Une modelisation du comportement magnetique d'un compose de l'iridium pentavalent: LaLi12Ir12O3

A new interpretation is proposed for the magnetic properties of perovskite-type iridium (+V) oxide $\text{LaLi}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Ir}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{O}{}_3$. In its unusual +5 oxidation state iridium has a t⁴_2ge⁰_g configuration. The magnetic susceptibility has been calculated assuming cubic symmetry of the crystal field and a Coulomb repulsion of the same order of magnitude than spin-orbit coupling. Fitting of the experimental data leads to a single spin-orbit constant $\text{ζ ? 3470}\text{cm}{}^{\mathrm{?1}}$ close to that of previously investigated Ir(+V) compounds.     

Control of the growth-induced magnetic anisotropy in ferrimagnetic garnet films grown by liquid-phase epitaxy

The influence of melt composition and growth temperature T_g on the growth-induced magnetic anisotropy constant K^g_u in Bi substituted LPE ferrimagnetic garnet films has been investigated. In films grown from Bi₂O₃ based and from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts the value of K^g_u increased upon decreasing T_g, associated with an increasing incorporation of B1. However, at given Bi content the films grown from Bi₂O₃ based fluxes generally exhibited smaller values of K^g_u than those from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts. The addition of small amounts of Ca²⁺ to the Bi₂O₃ based melts resulted in (Y,Bi)-garnet films changing from n- to p-type electrical conductivity at a minimum value of K^g_u. Additions of Si⁴⁺ to a $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melt reduced the uniaxial magnetic anisotropy of La-YIG-Ga films accompanied by a change from p- to n-type conductivity. Similarly, (Gd,Bi)-garnet films from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts changed from n- to p-type conductivity upon decreasing T_g where K^g_u changes sign from negative to positive. From the temperature dependence of the electrical conductivity the electron and hole concentrations in some of these films were estimated suggesting that the sign change of K^g_u in the investigated (Gd,Bi)-garnet films and the minimum of K^g_u in the investigated (Y,Bi)-garnet films and (La,Y)-garnet films occur at donor-acceptor compensation. This experimental evidence led us to conclude that the growth induced magnetic anisotropy may be correlated with the presence of donor and acceptor centers in the garnet structure.     

Sur la phase CsVCl3: Etude cristallographique et magnetique

The crystal structure of CsVCl₃ has been determined by means of a Patterson synthesis and refined by full-matrix least-squares to a residual R = 0.06. The space group is $\text{P}\text{6}{}_3\text{mmc}$ with $\text{a}\text{= 7.228 (3)}\text{A}\text{?}$ and $\text{c}\text{= 6.030 (3)}\text{A}\text{?}$. The structure of CsVCl₃ belongs to the CsNiCl₃ type. The magnetic properties have been interpreted on the basis of a $\text{S}\text{=}\text{3}\text{2}$ model for Heisenberg one-dimensional interactions. The strong antifer-romagnetic intrachain V-V interactions ($\text{J}\text{k}\text{= ?115}\text{K}$) seem to result from direct t_2g - t_2g coupling and from 90° correlation superexchange coupling using the 3s chlorine orbital.     

Copper doped zinc oxide Y2BaZnO5: ERS and optical investigation

In copper doped Y₂BaZnO₅ oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g₁ = 2.049₅, g₂ = 2.051₅, g₃ = 2.275, $\text{¦}\text{A}{}_1\text{¦ = 13 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$, $\text{¦}\text{A}{}_2\text{¦ = 10 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$ and $\text{¦}\text{A}{}_3\text{¦ = 147.5 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$. Since $\text{g}{}_1\text{?}\text{g}{}_2$ an approximate C_4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm^?1 which can be assigned to the transitions A₁ → B₁, B₂ → B₁ and E → B₁ respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.     

