Lutetium and thulium based rare earth bulk metallic glasses

We report the formation of lutetium and thulium based bulk metallic glasses based on the correlations between the thermodynamic, kinetic, elastic and other properties of metallic glasses. The two novel rare earth based bulk metallic glasses (REBMGs) exhibit excellent glass formation ability, high elastic moduli, considerable smaller Poisson’s ratio, high thermal stability, and even higher mechanical strength than that of typical high strength Zr-based BMGs. The reasons for the properties of the Lu- and Tm-based and other REBMGs are discussed.     

Bulk metallic glasses based on binary rare earth elements

Bulk metallic glasses (BMGs) are usually based on single element such as Zr, Cu, and Fe. In this work, we report the formation of a series of BMGs based on arbitrarily selected binary rare earth elements. Compared with single-base BMGs, the binary-base BMGs have unique characteristics of excellent glass-forming ability, tunable physical, chemical and mechanical properties. The binary-base BMGs might be of significance in scientific studies and have potential applications, and the approach for formation of metallic glasses has implications in the search for new BMG systems.     

Heusler compounds and spintronics

Heusler compounds are a large group of intermetallic compounds with over 1000 members with similar crystal structures having a vast array of tunable properties. These properties depend on the number of valence electrons per formula unit allowing tuning of properties through composition and alloying. The Heusler lattice parameters span many metal oxides and semiconductors and their crystal structures are closely related. For spintronic applications, the magnetic and half-metallic properties, in particular, are of great interest. In this paper the electronic and magnetic properties of Heusler compounds are discussed as well as the importance of composition and defect control on tailoring their properties. Examples of applications include the great success of Heusler magnetic tunnel junction in metallic spintronic devices. The potential of going beyond metallic spintronics to the integration of Heusler compounds with III–V semiconductors for semiconductor spintronics device physics and technology, the tuning of magnetic properties, and the fabrication of Heusler compound heterostructures and superlattices are also discussed.     

The structure of SiO2-GeO2 glasses: A spectroscopic study

Four glasses of the SiO₂-GeO₂ binary system have been synthesized via a sol-gel route followed by a heat treatment and a quench. Glass structure has been determined by Ge K-edge X-ray absorption spectroscopy (XAS) at low temperature and Raman spectroscopy. These mixed glasses present a continuous random network of interconnected GeO₄ and SiO₄ tetrahedra, with GeO₄ tetrahedra similar to the GeO₄ units in GeO₂ glass and continuous compositional variations from GeO₂-rich regions to SiO₂-rich regions. Such a random mixture is consistent with physical properties of these binary glasses as well as with the chemical dependence of their polyamorphism at high pressure. This EXAFS-derived mean Ge-O-Si angles are close to the Ge-O-Ge mean angle in GeO₂ glass, 134° and 130°, respectively. This misfit with the Si-O-Si angles might explain the ease of formation of isolated and pair defects centers, which are suspected to be at the origin of photo-induced modifications of optical properties in Ge-bearing SiO₂ glasses.     

High mixing entropy bulk metallic glasses

Bulk metallic glasses (BMGs) are usually based on a single principal element such as Zr, Cu, Mg and Fe. In this work, we report the formation of a series of high mixing entropy BMGs based on multiple major elements, which have unique characteristics of excellent glass-forming ability and mechanical properties compared with conventional BMGs. The high mixing entropy BMGs based on multiple major elements might be of significance in scientific studies, potential applications, and providing a novel approach in search for new metallic glass-forming systems.     

Chemical processing of rare earth chalcogenides

Chalcogenides are compounds containing sulfur, selenium and tellurium and are well known for their semiconducting and optical properties. Their characteristic absorption at low frequencies render these materials excellent for long wavelength transmission. In the past few years, the need for far infrared transmitting materials to be used in target acquisition equipment formed the basis for identifying several new crystalline sulfide materials which transmit into the extended far infrared (IR) spectral region. Rare earth sulfides exhibiting excellent transmission into the far infrared (8-14 μm) emerged as a new group of infrared window materials. This paper reviews the status of binary and ternary rare earth sulfide compounds for optical window application. Conventional and non-conventional techniques used for processing these materials will be discussed in complete detail. The use of metallorganic precursors and modification of the precursor chemistry to tailor the composition of the final ceramic will be described. The potential of these emergent low temperature chemical processing techniques such as sol-gel, precipitation and co-precipitation for synthesis of non-oxide ceramics will also be addressed, particularly in light of their successful application in processing of novel electronic oxide ceramics, glasses and composites.     

