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We demonstrate the origin of the modification to the primary Mg 2 Si phase induced by ultrasonic treatment (UST) of a P-modified Al–Mg 2 Si alloy through combined experimental and theoretical investigations. Multicomponent Al–Mg 2 Si alloys contain various secondary phases including primary Mg 2 Si, Q, Si, θ, and Zn phases. Regardless of the cooling rate, applying UST transforms the coarse, irregular dendritic Mg 2 Si phase into a fine, compact phase. High-resolution transmission electron microscopy revealed that in the absence of UST, the Mg 3 P 2 phase acted as a preferential nucleation site for the primary Mg 2 Si phase. By contrast, when UST was applied, the MgO particles were the main nucleation sites for this phase. First-principles calculations confirmed the higher nucleation potency of the MgO phase compared with that of the Mg 3 P 2 phase. UST resulted in the deagglomeration of MgO particles while improving their wettability to molten Al, allowing the more potent MgO particles to act as nucleation sites for the primary Mg 2 Si phase. Our experimental and theoretical results show that UST alters the primary Mg 2 Si nucleation pathway from the Mg 3 P 2 phase to the more potent MgO particles activated by UST, resulting in a significant modification of the primary Mg 2 Si phase in chemically modified Al–Mg 2 Si alloys. [Display omitted] • Multicomponent Al alloy contains various secondary phases (Mg 2 Si, Q, Si, θ, and Zn). • Mg 3 P 2 phase acts as a preferential nucleation site for Mg 2 Si phase in P-modified alloy. • Ultrasonication converts the coarse dendritic Mg 2 Si phase into a fine compact phase. • UST deagglomerated the MgO particles while improving their wettability to molten Al. • UST alters the nucleation pathway of primary Mg 2 Si from Mg 3 P 2 to more potent MgO. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the relationship between the crystallographic structure of Cu-Sn intermetallic grains and Sn whisker growth was investigated. In order to prevent the influence of the elements in the alloy composition and the effect of the soldering process on the formation of the intermetallic layer, 99.99% pure Sn was vacuum evaporated onto Cu substrates. The Sn layer thickness was sub-micron region (∼400 nm in average) to reach considerable and rapid compressive stress on the tin layer originated by the intermetallic formation. The samples were stored at room temperature for 1 month. Different types of whiskers (nodule and filament) and the layer structure underneath were studied with a scanning ion microscopy and transmission electron microscopy. It was found that not only the thickness of the intermetallic layer and shape of the intermetallic grains affects the whisker growth but the crystallographic structure of the intermetallic grains as well. The susceptibility of the Sn layer to whisker development is higher in those regions where the intermetallic layer is composed of monocrystalline grains instead of those regions, where it is composed of polycrystalline grains. This effect can be explained by the higher compressive stress generated by the monocrystalline intermetallics compared to the polycrystalline ones. Graphical abstract Image 1 Highlights • Crystallographic structure of Cu 6 Sn 5 IMC grains effects on Sn whisker growth. • Sn whiskers are more likely over monocrystalline Cu 6 Sn 5 IMC than over polycrystalline. • This effect could be explained by the high elastic anisotropy of the Cu 6 Sn 5 IMC. • Monocrystalline Cu 6 Sn 5 IMC has higher Young's modulus than the polycrystalline. • Compressive stress on Sn layer is higher over monocrystalline Cu 6 Sn 5 IMC than over polycrystalline. [ABSTRACT FROM AUTHOR]

Abstract Optical and spectroscopic properties of Er3+/Pr3+-codoped Gd 3 Ga 5 O 12 single-crystal grown by Czochralski method have been studied. Absorption spectrum of the crystal was measured at room temperature and Er3+ absorption cross-section spectral distributions were calibrated from it. The Er3+ spectroscopic properties were analyzed on the basis of the Judd-Ofelt theory. Fundamental spectroscopic parameters were obtained that include absorption coefficient, cross-section spectral distribution, electronic transition oscillator strength, Judd-Ofelt parameters, fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency as well. Study shows that Pr3+-codoping results in substantial change of Er3+ spectroscopic properties, in qualitative consistent with the previous fluorescence studying result. In addition, refractive index of the crystal was measured at different wavelengths using prism coupling method, and the Sellmeier equation reported previously for Er3+-only doped Gd 3 Ga 5 O 12 crystal is corrected. Highlights • Juud-Ofelt spectroscopic properties of Er3+/Pr3+:Gd 3 Ga 5 O 12 crystal were studied. • Pr codoping results in substantial increase of the Judd-Ofelt parameters. • Pr codoping induces shortening of Er3+ 2.7 and 1.5 μm lifetimes from ms to sub-ms. • The effect is related to two resonant energy transfers from Er3+ to Pr3+. • Different efficiencies of the two transfers enable to realize 2.7 μm lasing. [ABSTRACT FROM AUTHOR]

Abstract Recently, alluaudite-type cathode materials with two types of large Na tunnels attract considerable attention. Hereby, a compound Na 2 Mn 2 V(PO 4) 3 was synthesized and its high quality single crystals were grown in the NaCl molten-salt media. The single-crystal diffraction data analysis shows that Na 2 Mn 2 V(PO 4) 3 belongs to the typical alluaudite-type structure with unit parameters of a = 12.0533(15) Å. b = 12.5844(16) Å, c = 6.4987(8) Å, β = 114.51(2)˚. The density functional theory calculations based on the nudged elastic band method were used to obtain the migration energy barrier of Na ions in Na 2 Mn 2 V(PO 4) 3 and Na 2 Fe 2 V(PO 4) 3. The results of calculations show that Na 2 Mn 2 V(PO 4) 3 has a better Na+ conductivity than Na 2 Fe 2 V(PO 4) 3. The electrochemical tests also demonstrate that Na 2 Mn 2 V(PO 4) 3 exhibits electrochemical activity operating at an average voltage of 3.5 V (vs. Na/Na+) delivering a capacity of 97 mAh g−1 at 10 mA g−1 rate. Graphical abstract Image 1 Highlights • Na 2 Mn 2 V(PO 4) 3 and Na 2 Fe 2 V(PO 4) 3 crystals were obtained using molten salt method. • Na 2 Mn 2 V(PO 4) 3 and Na 2 Fe 2 V(PO 4) 3 crystallize in the typical alluaudite-type structure. • The DFT calculations show that Na 2 Mn 2 V(PO 4) 3 has better Na+ conductivity. • Na 2 Mn 2 V(PO 4) 3 has 3.5 V average voltage and high capacity. [ABSTRACT FROM AUTHOR]

