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Pure metals can have ultrafast growth rates from their melts, such as a crystal of pure nickel that grows at a rate reaching 70 m s−1. These extraordinary growth rates suggest that metallic crystals might provide the next generation of phase-change materials. The huge crystal growth rates of metals are the consequence of kinetics without activated control, in sharp contrast to the prediction of the ‘classic’ theory of crystal growth. While the existence of barrierless growth kinetics is now well established in atomic melts, the physical explanation for the absence of an activation barrier to ordering remains unclear. It is something of a paradox that diffusion in the liquid metal is governed by thermal activation while the movement of the same atoms organizing into a crystal is not. Here we use computer simulations of crystallization in pure metals to explicitly resolve the origin of the barrierless growth kinetics.

We report the growth of bulk β-Ga 2 O 3 crystals based on crystal pulling from a melt using a cold container without employing a precious-metal crucible. Our approach, named oxide crystal growth from cold crucible (OCCC), is a fusion between the skull-melting and Czochralski methods. The absence of an expensive precious-metal crucible makes this a cost-effective crystal growth method, which is a critical factor in the semiconductor industry. An original construction 0.4–0.5 MHz SiC MOSFET transistor generator with power up to 35 kW was used to successfully grow bulk β-Ga 2 O 3 crystals with diameters up to 46 mm. Also, an original diameter control system by generator frequency change was applied. In this preliminary study, the full width at half maximum of the X-ray rocking curve from the obtained β-Ga 2 O 3 crystals with diameters ≤ 46 mm was comparable to those of β-Ga 2 O 3 produced by edge-defined film fed growth. Moreover, as expected, the purity of the obtained crystals was high because only raw material-derived impurities were detected, and contamination from the process, such as insulation and noble metals, was below the detection limit. Our results indicate that the OCCC technique can be used to produce high-purity bulk β-Ga 2 O 3 single crystalline substrate.

The magmatic processes responsible for triggering nature’s most destructive eruptions and their associated timescales remain poorly understood. Yellowstone Caldera is a large silicic volcanic system that has had three supereruptions in its 2.1-Ma history, the most recent of which produced the Lava Creek Tuff (LCT) ca. 631 ka. Here we present a petrologic study of the phenocrysts, specifically feldspar and quartz, in LCT ash in order to investigate the timing and potential trigger leading to the LCT eruption. The LCT phenocrysts have resorbed cores, with crystal rims that record slightly elevated temperatures and enrichments in magmaphile elements, such as Ba and Sr in sanidine and Ti in quartz, compared to their crystal cores. Chemical data in conjunction with mineral thermometry, geobarometry, and rhyolite-MELTS modeling suggest the chemical signatures observed in crystal rims were most likely created by the injection of more juvenile silicic magma into the LCT sub-volcanic reservoir, followed by decompression-driven crystal growth. Geothermometry and barometry suggest post-rejuvenation, pre-eruptive temperatures and pressures of 790–815 °C and 80–150 MPa for the LCT magma source. Diffusion modeling utilizing Ba and Sr in sanidine and Ti in quartz in conjunction with crystal growth rates yield conservative estimates of decades to years between rejuvenation and eruption. Thus, we propose rejuvenation as the most likely mechanism to produce the overpressure required to trigger the LCT supereruption in less than a decade.