Studies on crack growth rate under high temperature creep,fatigue and creep-fatigue interaction—II: On the role of fracture mechanics parameter aeffσg

For high temperature creep, fatigue and creep-fatigue interaction, several authors have recently attempted to express crack growth rate in terms of stress intensity factor $\text{K}{}_{\mathrm{I}}\text{= α}\text{aσ}{}_{\mathrm{g}}$, where a is the equivalent crack length as the sum of the initial notch length a₀ and the actual crack length $\text{a}{}^1$, that is, $\text{a = a}{}_0\text{+ a}{}^1$. On the other hand, it has been shown by Yokobori and Konosu that under the large scale yielding condition, the local stress distribution near the notch tip is given by the fracture mechanics parameter of $\text{aσ}{}_{\mathrm{g}}\text{?(σ}{}_{\mathrm{g}}$), where a is the cycloidal notch length, σ_g is the gross section stress and $\text{?(σ}{}_{\mathrm{g}}$) is a function of σ_g. Furthermore, when the crack growth from the initial notch is concerned, it is more reasonable to use the effective crack length a_eff taking into account of the effect of the initial notch instead of the equivalent crack length a. Thus we believe mathematical formula for the crack growth rate under high temperature creep, fatigue and creep-fatigue interaction conditions may be expressed at least in principle as function of $\text{a}{}_{\mathrm{eff}}\text{σ}{}_{\mathrm{g}}\text{, σ}{}_{\mathrm{g}}$ and temperature.In the present paper, the geometrical change of notch shape from the instant of load application was continuously observed during the tests without interruption under high temperature creep, fatigue and creep-fatigue interaction conditions. Also, the effective crack length a_eff was calculated by the finite element method for the accurate estimation of local stress distribution near the tip of the crack initiated from the initial notch root. Furthermore, experimental data on crack growth rates previously obtained are analysed in terms of the parameter of $\text{a}{}_{\mathrm{eff}}\text{σ}{}_{\mathrm{g}}$ with gross section stresses and temperatures as parameters, respectively.     

Oxidation of thin Cd,Cu and Te films under continuous laser irradiation

Thin films of Cd, Cu and Te are irradiated in air by means of a continuous, unfocused laser beam. The diameter of the oxidized zone varies empirically with time like: $\text{d = d}{}_0\text{exp}\text{[}\text{?(t ? t}{}_1\text{)}\text{t}{}_2\text{]}$, where t₁ and t₂depend on the power of the laser beam. Temperature calculations indicate that melting of the elemental constituents is probably involved in the transformation.     

ESR evidence for the existence of rutile-type,nonstoichiometric vanadium antimonate

A nonstoichiometric vanadium antimonate has been synthesized from a high temperature solid state reaction of V₂O₅ and Sb₂O₃. Powder-X-ray diffraction data of this phase could be indexed on a tetragonal basis with $\text{a}\text{= 4.60}\text{A}\text{?}$, $\text{c}\text{= 3.02}\text{A}\text{?}$. The phase exhibits a well resolved hyperfine ESR spectrum at 298 K due to V(4+)(3d′) ions interacting with ${}^{51}\text{V}\text{(}\text{I}\text{=}\text{7}\text{2}\text{)}$, thus establishing its identity as a rutile type phase postulated earlier. The ESR parameters are $\text{g}{}_{\mathrm{}}\text{= 1.933±0.002}$, g_⊥ = 1.984±0.002, $\text{A}{}_{\mathrm{}}\text{= 193±3}\text{G}$, A_⊥ = 75±3G. Present results are discussed in relation to ESR of V(4+) in other rutile-type hosts.     

Theorems of zaremba type for thermoelastic solid

It was shown in [2] that any solution of the equation of coupled dynamic thermoelasticity (a) $\text{[(?}{}^2\text{??}{}_{\mathrm{t}}{}^2\text{)(?}{}^2\text{??}{}_{\mathrm{t}}\text{)?∈?}{}_{\mathrm{t}}\text{?}{}^2\text{]phi = 0, (?}{}_{\mathrm{t}}\text{= ?/?t)}$, subject to homogeneous initial conditions admits the representation $\text{phi = phi}{}_1\text{+ phi}{}_2$, where (b) $\text{(?}{}^2\text{??}{}_{\mathrm{t}}{}^2\text{?∈?}{}_{\mathrm{t}}\text{?∈?∈K 1)phi}{}_1\text{= 0}$, and (c) $\text{?}{}^2\text{??}{}_{\mathrm{t}}\text{+∈+teK (s)phi}{}_2\text{= 0}$. Here $\text{K = K(t, epsi)}$ is a given function and ¹ denotes the operation of convolution with respect to time $\text{t}$. In the present paper three uniqueness theorems associated with (a), (b) and (c) are given, and a domain of influence theorem for (b) is established. Next, these theorems are used to show that there exist such couplings between the external mechanical and thermal fields applied to the boundary of a thermoelastic solid that inside the body the temperature is either of a wave type or of a diffusive type, but not of both types.     

