Phase relation of LaFe 11·6 Si 1·4 compounds annealed at different high-temperature and the magnetic property of LaFe 11·6– x Co x Si 1·4 compounds

LaFe _11·6 Si _1·4 compounds are annealed at different high temperatures from 1323 to 1623?K. The powder X-ray diffraction patterns show that large amount of NaZn₁₃-type phase begins to be observed in LaFe _11·6 Si _1·4 compound after being annealed at 1423?K for 5?h. In the temperature range from 1423 to 1523?K, the $\boldsymbol{\alpha} $ -Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed in the XRD pattern in the LaFe _11·6 Si _1·4 compound annealed at 1523?K (5?h). With annealing temperature increasing to 1573?K and 1673?K, La ₅ Si ₃ phase is detected, and there is a certain amount of LaFeSi phase when the annealing temperature is 1673?K. The amount of impurity phases in the LaFe _11·6 Si _1·4 compound annealed by the two-stage annealing consisting of high temperature ( $\boldsymbol{>}$ 1523?K) and 1523?K is larger than that of the single stage annealing at 1523?K under the same time. According to the results of different high-temperature annealing, LaFe $_{{\bf 11{\cdot}6}-\boldsymbol{x}}$ Co $_{\boldsymbol{x}}$ Si _1·4 ( $\boldsymbol{0{\cdot}1} \boldsymbol{\le} \boldsymbol{x} \boldsymbol{\le} \boldsymbol{0{\cdot}8}$ ) compounds are annealed at 1523?K (5?h). The main phase is NaZn13-type phase, and the impurity phase is a small amount of $\boldsymbol{\alpha} $ -Fe in LaFe $_{{\bf 11{\cdot}6}-\boldsymbol{x}}$ Co $_{\boldsymbol{x}}$ Si _1·4 compounds. With increase in Co content from $\boldsymbol{x} \boldsymbol{=} \boldsymbol{0{\cdot}1}$ to $\boldsymbol{0{\cdot}8}$ , the Curie temperature $\boldsymbol{T}_{\!\boldsymbol{\rm C}}$ , goes up from 207 to 285?K. The introduction of Co element weakens the itinerant electron metamagnetic transition, and also results in the change of magnetic transition type from first to second order at about $\boldsymbol{x = 0{\cdot}5}$ . The magnetic entropy change decreases from 19·94 to 4·57?J /kg K with increasing Co concentration at a low magnetic field of 0?C2?T. But the magnetic hysteresis loss around $\boldsymbol{T}_{\!\boldsymbol{\rm C}}$ reduces remarkably from 26·2?J /kg for $\boldsymbol{x = 0{\cdot}1}$ to 0?J /kg for $\boldsymbol{x} \boldsymbol{=} \bf 0{\cdot}8$ .     

Influence of pH and bath composition on properties of Ni–Fe alloy films synthesized by electrodeposition

Fe?CNi films were electrodeposited on ITO glass substrates from the electrolytes with different molar ratio of Ni $^{\boldsymbol{2+}}$ /Fe $^{\boldsymbol{2+}}$ and different pH values (2 $\boldsymbol{\cdot}$ 1, 2 $\boldsymbol{\cdot}$ 9, 3 $\boldsymbol{\cdot}$ 7 and 4 $\boldsymbol{\cdot}$ 3) at 25 $\boldsymbol{^\circ}$ C. The properties of Fe?CNi alloy films depend on both Ni $^{\boldsymbol{2+}}$ and Fe $^{\boldsymbol{2+}}$ concentrations in electrolyte and pH values. The content of Ni increases from 38% to 84% as the mole ratio of NiSO $_{\boldsymbol{4}}$ /FeSO $_{\boldsymbol{4}}$ increasing from 0 $\boldsymbol{\cdot}$ 50/0 $\boldsymbol{\cdot}$ 50 to 0 $\boldsymbol{\cdot}$ 90/0 $\boldsymbol{\cdot}$ 10 in electrolyte and slightly decreases from 65% to 42% as the pH values increase from 2 $\boldsymbol{\cdot}$ 1 to 4 $\boldsymbol{\cdot}$ 3. The X-ray diffraction analysis reveals that the structures of the films strongly depend on the Ni content in the binary films. The magnetic performance of the films shows that the saturation magnetization ( $\boldsymbol{M}_{\boldsymbol{\rm s}})$ decreases from 1775 $\boldsymbol{\cdot}$ 01 emu/cm $^{\boldsymbol{3}}$ to 1501 $\boldsymbol{\cdot}$ 46 emu/cm $^{\boldsymbol{3}}$ with the pH value increasing from 2 $\boldsymbol{\cdot}$ 1 to 4 $\boldsymbol{\cdot}$ 3 and the saturation magnetization ( $\boldsymbol{M}_{\boldsymbol{\rm s}})$ and coercivity ( $\boldsymbol{H}_{\boldsymbol{\rm c}})$ move up from 1150 $\boldsymbol{\cdot}$ 44 emu/cm $^{\boldsymbol{3}}$ and 58 $\boldsymbol{\cdot}$ 86 Oe to 2498 $\boldsymbol{\cdot}$ 88 emu/cm $^{\boldsymbol{3}}$ and 93 $\boldsymbol{\cdot}$ 12 Oe with the increase of Ni $^{\boldsymbol{2+}}$ concentration in the electrolyte, respectively.     

