Ordering Of Mg Research Articles

Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2

Summary O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.

4d3 Ru5+ triangular lattice antiferromagnets: Layered rock-salt β-Li3Mg2RuO6 and ion-exchanged delafossite Ag3Mg2RuO6

The crystal structure and magnetic properties of Ru5+ triangular lattice antiferromagnets β-Li3Mg2RuO6 and Ag3Mg2RuO6 are reported. We successfully synthesized a pseudohexagonal layered rock-salt type phase β-Li3Mg2RuO6 with 2:1 ordering of Mg and Ru, which is a polymorph of an orthorhombic partial ordered rock-salt phase α-Li3Mg2RuO6. Shortening a calcinating time and adding excessive amounts of Li can prevent a polymorphic transformation from β-Li3Mg2RuO6 to α-Li3Mg2RuO6. An ordered delafossite compound Ag3Mg2RuO6 has been obtained by topochemical molten salt ionic exchange reaction to β-Li3Mg2RuO6. In β-Li3Mg2RuO6 and Ag3Mg2RuO6, multiple superexchange pathways Ru5+–O2−–O2−–Ru5+ leads to large antiferromagnetic interactions of θW ​= ​−113.9 and −108.1 ​K, respectively, despite a long distance between the magnetic Ru5+ ions. In addition, β-Li3Mg2RuO6 and Ag3Mg2RuO6 exhibit antiferromagnetic orderings with a trace of spin glasslike contribution at TN ​= ​13 and 24 ​K, respectively, which is evidenced by the heat capacity measurement. While β-Li3Mg2RuO6 exhibits a magnetic behavior that follows the Curie-Weiss curve up to just above TN, Ag3Mg2RuO6 exhibits a magnetic behavior that deviates from the Curie-Weiss curve below 100 ​K, which is considerably higher than TN. The different magnetic behaviors suggest a difference in magnetic dimensionality, indicating that the difference in the coordination environment around interlayer between Li+ and Ag+ ions gives rise to considerably different interlayer superexchange pathways in both systems.

Compositional ordering in relaxor ferroelectric Pb(BB′)O3 : Nearest neighbor approach

Relaxor ferroelectrics, which form a peculiar class of functional materials, are often composed of complex perovskites $\mathrm{Pb}({BB}^{\ensuremath{'}}){\mathrm{O}}_{3}$, as represented by $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$ where the compositional ordering of Mg and Nb is believed to be essential to its relaxor properties. In this work, analysis using a first-principles-based model shows that, while the electrostatic interactions are important, the nearest neighbor assumption, which was used for metallic alloys, can be adopted to understand the compositional ordering in $\mathrm{Pb}({BB}^{\ensuremath{'}}){\mathrm{O}}_{3}$. Numerical simulations with the Kawasaki Monte Carlo method can model the experimentally observed compositional ordering by maximizing the number of the unlike $B\text{\ensuremath{-}}{B}^{\ensuremath{'}}$ pairs (or the Bethe's parameter), which is the overriding factor that determines the ordering. Subtle points of configuration energy degeneracy are also discussed, which explains the partial disorder inherently present in such systems.

Interfacial bonding of CuZr metallic glass via oxide: A molecular dynamics study

A layer of oxygen is introduced into a Cu64Zr36 MG to achieve interfacial bonding. The oxidation kinetics, diffusion behavior, local structure, and mechanical performance of the oxide-bonded MG were investigated via molecular dynamics simulations. The growth of the oxide layer follows the inverse-logarithmic law, indicating that this process is controlled by the ionic drift through the oxide in response to electric fields. The introduction of oxygen atoms seriously deteriorates the short-range ordering of MG by suppressing the formation of icosahedral clusters. Uniaxial tensile tests indicate that the oxide-bonded MG has favorable ductility, while its ultimate tensile strength is reduced.

