Diffusion of oxide ions in LaFeO3 single crystal

The tracer diffusion coefficient, $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$, of oxide ions in LaFeO₃ single crystal was determined over the temperature range of 900–1100°C by the gas-solid isotopic exchange technique using ¹⁸O as a tracer. For the determination of $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$, the depth profile of ¹⁸O was measured by means of a secondary ion mass spectrometer (SIMS). The surface exchange reaction was found to be slow and the surface exchange rate constant, k, was determined together with $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$. It was found that $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ at 950°C is proportional to P^?0.58_O2, where P_O2 is an oxygen pressure. The vacancy mechanism was determined for the diffusion of oxide ions from the P_O2 dependence. The vacancy diffusion coefficient, D_V, for LaFeO₃ was nearly the same as that for LaCoO₃ at the same temperature. The activation energy for migration of oxide ion vacancies was 74 kJ · mole^?1 for both oxides.     

Self-diffusion of yttrium in monocrystalline yttrium oxide: Y2O3

Yttrium self-diffusion in monocrystalline yttrium oxide (Y₂O₃) is studied by means of the classical radio tracer technique. The few reliable diffusion data obtained in the temperature range 1600–1700°C lead to the following diffusion coefficient

$\text{D=3.5×10}{}^{\mathrm{?9}}\text{exp}\text{?}\text{72}\text{RT}\text{(}\text{kcal/mole}\text{)}\text{m}{}^2\text{sec}{}^{\mathrm{?1}}$

.Experimental errors on the above numerical values are large and give, for the preexponential and energy terms, respectively:

$\text{2.10}{}^{\mathrm{?7}}\text{<D}{}_0\text{<3.10}{}^{\mathrm{?10}}\text{m}{}^2\text{sec}{}^{\mathrm{?}}$

$\text{62<Q<82}\text{kcal/mole}$

.Nevertheless these results seem in good agreement with those deduced from high-temperature and low-stress creep experiments. The theoretical aspect of self-diffusion of yttrium in Y₂O₃ is studied in terms of point defects and lattice disorder due to the equilibrium between the oxide and its environment. This last part is confined to the restricted range of high oxygen partial pressure in which oxygen interstitials are supposed to be majority defects. Intrinsic and extrinsic diffusion behavior are both considered on the basis of a vacancy diffusion mechanism.     

Nonstoichiometry and defect structure of the perovskite-type oxides La1−xSrxFeO3−°

In order to elucidate the defect structure of the perovskite-type oxide solid solution La_1?xSr_xFeO_3?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, P_O2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of P_O2 ≥ 0.13 atm, δ in La_1?xSr_xFeO_3?δ was found to be close to 0. With decreasing log P_O2, δ increased and asymptotically reached $\text{x}\text{2}$. The value corresponding to $\text{δ =}\text{x}\text{2}$ was about ?10 at 1000°C. With further decrease in log P_O2, δ slightly increased. For LaFeO_3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log P_O2 is interpreted on the basis of the defect equilibrium among Sr′_La (or V?_La for the case of LaFeO_3?δ), V^··_O, Fe′_Fe, and Fe^·_Fe. Calculations were made for the equilibrium constants K_ox of the reaction

$\text{1}\text{2}\text{O}{}_2\text{(g) + V}{}^{\mathrm{··}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= O}{}^{\mathrm{x}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe}}$

and K_i for the reaction

$\text{2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= Fe}{}^{\mathrm{\prime }}{}_{\mathrm{Fe}}\text{+ Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe·}}$

Using these constants, the defect concentrations were calculated as functions of P_O2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.     

Electrical conductivity and defect structure of Nd2O3+x

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 NdO_1·+x are fully ionized and partially doubly ionized metal vacancies. From the thermogravimetric measurements, the departure from stoichiometry, x in NdO_1·5+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.     

