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.     

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.     

An investigation of the bismuth-rhenium-oxygen system by analytical electron microscopy

The phases Bi₃ReO₈, Bi(ReO₄)₃, Bi₃Re₃O₁₁ and BiRe₂O₆ have been prepared and characterised by X-ray emission in an analytical electron microscope. The results are in excellent agreement with the thin crystal approximation. Powder and single crystal X-ray data show that Bi₃ReO₈ is cubic, $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 11.59(1)}\text{A}\text{?}$, space group P2₁3. Bi₃Re₃O₁₁ is cubic, $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 9.349(2)}\text{A}\text{?}$, space group Pn3. Infra red spectra are presented for Bi₃ReO₈ and Bi(ReO₄)₃. The relationship to the rare earth-rhenium-oxygen system is discussed.     

Stability of layered bismuth compounds in relation to the structural mismatch

The relation between the stability and the structural mismatch in layered bismuth compounds, (Bi₂O₂)²⁺(A_n?1B_nO_3n+1)^2?, was formulated on the basis of an elastic model. The pseudo-tetragonal lattice parameter, $\text{a}$, of layered bismuth compounds was estimated from the following equation,

$\text{a}\text{=}\text{[}\text{a}{}_{\mathrm{<mtext>B</mtext>}}\text{′}{}^2\text{ap}\text{′}{}^2\text{(nK+1)}\text{(}\text{ap}\text{′}{}^2\text{+}\text{a}{}_{\mathrm{<mtext>B</mtext>}}\text{′}{}^2\text{nK}\text{)]}$

$\text{1}\text{2}$

where a_B′ is the lattice parameter of the unconstrained Bi₂O₂ unit, a_P′ the lattice parameter of the unconstrained perovskite-like unit, n the number of perovskite like layer in one structural unit, and K a constant. The change of the strain energy for ionic substitutions was estimated from the elastic relationships. It was found that the increase of n in certain component systems causes the increase of the lattice parameter, $\text{a}$, and the increase of the strain energy. This provides an explanation for the existence of maximum of n. New compounds, Pb₃Bi₄Ti₆O₂₁ ($\text{a}\text{=5.476}$, $\text{b}\text{a}\text{=1.000}$ and $\text{c}\text{=58.1}\text{A}\text{?}$) and Pb₄Bi₄Ti₇O₂₄ ($\text{a}\text{=5.485}$, $\text{b}\text{a}\text{=1.000}$ and $\text{c}\text{=66.2}\text{A}\text{?}$) were described.     

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.     

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.     

Preparing new extremely difficult-to-form crystal structures

Simple ways have been found to prepare CaTi₃Al₈O₁₉ and LaTi₂Al₉O₁₉ as prototypes of difficult-to-prepare compounds. The structures are monoclinic with very large unit cells. The new technique has been successfully tried on $\text{Na}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Ca}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Al}{}_{11.5}\text{Ti}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{O}{}_{19}$.     

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.$\text{LaVO}{}_4\text{=}\text{LaVO}{}_3\text{+}\text{1}\text{20}{}_2\text{δ=328}\text{kJ}\text{mol}\text{°=135}\text{J}\text{mol·deg.}$,$\text{LaMnO}{}_3\text{=}\text{1}\text{2}\text{La}{}_2\text{O}{}_3\text{+}\text{MnO}$     

La liaison metal — metal dans les clusters M12O36: II — Preparation et etude structurale de la phase La3Ru3O11

La₃Ru₃O₁₁ was prepared either by oxidation of mixtures of $\text{3}\text{2}\text{La}{}_2\text{O}{}_3$: 3 Ru with KClO₃ at 900°C or by the oxidation of LaRuO₃ at 920°C with KClO₃, both in a gold boat introduced in a sealed silica tube. The crystal structure of this compound ($\text{a}\text{= 9.466(2)}\text{A}\text{?}\text{, S.G. Pn}\text{3,}\text{Z}\text{=4}$) has been solved by Fourier and least-squares methods to R = 0.022 (R_W = 0.031). As for the previously described Bi₃Ru₃O₁₁ and La₄Ru₆O₁₉, it contains ruthenium in formal oxidation state of 4.33; however, there is no longer metal - metal interaction, owing to the greater Ru - Ru distance (3.00 Å) and the closer approach of bridging oxygen (2.47 Å) within the dimeric unit Ru₂O₁₀. Therefore, this interaction is not a prerequisite for the formation and stability of the three-dimensional network Ru₁₂O₃₆.     