Warwickite from St. Lawrence County, New York: Mineral association, chemical composition, cation ordering, and splitting of the warwickite M1 site

ABSTRACTWarwickite has been discovered in the Edwards and Balmat #3 mines in the Balmat-Edwards mining district, St. Lawrence County, New York, located in the Adirondack Lowlands. The samples from the two mines are similar in chemistry and atomic arrangement but differ chemically from previously described samples; they are among the most Fe-poor samples described to date. The warwickite in the Edwards Mine sample occurs as 1–2 mm-diameter green crystals associated with pink spinel, forsterite, phlogopite, and pyrite in an impure dolomitic marble, whereas warwickite in the specimens from the Balmat #3 mine, approximately 10 km distant, occurs as brown to amber colored, slender, elongate, millimeter-size crystals in a calcitic marble in association with pink spinel, phlogopite, anhydrite, pyrite, and galena. Chemical analyses of the two specimens by electron microprobe show similar empirical formulas of (Mg1.43Ti0.36Al0.18Cr3+0.02Zr0.01)Σ2.00B0.98O4 (Edwards Mine) and (Mg1.39Ti0.40Al0.18Cr3+0.01Zr0.01Fe2+0.01)Σ2.00B0.94O4 (Balmat mine). The atomic arrangement of a specimen from each mine was determined, and the high-precision refinements provide new insight into the warwickite structure. The M1 site in warwickite is split into two sites to accommodate two occupants with differing bonding requirements; the M1 site contains Mg and the M1′ site hosts Ti, with the two sites being separated by approximately 0.2 Å. The optimized structural formula for both warwickite samples is similar to [M1(Mg0.84Al0.14Ti0.024+)2.74M1′(Ti0.914+Mn0.082+Mg0.01)1.30]Σ4.04M2(Mg0.86Al0.10Ti0.044+)4.00B4O16], demonstrating ordering of Mg at M1 and M2 and Ti at M1′. The site-splitting demonstrates how divalent Mg and tetravalent Ti can exist at a site in solid solution by ordering the two cations at split sites.

Local atomic order and hierarchical polar nanoregions in a classical relaxor ferroelectric

The development of useful structure-function relationships for materials that exhibit correlated nanoscale disorder requires adequately large atomistic models which today are obtained mainly via theoretical simulations. Here, we exploit our recent advances in structure-refinement methodology to demonstrate how such models can be derived directly from simultaneous fitting of 3D diffuse- and total-scattering data, and we use this approach to elucidate the complex nanoscale atomic correlations in the classical relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN). Our results uncover details of ordering of Mg and Nb and reveal a hierarchical structure of polar nanoregions associated with the Pb and Nb displacements. The magnitudes of these displacements and their alignment vary smoothly across the nanoregion boundaries. No spatial correlations were found between the chemical ordering and the polar nanoregions. This work highlights a broadly applicable nanoscale structure-refinement method and provides insights into the structure of PMN that require rethinking its existing contentious models.

Relaxor Behavior in Ordered Lead Magnesium Niobate (PbMg1/3Nb2/3O3) Thin Films

AbstractThe local compositional heterogeneity associated with the short‐range ordering of Mg and Nb in PbMg1/3Nb2/3O3 (PMN) is correlated with its characteristic relaxor ferroelectric behavior. Fully ordered PMN is not prepared as a bulk material. This work examines the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg2/3Nb1/3)O3 and PbNbO3, as suggested by the random‐site model. 100 nm thick, phase‐pure films are grown epitaxially on (111) SrTiO3 substrates using alternate target timed pulsed‐laser deposition of Pb(Mg2/3Nb1/3)O3 and PbNbO3 targets with 20% excess Pb. Selected area electron diffraction confirms the emergence of (1/2, 1/2, 1/2) superlattice spots with randomly distributed ordered domains as large as ≈150 nm. These heterostructures exhibit a dielectric constant of 800, loss tangents of ≈0.03 and 2× remanent polarization of ≈11 µC cm−2 at room temperature. Polarization–electric field hysteresis loops, Rayleigh data, and optical second‐harmonic generation measurements are consistent with the development of ferroelectric domains below 140 K. Temperature‐dependent permittivity measurements demonstrate reduced frequency dispersion compared to short range ordered PMN films. This work suggests a continuum between normal and relaxor ferroelectric behavior in the engineered PMN thin films.