High-pressure/high-temperature phase relations and vibrational spectra of CsSbF6

CsSbF₆(II) under ambient conditions is trigonal, space group $\text{D}{}_{\mathrm{3d}}{}^5\text{-R}\text{3}\text{m}$. At 187.8°C it undergoes a phase transition with an enthalpy change of 5.267 ± 0.316 kJ mole^?1, to phase CsSbF₆(I). CsSbF₆ decomposes with loss of fluorine at atmospheric pressure at high temperatures, but under pressure the decomposition is prevented and a melting point of 310°C at atmospheric pressure can be inferred. The $\text{II}\text{I}$ phase boundary and melting curve were studied as functions of pressure. The infrared and Raman spectra of CsSbF₆(II) were studied in the temperature range of ?256 to 20°C, at ambient pressure. The crystal chemistry of the CsSbF₆ and its relationship with other related compounds is discussed.     

Electrical conductivity in strontium titanate

The electrical conductivity of polycrystalline SrTiO₃ was determined for the oxygen partial pressure range of 10° to 10^?22 atm and temperature range of 800 to 1050°C. The data were found to be proportional to the $\text{?1}\text{6}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range 10^?15–10^?22 atm, proportional to for the oxygen pressure range 10^?8–10^?15 atm, and proportional to for the oxygen pressure range 10⁰–10^?3 atm. These data are consistent with the presence of very small amounts of acceptor impurities in SrTiO₃.     

A study of infrared absorption in the oxidation of zinc-substituted magnetites to defect phase γ and hematite

The effect of substitution extent on formation of superstructure-ordered vacancies in zinc-substituted lacunar spinels of type $\text{(}\text{Zn}{}^{\mathrm{2+}}{}_{\mathrm{x}}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{1?x}}\text{)}{}_{\mathrm{A}}\text{(}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>(5+x)</mtext><mtext>3</mtext>}}\text{□}{}_{\mathrm{<mtext>(1?x)</mtext><mtext>3</mtext>}}\text{)}{}_{\mathrm{B}}\text{O}{}^{\mathrm{2?}}{}_4$ was investigated using ir spectrometry. Only those lacunar phases whose substitution extent x is less than about 0.3 show a vacancy ordering on octahedral sites. In addition, referring to the disappearance of the 635-cm^?1 absorption band, which is characteristic of these lacunar spinels, we show that the transformation temperature of the γ phases into αFe₂O₃ increases with zinc substitution extent. For the α phase obtained at 700°C we have found a linear variation between the intensity difference of the 390- and 450-cm^?1 absorption bands and the percentage of αFe₂O₃.     

Study of copper-chromium oxide catalyst: I. Thermal decomposition of copper(III) chromate,CuCrO4

The kinetics, mechanism, and activation energy of the isothermal decomposition of CuCrO₄ was studied using an isothermal TG method and an X-ray high-temperature diffraction technique in either air or a flowing atmosphere of N₂. The enthalpy change ΔH of the decomposition reaction

$\text{2}\text{CuCrO}{}_4\text{→}\text{CuO}\text{+}\text{CuO}\text{+}\text{CuCr}{}_2\text{O}{}_4\text{+}\text{3}\text{2}\text{O}{}_2$

was determined by DSC analysis. The mechanism of the thermal decomposition of CuCrO₄ is well represented by the standard Avrami-Erofeev kinetic equation $\text{[?}\text{ln}\text{(1 ? α)]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= kt}$. According to this mechanism, the reaction rate is controlled by the formation and growth of nuclei on the surface of the reactant. The activation energy E_A of the process in air is E_A = (248 ± 8) kJ mole^?1, in flowing atmosphere of nitrogen E_A = (229 ± 8) kJ mole^?1. ΔH in air is 110 kJ mole^?1, in flowing nitrogen 67 kJ mole^?1. The lower values of ΔH and E_A in the flowing atmosphere of nitrogen are due to the fast elimination of O₂ from the reaction interface. However, the decay of the crystalline portion of CuCrO₄ during its thermal decomposition, studied by the X-ray diffraction, is controlled by a different reaction mechanism (first-order kinetics). The reaction mechanism is discussed in the relation to the crystal structure of the reactants.     

