Crystal chemistry of γ-(Zn, Me)3(PO4)2 solid solutions

A number of γ-(Zn,$\text{Me}$)₃(PO₄)₂ solid solutions with the “γ-Zn₃(PO₄)₂” structure have been prepared and equilibrated at about 1070 K ($\text{Me}\text{= Mg, Mn, Fe, Co, Ni, Cu, and Cd}$). Approximate homogeneity ranges are given. The monoclinic unit cell dimensions have been accurately determined from Guinier-Hägg photographs. The structure contains five- and six-coordinated cations. Correlations between homogeneity ranges, unit cell dimensions, cation radii and cation distributions are pointed out, and the phases are also compared with isotypic (Mg,$\text{Me}$₃(PO₄)₂ and (Co,$\text{Me}$)₃(PO₄)₂ solid solutions.     

The cation distribution between five- and six-coordinated sites in some (Mg,Me)3(PO4)2) solid solutions

Approximate homogeneity ranges at about 1073 K have been determined for some (Mg,$\text{Me}$)₃(PO₄)₂ solid solutions. X-ray powder diffraction data are given and the observed changes in unit cell dimensions are discussed. The Mg₃(PO₄)₂ structure, isotypic with γ-Zn₃(PO₄)₂, contains five- and six-coordinated cation sites, M1 and M2 respectively. The M1 site preference order is Zn²⁺ > Co²⁺ > Fe²⁺ > Mg²⁺ > Mn²⁺.     

Preparation et caracterisation des ferrites de calcium CaFe2+nO4+n a valeurs fractionnaires de n (32, 52) et leur incidence sur le diagramme Fe-Ca-O A 1120°C

The synthesis of two new calcium ferrites belonging to the CaFe_2+nO_4+n family, with the fractional values $\text{n =}\text{3}\text{2}$ and $\text{5}\text{2}$, has been done.Their crystalline structures have been determined. A stacking process of blocks with the CaFe₂O₄ composition and blocks with the FeO composition, like for the other terms of the series with n integer (1, 2, 3) allows to describe them.The schematic representation of this new example of intergrowth has been carried out according to A.F. Wells' method.The existence of these ferrites has lead us to specify the Fe-Ca-O diagram at 1120°C in the FeO-Ca₂Fe₂O₅-CaFe₂O₄ - Fe₃O₄ region.     

Un exemple de chaînes antiferromagnetiques alternees de spin 12: CuWO4

The ordering of Cu and W atoms in the distorted wolframite structure of CuWO₄ gives rise to zigzag chains of edge sharing CuO₆ octahedra linked by similar chains of WO₆ octahedra. The existence of two kinds of connections between the CuO₆ octahedra leads to alternating antiferromagnetic interactions along the chains. The magnetic behavior is explained using a Heisenberg type model of Duffy and Barr with the largest exchange integral : J = ? 67 K and an alternation parameter : a = 0.8. k_B EPR measurements have shown that threedimensional ordering occurs at $\text{T}{}_{\mathrm{N}}\text{? 24}\text{K}$.     

Tunneling barrier structure of NbPb and Nb(PbIn) thin film Josephson junctions studied by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis

The structure of the insulant barrier of $\text{Nb}\text{Pb}$ and $\text{Nb}\text{(PbIn)}$ thin film Josephson tunnel junctions is studied in detail by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis. The properties of these two types of junction are strictly related to the thin (2–3 nm) oxide acting as a barrier between the superconducting electrodes. Two oxides were found in each barrier: Nb₂O₅ and PbO in the $\text{Nb}\text{Pb}$ junction and Nb₂O₅ and In₂O₃ in the $\text{Nb}\text{(PbIn)}$ junction. In addition, the present analysis shows a change with time of the PbO in contact with Nb₂O₅: this result is correlated with junction aging. Finally, a comparison in terms of the stability of the two junctions is made: $\text{Nb}\text{(PbIn)}$ devices seem to display a more stable behaviour with time.     

Interrelation of crack opening displacement and J-integral

The relationship between $\text{J-}\text{integral}$ and crack opening displacement δ is based on theoretical as well as experimental investigations and is of the general form $\text{J = Mσ}{}_{\mathrm{r\delta }}$. The significance of M and its possible dependence on specimen geometry and material properties is unknown. An attempt is made in the present paper to identify the different variables and to account for them in $\text{H-δ}$ relationship. It is observed that if the material properties remain constant, $\text{M}$ increases with $\text{a/W}$ ratio upto 0.5 and then probably decreases for higher $\text{a/W}$ ratios. If the specimen geometry and size is maintained constant then it is observed that $\text{M}$ increases with decreasing yield strength and a corresponding increase in work hardening exponent.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

High pressure form of fluoride garnets Na3M2Li3F12 (M=Al & Fe)

The fluoride garnet, Na₃Fe₂Li₃F₁₂, transforms to a single phase with the cryolite (ordered perovskite) structure under 60 kb above 400°C. The lattice constants, a=5.338, b=5.498, c=7.666 Å and β=90.0°, are smaller than those of Na₃FeF₆, due to the substitution of Na for Li ions in the structure. The measurements of magnetic susceptibility and Mössbauer effect indicate that Fe ions are in the high spin trivalent state and in octahedral site. Na₃Al₂Li₃F₁₂, cryolithionite, decomposes to the cryolite and α-Li₃AlF₆ under high pressures examined.     