High temperature standard gibbs free energy determinations for Co-o systems by e.m.f. measurements. A statistical approach to evaluate the reliability of the current methods

The standard Gibbs free energies of the following reactions: $\text{Co +}\text{1}\text{2}\text{O}{}_2\text{? CoO}$ (1) and $\text{3CoO +}\text{1}\text{2}\text{O}{}_2\text{? Co}{}_3\text{O}{}_4$ (2) have been calculated from the e.m.f. measurements carried out using a simple compartment solid state galvanic cell, as well for the reaction: 3Co + 20₂ ? Co₃O₄ (3) The temperature-equilibrium oxygen partial pressure relationship has been evaluated. A phase diagram for Co, CoO and Co₃O₄ is proposed in the temperature range 600–900 °C. A statistical analysis on reported ΔG_f⁰ values at 1100 K for reaction (1) has been performed and the results are discussed.     

Luminescence of some oxygen-octahedric ferroelectrics exposed to an electron beam

Spectral and temperature dependence of cathodo luminescence (CL) was studied in oxygen-octahedric ferroelectrics Ba_XSr_1-XNb₂O₆, $\text{PbMg}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3$, LiNbO₃, SrTiO₃, Ba₂NaNb₅O₁₅, and PLZT-ceramics. CL in these materials is of admixture type. In the region of ferroelectric phase transition (PT) of Ba_XSr_1-XNb₂O₆ and $\text{PbMg}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3$ an anomaly in CL is observed. Redistribution of recombination flows between the centers of radiative and non-radiative recombinations in PT region due to variation of dielectric constant is proposed to account for this phenomenon.     

Electronic and spin configurations of Co3+ and Ni3+ ions in oxides of K2NiF4 structure: A magnetic susceptibility study

In La₄LiCoO₈, Li⁺ and Co³⁺ ions are ordered in two dimensions and Co³⁺ ions undergo transitions from the low-spin to the intermediate as well as the high-spin states. Both Sr₄TaCoO₈ and Sr₄NbCoO₈ exhibit low to intermediate-spin state transitions of Co³⁺ ions. In the system LaSr_1?xBa_xNiO₄, the e_g electrons are essentially in extended states forming a band. With increase in x, the band width decreases accompanying an increase in unit cell volume; high-spin Ni³⁺ ions are formed to a small extent with increasing x, but there is no spin-state transition. In LaSrAl_1?xNi_xO₄, at small x, there is a small proportion of high-spin Ni³⁺; when x ≈ 0.6, there is an abrupt decrease in the $\text{c}$/$\text{a}$ ratio, signalling the formation of the band. In LnSrNiO₄, the $\text{c}$/$\text{a}$ ratio decreases sharply between Ln = La and Nd; this is likely to be accompanied by a broadening of the band.     

Proprietes d'echange ionique du pyrochlore TlNbO3 en presence de nitrates fondus ou solides

We have checked the ion-exchange properties of TlNbO₃ in molten or solid nitrates. For Ag⁺ and Pb⁺⁺, limited solid solutions of pyrochlore type are observed: T1_1?xAg_xNbO₃ (x < 0,75) and $\text{T}\text{1}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{Pb}{}_{\mathrm{<mtext>x</mtext><mtext>2</mtext>}}\text{NbO}{}_3\text{(}\text{x}\text{≤ 0,75)}$. Localisation of Ag⁺ and Pb⁺⁺ on the 16d positions of the space group Fd3m is confirmed by analysis of X-ray powder diffraction data. The thermal stability of the solid solutions is described and competition between pyrochlore and perovskite type is discussed.     

The role of TiO2 and ZrO2 in Na2OMO2SiO2 glasses

The glass transition temperatures of $\text{(1?x)}\text{Na}{}_2\text{O}\text{·}\text{1}\text{2}\text{x}\text{MO}{}_2\text{·2}\text{SiO}{}_2$ and Na₂O·xMO₂·(2 ?x)SiO₂ glasses, with M = Ti or Zr, have been related to the structural role and coordination of Ti and Zr. The role of network-former, intermediate or modifier of a cation has been fundamentally linked to ionic field strength; T_g values depend on ionic field strength and coordination. Titanium behaves like an intermediate oxide; its coordination ranges between four and six, depending on $\text{Ti}\text{Si}$ ratio. The role of zirconium changes according to the degree of substitution for Na or Si and progressively approaches that of a modifier ion.     