Hydrodynamic properties and statistical coil dimensions of poly(o-chlorostyrene)

The theta temperature for the system poly(o-chlorostyrene)-methyl ethyl ketone has been determined as 24·5°. The samples used in the determination were prepared by radical polymerization. The dependence of intrinsic viscosity on molecular weight has been measured in methyl ethyl ketone at 24·5° and found to be $\text{η}{}_{\mathrm{\theta }}\text{= 4·68 × 10}{}^{\mathrm{?4}}\text{M}{}_{\mathrm{<mtext>w</mtext>}}{}^{\mathrm{<mtext>M1</mtext><mtext>2</mtext>}}$. The ratio 〈s₌²〉/M was found, by light scattering, to be 5·60 × 10^?18 cm². Analysis of the solution properties indicates that the Kurata-Yamakawa theory is valid in the vicinity of the Flory temperature (UCST).     

Electrical conductivity in strontium titanate with nonideal cationic ratio

The electrical conductivity of polycrystalline strontium titanate with ($\text{Sr}\text{Ti}\text{= 0.996, 0.99,}\text{and}\text{0.98}$ 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 $\text{?}\text{1}\text{6}$ power of oxygen partial pressure for P_O2 < 10^?15atm, proportional to for the pressure range 10^?8–10^?15 atm, and proportional to for P_O2 > 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.     

Electrical conductivity in calcium titanate

The electrical conductivity of polycrystalline CaTiO₃ was measured over the temperature range 800–1100°C while in thermodynamic equilibrium with oxygen partial pressures from 10^?22 to 10⁰ atm. The data were found to be proportional to the $\text{?}\text{1}\text{6}\text{th}$ power of the oxygen partial pressure for the oxygen pressure range 10^?16 – 10^?22 atm, proportional to for the oxygen pressure range 10^?8 – 10^?15 atm, and proportional to for the oxygen pressure range greater than 10^?4 atm. The region of linearity where the electrical conductivity varies as $\text{?}\text{1}\text{4}\text{th}$ power of P_O2 increased as the temperature was decreased. The observed data are consistent with the presence of small amounts of acceptor impurities in CaTiO₃. The band-gap energy (extrapolated to zero temperature) was estimated to be 3.46 eV.     

Standard enthalpy of solution and formation of cesium chromate. Derived thermodynamic properties of the aqueous chromate,bichromate, and dichromate ions,alkali metal and alkaline earth chromates,and lead chromate

Calorimetric measurements of the enthalpy of solution of cesium chromate gave ΔH_soln = (7622 ± 24) cal_th mol^?1 for a dilution of Cs₂CrO₄·21128H₂O. This result, along with the enthalpy of dilution gave the standard enthalpy of solution, ΔH_soln^o = (7512 ± 31) cal_th mol^?1, whence the standard enthalpy of formation, ΔH_f⁰(Cs₂CrO₄, c, 298.15 K), was calculated to be ?(341.78 ± 0.46) kcal_th 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) cal_th K^?1 mol^?1, respectively. There is evidence that ΔH_f⁰(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 (CrO₄^2?), bichromate (HCrO₄^?), and dichromate (Cr₂O₇^2?) ions. The new values at 298.15 K are as follows:

     

13.

