu2Ge2O7 germanates have been prepared by solid-state reactions via multistep firing of stoichiometric mixtures of Sm2O3 (Eu2O3) and GeO2 in air at temperatures from 1273 to 1473 K. The molar heat capacity of the samarium and europium germanates has been determined by differential scanning calorimetry in the range 350–1000 K and the C p (T) data have been used to evaluate their thermodynamic properties.  相似文献   

6.
A series of Gd11–xy Yb x Er y GeP3O26 germanate phosphates differing in the ratio of the Yb3+ and Er3+ active ions have been synthesized, and their luminescence spectra have been measured. According to X-ray diffraction characterization results, all of the synthesized germanate phosphates are single-phase and have a triclinic structure (sp. gr. P1). We have measured upconversion luminescence spectra due to the Er3+ 2H11/2, 4S3/24I15/2 and 4F9/24I15/2 radiative transitions in the synthesized gadolinium ytterbium erbium germanate phosphates and determined the luminescence upconversion energy yield (B en) in Gd11–xy Yb x Er y GeP3O26. The effects of the concentrations and ratio of the dopants in the Gd11(GeO4)(PO4)3O10 germanate phosphate host on B en and the ratio of the luminescence intensities in the red and green spectral regions (R/G) have been assessed.  相似文献   

7.
Platelike Li1 ? x Na x Cu2O2 single crystals up to 2 × 10 × 10 mm in dimensions have been grown by slowly cooling (1 ? x)Li2CO3·xNa2O2·4CuO melts in alundum crucibles in air. Li1 ? x Na x Cu2O2 solid solutions in the LiCu2O2-NaCu2O2 system have been shown to exist in the composition range 0.78 < x < 1. The temperature stability ranges of NaCu2O2 and LiCu2O2 are 780–930 and 890–1050°C, respectively. The Mössbauer spectra and electrical conductivity of the crystals have been measured.  相似文献   

8.
The formation mechanisms of Li x Na1 ?x Ta y Nb1 ? y O3 perovskite solid solutions in the Li2CO3-Na2CO3-Nb2O5-Ta2O5 system have been studied by x-ray diffraction, differential thermal analysis, thermogravimetry, IR spectroscopy, and mass spectrometry at temperatures from 300 to 1100°C. The results indicate that the synthesis of Li x Na1 ? x Ta y Nb1 ? y O3 solid solutions involves a complex sequence of consecutive and parallel solid-state reactions. An optimized synthesis procedure for Li x Na1 ? x Ta y Nb1 ? y O3 solid solutions is proposed.  相似文献   

9.
We have studied general trends of crystallization from high-temperature solutions in the K2O-P2O5-V2O5-Bi2O3 system at P/V = 0.5?2.0, K/(P + V) = 0.7?1.4, and Bi2O3 contents from 25 to 50 wt % and identified the stability regions of BiPO4, K3Bi5(PO4)6, K2Bi3O(PO4)3, and K3Bi2(PO4)3 ? x (VO4) x (x = 0?3) solid solutions. The synthesized compounds have been characterized by X-ray powder diffraction and IR spectroscopy, and the structure of two solid solutions has been determined by single-crystal X-ray diffraction (sp. gr. C 2/c): K3Bi2(PO4)2(VO4), a = 13.8857(8), b = 13.5432(5), c = 6.8679(4) Å, β = 114.031(7)°; K3Bi2(PO4)1.25(VO4)1.75, a = 13.907(4), b = 13.615(2), c = 6.956(2) Å, β = 113.52(4)°.  相似文献   

10.
Empirical calculational approaches have been used to evaluate the enthalpy, entropy, heat capacity, and melting point of iron(II) niobate and iron(II) tantalate and the coefficients A, B, and C in an equation for the temperature dependence of their heat capacity. The melting point of FeTa2O6 has been experimentally determined to be 1891 ± 5 K. The calculated heat capacity (C°p (298.15 K)) of iron tantalate and the Gibbs energies of formation of FeN2O6 and FeTa2O6 have been compared to previously reported data.  相似文献   

