A nominal GeO x (x ≤ 2) compound contains mixtures of Ge, Ge suboxides, and GeO 2, but the detailed composition and crystallinity could vary from material to material. In this study, we synthesize GeO x nanoparticles by chemical reduction of GeO 2, and comparatively investigate the freshly prepared sample and the sample exposed to ambient conditions. Although both compounds are nominally GeO x, they exhibit different X-ray diffraction patterns. X-ray absorption fine structure (XAFS) is utilized to analyse the detailed structure of GeO x. We find that the two initial GeO x compounds have entirely different compositions: the fresh GeO x contains large amorphous Ge clusters connected by GeO x, while after air exposure; the Ge clusters are replaced by a GeO 2-GeO x composite. In addition, the two GeO x products undergo different structural rearrangement under H 2 annealing, producing different intermediate phases before ultimately turning into metallic Ge.

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In the fresh GeO x, the amorphous Ge remains stable, with the GeO x being gradually reduced to Ge, leading to a final structure of crystalline Ge grains connected by GeO x. The air-exposed GeO x on the other hand, undergoes a GeO 2→GeO x→Ge transition, in which H 2 induces the creation of oxygen vacancies at intermediate stage. A complete removal of oxides occurs at high temperature. Ge is one of the promising candidates for anode materials in Li-ion batteries.

It has a theoretical capacity as high as 1600 mA h g −1 (upon formation of a Li 4.4Ge alloy) and excellent Li + diffusion rate at room temperature. However, the drastic volume expansion in crystalline Ge that occurs after Li insertion leads to capacity fading which limits its use in practical Li-ion devices. Researchers have been seeking methods to enhance the stability of Ge anodes, such as minimizing the size of Ge, surface functionalization, morphology engineering, and forming a composite structure by coating Ge with a layer of carbon. Recently, amorphous GeO x (x. It has been proposed that presence of Ge 0 in GeO 2 has a unique role in that it can serve as a catalyst to drive reaction (1) in the inverse direction, hence the formation of LiO 2 is reversible. This catalytic effect of Ge has been demonstrated by Seng et al. Using a GeO 2/Ge/C nanocomposite as an anode for a Li battery test.

A nominal GeO x structure contains a mixture of Ge dioxides and sub-oxides, as well as elemental Ge. It is critical to understand the composition and the structure of GeO x to achieve better control of the crystallinity and grain size of the different constituents in terms of improving the battery performance. Although there has been a large amount of work on synthesizing nanostructured GeO x with new configurations, less attention has been given to understanding the starting material itself before introducing it into a battery test. GeO x contains a mixture of Ge, GeO x, and GeO 2, and in an oxidizing (or reducing) environment, these three components can transform from one species to another,. In fact, GeO x has been deliberately synthesized and served either as the precursor for making Ge nanocrystals and/or GeO 2 nanostructures for the purpose of fabricating electronic and optical devices,.

Although there have been relatively large amount of early studies done on Ge nanocrystal embedded GeO x or SiO x thin films for the purpose of electronic devices fabrication, few reports are available on the structure characterization of the free-standing Ge/GeO x/GeO 2 nanocomposite in terms of battery applications. In particular, since amorphous Ge and GeO x are more promising for Li-ion anodes than their crystalline counterparts, the standard crystal structure analysis tool X-ray diffraction (XRD) is no longer capable of characterizing the crystal structure of GeO x. Transmission electron microscopy (TEM) with high resolution can tell the crystallinity of individual nanoparticles. However, for amorphous structure, distinguishing different components (e.g.

Ge and GeO x) almost entirely relies on the contrast of the image. In addition, the small sampling size of TEM lacks information on the averaged chemical composition of the material. Aside from the crystal structure, understanding the chemical components in GeO x from the electronic structure perspective is also important. GeO x contains Ge in various oxidation states, from Ge 0 up to Ge 4+. The conventional characterization technique for studying the electronic structure of GeO 2/Ge materials is photoelectron spectroscopy.

