A fabrication method for type-II Ge clathrate film by annealing of Ge film covered with Na layer

Kumar, Ranjeet; Hazama, Yuta; Ohashi, Fumitaka; Jha, Himanshu S.; Kume, Tetsuji

doi:10.1016/j.tsf.2021.138859

Cited by 11 publications

(21 citation statements)

References 30 publications

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“…However, synthesis of the type II Ge clathrate phase has been more elusive; this is because the traditional synthetic approach for type II Si clathrates, thermal decomposition of the Na 4 Si 4 Zintl phase under vacuum, , is more difficult for the Ge analogue (Na 4 Ge 4 ) and generally results in the formation of many phases (Figure ). Recently, the selective growth of the type II Ge phase via thermal decomposition has been accomplished with specially designed reactors or via thin-film growth methods. − …”

Section: Introductionmentioning

confidence: 99%

Synthesis of Type II Ge and Ge–Si Alloyed Clathrates Using Solid-State Electrochemical Oxidation of Zintl Phase Precursors

et al. 2022

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Germanium clathrates with the type II structure are openframework materials that show promise for various applications, but the difficulty of achieving phase-pure products via traditional synthesis routes has hindered their development. Herein, we demonstrate the synthesis of type II Ge clathrates in a two-electrode electrochemical cell using Na 4 Ge 4−y Si y (y = 0, 1) Zintl phase precursors as the working electrode, Na metal as the counter/reference electrode, and Na-ion conducting β″-alumina as the solid electrolyte. The galvanostatic oxidation of Na 4 Ge 4 resulted in voltage plateaus around 0.34−0.40 V vs Na/Na + with the formation of different products depending on the reaction temperature. When using Na 4 Ge 3 Si as a precursor, nearly phase-pure, alloyed type II Ge−Si clathrate was obtained at 350 °C. The Na atoms in the large (Ge,Si) 28 cages of the clathrate occupied off-centered positions according to Rietveld refinement and density functional theory calculations. The results indicate that electrochemical oxidation of Zintl phase precursors is a promising pathway for synthesizing Ge clathrates with type II structure and that Si alloying of the Zintl phase precursor can promote selective clathrate product formation over other phases.

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Section: Introductionmentioning

confidence: 99%

Synthesis of Type II Ge and Ge–Si Alloyed Clathrates Using Solid-State Electrochemical Oxidation of Zintl Phase Precursors

et al. 2022

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“…The completely guest-free clathrate (Ge 136 ) has the highest formation energy and therefore should be harder to synthesize than the Na-filled clathrates. Indeed, to our knowledge, most previous attempts at synthesizing guest-free type II germanium clathrates have resulted in the formation of Na-filled clathrates ,, or low-Na/K content clathrates , as one of the major products along with other by-products. Special techniques such as the application of an electric field in an Ar environment, and chemical oxidation, or thermal decomposition in ionic liquid media were needed to obtain nearly guest-free type II Ge clathrates (δ ∼ 0 in Na δ Ge 136 ).…”

Section: Resultsmentioning

confidence: 99%

“…Understanding the mobility of guest atoms within clathrate structures is important not only for battery applications but also because the synthesis of some clathrates relies on the removal of these metals via thermal evaporation − or oxidative deintercalation. ,− Our research group’s recently reported method for synthesizing type II germanium clathrate (Na 24−δ Ge 136 ) via solid-state electrochemical oxidation of the Zintl phase compound Na 4 Ge 4 showed that the products were temperature dependent, with the type II Ge clathrate forming at a relatively low temperature (300 °C), hexagonal Na 1– x Ge 3+ z at intermediate temperature (350 °C), and diamond cubic α-Ge at higher temperature (400 °C). However, to the best of our knowledge, none of the previous studies focused on understanding the mechanism of the precursor oxidation, and little attention has been paid to understanding how Na atoms are removed from the precursor that is used to synthesize the clathrates.…”

Section: Introductionmentioning

confidence: 99%

Type II Germanium Clathrates from Zintl Phase Precursor Na₄Ge₄: Understanding Desodiation Processes and Sodium Migration Using First-Principles Calculations