Computation of X-ray powder diffractograms of cement components and its application to phase analysis and hydration performance of OPC cement

The importance of computed X-ray diffraction patterns of various polymorphs of alite (M₃, T₁, R{\bf \emph{M}_{3}, \emph{T}_{1}, \emph{R}}), belite (b\boldsymbol{\beta}, g\boldsymbol{\gamma}), aluminate (cubic, orthorhombic), aluminoferrite, gypsum and hemihydrate in the quantitative phase analysis of cement and its early stage hydration performance is highlighted in this work with three OPC samples. The analysis shows that the predominant silicate phases present in all the samples are M₃{\bf \emph{M}_{3}}-alite phase and b\boldsymbol{\beta}-belite phase, respectively. Both cubic and orthorhombic phases of C ₃ A, brownmillerite, gypsum and hemihydrates are present at different levels. Quantitative phase analysis of cement by Rietveld refinement method provides more accurate and comprehensive data of the phase composition compared to Bogue method. The comparative hydration performance of these samples was studied with w/c{\bf \emph{w/c}} ratio, 0·5 and the results are interpreted in the light of difference in phase compositions viz. b\boldsymbol{\beta}-C ₂ S/C ₃ S ratio, fraction of finer cement particles present in the samples and theoretical modeling of C ₃ S hydration.     

The structure of the unidirectionally solidified Al-Al2Au eutectic

The structure of a number of unidirectionally solidified Al-Al₂Au alloys of eutectic and off-eutectic compositions has been investigated over a wide range of growth rates (1.6×10^–4 to 1.66×10^–2cm sec^–1) using a thermal gradient of approximately 80 to 100 lamellar interface || (001)_{Al 2 Au} || (01 1) _Al [ 1 1 0 ]_{Al 2 Au} || [ 1 0 0 ] _Al growth direction of lamellae and rods || [ 1 1 0 ]_{Al2 Au} || [ 1 0 0 ]_Al \begin{gathered} lamellar interface \left\| {(001)_{Al_{ 2} Au} } \right.\left\| {(01 1)} \right._{Al} \hfill \\ \left[ {1 1 0} \right]_{Al_{ 2} Au} \left\| {\left[ {1 0 0} \right]} \right._{Al} \hfill \\ growth direction of \hfill \\ lamellae and rods \left\| {\left[ {1 1 0} \right]_{Al_2 Au} \left\| {\left[ {1 0 0} \right]_{Al} } \right.} \right. \hfill \\ \end{gathered}     