Abstract The effect of a galia (Ga 2 O 3) addition on the crystallographic phase transformations and the grain growth behavior of yttria stabilized zirconia (YSZ) were investigated regarding powders containing different amounts of galia in the range of 0–25 mol %. Ternary compositions of galia- YSZ sponge-like cryogels were prepared by the sol-gel method combining freeze-drying process and calcination of dried powders at different temperatures for 2 h in air. Crystallographic phase transitions were analyzed via X-ray diffraction (XRD) and exceptional powder particle morphology of internal nano voids derived from the freeze-drying technique was investigated by using Scanning Transmission Electron Microscope (STEM). It was shown that galia supressed the grain growth process in yttria stabilized zirconia and had no effect on the internal voids obtained. Highlights • Galia addition inhibited 8YSZ crystallization and extended the amorphous range. • Galia addition elevated the activation energy for the grain growth process in 8YSZ. • Internal nano-voids were formed via sol-gel synthesis followed by freeze-drying. [ABSTRACT FROM AUTHOR]

Abstract We reported a new layered ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O which crystallizes in two-dimensional (2D) nanosheets morphology in our previous work. Herein, two-dimensional hexagonal ZnCo 2 O 4 nanosheets were synthesized by the thermal transformation of the ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O precursor. Benefiting from this special hexagonal nanosheet morphology, the as-prepared ZnCo 2 O 4 electrode has induced a pseudo-capacitance contribution, leading to a stable discharge capacity of 688 mAh g−1 (at 5.0 A g−1) over 1000 cycles. To the best of our knowledge, the rate performance of ZnCo 2 O 4 for lithium ion batteries (LIBs) is superior to those of previously reported ZnCo 2 O 4 electrodes. Further applied to sodium ion batteries, ZnCo 2 O 4 electrode show fascinating performance with the specific capacity of 463 mAh g−1 after 60 cycles. This study provides a promising strategy for developing high-quality ZnCo 2 O 4 nanosheet electrodes for long-cycle-life and high-power LIBs and sodium ion batteries (SIBs). Graphical abstract Image 1 Highlights • Hexagonal ZnCo 2 O 4 nanosheet has been synthesized from the hydroxide precursor. • Our ZnCo 2 O 4 electrode exhibits high-rate performance for lithium ion battery. • Our ZnCo 2 O 4 electrode show fascinating performance in sodium ion storage. [ABSTRACT FROM AUTHOR]

Abstract Grain size, growth morphology, and grain boundary were considered to affect hardness and fracture toughness of hard coatings. An effective approach is currently developed to improve their hardness and toughness via tailoring their architectures through grain boundary control. V-Al-C coatings consisting of variable architectures were prepared by reactive sputtering V 2 AlC target with different CH 4 flow rates in this study. The results indicated that, when the carbon content increased from 37.32 at.% to 71.4 at.%, the microstructure of V-Al-C coatings was tailored to span a wide changes from coarse columnar grain to fibrous columnar grains and finally to nanocomposite structure consisted of the (V, Al)C nanocrystallites and sp2-rich a-C. Especially, the maximum hardness of 28.74 GPa and the excellent toughness with high H/E value of 0.11 were obtained once the coating displayed fibrous columnar structure, such good mechanical properties benefited the lowest wear rate of 2.8 × 10−16 m3/Nm. Instead, the nanocomposite structure showed the lower fracture resistance due to the dominated amorphous carbon matrix. All coatings with nanocomposite structure exhibited low friction coefficient of ∼0.18, which was attributed to the coupling lubrication originated from both V 2 O 5 Magnéli phases and amorphous carbon formed during friction process. The enhanced mechanical and tribological properties were also discussed in terms of the columnar boundaries evolution as a function of carbon content. Graphical abstract Image 1 Highlights • Significant microstructure changes were tuned with varying the content of a-C. • Coating with fibrous columnar grain rendered enhanced mechanical properties. • The influence mechanism of boundaries on mechanical properties was discussed. • Structure zone diagram with C content was established in this study. • The synergistic lubrication of V 2 O 5 Magnéli phase and amorphous C was observed. [ABSTRACT FROM AUTHOR]

Abstract ZnTe crystal is a promising electro-optical crystal materials applied for THz generation and detection. However, there is still a big challenge to obtain large sized high quality ZnTe crystals. In this work, large sized ZnTe bulk crystals with Φ30 mm × 150 mm were grown by the traveling solvent melting zone (TSMZ) method. With the characterization of the optical and electrical properties of as-grown ZnTe crystals, the band gap (2.22 eV), high IR transmittance (around 60%), high resistivity (3.5 × 103 Ω·cm), low density (1.3 × 105 cm−2) and small sizes (3 μm - 5 μm) of Te inclusions in ZnTe crystals, low etch pit densities (1.5 × 105 cm−2), high peak intensity to FWHM ratio (2.5 × 104) of the LO peak in the Raman spectra were obtained. Furthermore, the THz transmission spectra was measured and the maximum transmittance is more than 40% at the range of 0.3 - 3 THz. Based on these results, high quality and large aspect ratio ZnTe bulk crystals can be obtained by the TSMZ technique. Our work has greatly facilitated the application of ZnTe crystals in THz device. Highlights • Large aspect ratio of ZnTe bulk crystals were successfully grown by TSMZ technique under the condition of seedless. • A large number of high purity ZeTe polycrystallines powder was synthesized successfully. • The optical and electrical properties of different parts of the ZnTe ingot were analyzed. • The transmission properties of THz wave in ZnTe crystal were briefly evaluated. [ABSTRACT FROM AUTHOR]

Abstract Spherical and uniform CuAlMn shape memory foams (SMFs) with quasi-oligocrystalline microstructure and various foam structures were manufactured by the silica-gel beads infiltration method. The strut architecture was quantitatively characterized by strut node size N , strut length L and L/N , and the oligocrystalline degree of foams was characterized by grain size d over N (d/N) for the first time. d/N is found to increase linearly with L/N due to the constricted effect of complex strut architecture on two-dimensional grain growth. The coupling effect of strut sizes and oligocrystalline degree on properties of the SMFs was explored. Too thin struts (smaller N) result in higher quenching rate and consequently more quenched-in vacancies, hindering the thermal-induced martensitic transformation and low-amplitude martensite damping. The peak damping becomes more dependent on d/N and tends to increase with increasing d/N , while the high-amplitude martensite damping improves linearly with d/N. The compression recovery strain also increases linearly with d/N under certain porosity, although higher porosity tends to compromise the favorable effect of higher d/N. The results demonstrate that higher d/N, which corresponds to higher oligocrystalline degree and lower grain constraints, favors the boundary mobility and martensite accommodation and thus improves the damping and compression recovery properties of Cu-based SMFs. Graphical abstract Image 1 Highlights • Oligocrystalline degree of SMFs was quantitatively characterized for the first time. • The strut architecture influences the grain growth and oligocrystalline degree. • Too thin struts hinder the thermal-induced M transition and low-amplitude M damping. • Damping and recovery ability increase linearly with d/N for lower grain constraints. • Relatively high recovery strain remains in high porosity foams with higher d/N. [ABSTRACT FROM AUTHOR]