Tapiolite [FeTa2O6] and columbite-group minerals [(Fe,Mn)(Ta,Nb)2O6] are common Nb-Ta-bearing accessory minerals in rare-element granites and pegmatites. Their compositional gap has inspired several experimental studies, but none of them have succeeded in reproducing the parameters that influence the compositional gap. In this study, tapiolite and columbite-group minerals (CGM) were crystallized from water-saturated, flux-rich granitic melts at various conditions of pressure, temperature, oxygen fugacity, and Ti contents. Crystals with a size as small as 500 nm were analyzed with a field emission gun (FEG) electron microprobe. The results show that temperature, pressure, and Ti content only slightly affect the compositional gaps between tapiolite and CGM, whereas high fO2 leads to complete solid solution between a rutile-structured component Fe3+TaO4 and (Fe,Mn)Ta2O6. The experimental CGM-tapiolite compositional gaps are compared with natural CGM-tapiolite pairs from rare-element granites and pegmatites worldwide. This study reveals that the crystallographic structure of tapiolite and CGM could be the dominant parameter that influences the position of the compositional gap. Order-disorder in CGM and tapiolite is tightly linked to disequilibrium crystallization triggered by supersaturation. Significant isothermal Nb-Ta fractionation is observed inside CGM crystals that grow at high degrees of supersaturation. The effect of supersaturation prevails over the solubility effect that is known to increase the Ta/(Ta+Nb) ratio in CGM and coexisting melts. Thus, even if global equilibrium in terms of the solubility of Nb-Ta-bearing minerals is attained, the Ta/(Nb+Ta) ratio in the crystals may differ significantly from equilibrium. It implies that Nb-Ta fractionation in Nb-Ta oxides is controlled by crystallization kinetics rather than equilibrium chemical fractionation (or any other processes such as F-complexing of Ta or fluid exsolution) in dynamic systems that can rapidly reach supersaturated conditions. These results have important implications for the understanding of crystallization processes in highly evolved and pegmatite-forming magmas.

The growth of spherical crystals in binary alloy melts with thermal diffusion effects under oscillatory flow is investigated analytically. Using the multiple scale method, we derive approximate analytical solutions for both the crystal interface growth rate and the solute concentration. Our results demonstrate that the Soret effect significantly influences both the solute concentration near the crystal interface and the crystal growth rate. Specifically, with a positive Soret coefficient, the growth rate of spherical crystals in a binary dilute alloy melt decreases as the coefficient increases, while the solute concentration near the interface increases. In contrast, with a negative Soret coefficient, the growth rate of the spherical crystals increases as the coefficient decreases, and the solute concentration near the interface decreases. Additionally, the presence of oscillatory flow markedly promotes the grain refinement induced by the Soret effect.

Analogous to surface premelting, we show that a crystal surface can undergo a pre-solid–solid transition. This means that it develops a thin polymorphic crystalline layer before reaching the solid–solid transition temperature if two crystals can form a low-energy coherent interface. We confirm this in simulations and colloid experiments at single-particle resolution. The power-law increase of surface layer thickness is analogous to premelting. Different kinetics and reversibilities of surface-crystal growth are observed in various systems. Surface crystals exist not only under thermal equilibrium but also during melting, crystallization and grain coarsening. Furthermore, the premelting and pre-solid–solid transition can coexist, resulting in double surface wetting layers. We hypothesize that such surface phenomena also exist in some atomic and molecular crystals, and this could provide a mechanism to tune the properties of the materials.Premelting refers to the formation of a thin liquid film on a crystal’s surface before it properly melts. Now, a similar mechanism is shown to occur before solid–solid transitions in colloidal crystals: the formation of a polymorphic crystalline layer.

The partitioning of a large suite of trace elements between biotite and water-saturated granitic melt was measured at 2 kbar and 700—800 ˚C. To reach equilibrium and to grow biotite crystals large enough for analysis, runs usually lasted from 30 to 45 days. In every charge, a few trace elements were initially doped at the 0.1—0.5 wt. % level and analyzed by electron microprobe after the run. First-row transition metal ions are highly compatible in biotite with Dbiotite/melt of 17 for Ti, 35 for V, 47 for Co, 174 for Ni, and 5.8 for Zn. A very notable exception is Cu with Dbiotite/melt < 0.9. This is likely one of the reasons why Cu is enriched together with Mo (Dbiotite/melt = 0.29) in porphyry deposits associated with intermediate to felsic plutons, while the other transition metals are not. Both Nb and Ta are mildly compatible in biotite with Dbiotite/melt being larger for Nb (3.69) than for Ta (1.89). Moderate (15—30%) biotite fractionation would be sufficient to reduce the Nb/Ta ratio from the chondritic value to the range observed in the continental crust. Moreover, the strong partitioning of Ti into biotite implies that already modest biotite fractionation suppresses the saturation of Ti-oxide phases and thereby indirectly facilitates the enrichment of Ta over Nb in the residual melt. The heavy alkalis, alkaline earths, and Pb are only mildly fractionated between biotite and melt (Dbiotite/melt = 3.8 for Rb, 0.6 for Cs, 0.6 for Sr, 1.8 for Ba, 0.7 for Pb). The rare earth elements are generally incompatible in biotite, with a minimum for Dbiotite/melt of 0.03–0.06 at Gd, Tb, and Dy, while both the light and heavy rare earths are less incompatible (e.g. Dbiotite/melt = 0.6 for La and 0.3 for Yb). This behavior probably reflects a partitioning into two sites, the K site for the light rare earths and the octahedral Mg site for the heavy rare earths. There is no obvious dependence of the rare earth partition coefficients on tetrahedral Al in the biotite, presumably because charge balancing by cation vacancies is possible. Allanite was found as run product in some experiments. For the light rare earths, Dallanite/melt is very high (e.g. 385 to 963 for Ce and Nd) and appears to increase with decreasing temperatures. However, the rather high solubility of allanite in the melts implies that it likely only crystallizes during the last stages of cooling of most magmas, except if the source magma is unusually enriched in rare earths.