Thermal expansion of copper,silver, and gold below 30 K

A variable transformer technique has been used to determine the linear thermal expansion coefficients of the noble metals from 4 to 30 K. The precision of the data initially was ±0.04 Å, and this was later increased to ±0.015 Å, resulting in a sensitivity of approximately 2×10^?11 for relative length changes of a 10-cm-long sample. The results agree at all temperatures (to better than 5%) with those of White and Collins who used a differential capacitor technique. The differences are 2% or less above 20 K for Cu, above 8 K for Ag, and at all temperatures for Au. The differences between the two sets of data for the three metals are not systematic (α_WC greater for Cu, less for Ag) and may be due to differences in sample purity since much larger low-temperature anomalies were found within each set for certain samples of Cu and Ag. The resulting electronic Grüneisen parameters γ_e and theT=0 lattice Grüneisen parameters γ₀ are as follows: $$\begin{gathered} copper \gamma _{\text{e}} = 0.91 \pm 0.05 \gamma _{\text{0}} = 1.67 \pm 0.02 \hfill \\ silver \gamma _{\text{e}} = 1.18 \pm 0.15 \gamma _{\text{0}} = 2.29 \pm 0.03 \hfill \\ gold \gamma _{\text{e}} = 1.6 \pm 0.5 \gamma _{\text{0}} = 2.96 \pm 0.04 \hfill \\ \end{gathered} $$ The values of γ₀ are in reasonable (5% at worst) agreement with elastic constant values.     

Spherical and rod-like Gd 2 O 3 :Eu 3?+? nanophosphors—Structural and luminescent properties

A comparative study of spherical and rod-like nanocrystalline Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ (Gd $_{\boldsymbol{1\cdot92}}$ Eu $_{\boldsymbol{0\cdot08}}$ O $_{\boldsymbol 3}$ ) red phosphors prepared by solution combustion and hydrothermal methods have been reported. Powder X-ray diffraction (PXRD) results confirm the as-formed product in combustion method showing mixed phase of monoclinic and cubic of Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ . Upon calcinations at 800 $^{\boldsymbol\circ}$ C for 3?h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH) $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ phase and it converts to pure cubic phase of Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ on calcination at 600 $^{\boldsymbol \circ}$ C for 3?h. TEM micrographs of hydrothermally prepared cubic Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ phase shows nanorods with a diameter of 15?nm and length varying from 50 to 150?nm, whereas combustion product shows the particles to be of irregular shape, with different sizes in the range 50?C250?nm. Dominant red emission (612?nm) was observed in cubic Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ which has been assigned to $^{\boldsymbol 5}{\bf \textit{D}}_{\boldsymbol 0}$ $\boldsymbol \to$ $^{\boldsymbol 7}{\bf \textit{F}}_{\boldsymbol 2}$ transition. However, in hexagonal Gd(OH) $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ , emission peaks at 614 and 621?nm were observed. The strong red emission of cubic Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap ( $\boldsymbol{E}_{\boldsymbol{\rm g}}$ ) was noticed in as-formed and heat treated systems in both the techniques. This is due to more ordered structure in heat treated samples and reduction in structural defects.     

Dynamics of Rotating Two-phase System Under Transversal Vibration

Mean dynamics of light granular matter in liquid in the rotating horizontal cylinder subjected to transversal vibrations is experimentally investigated. The excitation of outstripping and lagging azimuth motion of the interface with respect to the cavity is revealed at definite ratios of rotation and vibration frequencies ${\Omega _\upsilon } \mathord{\left/ {\vphantom {{\Omega _\upsilon } {\Omega_r }}} \right. \kern-0em} {\Omega _r }$ . The motion is generated by the inertial oscillations arising in the system in a resonant way. The formation of regular spatial structures on the interface is revealed at intensive outstripping motion. These structures have azimuth and axial periodicity and their shape depends on the type of inertial waves arising in the cavity. Intensity and direction of azimuth flows as well as shape of patterns on the granular matter–liquid interface are determined by the ratio $ {\Omega _\upsilon } \mathord{\left/ {\vphantom {{\Omega _\upsilon } {\Omega _r}}} \right. \kern-0em} {\Omega _r }$ . It is shown, that the lagging motion exists at $ {\Omega _\upsilon } \mathord{\left/ {\vphantom {{\Omega _\upsilon } {\Omega _r }}} \right. \kern-0em} {\Omega _r }<1$ , and the outstripping one exists at $ {\Omega _\upsilon } \mathord{\left/ {\vphantom {{\Omega _\upsilon } {\Omega _r }}} \right. \kern-0em} {\Omega _r }>1 $ . Combined action of vibrations and rotation provides an efficient mechanism of mass transfer control, the intensity of mean flows in the cavity frame can be of the same order of magnitude as the rotation velocity.     