Two Ce 3+ doped sodium strontium (calcium) silicates, Na 2 SrSi 2 O 6 :Ce 3+ and Na 2 CaSi 2 O 6 :Ce 3+ , were prepared by high temperature solid state reaction. They both crystallize in trigonal crystal system with space group R 3 ¯ m. Substitution of three independent Ca 2+ sites for Ce 3+ ions yields blue emission when excited by UV light (λ e x  = 352 nm). Accordingly, Ce 3+ ions occupying two distinct Sr 2+ sites generate UV to blue light under 300-nm UV excitation. A series of Na 2 Ca 1- x Sr x Si 2 O 6 :Ce 3+ ( x  = 0–1) were prepared. All the samples form solid solutions and are isotypic confirmed by Rietveld refinements. Increasing Sr 2+ content leads to asymmetrical blue shift of PL spectra. Refinement results clarify preferable site occupancy of Sr 2+ in Na 2 CaSi 2 O 6 compound which results in the irregular shift. The migration of Ce 3+ ions between M3 and M4 sites is the key point of this phenomenon. This mechanism could be a guideline to optimize the emissions of emitting centers with multiple sites. [ABSTRACT FROM AUTHOR]

To improve the thermoelectric properties of as-grown electrodeposited films, their crystallinity should be increased by promoting crystal growth and suppressing formation of micro-pores. Here, we prepared as-grown bismuth telluride (Bi 2 Te 3 ) electrodeposited films using sputtered Bi 2 Te 3 seed layers (AES films) on a glass substrate. The seed layers were thermally annealed in advance and the as-grown electrodeposited Bi 2 Te 3 films were formed under galvanostatic conditions in nitric acid-based solution. The in-plane thermoelectric properties of the AES films were measured at approximately 300 K, and the properties of the electrodeposited films alone were calculated from the measured values. The maximum power factor of the as-grown electrodeposited film was 4.2 μW/(cm·K 2 ), which was approximately eight times higher than that of the electrodeposited films grown using a standard method (without the use of the seed layer) mainly because of the significant increase in electrical conductivity. Surface scanning electron microscopy revealed that the AES films consisted of nano-sized crystal grains with densification in the morphology, thus presenting a smooth, homogeneous surface. However, the electrodeposited films obtained using standard methods exhibited dendritic crystals on the top surface, and a large area of micro-pores on the bottom surface of the film after detachment from the substrate. X-ray diffraction analysis clearly showed peaks of the rhombohedral phase of Bi 2 Te 3 in the AES film, indicating that crystal growth also occurred in the electrodeposited film. Therefore, we concluded that the thermoelectric properties of the as-grown electrodeposited Bi 2 Te 3 films increased because of the improved crystallinity and the suppressed micro-pores in the films. [ABSTRACT FROM AUTHOR]

The morphology of microstructure affects the quality of Invar alloy mould when it is repaired with laser melting deposition (LMD). However, it is quite hard to observe the evolution of microstructure in real time. The current study adopted a CA-FE model, i.e, cellular automaton coupled with finite element, to simulate the microstructure evolution of Invar alloy in the LMD process. The mechanism of columnar-to-equiaxed transition in the molten pool was investigated based on the simulation results. In addition, an analysis was completed by comparing the simulation with the experimental results, which verified the feasibility of simulating the microstructure evolution with the CA-FE model in the LMD process. The results indicated that the bottom of the molten pool is filled by the epitaxial growth of columnar grains and the orientation of the columnar grains is consistent with the direction of the maximum temperature gradient in the molten pool. The top of the molten pool is occupied by equiaxed grains. This study provides a referenced value on the quality improvement of the mould repaired by LMD. [ABSTRACT FROM AUTHOR]

Pure kesterite Cu 2 ZnSnSe 4 (CZTSe) absorbers with a large average grain size are vital for high-efficiency CZTSe solar cells, which are greatly influenced by the annealing atmosphere. Sputtered CZTSe precursors were annealed in the presence and absence of a selenium-containing atmosphere, and these materials were incorporated into solar cells. When annealed in an Ar atmosphere, the CZTSe absorbers were found to be composed of small grains with the presence of voids and secondary phases. When H 2 Se was added into the chamber at a temperature of 550 °C, the CZTSe grains increased in size and the presence of the voids and secondary phases reduced. When H 2 Se was added at a lower temperature (300 °C) earlier in the annealing process, the average grain size increased further and device efficiencies were higher. When H 2 Se was continuously added into the chamber during the whole selenization process, the average grain size increased to approximately 2 μm, the undesired secondary phases were not detected and the efficiency of the CZTSe devices reached a maximum of 6.78%. This work showed that exposing the CZTSe precursors to a selenium atmosphere during annealing increased the average grain size and reduced the presence of undesirable secondary phases, thus improving the performance of CZTSe absorbers and solar cells. [ABSTRACT FROM AUTHOR]

In this study, a solution chemical route for the synthesis of ultrafine WC-15 wt %Co cemented carbides was proposed with WC-6Co aggregates as raw materials. The chemical Co was uniformly distributed around the WC-6Co aggregates and the Co layers in the raw materials had been well preserved. During sintering, the chemical Co could diffuse along the Co layers and thus avoid the aggregation and growth of WC grains. Additionally, the homogeneous distribution of Co phase and the existent of Co layers promoted the WC reprecipitations on the same crystal during the solution/re-precipitation process. The fine WC grains and the homogeneous of WC and Co phases resulted in the high hardness and transverse rupture strength. [ABSTRACT FROM AUTHOR]

6H-SiC porous SiC ceramics accompanied by the formation of large clubbed and tabular grains were successfully fabricated at 1800 °C under an applied pressure of 50 MPa for 5 min by spark plasma sintering technique without introducing any pore-creating agent. The phase composition, microstructure and properties of porous SiC ceramics were investigated. The measured porosity of the specimens was 35.7% and the mean pore size varied in the range of 0.3–3 μm. The sintered specimen had a strength of 103 MPa, a fracture toughness of 2.89 MPam 1/2 , and a density of 1.85 g/cm 3 . The mechanisms of porous structure and grain growth were elucidated. [ABSTRACT FROM AUTHOR]

In-situ WC grains were synthesized by using in-situ metallurgical reaction in W-Fe-Ni-C alloys system. The growth mechanisms as well as the coarsening process of WC grains were analyzed by XRD, SEM and ab initio calculation. Results show that the morphology evolution of in-situ WC growth unit evolves from sphere-like→icosahedron→octahedron→truncated-octahedron→flat-tri-prism. The final flat-tri-prism is bound by two basal facets {001} and three prismatic facets { 1 ¯ 10}. In short, the growth process of in-situ WC grain includes two independent stages, one is the formation of WC growth unit on basal facets {001}, and the other is the lateral stack of WC growth units in facets {001} as well as the vertical stack of WC growth units along 〈001〉 direction. Finally the in-situ WC grain grows into multi-layered triangular prism. The coarsening of in-situ WC grains, known as the Ostwald ripening, is partly due to the prior formed WC grains basal facets { 1 ¯ 10} can act as the heterogeneous nucleus of other newly generated WC grains hence promoting the forming of in-situ WC nucleus. The excellent mechanical properties, such as high hardness and good toughness, of WC grain benefit from its growth characteristics. [ABSTRACT FROM AUTHOR]

