Formation of Ga–Pd–Sc icosahedral quasicrystal and approximant phases

ABSTRACT

We report the formation of an icosahedral quasicrystal and its approximant in the Ga–Pd–Sc alloy. The primitive-type quasicrystal with a six-dimensional lattice constant of 0.713?nm formed in the melt-quenched Ga₅₃Pd₃₀Sc₁₇ alloy, with a similar composition to that of the Ga₅₅Pd₃₀Sc₁₅ 1/1 approximant. The atomic-scale observation and chemical analysis of the 1/1 approximant by scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy showed that the approximant consisted of Tsai-type clusters with a characteristic chemical ordering. Furthermore, a series of approximants were observed in the Ga₅₅Pd₃₀RE₁₅ alloys by replacing Sc with other rare-earth elements (REs) (RE?= Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). These approximants, which have relatively small lattice constants and consequently smaller RE–RE distances compared with those for other RE-containing Tsai-type approximants, may be candidates for materials with novel electronic and magnetic properties similar to those observed in Au-based quasicrystals and approximants.     

{ }-{ } Double twinning in magnesium

Microstructural investigations have been carried out on a fully lamellar Ti₄₉Al₄₇Cr₂Nb₂     

Interactions between interfacial dislocations and γ/γ′ interface during high temperature – low stress creep in nickel-based single crystal superalloy

ABSTRACT

The interaction between interfacial dislocations and γ/γ′ interface is critical to the high temperature creep properties of single crystal superalloys. However, only a few studies have paid attention to the detailed structure such as local interfacial morphologies and the elemental distribution around interfacial dislocations. In this paper, the interfacial protrusions and related dislocations in a single crystal superalloy after creep at high temperature – low stress have been investigated in detail. It is found that the morphology and size of the interfacial protrusions remain almost the same during the early and middle stages of high temperature creep, which indicates a local equilibrium at the interfacial protrusions. Steps at different height are formed at the γ/γ′ interface at the initial stage of high temperature creep since dislocations could move along the γ/γ′ interface, which indicates that dislocation motion at different creep stage may affect the morphology of γ/γ′ interface.     

Room temperature ferromagnetism and photoluminescence of nanocrystalline Zn1 − xCoxO thin films prepared by sol–gel MOD

Zn_1???xCo_xO (ZC) [x?=?0, 1, 3, 5, 7 and 9?mol%] thin films were prepared by sol–gel combined metallo-organic decomposition method. The films were deposited on the Si substrate with spin-coating technique and annealed at 600?°C for 3?h. X-ray diffraction pattern shows the formation hexagonal wurtzite phase and distortion (c/a) decreases with increasing Co concentration in ZnO. The average grain size is measured using Scherer relation. Atomic force microscopy is used to confirm the formation of nanograins resulted by the use of polyethylene glycol as surfactant. The photoluminescence was recorded by using He-Cd laser of excitation wavelength 325?nm in wavelength region of 350–650?nm which exhibits some influence of Co doping on the multiplication of defects such as O vacancies, Zn interstitials and grain boundary defects. All thin films show room temperature ferromagnetism except pure ZnO which is diamagnetic and 9?mol% of Co shows paramagnetism. This behaviour is interpreted as due to fluctuations in the magnetic ordering, depending on grain size and site location in grain boundaries or oxygen vacancies.     

Formation of FeNi with L10-ordered structure using high-pressure torsion

FeNi with the L1₀-ordered structure is formed over an astronomical timescale in meteorites. In this study, severe plastic deformation using high-pressure torsion (HPT) is employed for the production of the L1₀ structure in the laboratory. Its formation is confirmed by X-ray diffraction analysis and transmission electron microscopy. Processing of elemental nanopowders by HPT is an effective method for the formation of the L1₀ phase, which is enhanced by the addition of Co to FeNi or annealing after HPT. The formation of the phase must be associated with enhanced diffusion through HPT.     

Quantification of dislocation structures at high resolution by atomic force microscopy of dislocation etch pits

Atomic force microscopy of dislocation etch pit structures is a convenient means of characterising the dislocation structure in etchable materials at high resolution for dislocation spacing extending down to 25 nm . This is demonstrated for single crystals of CaF₂. The local deformation zone generated around nanoindents at ambient temperature and the low-angle boundaries generated in the bulk during uniaxial compression at elevated temperatures are presented as examples.     

Secondary defects induced by ion and electron irradiation of GaSb

Secondary defects induced by ion and electron irradiation up to 6?dpa (displacements per atom) at liquid-nitrogen temperature in GaSb thin films are compared. For Sn ion (60?keV) irradiation, voids were observed. However, for high-energy electron (2?MeV) irradiation, interstitial-type dislocation loops were produced. The densities of voids and interstitial-type dislocation loops were almost equivalent (8?×?10¹⁴?voids/m² and 3?×?10¹⁴?loops/m²) after irradiations at the same damage level of 6?dpa. It is concluded that the formation of voids by ion irradiation follows the creation of localised vacancy defects in cascade damage.     

Effect of cooling rate on size-dependent atomic ordering of CoPt nanoparticles

We report on the effect of cooling rate on the size-dependent atomic ordering of CoPt nanoparticles using aberration corrected high-resolution transmission electron microscopy. It was found that cooling rate plays a crucial role in promoting atomic ordering during the cooling process after annealing. Nanoparticles of ≈3?nm in diameter show the A1-disordered phase after annealing at 873?K for 1?h followed by rapid cooling (110?K/min), while the L1₀-ordered phase is obtained when the cooling rate is slow (1.5?K/min). The disordered phase is also obtained by rapid cooling after annealing at 973?K for 1?h. These results unambiguously indicate that the order–disorder transformation temperature is reduced to a temperature at least lower than 873?K for CoPt nanoparticles smaller than 3?nm in diameter. The slow cooling process promotes the atomic ordering, which resulted in an enhancement of magnetic coercivity as high as 2200?Oe. This study demonstrates that hard magnetic properties of the CoPt nanoparticles can be improved by controlling the cooling rate after heat treatments.     

Healers,Leaders and Entrepreneurs: Shamanic Revival in Southern Siberia

While it is generally agreed that in the postmodern world all tradition is invented, in many post-colonial contexts the emerging identities are spelled out in the idiom of ‘traditional heritage’. This article considers the social field of ‘shamanism’ as it has been shaped in the post-Soviet years in Tuva, an autonomous republic within the Russian Federation in Southern Siberia, and analyses Tuvan shamanism as a product of local historical and social forces, and global processes. Based on both the ethnography of the organisational structure of contemporary Tuvan shamanism, and portraits of different categories of practitioners, the article analyses continuity and change in various aspects of what is locally seen as ‘traditional knowledge’, and discusses different skills, orientations, and divisions of labour among the practitioners. Shamanism in post-Soviet Siberia is seen as a postmodern religious movement enmeshed in global structures and processes, and it is only in this context that a local tradition can become alive and meaningful again.     

A Review of Reviews Examining Neurological Processes Relevant to Impact of Parental PTSD on Military Children: Implications for Supporting Resilience

In this study, 10 recent meta-analytic and systematic review studies were synthesized on the neurological underpinnings of stress and trauma with implications for the impact of parental post-traumatic stress disorder (PTSD) and resilience among military children. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) group guidelines and utilizing a validated quality assessment tool, this systematic review of reviews incorporated results from more than 35,971 individuals with stress exposures, effects, or disorders and healthy controls. This synthesis found support for important gene, physiology, and environment correlations and interactions that predict increased risk for stressful life events and PTSD, but not direct transmission, among military children. Future research is needed to determine if these constitute indirect pathways of intergenerational transmission in military children.