Glass-forming Mg-Cu-RE (RE = Gd, Pr, Nd, Tb, Y, and Dy) alloys with strong oxygen resistance in manufacturability

One of the unsolved problems for the manufacturability and the applications of bulk metallic glasses is that their glass-forming ability is very sensitive to the preparation vacuum and impurity of components because oxygen in the environments would markedly deteriorate the glass-forming ability. Here we report that the addition of rare earth elements can significantly improve the glass-forming ability and manufacturability of Mg-based alloys. The Mg-based glass-forming alloys can withstand very low vacuum in preparation process. The beneficial effects of the Gd addition on the glass-forming ability and oxygen resistance during the Mg-based glass formation are explored.     

Optical properties of chalcogenide glasses

Over the past two decades chalcogenide glasses have been researched in order to assess their suitability as passive bulk optical component materials for 3–5μm and 8–12μm infrared applications. This research has led to a greater understanding of the physical properties of these materials, and the present paper concentrates on the optical properties and applications of these bulk chalcogenide glasses. The various factors influencing the intrinsic and extrinsic optical loss mechanisms in materials are discussed, numerical data on the basic optical properties of chalcogenide glasses is presented and applications are discussed.     

Formation and properties of RE55Al25Co20 (RE = Y,Ce, La,Pr, Nd,Gd, Tb,Dy, Ho and Er) bulk metallic glasses

We report that a series of ternary RE₅₅Al₂₅Co₂₀ (RE = Y, Ce, La, Pr, Nd, Gd, Tb, Dy, Ho and Er) alloys can be readily cast into bulk glasses by a conventional casting method. The characteristics and properties of these new bulk metallic glasses (BMGs) are studied and compared. Due to the chemical comparability and well-regulated variety in atomic size, properties and elastic constants of these rare earth elements, the RE₅₅Al₂₅Co₂₀ BMGs could be regarded as a model system to investigate the glass-forming ability, thermal stability, glass transition, crystallization behavior, liquid fragility, elastic and mechanical properties as well as their relationships. An attempt is made to highlight commonality and contrasts of the effects of various factors on the metallic glasses formation and properties.     

Development of quaternary Fe-based bulk metallic glasses with high saturation magnetization above 1.6 T

Quaternary Fe-based ferromagnetic bulk metallic glasses (BMGs) with saturation magnetization above 1.6 T were successfully fabricated in Fe–Si–B–P alloy system by copper mold casting. These BMGs exhibit low coercive force of 1.6–1.9 A/m, high effective permeability of 16,500–17,200 and low core loss. In additional, these BMGs exhibit good mechanical properties as well, i.e., high strength of 3200 MPa and plasticity of 1.1%. They are promising to be used as magnetic functional and structural materials in the future.     

Scratching-induced large-area and tunable perpendicular anisotropy in flexible metallic glass under ambient conditions

The scratching-induced tunable perpendicular anisotropy in amorphous FeSiB ribbon surface has been directly observed in room temperature and air atmosphere. The magnetic stripe domain width and contrast strength can be easily tuned according to the scratch size, and the magnetic signature is erasable in nano-scale by indentation, which greatly facilitates the direct magnetic patterning. The result presents a simple way of fabricating the large-area magnetic film with controllable perpendicular anisotropy, remarkable intrinsic flexibility and high strength directly from amorphous FeSiB ribbon under ambient conditions, which may simulate much scientific and engineering interest, leading to the novel applications of metallic glasses.     

Bulk metallic glasses based on ytterbium and calcium

We report the formation of a family of bulk metallic glasses (BMGs) based on rare earth element of ytterbium and alkaline earth element of calcium. The glass-forming ability, atomic packing density and corrosion behaviors of the BMGs show an extremum around the eutectic point with the change of the concentration of Yb and Ca.     

A7MIIRE2(B5O10)3系列紫外非线性光学晶体的研究进展

稀土硼酸盐非线性光学(NLO)材料由于其在激光技术领域的重要应用而备受关注,这主要是因为三价稀土离子如Y³⁺、Sc³⁺、Lu³⁺等可以有效抑制d-d和f-f电子跃迁从而扩宽化合物的透过范围,同时稀土原子与氧原子结合成畸变的多面体可增强材料的非线性光学效应。A₇M^IIRE₂(B₅O₁₀)₃系列(RE为稀土金属,A为碱金属、M为二价金属)化合物是稀土硼酸盐中一类重要的材料,其A、M以及RE位点具备灵活的占据方式,近年来得到了广泛关注。通过化学元素取代法,研究者们对该类化合物的种类进行拓展,目前已经合成出数十种属于该体系的化合物。这些化合物的截止边大多处在紫外甚至是波长小于200 nm的深紫外波段,非线性光学效应为0.4~2.1倍KDP,在紫外以及深紫外波段非线性光学领域中展现出了应用潜力。本文对其研究现状进行了总结,分析了其微观结构与光学性能之间的关系,并指出不同位点组分对材料非线性光学性能的影响,以期对此类化合物今后的发展提供参考。     