Present work aims to investigate the unique microstructural development during severe plastic deformation (SPD) of aluminum and its alloys under cryogenic temperature and during the post cryo-SPD annealing treatment. The influence of alloy chemistry and stacking fault energy (SFE) on recovery, recrystallization and grain growth phenomenon has been examined by various characterization techniques. Commercially pure Al alloy, non-heat treatable Al-4.5%Mg alloy and heat treatable Al-4.5%Cu alloy exhibiting varied SFE have been selected for this investigation. First, a significant variation in the cryo-SPDed microstructure has been observed between pure aluminum and its alloys. It has been attributed to the ‘polyslip’ deformation mechanism prevalent only in pure aluminum due to its very high SFE. Second, due to this inherent difference in their cryo-SPDed microstructures and influence of alloying elements, both the Al alloys show a substantial difference in their microstructural response during annealing in comparison with pure Al. For pure aluminum, grain rotation and coalescence is the dominating restoration mechanism. However, for aluminum alloys, rapid vacancy-assisted recovery, polygonization and recrystallization of equiaxed, high-angled, sub-micrometric grains have been observed. The grain growth mechanism of these recrystallized grains is heavily influenced by solute drag and particle drag effects. For non-heat treatable Al-4.5%Mg alloy, abnormal grain growth has been observed. In heat treatable Al-4.5%Cu alloy, nano-particles have precipitated in the grain boundaries, thereby retarding the grain growth process and inducing high microstructural thermal stability. [ABSTRACT FROM AUTHOR]

The grain growth behaviors of a nickel-based superalloy after full recrystallization are investigated by hot compression test plus annealing treatment. Electron backscattered diffraction technology (EBSD) is utilized to analyze the grain boundary features. It is found that the annealing parameters greatly affect the average grain size, and annealing twin boundaries, including ∑3, ∑9, and ∑27 boundaries. The fully-recrystallized grains can rapidly grow up at relatively high annealing temperatures with the increase of annealing time. Meanwhile, large fractions of annealing twin boundaries form at the initial stage of annealing treatment. However, with the further increase of annealing time, the content of annealing twins slightly drops due to the migration of grain boundaries or twin boundaries. When the annealing temperature is increased, the shape of annealing twin is apparently lengthened while the number of annealing twin sharply decreases. In addition, the kinetics model for grain growth after full recrystallization is established and validated by the experimental observations. [ABSTRACT FROM AUTHOR]

CeO 2 films with mixed doping of gadolinium and zirconium were deposited on NiW substrates by chemical solution deposition. The influences of mixed doping on the epitaxial growth and microstructure of films were systematically investigated. The morphological evolution of films with different dwell times was also discussed. The phase formation, texture and surface morphology of (Ce 0.8 Gd 0.2 ) 1- x Zr x O 2-δ (CGZO) films were characterized by X-ray diffraction and atomic force microscopy. It was noticed that Zr 4+ doping had stronger effect on the crystal structure of CeO 2 than Gd 3+ doping. The increasing doping content of Zr 4+ could be favorable for the self-limited grain growth of the CGZO films and promote the lattice match with substrate. Moreover, the sharp texture and smooth surface of CGZO film could be easily acquired by the mixed doping. The results indicated that the (Ce 0.8 Gd 0.2 ) 1- x Zr x O 2-δ film was beneficial for the subsequent film growth, which could be a candidate buffer layer for the coated conductors. [ABSTRACT FROM AUTHOR]

The spatially dependent spectral-kinetic and crystal structure properties of undoped and Pr 3+ - doped LiY 1−x Lu x F 4 mixed crystals grown by Bridgeman technique were studied along crystal growth direction. The distribution coefficients of Pr 3+ , Y 3+ and Lu 3+ in these crystals were determined. The rise of lattice parameters with increasing of the Pr 3+ concentration along the crystal growth direction was observed. [ABSTRACT FROM AUTHOR]

The role of sodium (Na) in cadmium telluride (CdTe) thin film photovoltaic absorbers deposited on a metal-coated substrate is investigated. Introducing Na during the growth of the structure influences the morphological and crystallographic properties of the CdTe layer grown by metal-organic chemical vapour deposition (MOCVD). It is observed that the introduction of Na between the metal and CdTe layers induces a slight randomisation via promotion of (400) and (220) orientations. It is shown that the inclusion of Na between the substrate and the Mo back metal contact enlarges the CdTe grains following a CdCl 2 treatment by 50% but weakens the adhesion to the substrate. The introduction of Na between the Mo back contact and CdTe layer promotes the formation of large faceted grains for the as-grown films with an average grain size ten times larger than in the case of Na free deposition while maintaining good adhesion to the substrate. There is no further grain growth following CdCl 2 treatment however the CdTe grain size is still double that of the Na-free samples. [ABSTRACT FROM AUTHOR]

Shear bands were developed during accumulative back extrusion of Mg-3Al-1Zn alloy at 130 °C. Transmission electron microscopy was employed to study the substructural evolution prior to and during the development of macro shear bands. The results illustrated that nanograins with mean size of 100 nm were formed within the bands. The observations revealed that flow localization in magnesium is preceded by interactions of deformation twins, dislocations and micro shear bands. The substructure within the bands is evolved through development of rectangular subgrains as well as subdivision of elongated grains. These substructures transformed subsequently into equiaxed nano-sized grains through continuous recrystallization. EBSD analysis confirmed the contribution of extension twinning during shear band development. [ABSTRACT FROM AUTHOR]

The Ti-44Al-8Nb-(W, B, Y) alloy sheet with a large thickness reduction of 85% was successfully obtained by hot pack rolling with 25% reduction per pass. The original coarse nearly lamellar structure with mean grain sizes of 120 μm was converted into a fine duplex microstructure with mean grain sizes of 5.3 μm. The as-worked alloy contains more than 70% vol. % of disordered α phases before the hot pack rolling. After the repeated deformation, these disordered α laths transform into interrupted fine recrystallization and recovery sub-grains. Then both α → α 2 ordering transformation and γ laths precipitation from the interrupted α phases take place during the cooling. Furthermore, the γ grains and γ laths also carry large strains and produce a large number of dislocations. These dislocations tangle and form dislocations networks which promote the discontinuous dynamic recrystallization nucleation and growth. As deformation proceeds during the subsequent hot pack rolling, the recrystallization, recovery and phase transformations of the previously formed recrystallization and recovery regions take place at tri-boundaries and inside the lamellar, resulting in the formation of fine duplex microstructure. At room temperature, the as-rolled alloy exhibits yield strength, ultimate tensile strength and ductility of 962 MPa, 1174 MPa and 1.01%, respectively. When temperature becomes as high as 850 °C, the failure strength still remains higher than 630 MPa with a good elongation value of above 45%. [ABSTRACT FROM AUTHOR]

