Multiple-phase Samples Research Articles

Calculation of pair distribution functions for multiphase systems

The total scattering method is becoming increasingly popular because of its ability to investigate the structures of disordered crystalline and amorphous materials. Also, in recent years, significant development of total scattering instruments and sample environments has allowed for the study of increasingly complex materials, including multiphase samples. The total scattering formalism has already been well described in the paper by Keen [J. Appl. Cryst. (2001), 34, 172–177] but it was limited to the single phase case. In the present paper the formulae for multiple phase samples (consisting of a physical mixture of two or more distinct phases) are derived for the calculation of pair distribution functions for analysis using reverse Monte Carlo and other methods. The equations for conversion between different representations of the pair distribution function are also provided.

双端固支谐振梁动态响应分析

谐振式传感器的高动态应用近年来得到越来越多的关注。典型谐振式传感器利用反映被测量的轴向载荷调制谐振梁的固有频率实现这种映射。高动态应用中的核心问题是动态轴向载荷下谐振梁的振动特性。本文以微元法为基础，利用基本的微元力学平衡关系建立了动态轴向力作用下谐振梁振动的数学模型，利用Mathieu方程的一般形式进行分析，引入了等效电路方法进行模型求解。通过对等效电路的仿真，得到了谐振梁在典型动态载荷下的振动响应。此外，本文研究了阻尼对谐振梁的影响，得出阻尼项仅影响谐振梁的振幅，基本不影响谐振梁的频率的结论。 The resonant sensor has attracted more attention because of its high sensitivity, small footprint, stability, compatibility with multiple-phase samples. The typical resonant sensor measures reso-nant frequency modulated by axial load to realize mass sensing. Dynamic characteristic is an im-portant factor to evaluate stability of resonant beam, and the key point is to analyze the dynamic response of the resonant beam under dynamic axial load. The article is based on infinitesimal method; mathematical model of vibration of resonant beam impacted by dynamic axial force was established through the resonant beam micro mechanical balance and analyzed through Mathieu equation. Equivalent circuit method was chosen to solve vibration model. The simulation of the circuit shows the dynamic response of resonant beam under the typical axial load. Besides, the article studied the effect of damping on the resonant beam and concluded the damping only influenced on vibration amplitude scarcely on frequency.

B Cation Ordered Double Perovskite Ba2CoMo0.5Nb0.5O6-δ As a Potential SOFC Cathode

This paper reports the evaluation of the cubic B site cation-ordered double perovskite system Ba2Co2−x(Mo1/2Nb1/2)xO6, resulting in the single phase composition Ba2CoMo0.5Nb0.5O6−δ (BCMN) with a mixed Co charge state stabilized by a combination of Mo and Nb doping as a new mixed conductor with potential SOFC cathode applications. X-ray, neutron, and electron diffraction show that hexagonal intergrowths found in multiple phase samples at lower Mo/Nb contents are suppressed in BCMN, which has large domains of rock-salt ordered B site cations with separate Co and Mo/Nb sites. Conductivity measurement and impedance spectroscopy investigation shows that BCMN has a considerably reduced dc conductivity compared with materials such as BSCF but exhibits comparable electrochemical properties to some existing cathode materials in symmetrical cell measurements, and shows higher structural stability and reduced reactivity with the Ce0.8Sm0.2O2−δ (SDC) electrolyte. The role of Mo in dioxygen activation is proposed to offset the reduction that the d0 Mo(VI) and Nb(V) cations on the B site produce in the electronic and ionic conductivity.

