共查询到20条相似文献,搜索用时 18 毫秒
1.
James V. Marzik Robert Kershaw Kirby Dwight Aaron Wold 《Journal of solid state chemistry》1982,44(3):382-387
Single crystals of PdPSe were shown to be n-type semiconductors. Weak Pauli paramagnetic behavior was observed, which is consistent with the presence of delocalized electrons. Electrical measurements showed a room-temperature resistivity ? = 70 ohm-cm, activation energy of resistivity Ea = 0.32 eV, and Hall mobility μ = 34 cm2 V?1 sec?1. Photoelectronic measurements in aqueous solutions of indicate that PdPSe has high quantum efficiencies below 800 nm. The indirect optical band gap is 1.28(2) eV. 相似文献
2.
Geometric constraints present in A2BO4 compounds with the tetragonal-T structure of K2NiF4 impose a strong pressure on the BOIIB bonds and a stretching of the AOIA bonds in the basal planes if the tolerance factor is , where RAO and RBO are the sums of the AO and BO ionic radii. The tetragonal-T phase of La2NiO4 becomes monoclinic for Pr2NiO4, orthorhombic for La2CuO4, and tetragonal-T′ for Pr2CuO4. The atomic displacements in these distorted phases are discussed and rationalized in terms of the chemistry of the various compounds. The strong pressure on the BOIIB bonds produces itinerant bands and a relative stabilization of localized dz2 orbitals. Magnetic susceptibility and transport data reveal an intersection of the Fermi energy with the d2z2 levels for half the copper ions in La2CuO4; this intersection is responsible for an intrinsic localized moment associated with a configuration fluctuation; below 200 K the localized moment smoothly vanishes with decreasing temperature as the d2z2 level becomes filled. In La2NiO4, the localized moments for half-filled dz2 orbitals induce strong correlations among the electrons above ; at lower temperatures the electrons appear to contribute nothing to the magnetic susceptibility, which obeys a Curie-Weiss law giving a μeff corresponding to , but shows no magnetic order to lowest temperatures. These surprising results are verified by comparison with the mixed systems La2Ni1?xCuxO4 and La2?2xSr2xNi1?xTixO4. The onset of a charge-density wave below 200 K is proposed for both La2CuO4 and La2NiO4, but the atomic displacements would be short-range cooperative in mixed systems. The semiconductor-metallic transitions observed in several systems are found in many cases to obey the relation , where and Tmin is the temperature of minimum resistivity ?. This relation is interpreted in terms of a diffusive charge-carrier mobility with at T = Tmin. 相似文献
3.
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
4.
Paul Poix 《Journal of solid state chemistry》1981,40(2):175-179
The study of K2NiF4 and perovskite structure type by the “method of invariants” leads to the relationship: , where (A-X)9 and (A-X)12 are the invariant values associated with cation A in coordination number 9 and 12. In the case where A = K+ and X = F?, we propose the relationship: where R is the coordination number. 相似文献
5.
The novel λ4-thia-λ5-phospha-h2-manganabicyclo[2.2.1]heptadienes (OC)3Mn[] (R1 = CH3, C6H5; R2 = CO2CH3, CO2C2H5, CO2C6H11) are formed by action of the activated alkynes R2C CR2 on the heterocycles [(OC)4MnPR12S]2 via the isolable, five-membered heterometallacyclopentadienes (OC)4(R2). The compound with R1 = CH3 and R2 = CO2CH3 crystallizes in the triclinic space group P with Z = 2 and separates quantitatively the thiophene derivative under CO pressure or by reaction with (NH4)2Ce(NO3)6. The use of various acetylenes and of acetylenes with different alkyl groups yields the unsymmetric substituted manganabicycloheptadienes (OC)3Mn[] (R2 = CO2CH3, R3 = R4 = CO2C2H5; R2 = R4 = CO2CH3, R3 = H). With propionic acid methylester the alkyne insertion proceeds regiospecifically. With Raney nickel selective S elimination under ring contraction and formation of the λ4-phospha-h2-manganabicyclo[2.1.1]hexenes (OC)3Mn[R12] (R1 = CH3: R2 = R3 = CO2CH3, CO2C2H5; R2 = CO2CH3, R3 = H; R1 = C6H5: R2 = R3 = CO2C2H5) occurs. (OC)3Mn[(CH3)2] (R2 = R3 = CO2CH3) crystallizes in the monoclinic space group P21/m with Z = 2. The IR and NMR spectra of the heterocycles are discussed in detail. 相似文献
6.