In the present study, uniaxial compression tests were employed between 1000 and 1100 °C under the strain rates of 10 −3 , 10 −2 and 10 −1 s −1 to investigate the hot deformation behavior of BT9 titanium alloy. Work hardening behavior interpretation and analytical investigations including calculation of deformation activation energy, and developing process maps were used to establish a numerical correlation between microstructural evolution and the flow behavior of the alloy. The results showed that dynamic recrystallization takes place at severe condition (T = 1000 °C and ε ˙ = 0.1 s −1 ), while dynamic recovery is the major microstructural mechanism at other condition. According to dynamic material model and Prasad's instability criterion, the maximum power dissipation of 52% and 46% occur at 1000 °C/0.1s −1 and 1150 °C/0.001 s −1 , respectively. Electron backscattered diffraction images and high resolution optical images also revealed that continuous dynamic recrystallization is the governing mechanism at these deformation conditions resulting in a significant grain refinement. Considering the calculated deformation activation energies, power efficiency domains and the microstructural observations, 1000 °C/0.1 s −1 was determined as the optimum deformation condition. [ABSTRACT FROM AUTHOR]

The effect of elevated-temperature annealing in the range of 1473 K–1673 K on the coarsening kinetics of nanoparticles and microstructural evolution in an as-fabricated 12Cr-ODS steel was systematically investigated. Results show that the nanoparticles were extremely stable and continued precipitating during annealing at 1473 K, whereas, significant coarsening took place during exposure at 1673 K, increasing by 177% and 423% in diameter for 1 h and 24 h, respectively. Furthermore, heterogeneously distributed voids were developed, sizes of which increased distinctly at 1573 K and 1673 K for longer holding time. This is probably due to the growth and/or aggregation of Ar-entrapped and pre-existed voids in the as-fabricated condition. Additionally, no obvious changes were observed in microstructure and texture at 1473 K, nevertheless, full recrystallization were achieved at 1673 K for 24 h, and the major texture was not altered except reduction of the intensity. The apparent activation energy for recrystallization was experimentally calculated as 424 ± 22 kJ/mol, which was almost the same as that for nanoparticle coarsening, i.e., 412 ± 55 kJ/mol, suggesting that recrystallization proceeded accompanying with nanoparticle coarsening that would in turn stimulate the recrystallization process. It was deduced that recrystallization in the as-fabricated 12Cr-ODS steel was presumably not able to occur until the nanoparticles were dissolving and/or coarsening during annealing. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Ti 22Al 25Nb 1.0B alloy has been investigated at the temperature range of 1000–1200 °C and strain rate range of 0.001–1.0s −1 by hot compression tests. The microstructural evolution with different lnZ parameters was also analyzed by optical microscopy (OM) and transmission electron microscopy (TEM). Results showed that the flow stresses and microstructure evolution were sensitive to deformation parameters. The peak stress level decreased with increasing deformation temperature and decreasing strain rate. The hot deformation activation energy was calculated to be 524.02 kJ/mol in the α 2 +B2 phase region and 378.59 kJ/mol in the B2 phase region, respectively. Under conditions of high lnZ values at 49.51–47.21 in the α 2 +B2 phase region, cracking and localized plastic flow occurred, which should be avoided in hot working process. According to the microstructure evolution in TEM, it was found that the main soften mechanism transformed from dynamic recovery to dynamic recrystallization at low lnZ values. At high lnZ values obtained in the B2 phase region, the dislocation pile-up and dynamic recovery (DRV) can be found in the high lnZ values rather than cracking or localized plastic flow due to low activation energy. The full dynamic recrystallization (DRX) occurs in the lnZ values at 29.7–25.09. With decreasing the value of lnZ to 24, the size of recrystallization grain becomes larger. The optimum hot working conditions are obtained at lnZ values at 45.34–25.09. [ABSTRACT FROM AUTHOR]

We succeeded in growing five new single crystalline compounds RPt 2 Cd 20 (R = La, Ce, Pr, Nd, and Sm) by the Cd self-flux method. These compounds are found to crystallize in the cubic CeCr 2 Al 20 -type crystal structure by the X-ray diffraction using single crystals. We measured the electrical resistivity, magnetic properties, and specific heat for all compounds. The resistivity for R = Ce, Nd, and Sm indicates an abrupt decrease, which might correspond to a magnetic transition. It is suggested that the ground state of CePt 2 Cd 20 is Γ 7 doublet from the magnetization measurement. The magnetization of PrPt 2 Cd 20 shows a metamagnetic behavior at 1.6 T in the paramagnetic state, which could be due to the crystalline electric field effect with non-Kramers Γ 3 doublet or Γ 1 singlet ground state. The contribution of optical phonon modes to the lattice specific heat is discussed in LaPt 2 Cd 20 . [ABSTRACT FROM AUTHOR]

Molybdenum trioxide ( h -MoO 3 , α -MoO 3 ·H 2 O and h -/ α -MoO 3 composites) were prepared by a simple method in aqueous solution at 90–95 °C, without using autoclave or other complex equipment. The synthetic conditions for different phases of MoO 3 were studied. The ratio of MoO 4 2− :H + and reaction temperature play important roles for the crystal phases of MoO 3 . By changing the amount of H + ions, the samples can be controlled as h -MoO 3 microrods or α -MoO 3 ·H 2 O microbelts. h -/ α -MoO 3 composites in homogeneous structure were obtained at higher temperatures. The study on the transformation process of h -MoO 3 → α -MoO 3 ·H 2 O → α -MoO 3 would be helpful in designing functional MoO 3 materials. The h -MoO 3 microrods and h -/ α -MoO 3 composites showed good photochromic behavior under sunlight irradiation. [ABSTRACT FROM AUTHOR]

A new mixed crystal of Yb 0.14 Gd 0.71 Y 0.15 COB was grown by the Czochralski method. The polarized absorption spectra of the crystal were measured, and the absorption cross sections were determined to be 0.81 × 10 −20 (E// X ), 0.98 × 10 −20 (E// Y ) and 0.74 × 10 −20 cm 2 (E// Z ) at 977 nm. The fluorescence bands corresponding to 2 F 5/2 → 2 F 7/2 transition were identified in 970–1125 nm wavelength range with four peaks located at 977, 1003, 1030 and 1081 nm. The emission cross-sections were calculated by a combination of the reciprocity method (RM) and Füchtbauer-Ladenburg (F-L) method. The fluorescence lifetime was recorded to be 2.59 ms. Effective continuous-wave (CW) laser operation was realized with this crystal, with a maximum laser output power of 9.28 W and a slope efficiency of 40.1% for laser operation. Our study may open up new opportunities toward the research and development of high-performance laser crystals. [ABSTRACT FROM AUTHOR]