Computer controlled decreasing ΔK fatigue threshold test

An automated fatigue threshold test was developed which decreases testing time, eliminates need for constant operator attention, and produces a plot of fatigue crack growth rate (FCGR) data as the test proceeds. A minicomputer interfaced to a servo-hydraulic test stand adjusts loads during the FCGR test to achieve a specified stress intensity range (AA). The value of $\text{ΔK}$ is decreased exponentially with crack growth to get the fastest load shedding without crack arrest. The procedure is as follows: apply load levels to obtain desired $\text{ΔK}$ for the crack length, $\text{a}$; using the specimen compliance, compute a new value for $\text{a}$; adjust loads to obtain corresponding $\text{ΔK}$ for that $\text{a}$; record $\text{a}$, $\text{ΔK}$, and cycle count ($\text{N}$); repeat. Plots of $\text{a}$ vs $\text{N}$, and $\text{da/dN}$ vs $\text{ΔK}$ are made by a separate program. The optimized load shedding and 24hr/day operation result in a considerable reduction in test time. The program was written in BASIC on a MTS Automated Test System. Visual crack growth measurements showed good agreement with computer acquired data for a test of ETP Cu.     

On the computation of mixed-mode K-factors for a dynamically propagating crack,using path-independent integrals J'k

The path-independent integral $\text{J'}{}_{\mathrm{k}}$, which has the meaning of energy release rate in elastodynamic crack-propagation, is used to numerically obtain the mixed-mode dynamic stressintensity factors for a crack propagating in a prescribed direction with a prescribed velocity. Moving isoparametric (non-singular) elements are used to model crack propagation. Even though J' is a vector integral and hence is coordinate invariant, the desirability of using specific coordinate systems to improve the accuracies of the numerical solutions for $\text{K-}\text{factors}$ is pointed out. Two procedures for extracting the mixed-mode $\text{K-}\text{factors}$ from the J' integral for a propagating crack are given. It is found that the component of J' along the crack-axis, i.e. $\text{J'}{}_1{}^0$, is always equal to or greater than the product of a crack-velocity-function and the component normal to the crack-axis, $\text{J'}{}_2{}^0$. Several examples of a slanted crack are presented to demonstrate the practical utility of the J' integral. A discussion is also presented concerning the velocity factors for dynamic $\text{K-}\text{factors}$, and energy release rate, in a finite body.     

Fracture of round bars loaded in mode III and a procedure for KIIIc determination

The available literature reports few studies on Mode $\text{III}$ fracture. In fact, even though the Mode $\text{III}$ fracture toughness, $\text{K}{}_{\mathrm{IIIc}}$ is an important factor in design and analysis of fractures under torsional loading, the procedure for the measurement of $\text{K}{}_{\mathrm{III}}$ is yet to be standardized.In this paper, the results of a simple analysis, which determines the displacement produced by the size dependent plasticity and the growth of crack in a circumferentially cracked round bar subjected to Mode $\text{III}$ loading, are presented. It is shown that plastic zone size decreases as bar diameter increases. This implies that whereas a small diameter bar can fail in a ductile manner, a large diameter bar may undergo a predominantly linear, elastic and brittle fracture even though the material is ductile.The analytical results are verified by experimental measurements on circumferentially cracked specimens loaded in Mode $\text{III}$. Based on this, one can determine the limiting value of the bar diameter, which must be tested to obtain a $\text{K}{}_{\mathrm{IIIc}}$ in a predominantly linear elastic condition. Further, a new and simple procedure for the determination of $\text{K}{}_{\mathrm{IIIc}}$ is proposed. This procedure enables one to determine the stress intensity factor at which a crack starts extension in the specimen under Mode $\text{III}$ loading.     

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.     

Crystal growth and characterization of In23PSe3

Crystals of $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PSe}{}_3$ were grown by chemical vapor transport of the elements. The phase is structurally related to the hyposelenophosphates, M^IIPSe₃, but contains both indium atoms and vacancies on the metal ion sites. The compound shows a high electrical resistivity (>10⁸ ohm-cm) and has an optical absorption edge at 1.9 (1) e.V.     