2023

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Type II germanium clathrates have recently been investigated for potential applications as anodes in batteries due to their cage-like structures that can accommodate electrochemical insertion of guest ions. To synthesize type II Ge clathrates (Ge136), several experimental routes use thermal or electrochemical desodiation of the Zintl phase compound Na4Ge4. However, the mechanism by which Na atoms are removed from the precursor to form clathrates is not well understood. Herein, we use first-principles density functional theory and nudged elastic band calculations to understand the reaction mechanism and formation energies of the products typically observed in the synthesis, namely, NaδGe136 (0 < δ < 24) type II clathrates and hexagonal phase Na1–x Ge3+z . Specifically, we confirm the energetic feasibility of Na vacancy formation in Na4Ge4 and find that the barrier for Na vacancy migration is only 0.37 eV. This relatively low energy barrier is consistent with the ease with which Na4Ge4 can be desodiated to form the products. We also discuss the energetics, sodium migration pathways, and potential electrochemical performance of Ge136 as anode material for Na-ion batteries. Overall, this study highlights how first-principles calculations can be used to understand the synthesis mechanism and desodiation processes in clathrate materials and will help guide researchers in the design and evaluation of new open framework compounds as viable materials for energy storage applications.

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“…We note that recently a new fabrication method for type-II Ge clathrate film was proposed in Ref. [18]. The pressure-induced structural changes and behavior of Ge 136 on compression were studied in Ref.…”

Section: Introductionmentioning

confidence: 99%

Pressure-induced structural transformation of clathrate Ge136 via ultrafast recrystallization of an amorphous intermediate

2022

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We study the pressure-induced structural transformation of Ge 136 clathrate by ab initio molecular dynamics and metadynamics. The system under pressure first undergoes amorphization followed by an ultrafast recrystallization to the β-tin structure on the time scale of 30 ps. The initial pressure-induced amorphization of clathrate is triggered by high pressure while the subsequent fast recrystallization to β-tin is driven by low temperature. Interestingly, the amorphous intermediate is still diffusive even at room temperature in spite of very strong undercooling, making the ultrafast recrystallization possible. The system provides an explicit example of structural transformation between two crystalline phases proceeding via noncrystalline intermediate. On fast decompression of the amorphous structure with incipient crystalline order, the recrystallization is blocked and the system instead proceeds to the tetrahedral low-density amorphous (LDA) phase.

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A fabrication method for type-II Ge clathrate film by annealing of Ge film covered with Na layer

Cited by 11 publications

References 30 publications

Synthesis of Type II Ge and Ge–Si Alloyed Clathrates Using Solid-State Electrochemical Oxidation of Zintl Phase Precursors

Synthesis of Type II Ge and Ge–Si Alloyed Clathrates Using Solid-State Electrochemical Oxidation of Zintl Phase Precursors

Type II Germanium Clathrates from Zintl Phase Precursor Na₄Ge₄: Understanding Desodiation Processes and Sodium Migration Using First-Principles Calculations

Pressure-induced structural transformation of clathrate Ge136 via ultrafast recrystallization of an amorphous intermediate

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A fabrication method for type-II Ge clathrate film by annealing of Ge film covered with Na layer

Cited by 11 publications

References 30 publications

Synthesis of Type II Ge and Ge–Si Alloyed Clathrates Using Solid-State Electrochemical Oxidation of Zintl Phase Precursors

Synthesis of Type II Ge and Ge–Si Alloyed Clathrates Using Solid-State Electrochemical Oxidation of Zintl Phase Precursors

Type II Germanium Clathrates from Zintl Phase Precursor Na4Ge4: Understanding Desodiation Processes and Sodium Migration Using First-Principles Calculations

Pressure-induced structural transformation of clathrate Ge136 via ultrafast recrystallization of an amorphous intermediate

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Type II Germanium Clathrates from Zintl Phase Precursor Na₄Ge₄: Understanding Desodiation Processes and Sodium Migration Using First-Principles Calculations