Intermediate phases during alkali metal intercalation in HfNCl

The mechanism of the chemical and electrochemical alkali metal intercalation reactions in β-HfNCl has been investigated through electrochemical potential spectroscopy (EPS), in-situ powder X-ray diffraction during electrochemical intercalation and room temperature chemical intercalation experiments. EPS experiments in lithium cells reveal the presence of a plateau, at 1.8 V vs. Li +/Li 0 accounting for ca. 0.14 mol Li, that indicates the formation of a new intermediate phase, and then a gradual decrease of potential with composition that extends up to very high lithium contents (ca. 1.1 per formula), consistent with the formation of a solid solution. Sodium electrochemical intercalation experiments showed a relatively similar behaviour with a plateau at 1.4 V vs. Na +/Na 0, corresponding to ca. 1.7 V vs. Li +/Li 0. In-situ monitored powder X-ray diffraction electrochemical intercalation experiments showed that the electrolyte solvent (ethylene carbonate/dimethyl carbonate, EC/DMC or propylene carbonate, PC) co-intercalated with the alkaline atom. This leads to a large expansion of the interlayer spacing that reaches a value of 21.06 Å in the lithium co-intercalated phase with EC/DMC, Li x (EC/DMC) y HfNCl, and 22.01 Å in the sodium co-intercalated phase with PC, Na x (PC) y HfNCl. Chemical intercalation using naphthyl-sodium solutions in tetrahydrofuran (THF) leads to solvent-free, multiple-phase samples showing in different proportions the pristine and the superconducting stage 2 and stage 1 phases. The composition of the intercalated samples depends on the pristine sample, the concentration of the naphthyl-sodium solution, the ratio Na:HfNCl and the reaction time. Pristine samples exhibiting low lithium intercalation degree upon electrochemical reduction gave the second stage as the major phase when treated with short reaction times or using low Na:HfNCl ratios, coexisting either with the host or with the first stage phase, whereas stage 1 is obtained as the major phase from pristine samples showing high electrochemical capacities. The staging behaviour and the multiphase nature of these samples account for the wide superconducting transitions and the different critical temperatures observed in these superconductors.

Extrinsic paramagnetic Meissner effect in multiphase indium-tin alloys

The authors report the observation of a paramagnetic Meissner effect (PME) in a two-phase In–Sn alloy in which the phases become superconducting at different temperatures. This observation has been tested and confirmed by constructing an artificial In–Sn sample in which one phase was deliberately encapsulated in another. The authors conclude that PME is extrinsic, rather than intrinsic, and thus describe it as an extrinsic paramagnetic Meissner effect (EPME). It is expected to occur in multiple-phase samples where more than one phase is superconducting and where a suitable microstructural phase distribution is developed. In such samples EPME can be produced at will.

Optical and electrical properties of AlCrN films grown by molecular beam epitaxy

Doping of AlN with Cr at percent level concentrations produces ferromagnetism persisting to above 300K. We have examined the electrical and optical properties of Cr-doped AlN grown by molecular beam epitaxy under conditions that produce single-phase or multiple phase material, as measured by x-ray diffraction. The band gap of single-phase AlN decreases from 6.2 to 6.1eV for a Cr concentration of 2at.%. This change originates from the Franz-Keldysh broadening of the band edge due to potential fluctuations caused by heavy Cr doping. The effect was more pronounced in multiple-phase samples (the secondary phases are Cr2N and AlxCry), producing an apparent band gap of 5.8eV. Two strong defect absorption bands with thresholds of 3 and 5eV are introduced by the Cr doping. The resistivity of single-phase AlCrN samples is higher than the resistivity of similarly grown undoped AlN films. Multiple-phase AlCrN samples show a high conductivity of the hopping type. The optical transmission spectra of multiphase AlCrN indicates appreciable absorption by free carriers and strong scattering, both most likely due to the presence of conducting inclusions.

MarqX: a new program for whole-powder-pattern fitting

MarqXis a computer program for the modelling of powder diffraction data. It can be used for an unconstrained profile fitting (pattern decomposition, PD) or constrained modelling of the whole powder pattern (Pawley method, PM), for single- as well as multiple-phase samples. The program output includes: lattice parameters or peak positions (for PM and PD, respectively), width and shape of the diffraction peak (in terms of half width at half-maximum and mixing parameter of a pseudo-Voigt function), corrected for the instrumental broadening component, intensity, peak area and profile asymmetry. In addition, errors on the goniometer zero and shift in sample position with respect to the goniometric axis can also be modelled, together with distance and relative intensity of the spectral components of the X-ray beam (e.g.Kα1andKα2). Specific output files are provided for line-profile analysis, including the Williamson–Hall plot and Warren–Averbach method.

Superconductivity in multiple phase Sr 2Ln 1−xCa xGaCu 2O 7 and characterization of La 2−xSr xCaCu 2O 6+δ

We have observed the occurrance of superconductivity at temperatures between 40 and 50K for multiple phase samples of Sr 2Ln 1−xCa xGaCu 2O 7 treated at 950–1000°C at 25 atmospheres oxygen pressure. We have not been able to find conditions at oxygen pressures of 25 atmospheres or below which make single phase samples superconducting. We also report the characterization of the properties of the simple double-layer 60K superconductor La 2−xSr xCaCu 2O 6±δ. The optimal properties occur at x = 0.35 and δ = 0.0.