Cumulative damage in creep

The effect of two step stress variation and intermittent loading on the creep behaviour of commercially pure aluminium and stainless steel has been investigated. In the two step stress variation, the first stress σ₁ was applied for a given time t₁ and the stress level was switched over to σ₂. The resultant creep rate ?_s2⁺ and the failure time t₂ have been observed. Under the intermittent loading programme, the stress cycle was applied in the order σ₁-zero-σ₁ and the average creep rate on each reloading has been observed. The experimental data appear to give a cumulative damage rule in the form

$\text{t}{}_1\text{t}{}_{\mathrm{r1}}\text{+}\text{t}{}_2\text{t}{}_{\mathrm{r2}}\text{e}\text{?}{}_{\mathrm{s2}}{}^{\mathrm{+}}\text{e}\text{?}{}_{\mathrm{s2}}\text{=1}$

where t_r is the creep rupture time corresponding to a given stress and ?_s2 is the creep rate under the second stress in normal creep.     

The discharge of a I12TaSe4 cathode for lithium battery

The discharge process was investigated on a lithium battery using $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$ as cathode. The battery works as primary battery. The potential gradually decreased from 2.1V to 1.8V upto a discharging of $\text{Li}\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4\text{≈0.5}$. Then it was almost constant at 1.8V until the discharging of about 2.0. Iodine is partially removed out of $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$, keeping the host TaSe₄ chain structure as it was in the first step of discharge. The new product has tetragonal crystal lattice having lattice parameters of $\text{a}\text{=9.532}\text{A}\text{?}$ and $\text{c}\text{=25.31}\text{A}\text{?}$, which is twice of c-parameter of $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$.     

A new parameter for prediction of creep crack growth rate at high temperature

By analysis based on a series of experimental data obtained by continuous observations using high temperature microscope during the creep test without interruption in vacuum of 10^?5 mm Hg for the purpose of the crack length measurements, a new mathematical equation for prediction of high temperature creep crack growth rate has been proposed in terms of disposable parameters, that is $\text{α}\text{a}{}_{\mathrm{<mtext>eff</mtext>}}\text{σ}{}_{\mathrm{g}}\text{,σ}{}_{\mathrm{g}}$ and temperature for 304 stainless steel within the range of $\text{α}{}_{\mathrm{g}}$ and temperature concerned. It can be seen that it is the best one to fit the experimental data among any other formula proposed hitherto.The new parameter proposed herein

$\text{8.48 × 10}{}^3\text{t}\text{log}{}_{10}\text{α}\text{α}{}_{\mathrm{<mtext>eff</mtext>}}\text{α}{}_{\mathrm{<mtext>g</mtext>}}\text{4.66 × 10}{}^2\text{+ 5.46}\text{log}{}_{10}\text{α}{}_{\mathrm{<mtext>g</mtext>}}$

where

$\text{α = 1.98 +0.36}\text{a}\text{w}\text{? 2.12}\text{a}\text{w}{}^2\text{+ 3.42}\text{a}\text{w}{}^3\text{, a≦0.7w}$

may be used for characterizing the creep crack growth rate just similar as Larson-Miller parameter for the creep life.     