Results on the rate of polymerization of acrylic acid by S2O2?8 ion in alkaline and acid conditions are presented. Rp depended upon and both in acid and alkaline solutions. The influence of ionic strength, the effect of pH on Rp and the catalytic effect of Ag+ and Cu2+ on the system have been discussed. Suitable mechanisms are proposed. 相似文献
7.
The electrical conductivity of sintered specimens of nonstoichiometric CeO2?x was measured as a function of temperature (750–1500°C) and oxygen pressure (1–10?22 atm). The isothermal compositional dependence of the electrical conductivity of CeO2?x was determined by combining recently obtained thermodynamic data, x = x(PO2, T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expressionover the temperature range 750–1500°C and from x = 0.001 to x = 0.1.This expression was rationalized in terms of the following simple relations for (a) the electron carrier concentrationwhere nCe′Ce is the number of Ce′Ce per cm3 and a0 is the lattice parameter and (b) the electron mobility. 相似文献
8.
An attempt has been made to treat the rare earth contribution to the magnetocrystalline anisotropy in RCo5 and R2Co17 compounds with a single ion model using a Hamiltonian of the form: Hex is regarded as arising mainly from the cobalt sublattice. Eigenvalues and eigenfunctions for the above Hamiltonian were obtained when the exchange field is perpendicular to the c-axis and compared with those when it is parallel to the c-axis. For values of Hex estimated from experiment it is found that the sign of B20 determines the direction preference of the rare earth sublattice magnetization. Comparison of theory with experiment shows that the correct sign of B20 can be predicted on the point charge model considering only the effect of rare earth nearest neighbors. The calculations also predict that the quantity |K1R(0) + K2R(0)| is nearly equal to the crystal field overall splitting (CFOAS) determined in the absence of exchange and is independent of the magnitude of the exchange field, provided that the exchange field is sufficiently large. The temperature dependence of |K1R + K2R| has also been calculated and found to agree semiquantitatively with available experimental results. 相似文献
9.
The kinetics of the interaction of hexaaquochromium(III) ion with potassium octacyanomolybdate(IV) have been studied using conductance and spectrophotometric data. The mechanism of the reaction is discussed and the effect of H+ ion and the ionic strength on the rate of the reaction determined. The reaction is found to be pseudo-first order with respect to potassium octacyanomolybdate(IV) and inverse first order with [H3O+]. The rate of the reaction increases with increase in ionic strength and temperature. Activation parameters have been calculated using the Arrhenius equation and have the values ΔE* = 1.3 × 102 kJ mol?1, ΔH* = 129 kJ mol?1, ΔS* = ?315 e.u., ΔF* = 2.3 × 102 kJ and A = 1.5 × 10?3. The mechanism proposed is based on ion-pair formation and the rate equation obtained is given by: kobs= 相似文献
10.
J. Mulak 《Journal of solid state chemistry》1977,21(2):117-126
Based on the experimentally determined temperature dependence of the paramagnetic susceptibility of tetragonal USiO4 within the temperature range 2–500°K, the crystal field parameters of D2d symmetry have been estimated (in cm?1): B02 = ?24, B04 = ?1.25, B44 = ?12.8, B06 = ?0.031, B46 = 0.51, and . The Γ5 doublet with the approximate composition: 0.78|±1> + 0.63|?3> is the ground level of the U4+ ion. Singlet Γ1 lying ca. 100 cm?1 above is the first excited level. The total splitting of the 3H4 term of the U4+ ion was estimated to be equal to ca. 7500 cm?1. 相似文献
11.