Spectroscopic properties of Eu-doped KLa(PO3)4 and LiLa(PO3)4 powders

KLa(PO₃)₄ (KLP) and LiLa(PO₃)₄ (LLP) doped with different concentrations of Eu³⁺ are grown by solid state reaction. The obtained powders are identified by X-ray diffraction, Raman and FT-IR spectroscopies. These polyphosphates KLa(PO₃)₄ and LiLa(PO₃)₄ crystallize in the monoclinic system but with different space groups respectively P2₁ and C2/c. The evolution of crystal lattice parameters as function of Eu³⁺ concentration in these host lattices was studied. Spectroscopic properties of the Eu³⁺-doped KLa(PO₃)₄ and LiLa(PO₃)₄ at room temperature (RT) are presented. The excitation spectra of the Eu³⁺ ion in condensed polyphosphates along the UV-Visible domain are registered. They show that the position of the charge transfer band (CTB) depends on the host lattices. The effect of structural characteristics of condensed polyphosphates on their optical and colorimetric properties was investigated for the first time. Colorimetric parameters of the Eu³⁺ ions red emission in KLP and LLP are determined and compared with other host matrices. Evolution of colorimetric properties as function of Eu³⁺concentration was discussed.     

On the path independent integral-Ĵ

The path independent integral, $\text{J}\text{?}$, is presented as the rate of energy flux during crack extension. This integral is an extension of the J-integral proposed by Rice and includes the existence of a fracture process region and the effect of plastic deformations, body forces, thermal strains and inertial of material.It is shown that the $\text{J}\text{?}\text{-}\text{integral}$ can include as special cases other fracture mechanics parameters such as J by Rice, $\text{G}\text{?}$ by Eftis et al., J¹ by Blackburn or f by Strifors.A definition of the $\text{J}\text{?}\text{-}\text{integral}$ in a three-dimensional problem is presented and possibility of applying the $\text{J}\text{?}\text{-}\text{integral}$ as fracture criterion is discussed.     

On the relationship between J-integral and crack opening displacement

This paper describes a simple method of calculating the material-dependent nondimensional factor β used in the well known relation $\text{J = βσ}{}_0\text{δ}$, or, in other words, of improving the most simple relation $\text{J = σ}{}_0\text{δ. β}$ as derived in this paper accounts for the effect of hardening and prior cold-work of the material. The results obtained by this very simple procedure compare quite favorably with experimental and numerical results of other authors.     

Low temperature compound formation in CuSn thin film couples

Transmission electron microscopy (TEM) and Auger electron spectroscopy have been used to study the morphology and kinetics of compound formation in vapor-deposited polycrystalline bimetallic $\text{Cu}\text{Sn}$ thin film diffused at low transport temperatures. The TEM observations show that two concurrent mechanisms, namely the interstitial transport of copper in tin and the grain boundary diffusion of tin in copper, lead to the sequential formation of η′ (Cu₆Sn₅) and ε (Cu₃Sn) intermetallic compounds. Preliminary Auger depth profiling data indicate linear growth kinetics for the η′ compound at 86°C implying that interfacial reaction kinetics is the rate-controlling step. A detailed model for the interdiffusion and reaction process in $\text{Cu}\text{Sn}$ thin films is presented.     

Crystal structure and spectroscopic studies of NaGd(PO3)4

Single crystals of gadolinium–sodium polyphosphate NaGd(PO₃)₄ were grown for the first time using a flux method and characterized by X-ray diffraction. This phosphate crystallizes in a monoclinic system with P2₁/n space group and with the following unit-cell dimensions: a = 9.767(3) Å, b = 13.017(1) Å, c = 7.160(2) Å, β = 90.564(5)°, V = 910.3(4) Å³ and Z = 4. The crystal structure was solved from 3451 X-ray independent reflections with final R(F²) = 0.0219 and R_w(F²) = 0.056 refined with 164 parameters (). The atomic arrangement can be described as a long chain polyphosphate organization. Two infinite (PO₃)∝ chains with a period of eight tetrahedra run along the [0 1 1] direction. The structure of NaGd(PO₃)₄ consists of GdO₈ polyhedra sharing oxygen atoms with phosphoric group PO₄. Each Na⁺ ion is bonded to eight oxygen atoms.     

Dielectric properties of Pb3 (PO4)2 | Pb3 (AsO4)2

The dielectric constants of Pb₃ (PO₄)₂ | Pb₃ (AsO₄)₂ at room temperature are intrinsic and fulfill the Lyddane - Teller - Sachs relation. At higher temperatures the specific conductivity increases with an activation energy of 0.56 eV leading to Maxwell - Wagner polarization effects thereby increasing the effective dielectric constant. Corresponding peaks in ∈' (T) are extrinsic and not attributed to structural phase transformations.