Microscopic strain in a grossular-pyrope solution anti-correlates with excess volume through local Mg-Ca cation arrangement, more strongly at high Ca/Mg ratio

Unit-cell volume and microstrain of Py 40 Gr 60 garnets vary with synthesis temperature and annealing time, showing a strong negative correlation, as is also seen in another garnet solid solution, Py 20 Gr 80 . This anti-correlation is explained by local Ca-Mg cation arrangement in which Ca-Ca and Mg-Mg third-nearest-neighbor (Same 3NN = S3NN) pairs form at rates other than those expected from random Ca-Mg distribution. S3NN pairs cause microstrain (Bosenick et al. 2000) but allow more efficient packing than random Ca-Mg pairings that contribute to excess volume, hence smaller cell volumes correlate with more microstrain. Both longer annealing time and higher heating temperature cause more S3NN formation, larger microscopic strain, and smaller unit-cell volume. The anti-correlation of microstrain and excess volume is weaker in our previous study of pyrope-rich solutions (i.e., Py 80 Gr 20 , Du et al. 2016) because excess volume varies little from Ca-Ca S3NN pairings in pyrope-rich solutions, whereas Mg-Mg S3NN pairings in grossular-rich solutions studied here are effective at reducing excess volume. Heating to 600 °C under room pressure or cold hydrostatic compression to 10 GPa does not reset microstrain. Margules’ formulations for microstrain and volume as a function of Ca/Mg ratio captures these features, especially the two-peaked distribution of microstrain with composition discovered by Du et al. (2016). The similar two-peaked distributions of microstrain and excess energies derived from ab initio calculation with short-range ordering of Mg and Ca cations (Vinograd and Sluiter 2006) indicate that the macroscopic thermodynamic mixing properties of solid solutions are directly related to arrangement of cations with large size misfit. The observed changes of microstrain with annealing temperature suggest that mixing properties measured from our pyrope-grossular garnet solid solutions synthesized at same temperature can serve as better experimental constrains for computational work.

Thermodynamic Origin of Irreversible Magnesium Trapping in Chevrel Phase Mo6S8: Importance of Magnesium and Vacancy Ordering

The rechargeable magnesium battery is an alternative to current Li-ion technologies, potentially offering a higher energy density by employing metal magnesium as an anode material. The realization of a magnesium battery, however, is hampered by the barrier to finding a cathode material that reversibly stores and releases Mg ions through electrochemical intercalation. Understanding the underlying mechanism that prevents successful Mg intercalation is now crucial for the design and exploration of new cathode candidates. Our work reports the critical effect of a thermodynamic factor, the ordering of Mg and interstitial vacancies, on the activity of a Chevrel phase Mo6S8 cathode. Specifically, we demonstrate that the irreversible trapping in the Chevrel phase at low Mg concentrations is thermodynamically driven by the ordering of Mg and vacancies instead of being kinetic in origin. Through a combination of nudged elastic band, geometry-confined static calculation, and ab initio molecular dynamics methods, we ...

Microstrain in pyrope-grossular garnet solid solution at high pressure: a case study of Py90Gr10 and Py10Gr90 up to 15 GPa

Single-phase, well-sintered, translucent polycrystalline garnets with compositions of Py90Gr10 and Py10Gr90 were synthesized at 6 GPa and 1400 °C using a multi-anvil apparatus. X-ray diffraction (XRD) data for these garnet solid solutions were collected with both high-resolution synchrotron X-ray and standard laboratory X-ray sources. Analysis of the FWHM of the XRD peaks using Williamson–Hall plot yields microstrains around 0.12% for Py90Gr10 and 0.09% for Py10Gr90. The FWHM of Py10Gr90 garnet as well as the derived microstrain remains constant up to 11 GPa, followed by a continuous increase to the experimental peak pressure 15 GPa caused by elastic strain in response to deviatoric/anisotropic stresses. The FWHM and microstrain for Py90Gr10 remain constant to the measurement limit at 7 GPa. The microstrain of pyrope-grossular garnets exhibits a nonlinear dependence on composition, showing two peaks near Py20Gr80 and Py80Gr20, which may be associated with local structural heterogeneities arising from Mg and Ca substitution. Using a third-order Birch–Murnaghan equation of state, the bulk modulus is constrained to be Κ 0 = 171.8 ± 2.1 GPa (with Κ 0 ′ fixed to 5.92) for Py10Gr90 and Κ 0 = 174.3 ± 2.5 GPa (with Κ 0 ′ fixed to 4.4) for Py90Gr10, both of which are much larger than that for intermediate composition close to Py50Gr50 but comparable to that for their corresponding end members. The relatively larger microstrain and higher bulk moduli for Py10Gr90 and Py90Gr10 garnets could be related to short-range ordering of Mg and Ca cations in garnet structure due to substitution, which results in different local environments for Mg and Ca cations along the pyrope-grossular solid solution.