11.
New solid solutions, Bi2?x?y Tm x Nb y O3+δ, with tetragonal and cubic structures have been synthesized in the Bi2O3-Tm2O3-Nb2O5 system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi1.8Tm0.15Nb0.05O3+δ is comparable to that of Bi1.75Tm0.25O3, the best conductor in the Bi2O3-Tm2O3 system.  相似文献   

12.
The multicomponent refractory oxide system Zn2(TiaSnb)1 ? x ZrxO4 (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 1: 0, 2: 1, 3: 1, 4: 1; x = 0?1.0; Δx = 0.05) has been studied by x-ray diffraction, using samples prepared by melting appropriate oxide mixtures in a low-temperature hydrogen-oxygen plasma. Two phases, both with wide homogeneity ranges, have been identified: α-phase, with a cubic inverse spinel structure, and β-phase, with a tetragonal spinel structure. The phase boundaries in the system have been determined. Structural data are presented for about 100 solid solutions of different compositions.  相似文献   

13.
In this paper, we report an ultralow thermal conductivity and a high-temperature phase stability of the (Nd1?x Ce x )2Zr2O7+x system over the temperature range from room temperature to 1600 °C and over a wide composition range (0.2 ≤ x ≤ 0.8), and the (Nd1?x Ce x )2Zr2O7+x system is therefore considered a strong candidate material for the fabrication of next-generation high-temperature thermal barrier coatings. The observed thermal conductivities (0.65–1.0 W/mK) are about 60–40% lower than those of undoped Nd2Zr2O7 over the same temperature range (100–700 °C) and indicate a glass-like behavior. For comparison, the variation in the thermal conductivity with the temperature of the (Gd1?x Ce x )2Zr2O7+x system with similar point defects was also measured, and the observed behavior was almost the same as that of undoped Gd2Zr2O7 and was mostly determined by phonon–phonon scattering (λ ∝ 1/T). The effect of point defect scattering and strong phonon scattering sources (rattlers) on the thermal conductivity is also discussed in this paper. The results of this study suggest that the ultralow thermal conductivity of (Nd1?x Ce x )2Zr2O7+x can be attributed to the presence of rattlers because of the large difference between the ionic radii of the Nd3+ and Ce4+ ions.  相似文献   

14.
Reaction between α-V2O5 and NaN3 has been studied at pressures from 5.0 to 6.0 GPa and temperatures from 600 to 800°C using Toroid high-pressure chambers. A new oxide, V3.047O7 (VO2.297), isostructural with simpsonite, Al4Ta3O13(OH), has been detected in samples with the initial composition 0.2NaN3 · V2O5 after high-temperature, high-pressure processing at p = 5.0 GPa and t = 800°C for 2 min. The crystal structure of the oxide has been refined by the Rietveld method using X-ray powder diffraction data: a = 7.35136(2) Å, c = 4.51462(2) Å, V = 211.294(1) Å3, Z = 2, sp. gr. P3. Each vanadium atom in this structure is coordinated by six oxygens in the form of a [VO6] octahedron. The synthesized oxide is a second compound with the simpsonite structure. We have measured the infrared transmission and Raman spectra of V3.047O7. Electrical measurements have demonstrated that the material is a semiconductor.  相似文献   

15.
Ho2Ti2O7 and LnYTi2O7 (Ln = Dy, Ho) pyrochlores have been synthesized using hydroxide coprecipitation, mechanical activation, and firing at 1600°C. The bulk and grain-boundary components of their conductivity have been determined for the first time by impedance spectroscopy. The 740°C bulk conductivity of Ho2Ti2O7 is 4 × 10?4 S/cm, and that of HoYTi2O7 is 1 × 10?3 S/cm, with activation energies E a = 1.01 and 1.17 eV, respectively, suggesting that these materials are new oxygen-ion conductors. The bulk conductivity of DyYTi2O7 (3 × 10?4 S/cm at 740°C, E a = 1.09 eV) is almost one order of magnitude lower than that of HoYTi2O7 (1 × 10?3 S/cm at 740°C, E a = 1.17 eV).  相似文献   