We report a step-like martensitic transformation and its effect on magnetocaloric properties in Ni 40.6 Co 8.5 Mn 40.9 Sn 10 unidirectional crystal grown using the Bridgman-Stockbarger technique followed by vacuum annealing at 1173 K for 72 h. This alloy undergoes successive first-order phase transitions which are attributed to the monotonic compositional variation along the crystal growth direction; the latter results in the increase of the full-width at half-maximum of the magnetic entropy change as a function of temperature (δ T FWHM ). For a magnetic field change of 2 and 5 T, the maximum magnetic entropy change are 9.7 and 16.0 J kg −1 K −1 with an extended δ T FWHM of 11 and 23 K, respectively. The average hysteresis loss for a field change of 2 T is 19 J kg −1 reducing the refrigerant capacity by 17%. [ABSTRACT FROM AUTHOR]

Flash Spark Plasma Sintering (FSPS) that combines flash sintering and electric field assisted sintering was used to densify SiC ceramics. FSPS was compared with ‘conventional’ SPS which used a moderate 100 °C·min −1 heating rates. Dense SiC specimens were obtained despite being at temperature of 1850–2050 °C for few seconds. FSPS lead to generation of hot-spots and thus caused localized exaggerated grain-growth. This allows producing silicon carbide ceramics with bimodal grain size distribution. Analysis of microstructure and strength of silicon carbide ceramics consolidated using flash heating allowed proposing several optimization routes of the FSPS process. [ABSTRACT FROM AUTHOR]

In this paper, we report a comparative study of rare-earth (RE = Y, Nd, Ce, and La) ions substituted Bi 1−x−y Sr x RE y FeO 3 (BSRFO) at y = 0.03 and x = 0.4 nanomultiferroic system. The samples were successfully synthesized using flash autocombustion reaction. X-ray diffraction analysis reveals that, the crystal structure is rhombohedral and hexagonal grain growth habit is seen by SEM microstructure. The doping of RE improved the magnetic properties specially Y 3+ and Nd 3+ ions. We argue that the addition of RE is likely to suppress the spiral spin modulation and at the same time increase the canting angle which favors the enhanced ferromagnetism behavior in different applications. [ABSTRACT FROM AUTHOR]

The influence of antimony (Sb) doping content on the structural properties of Cu(In, Al)Se 2 (CIAS) thin films and performance of photodetector has been investigated systematically. Here, we report the high-quality, phase-pure and well-crystallized CIAS thin films containing Sb element, where the lattice defects can be restrained effectively. Moreover, significant Sb-induced grain size enhancement, dense and smooth surface morphology can be observed, which originates from that the low melting point Sb-based compounds play as fluxing agents during the grain growth process. Most importantly, after Sb doping, the photodetector with the Al:ZnO (AZO)/CIAS/Mo structure demonstrates a two-orders of magnitude in photocurrent amplification, which indicates the reduced recombination of charge carriers in the depletion region. These findings provide additional insight into their use for the forthcoming photodetector application. [ABSTRACT FROM AUTHOR]

We report single crystal growth of the series of Ce T Al 3 compounds with T = Cu, Ag, Au, Pd and Pt by means of optical float zoning, where high crystal quality was confirmed in a thorough characterization process. With the exception of CeAgAl 3 , all compounds crystallize in the non-centrosymmetric tetragonal BaNiSn 3 structure (space group: I 4 mm , No. 107), whereas CeAgAl 3 adopts the related orthorhombic PbSbO 2 Cl structure ( Cmcm , No. 63). An attempt to grow CeNiAl 3 resulted in the composition CeNi 2 Al 5 . Low temperature resistivity measurements down to ∼ 0.1 K did not reveal evidence suggestive of magnetic order in CePtAl 3 and CePdAl 3 . In contrast, CeAuAl 3 , CeCuAl 3 and CeAgAl 3 display signatures of magnetic transitions at 1.3 K, 2.1 K and 3.2 K, respectively. This is consistent with previous reports of antiferromagnetic order in CeAuAl 3 and CeCuAl 3 as well as ferromagnetism in CeAgAl 3 , respectively. [ABSTRACT FROM AUTHOR]

A systematic investigation of the spectroscopy properties and semiconductor saturable absorber mirror mode-locking performances of highly doped Yb:Sr 3 Y 2 (BO 3 ) 4 (Yb:SYB) crystal was reported for the first time. The broad emission spectral bands indicate the great potential of Yb:SYB for ultrafast laser applications. 116 fs, 120 fs and 126 fs pulses lasers were generated with more than 1 W average output power from the a-cut, b-cut and c-cut Yb:SYB based oscillators, respectively. The corresponding slope efficiencies and optical to optical efficiencies could reach to 49–54% and 31–33%, respectively. The experimental results show the excellent potential of Yb:SYB crystal for generating highly efficient femtosecond lasers. [ABSTRACT FROM AUTHOR]

Electron Paramagnetic Resonance (EPR) and magnetic susceptibility measurements have been performed for La 3 Ga 5.5 Ta 0.5 O 14 single crystal doped intentionally with 3 wt% of Sm 3+ ions. X-band EPR measurements have been carried out with covering the field range 0–1.4 T and the temperature range 3–300 K. It has been found that two magnetically inequivalent sites having at least C 2 symmetry are responsible for the EPR spectra. The static magnetization measurements as a function of temperature and magnetic field have been done using a vibrating sample magnetometer (VSM). The field and temperature dependences of magnetization are measured in zero-field cooled (ZFC) and field cooled (FC) regimes in an applied field of 100 Oe. It is seen from magnetization measurements that the strong coupling regime is due to the presence of a strong coupling of the Sm 3+ ions to the lattice of LGT crystals. [ABSTRACT FROM AUTHOR]

The effect of scandium on the microstructure and texture of hot rolled and annealed binary Mg-Sc alloys has been studied. Hot rolled alloys develop weaker and more random basal texture than the corresponding texture of pure Mg after undergoing the same thermomechanical processing. The increase of Sc concentration leads to a systematic weakening of the texture, however texture randomization is not as prominent as in other Mg-RE alloys. The annealed texture of Mg-Sc alloys inherits features of the deformed texture, showing moderately weaker intensities of dominant components. The texture weakening is attributed to the heterogeneous deformation and nucleation of randomly oriented grains at micro shear bands. The microstructure and grain growth analysis suggest that Sc atoms have a low tendency to migrate towards grain boundaries and impose minimal drag effect. As a result, the grain growth is determined by grain boundary self-diffusion with an activation energy of ∼82 ± 8 kJ/mol. The results confirm the important role of solute segregation to grain boundaries in the development of annealed texture in Mg-based alloys. [ABSTRACT FROM AUTHOR]