Thermal equation of state of NaMg0.5Si2.5O6 and new data on the compressibility of clinopyroxenes

The results of studies of the P-V-T equations of state (EOS) of Na-pyroxene using the multi-anvil technique and synchrotron radiation at pressures up to 15.3 GPa and temperatures up to 1673 K are presented. By fitting the Birch-Murnaghan EOS, the following parameters were determined: V 0 = 407.2 (5) A3, the space group P2/n, K T0 = 103 (2) GPa, K T0 = 6.2 (7), ∂K T /∂T = −0.018 (7), α = 3.38(13) + 0.65(62)T. Thus, despite the small volume of the cell, Na-pyroxene has a sufficiently high bulk modulus. This can be caused by the appearance of antipathetic bonds in Na-polyhedron, Si-tetrahedra rotation, and the ordering of Mg and Si cations in the M1 position. Thus, it is substantiated that the phase transformations in the minerals accompanied by the presence of Si in octahedral coordination are characterized by a significant change in the physical characteristics, such as density (ρ) and bulk modulus (K T ). Such transformations occurring in the minerals and deep Earth can lead to significant jumps in the seismic wave velocities. Therefore, the presence of phases with silicon in sixfold coordination, such as Na-Ca majoritic garnet is of fundamental importance for understanding the Earth’s upper mantle.

Effect of different thickness crystalline SiC buffer layers on the ordering of MgB2 films probed by extended x-ray absorption fine structure

Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful method to investigate the local structure of thin films. Here, we have studied EXAFS of MgB2 films grown on SiC buffer layers. Crystalline SiC buffer layers with different thickness of 70, 100, and 130 nm were deposited on the Al2O3 (0001) substrates by using a pulsed laser deposition method, and then MgB2 films were grown on the SiC buffer layer by using a hybrid physical-chemical vapor deposition technique. Transition temperature of MgB2 film decreased with increasing thickness of SiC buffer layer. However, the Tc dropping went no farther than 100 nm-thick-SiC. This uncommon behavior of transition temperature is likely to be created from electron-phonon interaction in MgB2 films, which is believed to be related to the ordering of MgB2 atomic bonds, especially in the ordering of Mg–Mg bonds. Analysis from Mg K-edge EXAFS measurements showed interesting ordering behavior of MgB2 films. It is noticeable that the ordering of Mg–B bonds is found to decrease monotonically with the increase in SiC thickness of the MgB2 films, while the opposite happens with the ordering in Mg–Mg bonds. Based on these results, crystalline SiC buffer layers in MgB2 films seemingly have evident effects on the alteration of the local structure of the MgB2 film.

The 3.65 A phase in the system MgO-SiO2-H2O: Synthesis, composition, and structure

The 3.65 A phase, a member of the family of dense hydrous magnesium silicates (DHMS) in the system MgO-SiO 2 -H 2 O, was synthesized in a 77 h multi-anvil press experiment at conditions of 10 GPa and 425 °C by using a gel of composition MgSiO 3 plus water in excess as starting materials. From our multi-methodical study including SEM, TEM, EMP, IR, and Raman analysis, we determined the composition of the 3.65 A phase to be MgSi(OH) 6 . Powder XRD combined with Rietveld refinement revealed the 3.65 A phase to be isostructural with δ-Al(OH) 3 . The 3.65 A phase can be described as a hydrous A-site vacant perovskite with probably long-range random distribution of Si and Mg at octahedral sites. Locally, some ordering of Mg and Si might exist, as indicated from the spectroscopic measurements. The 3.65 A phase represents the second DHMS with exclusively sixfold-coordinated Si, the other being phase D. The 3.65 A phase is stable at pressures above about 9.0 GPa and temperatures below 500 °C. This limited P-T stability together with its high water content makes the 3.65 A phase an unrealistic mantle component. If at all, it might only occur under hydrous conditions in the coldest parts of deeply and extremely fast subducted old oceanic slabs.

Octahedral tilt twinning and compositional modulation in NaLaMgWO6

A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO(6). Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 x 7.8 x 7.9 A, which corresponds to a 12a(p) x 2a(p) x 2a(p) superstructure of the simple Pm3m perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a(-)a(-)c(0) with tilt angles of approximately 8 degrees about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6a(p). Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images.

