Synthesis and characterization of silicon clathrates of type I Na8Si46 and type II NaxSi136 by thermal decomposition

Vollondat, Romain; Roques, S.; Chevalier, Céline; Bartringer, J.; Rehspringer, Jean‐Luc; Slaoui, A.; Fix, Thomas

doi:10.1016/j.jallcom.2022.163967

Cited by 8 publications

(3 citation statements)

References 53 publications

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“…The tunability of the bandgap energy in the visible wavelength region by the alloying of Si and Ge clathrates has been theoretically 13,14) and experimentally 23,24) reported, and has attracted attention as a novel optical absorption material for photovoltaic devices. 18,23,[25][26][27][28] Attempts to realize practical applications have been made in recent studies, in which film forms of type II Si (Si 136 ) and Ge (Ge 136 ) clathrates were synthesized on Si, Ge and sapphire substrates. 18,20,[28][29][30][31][32] There are still many problems to be solved.…”

Section: Introductionmentioning

confidence: 99%

“…18,23,[25][26][27][28] Attempts to realize practical applications have been made in recent studies, in which film forms of type II Si (Si 136 ) and Ge (Ge 136 ) clathrates were synthesized on Si, Ge and sapphire substrates. 18,20,[28][29][30][31][32] There are still many problems to be solved. P-type electric conduction is one of the most important points for realizing the pn homojunction device of clathrate.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and optical properties of Ge clathrate films with and without Al doping

Aye¹,

Kawaura²,

Kumar³

et al. 2023

Jpn. J. Appl. Phys.

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An attempt to prepare thin films of Al-doped type II Ge clathrates Nax(AlyGe1-y)136 was performed by using amorphous Ge films including 0 to 7 atomic percent Al as the starting materials. The preparations were conducted by our recently established method which enables the deposition of Na on the starting material with simultaneous or subsequent annealing under a high vacuum. X-ray diffraction measurements confirmed the type II clathrate structure in the prepared film. Smaller lattice constants and an Al-Ge related Raman peak found in the Al-included samples suggested the partial substitution of Al for Ge in the clathrate structure. Optical transmission measurements indicated that the fundamental absorption edge is shifted to higher energies due to the inclusion of Al.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Synthesis and optical properties of Ge clathrate films with and without Al doping

Aye¹,

Kawaura²,

Kumar³

et al. 2023

Jpn. J. Appl. Phys.

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“…The top spectrum obtained from the starting Na x Si 136 before Li diffusion is in very good agreement with published results where the symmetries of the modes have been identified in conjunction with model calculations. 13,14,47 The three spectra at the bottom of the figure were typical of those obtained from the surface after Li diffusion. Spot 1 is essentially the normal Si clathrate spectrum with a slight red shift in all of the modes (blue curve), and regions like spot 2 were also commonly observed, showing a Si clathrate spectrum shifted much more significantly to lower frequency (green curve).…”

Section: Raman Scattering Study Of Li-doped Si Clathratementioning

confidence: 95%

Formation of Type II Silicon Clathrate with Lithium Guests through Thermal Diffusion

et al. 2023

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At low guest atom concentrations, Si clathrates can be viewed as semiconductors, with the guest atoms acting as dopants, potentially creating alternatives to diamond Si with exciting optoelectronic and spin properties. Studying Si clathrates with different guest atoms would not only provide insights into the electronic structure of the Si clathrates but also give insights into the unique properties that each guest can bring to the Si clathrate structure. However, the synthesis of Si clathrates with guests other than Na is challenging. In this study, we have developed an alternative approach, using thermal diffusion into type II Si clathrate with an extremely low Na concentration, to create Si clathrate with Li guests. Using time-of-flight secondary-ion mass spectroscopy, X-ray diffraction, and Raman scattering, thermal diffusion of Li into the nearly empty Si clathrate framework is detected and characterized as a function of the diffusion temperature and time. Interestingly, the Si clathrate exhibits reduced structural stability in the presence of Li, converting to polycrystalline or disordered phases for anneals at temperatures where the starting Na guest Si clathrate is quite stable. The Li atoms inserted into the Si clathrate lattice contribute free carriers, which can be detected in Raman scattering through their effect on the strength of Si−Si bonds in the framework. These carriers can also be observed in electron paramagnetic resonance (EPR). EPR shows, however, that Li guests are not simple analogues of Na guests. In particular, our results suggest that Li atoms, with their smaller size, tend to doubly occupy cages, forming "molecular-like" pairs with other Li or Na atoms. Results of this work provide a deeper insight into Li guest atoms in Si clathrate. These findings are also relevant to understanding how Li moves through and interacts with Si clathrate anodes in Li-ion batteries. Additionally, techniques presented in this work demonstrate a new method for filling the Si clathrate cages, enabling studies of a broad range of other guests in Si clathrates.

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Silicon Clathrate‐Supported Catalysts with Low Work Functions for Ammonia Synthesis

Al Maksoud,

Bacha,

Pixius

et al. 2024

Advanced Materials

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Diamond‐type silicon has a work function of ≈4.8 eV, and conventional n‐ or p‐type doping modifies the value only between 4.6 and 5.05 eV. Here, it is shown that the alkali clathrates AxSi46 have substantially lower work functions approaching 2.6 eV, with clear trends between alkali electropositivity and clathrate cage size. The low work function enables alkali clathrates such as K8Si46 to be effective Haber‐Bosch catalyst supports for NH3 synthesis. The catalytic properties of Si, Ge, and Sn‐based clathrates are investigated while supporting Fe and Ru on the surface. The activity largely scales with the work function, and low activation energies below 60 kJ mol−1 are observed due to strong electron donation effects from the support. Ru metal and Sn clathrates seem to be unsuitable for stability issues. Compared to other similar hydride/electride catalysts, the simple structure and composition combined with stability in air/water make a systematic study of these clathrates possible and open the door to other electron‐rich Zintl phases and related intermetallics as low‐work function materials suitable for catalysis. The observed low work function may also have implications for other existing electronic applications.

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Synthesis and characterization of silicon clathrates of type I Na8Si46 and type II NaxSi136 by thermal decomposition

Cited by 8 publications

References 53 publications

Synthesis and optical properties of Ge clathrate films with and without Al doping

Synthesis and optical properties of Ge clathrate films with and without Al doping

Formation of Type II Silicon Clathrate with Lithium Guests through Thermal Diffusion

Silicon Clathrate‐Supported Catalysts with Low Work Functions for Ammonia Synthesis

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