The crystallographic orientation relationship between Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in the composite material Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al–Mg–Si alloy

The formation mechanism of spinels on Al₂O₃ particles in the Al₂O₃/Al–1.0 mass% Mg₂Si alloy composite material has been investigated by transmission electron microscopy (TEM) in order to determine the crystallographic orientation relationship. A thin sample of the Al₂O₃/Al–Mg–Si alloy composite material was obtained by the FIB method, and the orientation relationship between Al₂O₃ and MgAl₂O₄, which was formed on the surface of Al₂O₃ particles, was discovered by the TEM technique as follows:

Microstructure, topology and X-ray diffraction in Ag-metal reinforced polymer of polyvinyl alcohol of thin laminates

A polymer composite of Ag-metal reinforced polyvinyl alcohol (PVA) is synthesized in shape of thin laminates of 200–300 μm thickness. The process involves a chemical Ag⁺ dispersion in PVA and in-situ reduction-reaction with active PVA molecules under hot conditions (with stirring) in water at 60–70°C temperature. The product results in a metal Ag-polymer complex dispersed in the solution. After evaporating part of water, a derived viscous solution is casted (in hot conditions) in shape of a thin laminate in a glass mould. In addition to chemical reducer, active OH-groups (free from H-bonding) in PVA molecules of refreshed surfaces act as head groups to adsorb Ag⁺ and drive a directional growth. Short fibrils of Ag-metal thus occur in reaction over the PVA molecules. Casting thin laminates from a liquid sample Ag-PVA allows the fibrils (also the polymer molecules) to align along the surface. Selected Ag-contents up to 5.0 wt.% in Ag-PVA laminates are studied in terms of scanning electron micrograph, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. Average size, morphology and aspect ratio (ϕ) vary in Ag-metal depending on the Ag-content. As long Ag-metal fibrils as 2–5 μm, ϕ=35, occur in a sample of 2.0 wt.% Ag. The Ag-metal reflects in two characteristic 3d_5/2 and 3d/_3/2 XPS bands of 368.3 and 374.1 eV respectively.     

Combined effect of partial calcination and sintering condition on low loss Mn-Zn ferrite

In order to achieve highly densified lower loss Mn-Zn ferrite materials, various powder processing routes have been under investigation. In this report, a lower sintering temperature with lower oxygen partial pressure and proper attrition milling duration are suggested. From the previous study, a partial calcination procedure was studied and an optimum partial calcination level was found. Accordingly, Mn_0.71Zn_0.22Fe_2.07O₄ ferrite was prepared by calcination with small amounts of CaCO₃, SiO₂, Nb₂O₅ and SnO₂. The partially calcined ferrites were made by calcining the mixture of the whole amount of ZnO and amount of Fe₂O₃ and Mn₃O₄ and sintering the mixture of the calcined powders and the remaining of Fe₂O₃ and Mn₃O₄. Initially, from the 40 min secondary milling and the partial calcination, lower temperature (1300°C) sintered samples showed a power loss of 340 mW cm^–3 at 90°C. Secondly, several milling durations showed secondary milling had a more profound effect on magnetic properties than primary milling. The 20 min primary and 90 min secondary milling showed lower core loss around 320 mW cm^–3 at 1300°C and 1250°C, suggesting the sintering temperature could be reduced to 1250°C. Thus, the proper sintering condition of lower oxygen partial pressure at 1250°C was studied. As a result, lower loss with higher density was realized.     

Effect of substitution of sand stone dust for quartz and clay in triaxial porcelain composition

Quartz and kaolin were partially substituted by sand stone dust (a siliceous byproduct of Indian stone cutting and polishing industries) in a traditional triaxial porcelain composition consisting of kaolin, quartz and feldsper. The effect of substitution upon heating at different temperatures (1050–1150 $\boldsymbol{^\circ}$ C) were studied by measuring the linear shrinkage, bulk density, porosity and flexural strength. Qualititative phase and microstructural analysis on selected samples were carried out using XRD and SEM/EDX technique. The results show that the samples of all the batches achieved higher density (2 $\boldsymbol\cdot$ 50 g/cc) and almost full vitrification ( $\boldsymbol <$ 0 $\boldsymbol{\cdot}$ 1% apparent porosity) at around 1115 $\boldsymbol{^\circ}$ C compared to around 1300 $\boldsymbol{^\circ}$ C for traditional triaxial porcelain composition. As high as 70 MPa flexural strength was obtained in most of the vitrified samples. No significant variation in physico-mechanical properties was observed in between the composition. XRD studies on selected samples show presence of mainly quartz phase both at low and high temperatures. SEM photomicrographs of the 1115 $\boldsymbol{^\circ}$ C heated specimen show presence of quartz grain and glassy matrix. Few quartz grains (20–40 $\boldsymbol{\mu}$ m) are associated with circumferential cracks around them.     

Velocity Distribution of Vibration-driven Granular Gas in Knudsen Regime in Microgravity

Dynamics of quasi-2D dissipative granular gas is studied in micro-gravity condition (of the order of 10^− 4 g) in the limit of Knudsen regime. The gas, made of 4 spheres, is confined in a square cell enforced to follow linear sinusoidal vibration in ten different vibration modes. The trajectory of one of the particles is followed for 2 hours, and is reconstructed from video data by particle tracking. From statistical analysis, we find that (i) loss due to wall friction is small, (ii) trajectory looks ergodic in space, and (iii) distribution ρ(ν) of speed follows an exponential distribution, i.e., , with being a characteristic velocity along a direction parallel (y) or perpendicular (x) to vibration direction. This law deviates strongly from the Boltzmann distribution of speed in molecular gas. Comparisons of this result with previous measurements in earth environment, and what was found in 3D cell (Falcon et al., Europhys Lett 74:830, 2006) performed in environment of about ±5 ×10^− 2 g are given.     

Growth of strontium oxalate crystals in agar–agar gel

Single crystals of strontium oxalate have been grown by using strontium chloride and oxalic acid in agar–agar gel media at ambient temperature. Different methods for growing crystals were adopted. The optimum conditions were employed in each method by varying concentration of gel and reactants, and gel setting time etc. Transparent prismatic bi-pyramidal platy-shaped and spherulite crystals were obtained in various methods. The grown crystals were characterized with the help of FT–IR studies and monoclinic system of crystals were supported with lattice parameters a = 9·67628 ?, b = 6·7175 ?, c = 8·6812 ?, b\boldsymbol{\beta} = 113·566^°^{\boldsymbol\circ}, and V = 521·84 ?³ calculated from X-ray diffractogram.     

Modeling of thermally stimulated depolarization current (TSDC) using dipole–dipole interaction concept

The study of thermally stimulated depolarization current (TSDC) using the dipole–dipole interaction model is describedin this work. The dipole–dipole interaction model (DDIM) determines the TSDC peak successfully since it gives significant peak parameters (i.e. activation energy (E{\bf \textit{E}}) and pre-exponential factor (t₀){\boldsymbol\tau}_{{\bf 0}})) in addition to the dipole–dipole interaction strength parameter (d_i){\bf \textit{d}}_{{\bf i}}). Application of this model to study the peak parameters of some polymeric systems is presented.     

Is There a Unified Description of Conductivity of Layered Cuprates ?

We present a novel approach to the analysis of the normal state in-plane $\sigma _{ab} $ and out-of-plane σ_c conductivities of anisotropic layered crystals such as oxygen deficient YBa ₂ Cu ₃ O _x . It can be shown that the resistive anisotropy is determined by the ratio of the phase coherence lengths in the respective directions; i.e., $\sigma _{ab} /\sigma _c = \ell _{ab}^2 /\ell _c^2 $ . From the idea that at all doping levels and temperatures T the out-of-plane transport in these crystals is incoherent, follows that $\ell _c $ is T-independent, equal to the spacing $\ell _0 $ between the neighboring bilayers. Thus, the T-dependence of $\ell _{ab} $ is given by the measured anisotropy, and $\sigma _{ab} (\ell _{ab} )$ dependence is obtained by plotting $\sigma _{ab} {\text{ }}vs{\text{ }}\ell = {\text{ (}}\sigma _{ab} /\sigma _c )^{1/2} \ell _0 $ .The analysis of several single crystals of YBa ₂ Cu ₃ O _x (6.35 < x < 6.93) shows that for all of them $\sigma _{ab} (\ell ) $ is described by a universal dependence $\sigma _{ab} /\overline \sigma = f(\ell /\overline \ell ) $ with doping dependent parameters $\overline \sigma {\text{ }}and{\text{ }}\overline \ell $ .     

Dual-mode protein detection based on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-Au hybrid nanoparticles

A facile method of synthesizing Fe₃O₄-Au hybrid nanoparticles is reported utilizing the multifunctional nature of polyethyleneimine (PEI). An abundance of 5 nm gold nanoparticles were attached to 50 nm Fe₃O₄ nanoparticles via the covalent binding between the -NH₂ groups of the PEI and Au nanoparticles, as well as the electrostatic interaction between the negatively charged citrate-coated Au nanoparticles and the positively charged PEI-coated Fe₃O₄ nanoparticles. The as-prepared Fe₃O₄-Au hybrid nanoparticles, which combine the merits of magnetic materials and gold, were successfully employed for the first time in the dual-mode detection of carcinoembryonic antigen (CEA) via electrochemical and surface-enhanced Raman scattering (SERS) methods. Both methods make clever use of Fe₃O₄-Au nanoparticles and can accurately verify the presence of antigens. In particular, the electrochemical immunosensor detection displays a wide linear range (0.01–10 ng/mL) of response with a low detection limit (10 pg/mL), while the SERS method responds to even lower antigen concentrations with a wider detection range. The Fe₃O₄-Au hybrid nanoparticles therefore exhibit great potential for biomedical applications.      

Three oxidation states and atomic-scale <Emphasis Type="Italic">p–n</Emphasis> junctions in manganese perovskite oxide from hydrothermal systems

Perovskite oxides have provided magical structural models for superconducting and colossal magnetoresistance, and the search for nano-scale and/or atomic-scale devices with particular property by specific preparations in the same systems has been extensively conducted. We present here the three oxidation states of manganese (Mn³⁺, Mn⁴⁺, Mn⁵⁺) in the perovskite oxide, La_0.66Ca_0.29K_0.05MnO₃, which most interestingly shows the rectifying effect as atomic-scale p–n junctions (namely FY-Junctions) of single crystals and films. The family of cubic perovskite oxides were synthesised by the so-called hydrothermal disproportionation reaction of MnO₂ under the condition of strong alkali media. The new concept of the atomic-scale p–n junctions, based on the ideal rectification characteristic of the p–n junctions in the single crystal, basically originates from the structural linkages of [Mn³⁺–O–Mn⁴⁺–O–Mn⁵⁺], where Mn³⁺ and Mn⁵⁺ in octahedral symmetry serve as a donor and an acceptor, respectively, corresponding to the localized Mn⁴⁺ .     

The role of protons in ionic diffusion in (Mg, Fe)O and (Mg, Fe)2SiO4

The presence of hydrogen dissolved within iron-magnesium oxides and silicates results in an increase in the rate of Fe–Mg interdiffusion. Experimental data and point defect models suggest that the increased interdiffusivity is due to an increase in the total metal-vacancy concentration through stabilization of proton-vacancy defect associates in a hydrous environment. In the case of (Mg_1–x Fe _x )O, interdiffusion experiments under hydrothermal conditions at a fluid pressure of ∼0.3 GPa yield similar dependencies of interdiffusivity on Fe-content, oxygen fugacity, and temperature as under dry conditions, but interdiffusion coefficients are a factor of ∼3 larger. These data suggest that the increased interdiffusivities in (Mg_1–x Fe _x )O result from incorporation of defect associates formed between a metal vacancy and a single proton, For (Mg_1–x Fe _x )₂SiO₄, interdiffusion under hydrothermal conditions over a range of fluid pressures reveals a significant difference in the dependence of interdiffusivity on Fe content than obtained under dry conditions, combined with a strong dependence on water fugacity. These data indicate that the increased diffusivities in (Mg_1–x Fe _x )₂SiO₄ result from incorporation of defect associates involving a metal vacancy and 2 protons, It is anticipated that, at higher water fugacities, Fe–Mg interdiffusion in both materials will become dominated by these latter defects and that the interdiffusivity will increase linearly with water fugacity but will be independent of oxygen fugacity and iron concentration.

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