The crystal structure of an iron-rich variety of zanazziite belonging to heteropolyhedral framework roscherite-group beryllophosphates

The iron-rich variety of zanazziite Ca2[Mg0.65Fe0.35□1.0][Mg1.90Fe1.25Al0.5Mn0.35]Σ4Be4(PO4)6(OH)4(H2O,OH)2 · 4H2O, which is a heteropolyhedral framework roscherite-group beryllophos-phate from the Sapucaia pegmatite (Minas Gerais, Brazil), was studied by X-ray diffraction. The refinement was carried out in the triclinic and monoclinic systems. It was found that the cation distribution on octahedral sites in the crystal structure is in better agreement with the monoclinic symmetry (a = 15.876 A, b = 11.860 A, c = 6.607 A, β = 95.49°, sp. gr. C2/c). In the sample under study, no ordering of Mg or Fe atoms in octahedral sites is observed in sp. gr. P \( \bar 1 \), unlike the more iron-rich member of the roscherite group (atencioite).

An order-disorder model for omphacitic pyroxenes in the system jadeite-diopside-hedenbergite-acmite, with applications to eclogitic rocks

A new thermodynamic model for sodic pyroxenes involving jadeite-diopside-hedenbergite-acmite is presented. This model allows for ordering of Mg, Al, Fe2+, and Fe3+ on the M1 sites, with coupled Na and Ca ordering on the M2 sites. It is calibrated on the basis of experiments in three chemical subsystems together with available information on ordering in different pyroxenes and on the limited calorimetric data. Central to the determination of the parameters of the model is the use of relationships among the end-member Gibbs energies and the interaction energies in the various possible non-independent sets of end-members. An important aspect of this model, which uses the symmetric formalism, is that Fe-Mg (FM) and Al-Fe3+ (AF’) mixing is not assumed to be ideal. The model accounts successfully for the experiments at both 600 °C and at higher temperatures involving ordered and disordered pyroxenes coexisting with albite and quartz in NCMAS, NCFAS, NF’AS systems as well as the available calorimetry. It is also able to predict the positions and slopes of tielines in coexisting jadeite + omphacite and omphacite + augite found in nature at lower temperatures. Although the model requires a large number of energy parameters, some of these are not critical to the behavior of the model, while for others the constraints from experiment, calorimetry, ordering state and solvi lead to very limited allowable combinations. The model places some restrictive constraints on the shape of the phase relations in the jadeite–augite–acmite system. Petrological applications of the model are illustrated via a phase diagram example for a MORB bulk composition eclogite.

Chopinite, [(Mg,Fe)3(PO4)2, a new mineral isostructural with sarcopside, from a fluorapatite segregation in granulite-facies paragneiss, Larsemann Hills, Prydz Bay, East Antarctica

Chopinite, the Mg-dominant analogue of sarcopside, is a new mineral corresponding to synthetic Mg 3 (PO 4 ) 2 -II, a high-pressure polymorph of the meteoritic mineral farringtonite. A representative electron-microprobe analysis is SiO 2 0.32, P 2 O 5 47.32, Al 2 O 3 0.05, MgO 30.35, MnO 0.15, FeO 20.99, CaO 0.35, F 0.02, Cl 0.01, Sum 99.54 wt%, which gives Ca 0.02 Mg 2.20 Fe 0.86 Mn 0.01 Si 0.02 P 1.95 O 8 . Single-crystal X-ray diffraction gives monoclinic symmetry, P 2 1 /c, a = 5.9305(7) A, b = 4.7583(6) A, c = 10.2566(10) A, = β 90.663(9)°, V 289.41(6) A 3 , calculated density 3.34 g/cm 3 , Z = 2. Chopinite is of the olivine structure type, but with ordered vacancies and strongly distorted octahedra due to the valence 5+ for P, which results in marked ordering of Mg at M2, whereas Fe 2+ concentrates at M1, most likely because of its axial symmetry. The strongest lines in the powder pattern [ d in A, ( I calc ), ( hkl )] are 5.92 (42) (100), 3.84(100) (102), 3.48(52) (111, 012, 111), 2.51(72) (113, 113), 2.44 (73) (211, 211). Chopinite is colorless and transparent, biaxial (−), α 1.595(2), β1.648(2), γ1.656(2) (589 nm). 2V x (meas.) = 40(2)°, 2V x (calc.) = 41°; X // b , Z ^ a ~55°. Chopinite is found as four inclusions isolated in a fluorapatite segregation in a quartz mass in a paragneiss from Brattnevet, Larsemann Hills, East Antarctica. Grains are mostly anhedral and range from 0.1 × 0.3 mm to 0.2 × 0.6 mm in size. Minerals present in the chopinite-bearing specimen include wagnerite- Ma 5 bc , xenotime-(Y), stornesite-(Y), P-bearing K-feldspar and plagioclase, Ti-rich biotite, sillimanite, orthopyroxene, sapphirine, hercynite, and corundum. It is inferred to have formed as a result of high melt P concentrations by reaction of biotite with an anatectic melt in which P/Ca ratio exceeded that buffered by apatite saturation due to the very slow diffusion of P relative to Ca in anatectic melt.