Thermophysical properties of the intermetallic Mn3MN perovskites III. Heat capacity of the solid solution Mn3.2Ga0.8N     

Joaquín García  Juan Bartolomé  Domingo González  Rafael Navarro  Daniel Fruchart 《The Journal of chemical thermodynamics》1983,15(12):1169-1180

The heat capacity of the solid solution Mn_3.2Ga_0.8N was measured between 5 to 330 K by adiabatic calorimetry. A sharp anomaly with first-order character was detected at T_A = (160.5±0.5) K, corresponding to a magnetic rearrangement and a lattice expansion. No sharp anomaly was observed at T_c ≈ 260 K where the magnetic ordering takes place; instead, a smooth shoulder was detected. The thermodynamic functions at 298.15 K are $\text{C}{}_{\mathrm{<mtext>p,</mtext><mtext>m</mtext>}}\text{R}\text{= 15.16}$, $\text{S}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{R}\text{= 18.57}$, $\text{{H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(T)?H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(0)}}\text{R}\text{= 2896}\text{K}$, $\text{?{G}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(T)?H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(0)}}\text{RT}\text{= 8.85}$. At low temperatures the coefficient for the linear electronic contribution to the heat capacity was derived: γ = (0.031±0.003) J·K^?2·mol^?1. Moreover, the different contributions to the heat capacity were obtained and the electronic origin of the phase transitions was established.     

14.

Crystal structure,Mössbauer,and magnetic behavior of mixed valence compounds in the BaFeS system: Ba₃(Ba_1−xAl_x)Fe₂S₆[S_1−y(S₂)_y]     

J.T. Hoggins  L.E. Rendon-Diazmiron  H. Steinfink 《Journal of solid state chemistry》1977,21(2):79-90

The compounds $\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_6\text{[S}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(}\text{S}{}_2\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{]}$ and Ba_3.6Al_0.4Fe₂S₆[S_0.6(S₂)_0.4], designated I and II, were prepared by reacting BaS, Fe, and S powders and Al foils in graphite containers sealed in evacuated quartz ampoules at approximately 1100°C. The crystal structure of I was determined using 1682 independent, nonzero X-ray reflections, while 3589 were used for II. They are triclinic, $\text{A}\text{l}$:

$\text{a=9.002(2)}\text{A}\text{?}\text{,b=6.7086(8)}\text{A}\text{?}\text{,c=24.658(4)}\text{A}\text{?}\text{α91.49(2)°,}$

$\text{β=105.10(2)°y=90.74(2)°,ψ}{}_{\mathrm{calc}}\text{=4.15g/cm}{}^3\text{,for I:}$

$\text{a=8.993(6)}\text{A}\text{?}\text{,b=6.708(7)}\text{A}\text{?}\text{,c=24.70(1)}\text{A}\text{?}\text{α91.11(6)°,}$

$\text{β=105.04(6)°y=90.90(9)°,ψ}{}_{\mathrm{calc}}\text{=3.90g/cm}{}^3\text{,for II:}$

BaS₆ trigonal prisms share edges to form distorted hexagonal rings which form one-dimensional chains leaving two free lateral edges. The chains link in a stairstep manner with the rings offset along the [301] direction. These stairsteps join in a complicated manner to form a three-dimensional network. Fe ions are in two sites forming isolated FeS₄ tetrahedra and isolated Fe₂S₆ dimers by edge-sharing tetrahedra. The Al substitution occurs in the trigonal prisms which have free edges with Al replacing Ba. Room-temperature Mössbauer isomer shifts are 0.20 mm/sec. for I and 0.30 mm/sec for II. These data indicate that upon Al substitution charge compensation occurs by reducing Fe³⁺. Valence calculations indicate that Fe in edge-sharing tetrahedra are reduced while the Fe in the isolated tetrahedron remains unchanged. The effective charge distribution in the Al substituted compound is approximately Fe³⁺, Fe^2.5+ with electron delocalization across the shared edge. Room temperature electrical resistivity is 10⁵ ohm/cm. The compositions of the crystals are best represented by the formulas $\text{[}\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_7\text{]}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{·[}\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_6\text{(S}{}_2\text{)]}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ and [Ba₃AlFe₂S₇]_0.4·[Ba₄Fe₂S₇]_0.2·[Ba₄Fe₂S₆(S₂)]_0.4. The replacement of a sulfide by a disulfide ion is thought to be strongly dependent on the sulfur activity during the preparation.     

