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.     

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.     

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.     

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.     

Mutual solubility of n-butanol + water under high pressures

The mutual solubilities of {xCH₃CH₂CH₂CH₂OH+(1-x)H₂O} have been determined over the temperature range 302.95 to 397.75 K at pressures up to 2450 atm. An increase in temperature and pressure results in a contraction of the immiscibility region. The results obtained for the critical solution properties are: T_o(U.C.S.T.) = 397.85 K and x_o = 0.110 at 1 atm; $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(12.0±0.5)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at p < 400 atm and $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(7.0±0.7)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at 800 atm < p < 2500 atm; $\text{(}\text{dx}{}_{\mathrm{o}}\text{d}\text{T}\text{) = ?(4.0±0.5)×10}{}^{\mathrm{?4}}\text{K}{}^{\mathrm{?1}}$.     

Tracer diffusion coefficient of oxide ions in LaCoO3 single crystal

The tracer diffusion coefficient, $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$, of oxide ions in LaCoO₃ single crystal was determined over the temperature range of 700–1000°C by a gas-solid isotopic exchange technique using ¹⁸O tracer. For the determination, two methods, the gas phase analysis and the depth profile measurement, were employed. Under an oxygen pressure of 34 Torr, the temperature dependence of $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ in LaCoO₃ was expressed by

$\text{D1}{}_{\mathrm{<mtext>O</mtext>}}\text{(}\text{cm}{}^2\text{·}\text{sec}{}^{\mathrm{?1}}\text{) = 3.63 × 10}{}^4\text{exp}\text{?}\text{(74 ± 5)}\text{kcal}\text{·}\text{mole}{}^{\mathrm{?1}}\text{RT}$

$\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ at 950°C was found to be proportional to P^?0.35_O2. The diffusion of oxide ions occurs through a vacancy mechanism. The activation energy for the migration of oxide ion vacancies was estimated as 18 kcal · mole^?1.     

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

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

.     

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.     

Unusual effects of anisotropic bonding in Cu(II) and Ni(II) oxides with K2NiF4 structure

Geometric constraints present in A₂BO₄ compounds with the tetragonal-T structure of K₂NiF₄ impose a strong pressure on the BO_IIB bonds and a stretching of the AO_IA bonds in the basal planes if the tolerance factor is $\text{t ?}\text{R}{}_{\mathrm{<mtext>AO</mtext>}}\text{√2 R}{}_{\mathrm{<mtext>BO</mtext>}}\text{< 1}$, where R_AO and R_BO are the sums of the AO and BO 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 BO_IIB bonds produces itinerant bands and a relative stabilization of localized d_z² orbitals. Magnetic susceptibility and transport data reveal an intersection of the Fermi energy with the d²_z² 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 d²_z² level becomes filled. In La₂NiO₄, the localized moments for half-filled d_z² orbitals induce strong correlations among the electrons above $\text{T}{}_{\mathrm{<mtext>d</mtext>}}\text{? 200}\text{K}$; at lower temperatures the electrons appear to contribute nothing to the magnetic susceptibility, which obeys a Curie-Weiss law giving a μ_eff corresponding to $\text{S =}\text{1}\text{2}$, but shows no magnetic order to lowest temperatures. These surprising results are verified by comparison with the mixed systems La₂Ni_1?xCu_xO₄ and La_2?2xSr_2xNi_1?xTi_xO₄. 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 $\text{E}{}_{\mathrm{<mtext>a</mtext>}}\text{? kT}{}_{\mathrm{<mtext>min</mtext>}}$, where $\text{? = ?}{}_0\text{exp}\text{(}\text{?E}{}_{\mathrm{<mtext>a</mtext>}}\text{kT}\text{)}$ and T_min is the temperature of minimum resistivity ?. This relation is interpreted in terms of a diffusive charge-carrier mobility with $\text{E}{}_{\mathrm{<mtext>a</mtext>}}\text{? ΔH}{}_{\mathrm{<mtext>m</mtext>}}\text{? kT}$ at T = T_min.     

Effect of benzophenone on the H2O2-induced photopolymerization of methyl methacrylate

Benzophenone (BP) in low concentrations (<0.001 mol 1^?1) produces a rate enhancing effect in the H₂O₂-induced bulk photopolymerization of MMA. R_p is proportional to [H₂O₂]^0.4 and [BP]^0.4, and $\text{k}{}_{\mathrm{p}}{}^2\text{k}{}_1$ at 30° is 1.00 × 10^?2 1.mol^?1 sec^?1. In diluted systems, different solvents produce different kinetic effects, reaction order with respect to monomer being negative for IPA and THF as solvent, positive but <1.0 for benzene and chloroform, 1.2 for acetonitrile, CCl₄ and t-butanol and 1.8 for DMA. The variable solvent effect is attributed to modification of the initiation process by the various solvents to different extents. Kinetic analysis of data for bulk photopolymerization gives evidence for primary radical termination and degradative initiator transfer.     