Stability of the perovskite phase LaBO3 (B = V,Cr, Mn,Fe, Co,Ni) in reducing atmosphere I. Experimental results

The chemical stability of perovskites LaBO₃ where B = V, Cr, Mn, Fe, Co, Ni was studied by thermogravimetry at 1000°C in gas mixtures of $\text{CO}{}_2\text{H}{}_2$, $\text{O}{}_2\text{CO}{}_2$ and $\text{O}{}_2\text{Ar}$ at 1 bar.The stability limits of the perovskite phases expressed in terms of -log Po₂★ (Po₂★ = critical oxygen partial pressure in bar) were for LaCrO₃ and LaVO₃ (greater than 21.1), LaFeO₃ (16.95), LaMnO₃ (15.05), LaCoO₃ (7.0) and for LaNiO₃ (～0.6). The changes in standard enthalpy ΔH° and entropy ΔS° of the following reactions were obtained.$\text{LaVO}{}_4\text{=}\text{LaVO}{}_3\text{+}\text{1}\text{20}{}_2\text{δ=328}\text{kJ}\text{mol}\text{°=135}\text{J}\text{mol·deg.}$,$\text{LaMnO}{}_3\text{=}\text{1}\text{2}\text{La}{}_2\text{O}{}_3\text{+}\text{MnO}$     

Effect of loading history on stress corrosion cracking in high strength steel

The effect of preloading on crack nucleation time was examined with compact tension specimens having various notch radius in 0.1N-H²SO⁴ aqueous solution for 200°C tempered AISI 4340 steel. Crack nucleation time t_n increases by preloading for a given apparent stress intensity factor K_p2. The curve K_?2 vs. t_n deviates upward from the curve for the non preloading case. A linear relationship between the crack nucleation time and parameter is seen in semi-log diagram, where is taken as the value at t_n=α due to preloading. The apparent threshold stress intensity factor increases with K_?2 which is the apparent stress intensity factor of preloading. A detached crack is nucleated at some distance from the notch root and extends in a form of circle. This distance increases with increasing K_?2. The effect of load reduction during crack growth was examined. When the K-value was reduced from K₁ to K₂, an incubation time was observed before the crack started growing under the K₂-value. The incubation time t_m tends to increase with increasing ΔK = K₁-K₂. The threshold stress intensity factor was also found to increase for high load reduction.In order to explain these experimental results, a new dislocation model is proposed on the basis of stress induced diffusion of hydrogen in high stress region ahead of the notch root or a crack. This model suggests that the change in the crack nucleation time and the increase of the incubation time due to preloading or load reduction are caused by reducing the hydrostatic pressure and by spreading the hydrogen saturated region which requires more time for the hydrogen accumulation due to preloading or load reduction. The theory predicts the experimentally observed relations between and t_n and between log t_in and ΔK.     

Verres fluores a base de metaux lourds. Etude de la corrosion par la vapeur d'eau atmospherique

Chemical durability of $\text{ThF}{}_4\text{BaF}{}_2$ glasses has been investigated in atmospheric moisture conditions. Corrosion of the melt by the vapor contaminates all the vitreous bulk. The corrosion of OH free glass until T_g is only a surface phenomenon depending on a diffusion process.     

Perovskite-like compounds with bismuth layer structure: Some new materials and phase transitions

Simultaneous heterovalent substitutions in both the cationic sites of the already known bismuth layer type compound Bi₃TiNbO_g have been undertaken. Further, new compounds with an orthorhombic unit cell have been found: $\text{Bi}{}_2\text{Pb}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Bi}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{TiNb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{W}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{O}{}_{\mathrm{g}}\text{, Bi}{}_2\text{Pb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Bi}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TiNb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{W}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{O}{}_{\mathrm{g}}$ and $\text{Bi}{}_2\text{Pb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{Bi}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{TiNb}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{W}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_{\mathrm{g}}$. Their crystallographic characteristics have been determined. Phase transitions have been studied with the aid of dielectric measurements. The relations between crystallographic properties and peculiarities of phase transitions have been discussed.     

Crystal growth and characterization of In23PS3

Crystals of $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PS}{}_3$ were grown by chemical vapor transport of the elements from a charge zone maintained at 630°C. and a growth zone at 560°C. The crystals were characterized by chemical, x-ray, and densitometric techniques. $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PS}{}_3$ is structurally related to the M^IIPS₃ thiophosphides. The compound is an insulator and has an optical absorption edge of 3.1(1) e.V.     