The crystal growth of Bismuth-based compounds (mainly Bi 2 O 2 CO 3 ) on graphene with various degrees of oxidation in hydrothermal process is reported. The graphene sheets with different concentrations of oxygen-containing groups and defects, as a special carbon source, can effectively influence the phase compositions, morphologies and even photoelectric properties of graphene–Bi 2 O 2 CO 3 composites through the binding behavior of graphene oxide in the nucleation and growth process of Bi 2 O 2 CO 3 crystals. The cube-like crystals including mainly Bi 2 O 2 CO 3 phase with Bi 2 O 3 tightly wrapped by numerous graphene sheets are synthesized employing highly oxidized graphene oxide (HGO) as starting materials, while the partially oxidized graphene oxide (PGO) is used for synthesizing 3D flower-like hierarchical Bi 2 O 2 CO 3 microstructures just containing Bi 2 O 2 CO 3 phase adorned with sporadic graphene sheets. Furthermore, the higher charge separation yield is achieved for cubic composites with much more interfacial connection between the cube-like crystals and graphene sheets compared to flower-like crystals. The above results suggest an interesting approach for controlling the morphology and property of crystals by tuning the functional groups on graphene sheets used in the nucleation and growth process of crystals. [ABSTRACT FROM AUTHOR]

Kinetics of grain growth was measured in dense polycrystalline ultrapure alumina doped with 100 ppm of lanthanum. The evolution of grain size followed cubic kinetics, which can be attributed to the influence of solutes. Based on the increase of Gibbsian excess of segregating dopants with increase in the average grain size, it can be approximated that boundary velocity scales as inverse-square of grain size, leading to cubic grain growth kinetics. The activation energy of grain growth was found to be 418 ± 22 kJ mol −1 for La-doped alumina; comparable to that of undoped ultrapure alumina, and much lower than the activation energy of creep in La-doped alumina. The grain boundary mobility was found to be almost an order of magnitude lower than that of undoped ultrapure alumina, which can be attributed to the drag of oversized dopants segregated to the grain boundary core. These findings provide a basic understanding of the effects of segregating dopants on grain growth, and can be exploited in the production of coarsening resistant nanograined materials. [ABSTRACT FROM AUTHOR]

Isothermal constant true strain rate compression experiments coupled with electron back scattered diffraction (EBSD) analysis have been employed to understand the role of strain rate on the microstructural evolution during hot deformation of a hot isostatically processed nickel base superalloy. The flow behaviour of the alloy deformed at constant deformation temperature (1150 °C) and varying strain rates (0.001 s −1 , 0.01 s −1 , 0.1 s −1 , 1 s −1 ) revealed two distinct strain rate dependent deformation characteristics. Microstructural observations revealed prevalence of superplastic flow behaviour preceded by dynamic recrystallization (DRX) with dynamic grain growth at the lowest strain rate studied. Sluggish degree of DRX is observed at intermediate strain rates characterized by low volume fraction of DRX grains and dominant presence of deformation substructure bounded with diffuse grain boundaries. Accelerated DRX is noticed at the highest strain rate owing to the higher accumulated stored energy driven large misorientation gradient and adiabatic temperature rise. Discontinuous DRX is found to be the prevalent DRX mechanism in the investigated conditions, which is substantiated by the evidence of necklace type microstructure, serrated grain boundaries, misorientation gradient analysis and relative fraction of grain boundaries. Towards the end, the dependence of strain rate on the evolution of primary twin boundaries (Σ3) and higher order twin boundaries (Σ9 & Σ27) are studied. [ABSTRACT FROM AUTHOR]

The effects of sintering parameters, first and second step sintering temperatures (T 1 and T 2 , respectively), on the microstructure of magnesium aluminate spinel (MAS) were investigated. A single-step sintering (SSS) method was used to determine the appropriate temperatures for the first step. Different two-step sintering (TSS) regimes were used to investigate the effect of second step sintering temperatures on densification behavior and grain growth. The results show that, by using SSS method, the densification kinetics of MAS is different from grain growth kinetics. A MAS material with a high relative density of 96.17% and a homogeneous microstructure consisting of small grains (680 nm) is achieved under optimum TSS conditions (T 1 = 1650 °C/0 h and T 2 = 1550 °C/10 h). Compared with conventional specimen, the bending strength (240 MPa) and Vickers hardness (11.05 GPa) of the sintered samples fabricated under optimum TSS increased by 54.8% and 52.2%, respectively. [ABSTRACT FROM AUTHOR]

As a field-assisted technique, spark plasma sintering (SPS) enables densification of specimens in a very short period of time compared to other sintering techniques. For high performance thermoelectric material synthesis, SPS is widely used to fabricate nanograin-structured thermoelectric materials by rapidly densifying the nanopowders suppressing grain growth. However, the microstructural evolution behavior of thermoelectric materials by SPS, another important process during sintering, has been rarely studied. Here, we explore SPS as a tool to control the microstructure by long-time SPS. Using p-type (Bi 0.25 Sb 0.75 ) 2 Te 3 thermoelectric materials as a model system, we systematically vary SPS temperature and time to understand the correlations between SPS conditions, microstructural evolution, and the thermoelectric properties. Our results show that the relatively low eutectic temperature (∼420 °C) and the existence of volatile tellurium (Te) are critical factors to determine both microstructure and thermoelectric property. In the liquid-phase sintering regime, rapid evaporation of Te leads to a strong dependence of thermoelectric property on SPS time. On the other hand, in the solid-phase sintering regime, there is a weak dependence on SPS time. The optimum thermoelectric figure-of-merit (Z) of 2.93 × 10 −3 /K is achieved by SPS at 500 °C for 30 min. Our results will provide an insight on the optimization of SPS conditions for materials containing volatile elements with low eutectic temperature. [ABSTRACT FROM AUTHOR]

The solubilities of the most common grain-growth inhibitors (GGIs) Cr, V, Ta, Mo, Nb, Zr and certain combinations thereof in the binder phase of WC-Co hardmetals as well as hardmetals of the type WC-TiC-TiN-TaC-NbC-Co containing an fcc MC carbide (or carbonitride) phase “MC” (“WC-MC-Co” hardmetals) were analysed by means of WDS-EPMA. The carbon potential of the binder phase was fixed at its highest and lowest maxima by the presence of either graphite or eta (M 6 C) phases. In case of low-carbon hardmetals the composition of M 6 C, and in the MC-containing hardmetals the composition of the MC phase, was analysed. Two types of solubilities were determined. The first type was measured after controlled cool-down from liquid-phase sintering temperature and represented the binder phase state of an industrially prepared hardmetal. The second type representing the equilibrium solubility was measured in alloys annealed at 1000 °C for 168 h after liquid-phase sintering. The measured solubilities were subsequently used to prepare hardmetals with an optimised GGI concentration. The samples were analysed with respect to hardness, toughness, magnetic properties, transverse rupture strength and Weibull parameter. A complex doping with Cr, V and Ta with optimised concentrations near the solubility limit of these metals in the binder phase turned out to yield best combination of mechanical properties and reliability. This was successfully adopted in industrial production. [ABSTRACT FROM AUTHOR]