The electrical conductivity of polycrystalline strontium titanate with ( was determined for the oxygen partial pressure range of 100 to 10?22 atm and the temperature range of 850–1050°C. These data were found to be similar to that obtained for the sample with ideal cationic ratio. The observed data were proportional to the power of oxygen partial pressure for PO2 < 10?15atm, proportional to for the pressure range 10?8–10?15 atm, and proportional to for PO2 > 10?4atm. The deviation from the ideal Sr-to-Ti ratio was found to be accommodated by neutral vacancy pairs, (V″Sr V″0. The results indicate that the single-phase field of strontium titanate extends beyond 50.505 mole% TiO2 at elevated temperatures. 相似文献
12.
The extraction of Co(II) with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one ((H)PMBP) and tri-n-octylamine (TOA) is investigated in order to explore the influence of diluents and inorganic anions with synergistic acidic extractant + liquid anion exchanger systems. Although it is proved that the same species [HTOA]+ [Co(PMBP)3]? is extracted from various inorganic media, with toluene as the diluent, the presence of ClO4? SO42? or Cl? anion modifies the distribution of the anions which are associated to (HTOA)+ in the organic phase, leading to different synergistic equilibria; with Cl? or SO42?: + ,PMBP?) ?,Co(PMBP)3? (log K = 6.10) and with ClO4? : + + ,ClO4? ? ,Co(PMBP)3? + H+ + ClO4? (log K = 2.34) The same synergistic equilibrium is observed for the extraction of Ni(II) from ClO4? medium, with a comparable value of the constant (log K = 2.45). The synergistic effect is cancelled in n-octanol. 相似文献
13.
The extraction of In(III) from 1M (Na,H)(Cl,ClO4) media with 4-acylpyrazol-5-ones (HL) in toluene at 25°C is described by equilibria In 3+ + 3 ? + 3 H+ (log K = 1.48, 1.03, 0.87 with acyl = benzoyl, lauroyl, 2-thenoyl), InCl 2+ + 2 ? + 2 H+ (log K = 0.26, ?0.45, ?0.35 respectively) and In3+ + m Cl? ? InClm(3-m)+ (log βm available from literature). The extraction from 1M (Na,H)(Cl,NO3) medium is enhanced by addition of aliquat (TOMA+,Cl?) and the following synergic equilibrium takes place : + ,Cl?) ? , InCl2L2? (log K = 5.49, 5.25, 5.21 respectively). Cl? of (TOMA+,Cl?) is exchanged by NO3? with the equilibrium constant log K = 1.50. If (TOMA+,Cl?) is replaced by tri-n-octylammonium chloride, the synergic effect is largely reduced (log K = 4.17 with acyl = benzoyl). The extraction from chloride solutions containing ClO4? remains unchanged by addition of ammonium salts. 相似文献
14.
Calorimetric measurements of the enthalpy of solution of cesium chromate gave ΔHsoln = (7622 ± 24) calth mol?1 for a dilution of Cs2CrO4·21128H2O. This result, along with the enthalpy of dilution gave the standard enthalpy of solution, ΔHsolno = (7512 ± 31) calth mol?1, whence the standard enthalpy of formation, ΔHf0(Cs2CrO4, c, 298.15 K), was calculated to be ?(341.78 ± 0.46) kcalth mol?1. Recomputed thermodynamic data for the formation of the other alkali metal chromates have been tabulated. From their solubilities and enthalpies of solution, the standard entropies, S0(298 K), of BaCrO4 and PbCrO4 were estimated to be (38.9 ± 0.9) and (43.7 ± 1.2) calth K?1 mol?1, respectively. There is evidence that ΔHf0(SrCrO4, c, 298.15 K) may be in error. Thermochemical, solubility, and equilibrium data, have been combined to update the thermodynamic properties of the aqueous chromate (CrO42?), bichromate (HCrO4?), and dichromate (Cr2O72?) ions. The new values at 298.15 K are as follows:
CrO42?(aq) | (13.8 ± 0.5) | ?(210.93 ± 0.45) | ?(174.8 ± 0.5) |
HCrO4?(aq) | (46.6 ± 1.8) | ?(210.0 ± 0.7) | ?(183.7 ± 0.5) |
Cr2O72?(aq) | (67.4 ± 3.9) | ?(356.5 ± 1.5) | ?(312.8 ± 1.0) |