Nucleation mechanism of stress corrosion cracking from notches

Crack nucleation mechanism of hydrogen assisted cracking at notched cracks in aqueous solutions is investigated, using the compact type specimens with various notch radius in low-tempered 4340 steel. A detached crack initiates at some distance ahead of the notch root. The crack nucleation at the notched root is determined by the electrical potential method. When the crack initiates, the voltage difference starts to increase. The crack nucleation site is examined by SEM. The time for crack nucleation increases with the notch root radius, ρ, and decreases with the apparent stress intensity factor K_ρ. A linear relationship between the crack nucleation time, t_n, and the parameter ${}^2\text{K}{}_{\mathrm{\rho }}\text{/(πρ)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-(2K}{}_{\mathrm{\rho }}\text{/(πρ)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{th}}\text{}}$ is seen in semi-log diagram, where $\text{(2K}{}_{\mathrm{\rho }}\text{/(πρ)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{th}}$ is almost equal to the yield shear strength.In order to explain these experimental results, a new model of micromechanics is proposed on the basis of stress induced diffusion of hydrogen in the high stress region ahead of the notch root. This model suggests that the detached crack initiates at the elasto-plastic boundary where the hydrogen concentration is from 2 to 5 times higher than that of the notch root surface. The theory agrees with experiments with respect to $\text{{2K}{}_{\mathrm{\rho }}\text{/(πρ)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-(2K}{}_{\mathrm{\rho }}\text{/(πρ)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{th}}\text{}}$ vs t_n and t_n vs ρ.The empirical equation holds under constant t_n, K_ρ = K_o(ρ/ρ_eff)^m where K₀ is the stress intensity factor with ρ ≈ 0 under the present environment, ρeff is the effective notch radius and m is constant. The value of m is 0.25 for the crack nucleation time (t_n)_th corresponding to the threshold stress intensity factor (K_ρ)_th, 0.5 for t_n < (t_n)_th and 0 for ρ ≦ ρ_eff. The above equation agrees with the theoretical equation proposed by Tanaka and Mura for any t_n and ρ_eff.     

Growth of Ca3Fe2Ge3O12 and Ca3Fe(Al,Cr) Ge3O12 garnets in molten bismuth germanate glasses

Additions of Fe₂O₃ to CaO·Bi₂O₃·2 GeO₂ cause Ca₃Fe₂Ge₃O₁₂ garnets to precipitate from the resultant melt at 1250°C. Garnets with the composition Ca₃Fe(Al, Cr) Ge₃O₁₂ are also precipitated by adding either $\text{Al}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ or $\text{Cr}{}_2\text{O}{}_3\text{Fe}{}_2\text{O}{}_3$ mixtures. The well-formed crystals range from several to 100 μm in size and are obtained in 50 to 70% yields at $\text{Fe}\text{Bi}\text{= 0.4}$. Additions of Fe₂O₃ (up to $\text{Fe}\text{Bi}\text{= 1.0}$) to compositions containing ZnO, CdO, SrO, and BaO yield only dark glasses. The physical properties of these glasses suggest that Fe(III), in contrast to AL(III) & Ga(III), prefers octahedral coordination.     

Interactions of Cr2+ with the F− ligands in CdF2:Cr2+

Superhyperfine structure s.h.f.s. resulting from the Cr²⁺ - F^? interaction was studied in Cr²⁺ doped CdF₂ crystals. The s.h.f.s. observed can be described with by the following spin-Hamiltonian

$\text{H}\text{=}\text{g}{}_{\mathrm{eff}}\text{β}\text{HS}{}_{\mathrm{z}}\text{+ST}{}_{\mathrm{i}}\text{I+ST}{}_{\mathrm{j}}\text{I}$

The constants calculated are $\text{T}{}_{\mathrm{i\perp }}\text{≈}\text{T}{}_{\mathrm{i}}\text{= 50}\text{MHz}$$\text{T}{}_{\mathrm{j\perp }}\text{≈}\text{T}{}_{\mathrm{j}}\text{= 5}\text{MHz}$. The measurements were made with an ESR spectrometer at X band at 4.2 OK.