The growing interest in Li diffusion as a tool to determine timescales of short-time magmatic events, such as magma ascent during eruption, increases the necessity to better understand Li diffusion in common mineral phases. In this context, well-constrained diffusion coefficients and understanding of kinetic processes specific to mineral phases are of crucial importance. To gain further insight especially into the kinetic processes in plagioclase, we investigated the diffusion of Li between natural An61 plagioclase crystals and synthetic glasses of An80 plagioclase composition. Experiments were conducted at 200 MPa in rapid-heat/rapid-quench cold-seal pressure vessels (RH/RQ CSPVs) and internally heated pressure vessels (IHPVs) at temperatures between 606 and 1114 °C. Concentration and isotope profiles of Li were measured using femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). We adopted a multispecies diffusion model and specified boundary conditions for plagioclase of labradoritic composition. Using this model, we were able to distinguish between an interstitial (DLii) and a vacancy process (DLiA), with the interstitial process being 0.2–1 orders of magnitude faster than the vacancy process, depending on temperature. DLii=10-3.76±0.58exp⁡-180.0±12.0kJmol-1RTm2s-1DLiA=10-5.53±0.16exp⁡-151.7±3.2kJmol-1RTm2s-1 Our data indicate charge compensation of Li by Na in both the crystal and the glass. Chemical Li diffusion coefficients in An80 glass are up to 3 orders of magnitude slower compared to Li tracer diffusion in silicate and aluminosilicate glasses and melts, which is attributed to slow Na diffusion at high An content. Our results for chemical diffusion of Li in plagioclase crystals are 1.5–2 orders of magnitude slower than Li tracer diffusion in An- and Ab-rich plagioclase determined in previous studies. This indicates that earlier studies on natural intermediate plagioclase compositions have underestimated timescales by up to 2 orders of magnitude. For accurate determination of timescales from Li diffusion in plagioclase we suggest further exploring the role of Na and a possible dependence on An content.

We report the bulk growth of single-crystal CdZnTe and characterization of material associated with large-area wafers produced from the CdZnTe ingots. Our experimental vertical gradient freeze set-up enables accurate detection of the beginning and end of the crystallization step by careful monitoring of the thermal cycle. Single crystal, (111)-oriented ingots with a diameter of 80 mm were routinely obtained without grain boundary or twin. The size of the CdZnTe ingots was extended to 115 mm in diameter, enabling production of large-dimension substrates suitable for infrared focal-plane arrays with megapixel-resolution. Crystal quality was investigated by double-crystal x-ray rocking curve mapping and by chemical revelation of etch pits. Typical mean values for the rocking curve full width at half maximum were in the range 20–40 arcs. Evaluation of etch pit density on the (111)Te face furnished values in the low 10 4 /cm 2 .

Understanding the nature of solid-liquid interfaces is important for many processes of technological interest, such as solidification, liquid-phase epitaxial growth, wetting, liquid-phase joining, crystal growth, and lubrication. Recent studies have reported on indirect evidence of density fluctuations at solid-liquid interfaces on the basis of x-ray scattering methods that have been complemented by atomistic simulations. We provide evidence for ordering of liquid atoms adjacent to an interface with a crystal, based on real-time high-temperature observations of alumina-aluminum solid-liquid interfaces at the atomic-length scale. In addition, crystal growth of alumina into liquid aluminum, facilitated by interfacial transport of oxygen from the microscope column, was observed in situ with the use of high-resolution transmission electron microscopy.