Temperature-dependent Mössbauer and dielectric studies of Mg 0.95Mn 0.05Fe 1.0Ti 1.0O 4

The effect of tetravalent Ti +4 substitution in Mg 0.95Mn 0.05Fe 2O 4 on its magnetic and electrical properties has been studied using X-ray diffraction, Mössbauer spectroscopy, isothermal dc magnetization and dielectric measurements. X-ray diffraction studies have shown the structural transformation from cubic to tetragonal with the Ti +4 substitution. The Mössbauer spectra of Mg 0.95Mn 0.05Fe 1.0Ti 1.0O 4 recorded in the temperature range 20–300 K shows the presence of the magnetic as well as quadrupole interactions. The isothermal hysteresis loop infers that the system exhibits a ferrimagnetic ordering at room temperature. The Zero-field-cooled (ZFC) and field-cooled (FC) magnetization studies support ferrimagnetic ordering of Mg 0.95Mn 0.05Fe 1.0Ti 1.0O 4 at room temperature. Signatures of ferroelectric transition have been observed in the temperature range 200–300 K from dielectric measurements. The observed magnetic and dielectric behaviour indicate that this material exhibits multiferroic behaviour.

TEM Characterization of Nanostructured MgAl2O4 Synthesized by a Direct Conversion Process from γ‐Al2O3

Nanostructured MgAl2O4 spinel was synthesized by a direct conversion process from cubic γ‐Al2O3. The effect of post‐annealing temperature (300°, 500°, and 800°C) on MgAl2O4 phase formation was investigated using transmission electron microscopy, selected area electron diffraction (SAED), electron energy loss spectroscopy (EELS), and energy‐dispersive spectroscopy (EDS). Relative diffraction intensities as well as lattice parameter measurements from SAED revealed that MgAl2O4 spinel structure starts forming at temperatures as low as 300°C. EELS and EDS spectrum images also revealed an increase in elemental homogeneity with increasing annealing temperature. The degree of ordering of Mg and Al between octahedral and tetrahedral sites has been determined from relative diffraction intensities. Results show that annealing to 800°C leads to a spinel phase with an order parameter of 0.78.

Tailoring the microwave dielectric properties of Ba(Mg 1/3Ta 2/3)O 3 ceramics

Ba(Mg 1/3Ta 2/3)O 3 (BMT) is a very important microwave dielectric resonator material with a high dielectric constant of about 25, high quality factor and small temperature variation of resonant frequency. The preparation temperature of BMT ceramics is relatively high, about 1650 °C. The microwave quality factor of BMT depends on the ordering of Mg–Ta–Ta ions on the perovskite B-site. In the present paper we report how one can tailor the properties of BMT ceramics by glass addition, slight non-stoichiometry and by dopant addition. (a) It is found that addition of small amount of glasses such as B 2O 3, ZnO–B 2O 3, ZnO–2B 2O 3, ZnO–B 2O 3–SiO 2 reduces the sintering temperature, increases density, order parameter and quality factor. (b) Slight Mg or Ba deficiency improves densification, order parameter and quality factor whereas excess Mg or Ba deteriorated the properties (c) Small amounts of dopants such as Sb 2O 5, MnCO 3, ZrO 2, WO 3, SnO 2 and ZnO improve the microwave dielectric properties. It is found that the quality factor is maximum when the ionic radii of the dopant ions are close to the weighted average ionic radii of B site ions (i.e. Mg 1/3Ta 2/3), which is 0.653 Å.