The nickel-base superalloy, Inconel 718, is widely used in aircraft engines. The control of its final microstructure requires detailed knowledge on recrystallization, grain growth and second phase evolution during thermomechanical processing. The present study focuses on the in-situ evaluation of heterogeneous grain growth in the super-δ-solvus domain (above 1050 °C) using laser ultrasonics. This technology is dedicated to the ultrasonic characterization of microstructure evolution during thermomechanical processing of metals and alloys. The real time measurement of the ultrasonic attenuation provides the evolution of a representative grain size in the material. A criterion is developed to determine the onset and completion of heterogeneous grain growth stages associated with the dissolution of precipitates. The laser ultrasonic methodology is validated with ex-situ metallographic observations and quantitative characterization of the grain size heterogeneity. [ABSTRACT FROM AUTHOR]

The grain-growth behavior of cryogenically-rolled Cu–30Zn brass during isothermal annealing at 900 °C was examined. The observed microstructure coarsening was interpreted in terms of normal grain growth with a grain-growth exponent of ∼4. The relatively slow grain-growth kinetics was attributed to the formation of precipitates at the grain boundaries and the interaction of texture and grain growth. The development of a moderate-strength {110} α fiber texture (∼4 times random) as well as the presence of a limited number of twin variants within the grains suggested the occurrence of variant selection during annealing. [ABSTRACT FROM AUTHOR]

Nanocrystalline CoCrFeNi high entropy alloy, synthesized by mechanical alloying followed by spark plasma sintering, demonstrated extremely sluggish grain growth even at very high homologous temperature of 0.68 T m (900 °C) for annealing duration of 600 h. Mechanically alloyed powder had carbon and oxygen as impurities, which in turn led to the formation of two-phase mixture of FCC and Cr-rich carbide with fine distribution of Cr-rich oxide during spark plasma sintering. Sluggish grain growth is attributed to the Zener pinning effect from the fine dispersion of oxide, mutual retardation of grain boundaries in the presence of two phases, and sluggish diffusivity because of cooperative diffusion of multi-principle elements. [ABSTRACT FROM AUTHOR]

Gold has broad applications in jewelry, but suffers from low hardness. In the present work, we show that simultaneous addition of 0.1 wt.% Ce and Si can nearly double the hardness of fine gold. We further show that hardness can be tripled by subsequent cold processing. By systematic structural characterizations and thermal analysis, we find that Ce and Si tend to segregate to grain boundaries and impede grain growth. Our work is helpful for development of new gold micro alloys and for design of jewelry that is more wear and scratch resistant. [ABSTRACT FROM AUTHOR]

In the present work influence of annealing on precipitation phenomena, thermal stability and grain growth kinetics of a bulk ultrafine grained (UFG) Al 2014 alloy has been studied. As-received solution treated Al 2014 alloy is subjected to cryorolling (CR) to develop ultrafine grained microstructure and subsequently, annealing treatment in the range of 323 K (50 °C) to 673 K (400 °C) for the duration of 30 min is done to study its thermal stability. The recrystallization process of the cryorolled Al 2014 alloy starts at 373 K (100 °C) and completes at 523 K (250 °C). The UFG microstructure is retained in the CR Al 2014 alloy up to 623 K (350 °C). The high thermal stability of the UFG grained Al 2014 alloy is due to pinning action of precipitate particles of Cu 2 Al and AlCuMgSi phases which are within the range of 100 nm and lying along the grain boundaries. The activation energy required for grain growth of the CR Al 2014 alloy is found to be exceptionally high as compared to other processing routes. [ABSTRACT FROM AUTHOR]

Single crystals of Yb doped YVO 4 with dopant concentration in the range of 0.75–14.3 at.% were grown by optical floating zone technique. The lattice parameters of YVO 4 remain unaffected up to 2.94 at.% doping of Yb but a contraction in the lattice volume was observed at higher concentrations. Spectral decomposition analysis of the broad absorption at 985 nm suggests that in addition to the contributions from three transitions from the ground state of the crystal field induced Stark multiplets of 2 F 7/2 and 2 F 5/2 , it also has contribution from the transition from the first excited Stark level of 2 F 7/2 to the upper most Stark level of 2 F 5/2 . Further, the absorption spectra exhibited significant polarization dependence. It was found that while for σ- (E⊥c) polarized light the absorption band at ∼972 dominates for π- (E||c) dominant absorption is at ∼985 nm. The absorption cross-section was found to be maximum at 2.94 at.% of doping for both the polarization signifying quenching at higher concentration. The emission spectra of the Yb doped crystals were characterized by two overlapped broad emissions centered at 985 and 1010 nm. The emission at 985 nm dominated over the emission at 1010 nm at lower doping concentrations which reversed at higher doping concentration. It is interesting to note that the PL intensity at 1010 nm is stronger for excitation at 972 nm in comparison to that for 985 nm. [ABSTRACT FROM AUTHOR]

Ln 2 (WO 4 ) 3 crystals (Ln = La, Ho, Tm, Eu) have been synthesized using the conventional solid-state ceramic technique. X-ray diffraction was employed to identify the crystal structure of the compounds. Depending on the ionic radii of RE 3+ , two different structures are found, α-Eu 2 (WO 4 ) 3 (modulated scheelite-type) or γ-Sc 2 (WO 4 ) 3 (phase with negative thermal expansion coefficient). The optical characterization is based on absorption, photoluminescence, excitation and kinetic decay studies. Under UV excitation at the (WO 4 ) 2− absorption band, two different behaviors are recorded. La 2 (WO 4 ) 3 compounds show a broad visible emission band with a nanosecond range decay rate, and no energy transfer (ET) from the (WO 4 ) 2− moiety to the lanthanide ion is observed. However, evidences of ET are observed for Ln = Tm, Ho and Eu. In particular, the (WO 4 ) 2− → Eu 3+ ET is so high that the fluorescence of the (WO 4 ) 2− moiety is almost completely quenched. Consequently, upon UV excitation Eu 2 (WO 4 ) 3 provides an intense visible emission with a 120 μs day lifetime. Although (WO 4 ) 2− → Ln 3+ ET also occurs for Ln = Ho and Tm, the relatively small energy gap between energy levels of these ions avoids any detectable luminescence, which is quenched by multiphonon processes. Moreover, the effect of a structural phase transition in Ho 2 (WO 4 ) 3 crystals on their luminescence properties is analyzed. The broad range of PL response of Ln 2 (WO 4 ) 3 under UV excitation both in the spectral position of the emission bands (from UV to visible) as well as in the decay range (from ns to hundreds of μs) shows the tunability of wolframates for scintillator applications. [ABSTRACT FROM AUTHOR]