16.
CsSmP4O12 crystals have been prepared at 300°C in molten polyphosphoric acids containing Cs, Mg, and Sm cations, and their crystal structure has been determined: sp. gr. I \(\bar 4\) 3d, a = 15.1225(8) Å, Z = 12, CsNdP4O12 structure.  相似文献   

17.
Bi2–хLaхFe4O9 and Bi2Fe4–2xTixCoxO9 ferrites have been prepared by solid-state reactions at a temperature of 1073 K. X-ray diffraction data indicate that, in the Bi2–хLaхFe4O9 system, the limiting degree of La3+ substitution for Bi3+ ions in Bi2Fe4O9 does not exceed 0.05 and that the limiting degree of substitution in the Bi2Fe4–2xTixCoxO9 system lies in the range 0.05 < x < 0.1. The specific magnetization and specific magnetic susceptibility of the samples have been measured at temperatures from 5 to 300 K in a magnetic field of 0.86 T. The field dependences of magnetization obtained for the Bi2–хLaхFe4O9 and Bi2Fe4–2xTixCoxO9 ferrites at temperatures of 300 and 5 K demonstrate that partial isovalent substitution of La3+ for Bi3+ ions in Bi2Fe4O9 and heterovalent substitution of Ti4+ and Co2+ ions for two Fe3+ ions leads to partial breakdown of the antiferromagnetic state and nucleation of a ferromagnetic state.  相似文献   

18.
In this work, (Ba0.96Ca0.04)(Ti0.92Sn0.08)O3xmol MnO (BCTS–xMn) lead-free piezoelectric ceramics were fabricated by the conventional solid-state technique. The composition dependence (0 ≤ x ≤ 3.0 %) of the microstructure, phase structure, and electrical properties was systematically investigated. An O–T phase structure was obtained in all ceramics, and the sintering behavior of the BCTS ceramics was gradually improved by doping MnO content. In addition, the relationship between poling temperature and piezoelectric activity was discussed. The ceramics with x = 1.5 % sintering at temperature of 1330 °C demonstrated an optimum electrical behavior: d 33 ~ 475 pC/N, k p ~ 50 %, ε r ~ 4060, tanδ ~ 0.4 %, P r ~ 10.3 μC/cm2, E c ~ 1.35 kV/mm, T C ~ 82 °C, strain ~0.114 % and \(d_{33}^{*}\) ~ 525 pm/V. As a result, we achieved a preferable electric performance in BaTiO3-based ceramics with lower sintering temperature, suggesting that the BCTS–xMn material system is a promising candidate for lead-free piezoelectric ceramics.  相似文献   

19.
The crystal structure of a previously unknown compound KNa3[(UO2)5O6(SO4)] [space group Pbca, a = 13.2855(15), b = 13.7258(18), c = 19.712(2) Å, V = 3594.6(7) Å3] was solved by direct methods and refined to R 1 = 0.055 for 3022 reflections with |F hkl | ≥ 4σ |F hkl |. In the structure there are five sym-metrically nonequivalent uranyl cations. They are linked by cationcation (CC) interactions to form a pentamer whose central cation is U(2)O 2 2+ forming two three-centered CC bonds. All the uranyl ions are coordinated in the equatorial plane by five O atoms, which leads to the formation of pentagonal bipyramids sharing common edges to form layers parallel to the (100) plane. The sulfate tetrahedron links the uranyl layers into a 3D framework. The K+ and Na+ cations are arranged in framework voids. A brief review of CC interactions in U(VI) compounds is presented.  相似文献   

20.
Single crystals of four Ln2TiO5 polymorphs have been grown, and their structures have been determined: orthorhombic (Gd2TiO5, a = 10.460(5), b = 11.317(6), c = 3.750(3) Å, Pnam, Z = 4), hexagonal (Gd1.8Lu0.2TiO5, a = 3.663(3), c = 11.98(1) Å, P63/mmc, Z = 1.2), cubic (Dy2TiO5, a = 10.28(1) Å, Fd3m, Z = 10.4), and monoclinic (Dy2TiO5, a = 10.33(1), b = 3.653(5), c = 7.306(6) Å, β = 90.00(7)°, B2/m, Z = 2.4). The last polymorph has been identified for the first time.  相似文献   

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