Concentration quenching of Tb3+ luminescence in LaOBr and Gd2O2S phosphors

The concentration quenching of trivalent terbium ${}^5\text{D}{}_{\mathrm{3,4}}\text{→}{}^7\text{F}{}_{\mathrm{J}}$ emissions from UV-excited (La, Tb) OBr and (Gd, Tb)₂O₂S phosphors was studied. The activation concentration x was varied from 5·10^?5 to 0.2 for (La_1?xTb_x) OBr and from 10^?3 to 0.1 for (Gd_1?xTb_x)₂O₂S. ${}^5\text{D}{}_3\text{→}{}^7\text{F}{}_{\mathrm{J}}$ emissions (blue) were observed to quench first and the Tb³⁺ concentration giving rise to maximum intensity was 0.003 in (La, Tb) OBr and between 0.005 and 0.01 in (Gd, Tb)₂O₂S. The optimum concentration for ${}^5\text{D}{}_4\text{→}{}^7\text{F}{}_{\mathrm{J}}$ (green) emissions was 0.05 in (La, Tb) OBr and 0.03 in (Gd, Tb)₂O₂S. Dipole-dipole and dipole-quadrupole interactions are possible mechanisms for the quenching of emissions from the ⁵D₃ and ⁵D₄ levels.A method for determining the Tb³⁺ concentration in these phosphors, based on the intensity ratios of the ${}^5\text{D}{}_3\text{→}{}^7\text{F}{}_{\mathrm{J}}$ and ${}^5\text{D}{}_4\text{→}{}^7\text{F}{}_{\mathrm{J}}$ transitions, is also presented.     

Un nouveau conducteur protonique [H(H2O)n]12Sb12O36 (n ⩽ 1)

Single crystals of K₁₄Sb₁₂O₃₆F₂ undergo rapid ion exchange in 9N sulfuric acid to produce “hydronium” compound (H(H₂O)_n)₁₂Sb₁₂O₃₆ (n ? 1). Between 30 and 140°C this phase undergoes a partial and reversible dehydratation in which approximately 85 % of its “H₃O⁺” content is converted to H⁺.The structures of hydrated and dehydrated phases have been refined by full-matrix least squares, respectively to factor R = 0.030 and 0.047. The conductivity of $\text{(H(H}{}_2\text{O)}{}_{\mathrm{<mtext>n</mtext>}}\text{)}{}_{12}\text{Sb}{}_{12}\text{O}{}_{36}\text{(σ}{}_{20}\text{? 1O}{}^7\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) increases in an Arrhenius relationship with an activation energy of 8.8 kcal.mole^?1, the dehydrated compound (H(H₂O)_0.33)₁₂Sb₁₂O₃₆ has a much lower conductivity but the same activation energy.     

Influence of local-site symmetry on fluorescence lifetime in high-Nd-concentration laser materials

We have correlated the radiative fluorescence lifetime of the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level of Nd³⁺ in laser crystals, including the recently developed high-Nd-concentration materials such as NdP₅O₁₄, with the local Nd³⁺ site symmetry. At Nd³⁺ concentrations low enough for non-radiative interactions to be negligible, the fluorescence decay rate is determined by the deviation from local inversion symmetry, which admixes even- and odd-parity electronic wavefunctions, allowing ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ radiative decay by electric-dipole transitions.     

The conversion from CrO2 into orthorhombic CrOOH

The reaction, $\text{2}\text{CrO}{}_2\text{+}\text{H}{}_2\text{O}\text{→ 2}\text{CrOOH}\text{+}\text{1}\text{2}\text{O}{}_2$, was confirmed to be a topotactic reaction by X-ray diffraction technique using a single crystal of CrO₂ as starting material. The crystallographic axial relation between CrO₂ and CrOOH was as follows: ^c(CrO₂^//c(CrOOH), ^a(CrO₂)^∧a(CrOOH)^{= a}(CrO₂)^∧b(CrOOH)^{= 1.7°}.     

Les oxydes ATiMO5 : Echangeurs cationiques

The ion-exchange properties of the ATiMO₅ oxides (M = Ta, Nb), with a layer structure, are shown for the first time. By action of an acid solution on the ATiMO₅ compounds, the HTiMO₅ oxides were synthesized. The ion-exchange properties of the HTiMO₅ compounds were used to prepare new oxides which could not be obtained by direct action of the oxides - Tl Ti TaO₅, NH₄ Ti MO₅ - and hydrated compounds - ($\text{Na}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(}\text{H}{}_3\text{O}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$) TiMO₅.H₂O, ($\text{Li}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(}\text{H}{}_3\text{O}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$) $\text{TiMO}{}_5\text{.}\text{4}\text{3}\text{H}{}_2\text{O}$. The reversibility of the exchange properties was observed in every case. The crystallographical properties of these oxides were determined and 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.