15.

Standard enthalpies of formation of uranium compounds I. β-UO₃ and γ-UO₃     

E.H.P. Cordfunke  W. Ouweltjes  G. Prins 《The Journal of chemical thermodynamics》1975,7(12):1137-1142

The standard enthalpy of formation of γ-UO₃ has been critically assessed; the value ?(292.5 ± 0.2) kcal_th mol^?1 is suggested.The enthalpies of solution of β-UO₃ and γ-UO₃ in 3 M H₂SO₄ have been measured and used to derive:

$\text{ΔH}{}_{\mathrm{f}}{}^{\mathrm{°}}\text{(β?}\text{UO}{}_3\text{, 298.15}\text{K}\text{) = ?(291.6 ± 0.2)}\text{kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?}}$

     

16.

Electronic conductivity in nonstoichiometric cerium dioxide     

R.N. Blumenthal  R.K. Sharma 《Journal of solid state chemistry》1975,13(4):360-364

The electrical conductivity of sintered specimens of nonstoichiometric CeO_2?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 CeO_2?x was determined by combining recently obtained thermodynamic data, x = x(P_O2, T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expression

$\text{σ=410[x]e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{ohm cm}\text{)}{}^{\mathrm{?1}}$

over 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 concentration

$\text{n}{}_{\mathrm{ce}}\text{′}{}_{\mathrm{ce}}\text{=}\text{8x}\text{a}{}_0{}^3$

where n_Ce′Ce is the number of Ce′_Ce per cm³ and a₀ is the lattice parameter and (b) the electron mobility

$\text{μ=5.2(10}{}^{\mathrm{?2}}\text{)e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{cm}{}^2\text{/}\text{V sec}\text{)}$

.     

17.

EPR and magnetization of GdGa₂     

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 $\text{T}{}_{\mathrm{c}}\text{? 181°}\text{K}$. Above 250° K the susceptibility obeys the Curie-Weiss law $\text{χ}{}_{\mathrm{g}}\text{=}\text{2.66}{}_2\text{× 10}{}^{\mathrm{?2}}\text{(T ? 27.6)}\text{emu/g-Oe}$ 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, $\text{χ}{}_{\mathrm{g}}{}^{\mathrm{?1}}\text{= 35.95 (T ? 12.5) ?}\text{2.20 × 10}{}^4\text{(T ? 177)}$, 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.     

18.

NMR study of hydrogen molybdenum bronzes: H_1.71MoO₃ and H_0.36MoO₃     

R.C.T. Slade  T.K. Halstead  P.G. Dickens 《Journal of solid state chemistry》1980,34(2):183-192

Proton NMR relaxation times (T₂T₁, and T_1?) and absorption spectra are reported for the compounds H_1.71MoO₃ (red monoclinic) and H_0.36MoO₃ (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 H_1.71MoO₃ and as pairs of OH groups in H_0.36MoO₃. The room temperature lineshape for H_1.71MoO₃ 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 E_A = 22 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 10}{}^{\mathrm{?13}}\text{sec}$ for H_1.71MoO₃ and E_A = 11 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 3 × 10}{}^{\mathrm{?8}}\text{sec}$ for H_0.36MoO₃.     

19.

Extraction of indium(III) from chloride medium with 1-phenyl-3-methyl-4-acylpyrazol-5-ones. Synergic effect with high molecular weight ammonium salts.     

J.P. Brunette  M. Taheri  G. Goetz-Grandmont  M.J.F. Leroy 《Polyhedron》1982,1(5):457-460

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 $\text{HL}$ ? $\text{InL}{}_3$ + 3 H⁺ (log K = 1.48, 1.03, 0.87 with acyl = benzoyl, lauroyl, 2-thenoyl), InCl ²⁺ + 2 $\text{HL}$ ? $\text{InClL}{}_2$ + 2 H⁺ (log K = 0.26, ?0.45, ?0.35 respectively) and In³⁺ + m Cl^? ? InCl_m^(3-m)+ (log β_m 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 : $\text{InCl}{}_2$ + $\text{(TOMA}{}^{\mathrm{+}}$,Cl^?) ? $\text{(TOMA}{}^{\mathrm{+}}$, 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.     