This technique requires the samples to have a clean surface and be in good electrical contact with the substrate. However, nanostructured GeO x for Li-ion battery applications are more often in the form of powder. The GeO x therefore have irregular surfaces, which makes removing surface impurities and ensuring good electrical contact very difficult. Consequently, characterizing the electronic structure of these materials with photoelectron spectroscopy is very challenging. X-ray absorption spectroscopy, on the other hand, is an alternative tool for electronic structure characterization that is flexible in terms of sample preparation. X-ray absorption fine structure (XAFS) probes the local environment of an element of interest in the material. The spectrum originates from the interference between incoming and outgoing electrons after single and/or multiple scattering.

As a result, it is a local structure probe and doesn’t require the sample to be crystalline. By measuring the Ge K-edge XAFS, the chemical environment of Ge, such as its oxidation state (from the X-ray absorption near-edge structure, XANES), the coordination number, and the bond distance between Ge and the nearest neighbors (from the extended X-ray absorption fine structure, EXAFS) can be obtained,.

GeO x nanostructures can be synthesized using various approaches, such as hydrothermal methods, hydrolysis, and by chemical reduction. Herein we study the electronic structure of GeO x nanoparticles synthesized by simple chemical reduction. Such method produces GeO x which contains GeO 2, Ge sub-oxides, and most interestingly, Ge. This serves as a good starting point to investigate the electronic structure of the GeO x, and the transitions between the three components under various conditions. We first compare the freshly prepared GeO x, and the one stored in ambient condition for 3 days. These two samples were then used as starting materials, and were annealed in H 2 at various temperatures.

The change in the chemical environment of Ge under different annealing temperatures is studied. Results and Discussion The freshly prepared GeO x nanoparticles have an average size of 50 nm. Shows a representative transmission electron microscopy (TEM) image of these particles. X-ray diffraction (XRD) measurement reveals that the fresh GeO x and air-exposed GeO x have very different crystal structure. The fresh GeO x only contains two broad peaks, indicating its amorphous nature. The air-exposed GeO x, on the other hand, shows well-resolved features that resemble crystalline GeO 2 with a quartz structure. After annealing in H 2 at 300 °C, the XRD patterns of both fresh GeO x and air-exposed GeO x are both broadened to some extent, however, the features characteristic of GeO 2 are still present in the latter.

When the annealing temperature is increased to 500 °C, fresh GeO x crystallizes into an fcc structure, with diffraction peaks matching cubic-phase metallic Ge. These features are further sharpened under annealing at 700 °C. As for air-exposed GeO x, the 500 °C annealing results in a mixed phase containing both GeO 2 and Ge. From the intensity of the two peak series, the GeO 2 is still the major component.

A full conversion from GeO 2 to Ge is observed at 700 °C annealing. ( a) TEM image of as-prepared fresh GeO x nanoparticles. ( b– d) XRD patterns of GeO x nanoparticles before and after annealing in comparison with standards. ( b) fresh GeO x (sample series 1); ( c) air-exposed GeO x (sample series 2); ( d) standard XRD patterns of cubic Ge and quartz GeO 2.

Labels in ( b) and ( c): ( a) as-prepared samples; ( b) samples annealed at 300 °C; ( c) samples annealed at 500 °C; ( d) samples annealed at 700 °C. The intensity of 1-d is reduced in half to fit the panel. We analyse the crystalline grain size of our samples using the Scherrer equation (Eq. Ge K-edge XANES of GeO x nanoparticles.

