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1.
Use of Nd3+, Eu3+, and Gd3+ as local structural probes allows the determination of the rare earth positions in the NaxSr3?2xLnx(PO4)2 (Ln = La to Tb) and KCaLn(PO4)2 phases (Ln = rare earth). Moreover, a common feature of both series is a particularly high splitting of the excitation and levels of the Gd3+ ions. 相似文献
2.
Junichiro Mizusaki Masafumi Yoshihiro Shigeru Yamauchi Kazuo Fueki 《Journal of solid state chemistry》1985,58(2):257-266
In order to elucidate the defect structure of the perovskite-type oxide solid solution La1?xSrxFeO3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, PO2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of PO2 ≥ 0.13 atm, δ in La1?xSrxFeO3?δ was found to be close to 0. With decreasing log PO2, δ increased and asymptotically reached . The value corresponding to was about ?10 at 1000°C. With further decrease in log PO2, δ slightly increased. For LaFeO3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log PO2 is interpreted on the basis of the defect equilibrium among Sr′La (or V?La for the case of LaFeO3?δ), V··O, Fe′Fe, and Fe·Fe. Calculations were made for the equilibrium constants Kox of the reaction and Ki for the reaction Using these constants, the defect concentrations were calculated as functions of PO2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements. 相似文献
3.
The compound Th0.25 NbO3 melts congruently at 1390°C. Single crystals obtained by slow cooling from the melt are transparent and show uniaxial optical properties. A single-crystal X-ray analysis confirms the tetragonal cell found by Kovba and Trunov from a powder data and gives a = 3.90 Å and c = 7.85 Å. No systematic absence of the hkl reflections is observed on precession films. The relative intensities of the main reflections are characteristic of a perovskite-like arrangement ABO3 whose large dodecahedral A sites are only partly occupied. Several domains have been found in the perovskite-type solid solution (1 ? x) Th0.25NbO3-x NaNbO3. For 0 ? x ? 0.5 the phases have a tetragonal cell with and as in pure Th0.25 NbO3. When 0.6 ? x ? 0.8 the corresponding phases crystallize with a small cubic cell (Å), while phases with 0.9 ? x ? 1 have an orthorhombic cell (). 相似文献
4.
The Sr2+1?yLa3+yFeO3 system with 0.1 ≦ y ≦ 0.6 has been studied mainly by the Mössbauer effect. The results are discussed referring to the Ca1?xSrxFeO3 system. The following four kinds of electronic phases have been observed: the paramagnetic and the antiferromagnetic average valence phases and the corresponding mixed valence phases. Two kinds of Fe ions coexist, in general, in the mixed valence phases. In the antiferromagnetic mixed valence phase, typically at 4 K, the magnetic hyperfine field and the center shift each takes a wide range of value depending on the composition, while a beautiful correlation is kept between them. The extreme values are close to those expected for Fe3+ and Fe5+. The appropriate chemical formulas are, therefore, Ca1?xSrxFe(3+Δ)+0.5Fe(5?Δ)+0.5O3 and . 相似文献
5.
The spinels of the system LixMn1?xV2O4 (0 ? x ? 1) have been prepared at 700–750°C from LiV2O4 and MnV2O4. The lattice constants decrease linearly with increasing x. In the region x>0.75, the d-electrons of V should be delocalized as the VV distances are lower than the critical VV separation of 2.94 Å. Experimentally, the samples with x>0.6 show no IR absorption bands and the Seebeck coefficient is near zero. The Seebeck coefficient can be described with a model of intermediate polarons and can be expressed by the equation . 相似文献
6.
R. Ibañez A. Garcia C. Fouassier P. Hagenmuller 《Journal of solid state chemistry》1984,53(3):406-414
As a consequence of the weak phonon energies and the low crystal field, several excited states of Nd3+ are emitters in the NaxNdxM1?2xGa2G4 thiogallates (x ≤ 0.5 for M = Ca or Sr and ≤0.2 for M = Ba). The infrared emission is little affected by concentration quenching. NaNdGa4S8 is the first efficient stoichiometric sulfide so far reported. Unlike other sulfides previously investigated, the neodymium thiogallates show an intense excitation band, ascribed to electron transfer from the valence band to states constituted essentially by neodymium orbitals. 相似文献
7.
New lanthanum aluminates LaMAl11O19 (M2+ = Ni, Co, Mn, Mg1?xMnx, 0 ≤ x ≤ 1), with magnetoplumbite-like structure have been obtained as single crystals. This paper is particularly devoted to the Mn2+ and mixed compounds, which exhibit promising luminescent properties. Several characteristics of the crystals are given. The absorption spectra of the materials, as grown, are assigned to Mn2+ ions in tetrahedral sites. After annealing in air new absorptions attributed to octahedral Mn3+ ions, appear. The ESR spectra of Mn2+ in all these crystals exhibit axial symmetry. For x ≤ 0.25 they arise from isolated Mn2+ ions in slightly distorted tetrahedral sites and reveal a strong disorder effect. For x ≥0.5 the spectra consist of a single line, attributed to clusters of magnetically interacting Mn2+ ions. 相似文献
8.