20.

Anionic polymerization with alkaline earth counterions—II Propagation kinetics of living poly-4-vinylpyridine     

L.C. Tang  B. Francois 《European Polymer Journal》1983,19(8):715-719

4-Vinylpyridine was polymerized by cumyl barium in THF at 0°C. Detailed conductance studies at various concentrations of the living oligomer solution gave similar experimental results as for 2-vinylpyridine, i.e. triple ions exist in thermodynamic equilibrium with free ions and ion pairs. The dissociation constant of ion pairs increases from 1.96 × 10^?10 M at 15°C to 4.35 × 10^?10 M at ?70°C with enthapy and entropy of dissociation of ?3.9 kJ/mol and ?200 J mol^?1 K^?1 respectively. The extent of dissociation of ion pairs of living oligo-4-vinylpyridine is comparable to that of living polystyrene ($\text{K}{}_1\text{? 10}{}^{\mathrm{?10}}$) but higher than that of living poly-2-vinylpyridine ($\text{K}{}_1\text{? 10}{}^{\mathrm{?11}}$). This result is interpreted in terms of intramolecular complexation which is no longer favourable when the nitrogen atom is situated at the 4-position of the pyridine nucleus. Studies of propagation kinetics revealed that 4-vinylpyridine polymerizes by the same reaction mechanism as the 2-isomer, the active sites being essentially ion pairs. At 0°C, its propagation constant was found to be 211.1 M^?1 sec^?1 compared with 151.04 M^?1 sec^?1 for living poly-2-vinylpyridine. As for free radical polymerization, the polymers contain only about 26% isotactic triads.     

	$\text{S}{}^0\text{/}\text{cal}{}_{\mathrm{th}}\text{K}{}^{\mathrm{?1}}\text{mol}{}^{\mathrm{?1}}$	$\text{ΔH}{}_{\mathrm{f}}{}^0\text{/kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?1}}$	$\text{ΔG}{}_{\mathrm{f}}{}^0\text{/kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?1}}$
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)

Thermophysical properties of the intermetallic Mn3MN perovskites III. Heat capacity of the solid solution Mn3.2Ga0.8N

The heat capacity of the solid solution Mn_3.2Ga_0.8N was measured between 5 to 330 K by adiabatic calorimetry. A sharp anomaly with first-order character was detected at T_A = (160.5±0.5) K, corresponding to a magnetic rearrangement and a lattice expansion. No sharp anomaly was observed at T_c ≈ 260 K where the magnetic ordering takes place; instead, a smooth shoulder was detected. The thermodynamic functions at 298.15 K are $\text{C}{}_{\mathrm{<mtext>p,</mtext><mtext>m</mtext>}}\text{R}\text{= 15.16}$, $\text{S}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{R}\text{= 18.57}$, $\text{{H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(T)?H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(0)}}\text{R}\text{= 2896}\text{K}$, $\text{?{G}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(T)?H}{}_{\mathrm{m}}{}^{\mathrm{o}}\text{(0)}}\text{RT}\text{= 8.85}$. At low temperatures the coefficient for the linear electronic contribution to the heat capacity was derived: γ = (0.031±0.003) J·K^?2·mol^?1. Moreover, the different contributions to the heat capacity were obtained and the electronic origin of the phase transitions was established.     

Crystal structure,Mössbauer,and magnetic behavior of mixed valence compounds in the BaFeS system: Ba3(Ba1−xAlx)Fe2S6[S1−y(S2)y]

The compounds $\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_6\text{[S}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(}\text{S}{}_2\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{]}$ and Ba_3.6Al_0.4Fe₂S₆[S_0.6(S₂)_0.4], designated I and II, were prepared by reacting BaS, Fe, and S powders and Al foils in graphite containers sealed in evacuated quartz ampoules at approximately 1100°C. The crystal structure of I was determined using 1682 independent, nonzero X-ray reflections, while 3589 were used for II. They are triclinic, $\text{A}\text{l}$:

$\text{a=9.002(2)}\text{A}\text{?}\text{,b=6.7086(8)}\text{A}\text{?}\text{,c=24.658(4)}\text{A}\text{?}\text{α91.49(2)°,}$

$\text{β=105.10(2)°y=90.74(2)°,ψ}{}_{\mathrm{calc}}\text{=4.15g/cm}{}^3\text{,for I:}$

$\text{a=8.993(6)}\text{A}\text{?}\text{,b=6.708(7)}\text{A}\text{?}\text{,c=24.70(1)}\text{A}\text{?}\text{α91.11(6)°,}$

$\text{β=105.04(6)°y=90.90(9)°,ψ}{}_{\mathrm{calc}}\text{=3.90g/cm}{}^3\text{,for II:}$

BaS₆ trigonal prisms share edges to form distorted hexagonal rings which form one-dimensional chains leaving two free lateral edges. The chains link in a stairstep manner with the rings offset along the [301] direction. These stairsteps join in a complicated manner to form a three-dimensional network. Fe ions are in two sites forming isolated FeS₄ tetrahedra and isolated Fe₂S₆ dimers by edge-sharing tetrahedra. The Al substitution occurs in the trigonal prisms which have free edges with Al replacing Ba. Room-temperature Mössbauer isomer shifts are 0.20 mm/sec. for I and 0.30 mm/sec for II. These data indicate that upon Al substitution charge compensation occurs by reducing Fe³⁺. Valence calculations indicate that Fe in edge-sharing tetrahedra are reduced while the Fe in the isolated tetrahedron remains unchanged. The effective charge distribution in the Al substituted compound is approximately Fe³⁺, Fe^2.5+ with electron delocalization across the shared edge. Room temperature electrical resistivity is 10⁵ ohm/cm. The compositions of the crystals are best represented by the formulas $\text{[}\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_7\text{]}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{·[}\text{Ba}{}_4\text{Fe}{}_2\text{S}{}_6\text{(S}{}_2\text{)]}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ and [Ba₃AlFe₂S₇]_0.4·[Ba₄Fe₂S₇]_0.2·[Ba₄Fe₂S₆(S₂)]_0.4. The replacement of a sulfide by a disulfide ion is thought to be strongly dependent on the sulfur activity during the preparation.     

Standard enthalpies of formation of uranium compounds I. β-UO3 and γ-UO3

The standard enthalpy of formation of γ-UO₃ has been critically assessed; the value ?(292.5 ± 0.2) kcal_th mol^?1 is suggested.The enthalpies of solution of β-UO₃ and γ-UO₃ in 3 M H₂SO₄ have been measured and used to derive:

$\text{ΔH}{}_{\mathrm{f}}{}^{\mathrm{°}}\text{(β?}\text{UO}{}_3\text{, 298.15}\text{K}\text{) = ?(291.6 ± 0.2)}\text{kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?}}$

     

Electronic conductivity in nonstoichiometric cerium dioxide

The electrical conductivity of sintered specimens of nonstoichiometric CeO_2?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 CeO_2?x was determined by combining recently obtained thermodynamic data, x = x(P_O2, T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expression

$\text{σ=410[x]e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{ohm cm}\text{)}{}^{\mathrm{?1}}$

over 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 concentration

$\text{n}{}_{\mathrm{ce}}\text{′}{}_{\mathrm{ce}}\text{=}\text{8x}\text{a}{}_0{}^3$

where n_Ce′Ce is the number of Ce′_Ce per cm³ and a₀ is the lattice parameter and (b) the electron mobility

$\text{μ=5.2(10}{}^{\mathrm{?2}}\text{)e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{cm}{}^2\text{/}\text{V sec}\text{)}$

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EPR and magnetization of GdGa2

Paramagnetic resonance and magnetic measurements were performed on powdered samples of GdGa₂. The magnetic data indicated ferrimagnetic behavior with $\text{T}{}_{\mathrm{c}}\text{? 181°}\text{K}$. Above 250° K the susceptibility obeys the Curie-Weiss law $\text{χ}{}_{\mathrm{g}}\text{=}\text{2.66}{}_2\text{× 10}{}^{\mathrm{?2}}\text{(T ? 27.6)}\text{emu/g-Oe}$ 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, $\text{χ}{}_{\mathrm{g}}{}^{\mathrm{?1}}\text{= 35.95 (T ? 12.5) ?}\text{2.20 × 10}{}^4\text{(T ? 177)}$, 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.     

NMR study of hydrogen molybdenum bronzes: H1.71MoO3 and H0.36MoO3

Proton NMR relaxation times (T₂T₁, and T_1?) and absorption spectra are reported for the compounds H_1.71MoO₃ (red monoclinic) and H_0.36MoO₃ (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 H_1.71MoO₃ and as pairs of OH groups in H_0.36MoO₃. The room temperature lineshape for H_1.71MoO₃ 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 E_A = 22 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 10}{}^{\mathrm{?13}}\text{sec}$ for H_1.71MoO₃ and E_A = 11 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 3 × 10}{}^{\mathrm{?8}}\text{sec}$ for H_0.36MoO₃.     

Extraction of indium(III) from chloride medium with 1-phenyl-3-methyl-4-acylpyrazol-5-ones. Synergic effect with high molecular weight ammonium salts.

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 $\text{HL}$ ? $\text{InL}{}_3$ + 3 H⁺ (log K = 1.48, 1.03, 0.87 with acyl = benzoyl, lauroyl, 2-thenoyl), InCl ²⁺ + 2 $\text{HL}$ ? $\text{InClL}{}_2$ + 2 H⁺ (log K = 0.26, ?0.45, ?0.35 respectively) and In³⁺ + m Cl^? ? InCl_m^(3-m)+ (log β_m 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 : $\text{InCl}{}_2$ + $\text{(TOMA}{}^{\mathrm{+}}$,Cl^?) ? $\text{(TOMA}{}^{\mathrm{+}}$, 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.     

Anionic polymerization with alkaline earth counterions—II Propagation kinetics of living poly-4-vinylpyridine

4-Vinylpyridine was polymerized by cumyl barium in THF at 0°C. Detailed conductance studies at various concentrations of the living oligomer solution gave similar experimental results as for 2-vinylpyridine, i.e. triple ions exist in thermodynamic equilibrium with free ions and ion pairs. The dissociation constant of ion pairs increases from 1.96 × 10^?10 M at 15°C to 4.35 × 10^?10 M at ?70°C with enthapy and entropy of dissociation of ?3.9 kJ/mol and ?200 J mol^?1 K^?1 respectively. The extent of dissociation of ion pairs of living oligo-4-vinylpyridine is comparable to that of living polystyrene ($\text{K}{}_1\text{? 10}{}^{\mathrm{?10}}$) but higher than that of living poly-2-vinylpyridine ($\text{K}{}_1\text{? 10}{}^{\mathrm{?11}}$). This result is interpreted in terms of intramolecular complexation which is no longer favourable when the nitrogen atom is situated at the 4-position of the pyridine nucleus. Studies of propagation kinetics revealed that 4-vinylpyridine polymerizes by the same reaction mechanism as the 2-isomer, the active sites being essentially ion pairs. At 0°C, its propagation constant was found to be 211.1 M^?1 sec^?1 compared with 151.04 M^?1 sec^?1 for living poly-2-vinylpyridine. As for free radical polymerization, the polymers contain only about 26% isotactic triads.