Magnetic resonances of Fe and Ni nanoparticles in films of silicon suboxide produced by ion irradiation of triethoxysilane gels containing Fe or Ni solute atoms

The structure and magnetic properties of composite films obtained by ion irradiation or thermal treatment of triethoxysilane gels containing iron or nickel in solution are investigated by means of X-ray diffraction, electron microscopy and electron spin resonance. Ion irradiated gels are converted into silica glasses containing metallic nanoparticles with a narrow range of sizes. These particles exhibit a magnetic resonance with a preferential alignment of magnetic moments perpendicular to the surface. This unusual out of plane anisotropy seem to be ascribed to an interaction of the moments with radiation defects. The magnetization in irradiated film is comparable to that in films of same materials submitted to a thermal conversion at 1000 °C in vacuum. But the latter films are porous and contain particles of metal and silicide or silicate with a wider range of sizes.     

Dissoluble and degradable CaLi-based metallic glasses

We study the degradable and dissoluble features of a Ca-Li-Mg-Zn bulk metallic glass in pure water at room temperature. A remarkable degradable feature of the metallic glasses is that the degradation is controllable by changing the composition and components. The degradable metallic glasses with superior combined properties of polymer-like thermal plasticity at low temperature (40-70 °C), the ultralow elastic moduli comparable to that of human bones, and ultralow density (< 2 g/cm³) in known metallic glasses to date, and good machinability at a lower temperature in the supercooled liquid region could have potential applications. The metallic glasses also provide a model system to study the corrosion behavior in glasses.     

Elastic constant anomaly in Fe80−xMoxB20 metallic glasses

The extensional sound velocities V_E of Fe_80−xMo_xB₂₀(x = 6, 7, 8) metallic glasses have been measured between 100 and 600 K in a saturating magnetic field. Young's modulus (E = _E², = density) shows anomalous temperature dependence at and below the magnetic transition temperature of each glass studied. These anomalies are interpreted as arising from the change of long-range spin coupling energy at the Curie temperature in a molecular field approximation. Comparison is made with similar effects in other crystalline and non-crystalline magnetic materials.     

The influence of Mg substitution for Al on the properties of SiMeRE oxynitride glasses

The thermal-mechanical properties of 60Si20Mg20RE (RE: rare earth) oxynitride glasses can be tailored by the substitution of rare earths of decreasing ionic size. The Young’s modulus, hardness, glass transition temperature and viscosity all increase with the substitution La by Gd and Gd by Lu while the thermal expansion coefficients decrease. Compared to the 55Si25Al20RE oxynitride glasses, replacement of Al by Mg lowers the glass transition temperatures and viscosities and raises the thermal expansion coefficients substantially. On the other hand, the Young’s moduli are higher in the Mg-bearing glasses. These behaviors are seen to be a result in changes in the nature of the bonding in the glass structure.     

Crystal field effects in amorphous rare earth magnetic materials

A model proposed by Harris et al. in which crystal field affects are important, is extended to consider the magnetic properties of amorphous materials containing localized ionic moments of a single, heavy rare earth, magnetic element. The paramagnetic and ferromagnetic properties are investigated for all the heavy rare earths. It is found that the average spontaneous moment per ion in the amorphous state can be lowered below the free ion moment by more than 50%, but the relative reduction in Curie temperature is much less marked than found by Harris et al.     

稀土元素与In共掺对SnO2导电性能影响的第一性原理研究

AgSnO2触头材料中的SnO2近乎绝缘,为了提高触头材料的电性能提出了稀土材料La、Ce、Y和In共掺杂的方法.采用基于密度泛函的第一性原理对SnO2以及单掺杂稀土元素的SnO2和共掺稀土元素和In的SnO2晶胞进行能带和态密度的计算.结果表明:掺杂后的材料仍旧是直接带隙半导体材料,都具有热稳定性,共掺杂可以进一步使得导带底、价带顶向费米能级附近移动,进而窄化带隙;共掺杂比单掺的电子有效质量小,电导率大,其中Y和In共掺杂的导电性最好.共掺杂比单掺稀土元素更能提高AgSnO2触头材料的导电性,为触头材料的发展提供了理论依据.     

Halide glasses

The reasons for the formation of vitreous materials in halide systems are discussed in relation to the nature of the chemical bond. A review of fluoride, chloride, bromide and iodide glasses is presented and discussed in terms of stability and technical interest. The most interesting physical properties, especially optical, include the potential of ultra-low loss fiber for power and telecommunications applications. Recent structural investigations by X-ray, computer simulation, etc, allow the presentation of structural models explaining the glass formation by references to the corresponding crystalline halide materials. A structural systematic is described and compared with the traditional oxide glasses.