Valence state of the Fe ions in Sr1−yLayFeO3

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 Ca_1?xSr_xFeO₃ 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, Ca_1?xSr_xFe^(3+Δ)+_0.5Fe^(5?Δ)+_0.5O₃ and $\text{Sr}{}_{\mathrm{1?y}}\text{La}{}_{\mathrm{y}}\text{Fe}{}^{\mathrm{(3+\delta )+}}{}_{\mathrm{<mtext>(1+y)</mtext><mtext>2</mtext>}}\text{Fe}{}^{\mathrm{(5?\delta )+}}{}_{\mathrm{<mtext>(1?y)</mtext><mtext>2</mtext>}}\text{O}{}_3$.     

Nd3+, Eu3+, and Gd3+ ions as local probes in the NaxSr3−2xLnx(PO4)2 and KCaLn(PO4)2 rare earth phosphates

Use of Nd³⁺, Eu³⁺, and Gd³⁺ as local structural probes allows the determination of the rare earth positions in the Na_xSr_3?2xLn_x(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 ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and ${}^6\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ levels of the Gd³⁺ ions.     

Kinetics and mechanism of the interaction of hexaaquochromium(III) with octacyanomolybdate(IV) ions

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: k_obs=$\text{[}{}_{\mathrm{kK}}{}_{\mathrm{<mtext>E</mtext>}}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{k′K′k}{}_{\mathrm{E}}\text{k}{}_{\mathrm{h}}\text{][Mo(CN)}{}_8{}^{\mathrm{4?}}\text{]}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{k}{}_{\mathrm{<mtext>h</mtext>}}\text{+[}\text{K}{}_{\mathrm{<mtext>E</mtext>}}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{K′}{}_{\mathrm{E}}\text{k}{}_{\mathrm{h}}\text{][Mo(CN)}{}_8{}^{\mathrm{4?}}\text{]}$     

Peroxo salts as initiators of vinyl polymerization—2. Kinetics of polymerization of acrylic acid and sodium-acrylate by peroxodisulphate in aqueous solution—effect of pH and Ag+ catalysis

Results on the rate of polymerization of acrylic acid by S₂O^2?₈ ion in alkaline and acid conditions are presented. R_p depended upon $\text{[S}{}_2\text{O}{}^{\mathrm{2?}}{}_8\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{[monomer]}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ both in acid and alkaline solutions. The influence of ionic strength, the effect of pH on R_p and the catalytic effect of Ag⁺ and Cu²⁺ on the system have been discussed. Suitable mechanisms are proposed.     

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.     

Solid solubility of Ge,Si, and Mg in Fe2O3 and photoelectric behavior

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, Fe_1.95Ge_0.05O₃. 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 Fe_2?xGe_xO₃ 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 $\text{Fe}{}_2\text{O}{}_3\text{(Ge)}\text{0.7 M}\text{Fe(CN)}{}^{\mathrm{4?}}{}_6\text{,}\text{0.05 M}\text{Fe(CN)}{}^{\mathrm{3?}}{}_6\text{Pt}$ 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.     

Application de la RPE à la localisation des substitutions isomorphiques dans les micas: Localisation du Fe3+ dans les muscovites et les phlogopites

Electron spin resonance spectra attributed to four Fe³⁺ centers designated O_a, O_b, T_a, T_b have been observed in crystals of muscovite and phlogopite. The results are discussed using the spin Hamiltonian

with g_e ～ 2.002. The angular variation of the resonance lines is used to determine the ESR axes of the four different sites. Two species are octahedrally coordinated (O_a and O_b) and are assigned to two different surroundings of Fe³⁺ in the octahedral sheet. The remaining two species (T_a and T_b) may be assigned to the tetrahedral FeO₄. The T_a sites have a symmetry axis lying along one of the FeO bonds. The symmetry axis is created by an excess of negative charge on the oxygen bound to the neighboring tetrahedral substitution. Rhombic symmetry of the T_b sites is due to the presence of fluorine anions substituting some hydroxyl ions. One of the ESR axes is directed toward the fluorine ion.     

Etude comparative des structures type K4NiF4 et pérovskite par la méthode des invariants

The study of K₂NiF₄ and perovskite structure type by the “method of invariants” leads to the relationship: $\text{(A-X)}{}_9\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? (A-X)}{}_{12}\text{=}\text{constant}$, 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:

$\text{(K}{}^{\mathrm{+}}\text{?F)}{}_{\mathrm{R}}\text{= 2.832 R}{}^{\mathrm{<mtext>1</mtext><mtext>11.4</mtext>}}$

where R is the coordination number.     

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).