Sample series 1: fresh GeO x, series 2: air-exposed GeO x; ( a) as-prepared samples, ( b) samples annealed at 300 °C, ( c) samples annealed at 500 °C, ( d) samples annealed at 700 °C. A closer examination of the oxidation states in Ge can be performed by examining the 1 st derivative of the XANES spectra. The plots are shown in, and the peak positions (the edge jump) correspond to the oxidation states of Ge in the samples. This method allows us to obtain the evolution of Ge oxidation states during annealing in detail. The lower energy dashed line marks the edge jump of Ge 0 and the higher energy line marks the one of Ge 4+. Interestingly, the evolution of the edge jump positions as a function of annealing temperature is quite different between the two sets of GeO x.

Ge K-edge XANES of GeO x nanoparticles plotted in 1 st derivatives. The legend is the same as the one shown in.

For fresh GeO x at room temperature (spectrum 1-a in ), the edge jump is at energy slightly higher than Ge 0, while after annealing, all the edge jumps are aligned to the position of Ge 0 regardless of temperature. Instead of Ge 0, the Ge in fresh GeO x are slightly oxidized (i.e. At 500 °C, the decrease of CN Ge-O slows down. Recall from, metallic Ge features start to appear in the XRD, so at this stage, structural rearrangement start to occur. Note the Ge-O long-range order also improves as seen in.

A system with many oxygen vacancies is not thermodynamically stable, so O migrates, and produces GeO 2 and adjacent Ge start to join each other forming Ge-Ge bonds. At 700 °C, the high temperature leads to a total reduction of GeO x (reaction (7)), leading to a sudden transition from GeO x to Ge. Upon the removal of almost all O in GeO x, the Ge grows into cubic crystallites.

The relative rapidity of this transition may explain why these crystallites are somewhat smaller than those that form during the more gradual crystallization during annealing in the fresh GeO x samples. As the O is almost all removed, a distinct GeO x phase no longer exists. This is evidenced by the lack of a clear GeO2-related feature in the XANES spectrum from the air-exposed sample annealed at 700 °C (refer back to ), as well as the anomalously short Ge-O bond length obtained from EXAFS fitting (see ). The remaining O is likely only found as a capping layer on the Ge crystallites. The structures of the two GeO x samples and their behaviour under H 2 annealing can be summarized in the scheme shown in. The fresh GeO x contains both elemental Ge and GeO x (x closes to 1), both are amorphous and present in comparable amounts.

H 2 annealing induces the disproportionation and reduction of GeO x, forming more Ge clusters. Ge clusters crystalize at high annealing temperatures, and grain boundaries are filled with GeO x. Air-exposed GeO x, on the other hand, can be modelled as GeO 2 crystallites with O vacancies.

Ambient air introduces oxygen, and the initial product is mostly crystalline GeO 2 with GeO x where x closes to 2. H 2 annealing gradually creates more oxygen vacancies, reducing the presence of crystalline GeO 2 and leading to the formation of more Ge dangling bonds. The GeO x structure is completely eliminated at the temperature of 700 °C, when a transition to crystalline Ge occurs due to the H 2 reduction reaction. Conclusion As nominal GeO x compounds, the actual compositions could vary significantly from material to material, depending on the synthesis strategies and post-treatment conditions. We have demonstrated that the exact composition and structure of GeO x and its structural evolution during annealing can be successfully analyzed using XAFS. In our model system, GeO x nanoparticles were synthesized by chemical reduction of GeO 2, freshly prepared GeO x is found consisting of Ge clusters and GeO x (x closes to 1), both in amorphous forms. Such GeO x undergoes disproportionation when annealed in a reducing environment.

The amount of amorphous Ge increases, and finally crystallizes into metallic Ge, with GeO x presents at the grain boundaries. However, if the GeO x is exposed to ambient conditions, the elemental Ge domains are quickly replaced by oxides, and the nanoparticles turn into a GeO 2-like structure. Once such structure formed, the GeO x (x closes to 2) can be slowly reduced by H 2, under mild temperature, producing small Ge crystallites embedded in GeO x matrix. Once the temperature reaches 700 °C, there is a complete conversion of GeO x to Ge. The composition of GeO x can change significantly from its initial composition after exposure to oxygen, and this exposure also affects how the structural rearrangement takes place during post-treatment. These findings are of paramount importance to developing GeO x anodes for Li-ion batteries.