The structure of a crystal was established by X-ray analysis. The solution in the cell of symmetry , with a = 6.6702(5), b = 5.3228(8), c = 8.9091(8) Å, β = 100.546(7)°, Z = 1, has led to R = 0.033 and Rw = 0.036 for 2155 reflections with . This structure can be described as two octahedra-wide ReO3-type slabs connected through “planes” of PO4 tetrahedra. A new structural family KxP2W2nO6n+4 can be foreseen which is closely related to the orthorhombic P4W8O32 and the monoclinic RbxP8W8nO24n+16 series. 相似文献
9.
The electrical conductivity and departure from the stoichiometry of Nd2O3 have been measured over the temperature range of 900° to 1100°C and oxygen partial pressure of 1 to 10?16 atm. The hole conductivity of Nd2O3 is found to be proportional to , where n are 4.6, 4.9, and 5.1 at 900°, 1000°, and 1100°C, respectively. From the oxygen partial pressure dependence of the hole conductivity, it is shown that the predominant point defects in nonstoichiometric NdO1·+x are fully ionized and partially doubly ionized metal vacancies. From the thermogravimetric measurements, the departure from stoichiometry, x in NdO1·5+x, is 2.0 × 10?3 at 1000°C and 1 atm. By combining the electrical conductivity and weight change data, it is shown that the hole mobility is 6.3 × 10?4 (cm2/V·sec) at 1000°C and 1 atm. 相似文献
10.
Proton NMR relaxation times (T2T1, and T1?) and absorption spectra are reported for the compounds H1.71MoO3 (red monoclinic) and H0.36MoO3 (blue orthorhombic) in the temperature range 77 K < T < 450 K. Rigid lattice dipolar spectra show that both compounds contain proton pairs, as OH2 groups coordinated to Mo atoms in H1.71MoO3 and as pairs of OH groups in H0.36MoO3. The room temperature lineshape for H1.71MoO3 shows that the average chemical shielding tensor has a total anisotropy of 20.1 ppm. The relaxation measurements confirm that hydrogen diffusion occurs and give EA = 22 kJ mole?1 and for H1.71MoO3 and EA = 11 kJ mole?1 and for H0.36MoO3. 相似文献
11.
H. Hacker 《Journal of solid state chemistry》1976,17(3):319-322
Paramagnetic resonance and magnetic measurements were performed on powdered samples of GdGa2. The magnetic data indicated ferrimagnetic behavior with . Above 250° K the susceptibility obeys the Curie-Weiss law which corresponds to an effective moment of 7.95 Bohr magnetons. Over the range from 190 to 300°K the data obey a Néel type law, , which is indicative of ferrimagnetic order. The resonance measurements were performed at 9.013 gHz at 247, 296, and 349°K. The spectra were analyzed with a computerized curve-fitting technique that involves a linear combination of Lorentzian absorption and dispersion susceptibility components. Following demagnetization corrections, the g-factor was found to be 1.9832 while the half-power, half-linewidth was 592.7 Oersteds. 相似文献
12.
Solid solutions of GeO2 in Fe2O3 were prepared by mechanically mixing the solids and firing at 1000°C in air, and from a gel obtained by the addition of an alcohol solution of germanium ethoxide to iron dissolved in HNO3. The dried gel was then heated at 1000°C. The solubility limit is 5 mole% GeO2, Fe1.95Ge0.05O3. Similar procedures were used to prepare solid solutions with Si and the solubility limit is greater than 4 mole% SiO2. Firing of mixtures or gels of Fe2O3 containing Mg produces a spinel phase even at the lowest detectable concentrations. The resistivity of pressed pellets of Fe2?xGexO3 varies from about 106 ohm-cm for x = 0 to about 10?1 ohm-cm for x = 0.05. The photoassisted electrolysis of water at Ge-doped Fe2O3 electrodes is demonstrated. The photoelectrochemical cell showed a 0.29-V open-circuit voltage, 1.2-mA/cm2 short-circuit current, 0.31 fill factor, and 0.06% power efficiency. 相似文献
13.
Joaquín García Juan Bartolomé Domingo González Rafael Navarro Willem Jacobus Crama 《The Journal of chemical thermodynamics》1983,15(12):1109-1126
We present the heat capacities measured by adiabatic calorimetry from 6 to 350 K, and by differential scanning calorimetry from 300 to 500 K, of CsCrCl3 and RbCrCl3. A first-order transition at Tc = (171.1±0.1) K was detected for CsCrCl3. The RbCrCl3 showed at Tc = (193.3±0.1) K a transition with thermal hysteresis at temperatures just below the maximum. At T1 = (440±10) K a continuous transition was also detected. Furthermore, at TN ≈ 16 K, and for both compounds, a small bump due to magnetic long-range ordering was observed. The thermodynamic functions at 298.15 K are
CsCrCl3 | 15.38 | 26.49 | 3503.2 | 14.735 |
RbCrCl3 | 15.76 | 25.99 | 3556.8 | 14.384 |