In particular, they highlight the importance of carefully controlled synthesis of GeO x anodes – as even under identical preparation conditions, the composition and crystal structure can completely change based on whether or not the samples are exposed to ambient conditions. A controlled regime of air exposure followed by annealing in H 2 can further tailor the composition of the material. All the samples investigated here have nominal GeO x structures, but each of them possesses unique structures, which are identified by XAFS. With this in mind, the next step of the research includes the examination of Li battery performance with integration of these materials. The device performance can then be related to the fundamental structures of the GeO x. Amorphous Ge is preferable to crystalline Ge for Li-storage, but smaller clusters are also preferable to larger clusters.

If the composition of the GeO x is tunable, we will be able to find which configuration is desired as an anode material. Material Synthesis GeO x nanoparticles were prepared using a chemical reduction method. 2.0 g of GeO 2 (99.99%, Aladdin) was first dissolved in 36 mL deionized water, and 7 mL of NH 4OH (28%-30% NH 3, Aladdin) was added. Freshly prepared NaBH 4 (98%, Aladdin) solution (3.616 g in 20 mL deionized water) was quickly added to the mixture. The solution was vigorously stirred for 20h at room temperature. The resulting product was then filtered, washed with deionized water, and dried under vacuum at 50 °C. The freshly prepared GeO x was divided into two parts, one sealed in a glass vial and kept in a glove box filled with N 2 (denoted as fresh GeO x), and the other one was kept in a desiccator (humidity.

Characterization X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization was performed at the Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University. XRD was done using a PANalytical (Empyrean) apparatus with Cu Kα as the probing source. The morphology of the as-prepared GeO x was examined using TEM (Tecnai G2 F20, FEI).

The Ge K-edge XAFS experiments were conducted at beamlines BL01C1 at National Synchrotron Radiation Research Center (NSRRC), Taiwan and BL12B1 at SPring8, Japan. NSRRC is a 1.5 GeV storage ring operating at the beam current of 360 mA in top-up mode. The beamline, BL01C1 has energy range of 6–33 keV and a resolution ΔE/E of 2.3 × 10 −4. SPring-8 is an 8 GeV ring operating at the beam current of 100 mA in top-up mode. BL12B1 has an energy range of 5–25 keV with resolution ΔE/E of 10 −4. The GeO x powder was pressed into thin pellets and sealed in Kapton tape. The spectra were measured using transmission mode.

Commercially obtained GeO 2 powder (99.99%, Aladdin) was used as a reference. Graetz J., Ahn C. C., Yazami R. Nanocrystalline and thin film germanium electrodes with high lithium capacity and high rate capabilities.

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Hello there, I have installed Demeter with Macports on my Mac recently. My operating system is El Capitan. My issue is that I cannot see the plot area. I have followed two threads discussing this issue. The first one is 'No plot window in Athena/ Demeter on Mac OS X Yosemite' (where George suggested to change the gnuplot to x11 on the Athena preferences menu.

I could not find Athena preference menu and I was wondering if anyone could help with that. The second thread is 'No plot window on Mac El Capitan' (where Chloe could not find Athena Preferences menu as well.

Best regards, Laila. Hello there, I have installed Demeter with Macports on my Mac recently. My operating system is El Capitan. My issue is that I cannot see the plot area. I have followed two threads discussing this issue.

The first one is ‘’No plot window in Athena/ Demeter on Mac OS X Yosemite’’ (where George suggested to change the gnuplot to x11 on the Athena preferences menu. /I could not find Athena preference menu and I was wondering if anyone could help with that/.

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The second thread is ‘’No plot window on Mac El Capitan’’ (where Chloe could not find Athena Preferences menu as well. Best regards, Laila Ifeffit mailing list Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit.