Solubility, diffusion and electrical activity of Na in bulk Ge crystals

Extending the Performance Limit of Anodes: Insights from Diffusion Kinetics of Alloying Anodes

“…Owing to their ability to form an amorphous layer and high‐density dislocations near the propagating interface (see Figures 7c,d), alloying anodes following DCR diffusion enable the faster diffusion of carrier ions into the anodes. When the diffusivities of alloying anodes are compared, the diffusivities (≈3.0 × 10 −6 cm 2 s −1 for Na–Sn [ 82 ] and ≈3.6 × 10 −7 cm 2 s −1 for Na–Ge [ 112 ] ) of carrier ions in DCR‐governed alloying anodes are greater than those (≈5.1 × 10 −12 cm 2 s −1 for Li–Si [ 113 ] and ≈3.0 × 10 −10 cm 2 s −1 for Na–Sb [ 114 ] ) of ICR‐governed alloying anodes by more than three to five orders of magnitude. Therefore, the selection of the DCR‐governed alloying anodes can prevent the depletion of charge carriers at high current rates, making them suitable for high‐power operations.…”

“…This is especially true when the diffusivity of the carrier ions is lower in the SEIs than in the anodes. [ 118,119 ] For instance, the carrier‐ion diffusivity (≈1.8 × 10 −13 to 7.6 × 10 −11 cm 2 s −1[ 120 ] ) in SEIs is much lower than the typical values (e.g., ≈3.0 × 10 −6 cm 2 s −1 for Na–Sn [ 82 ] and ≈3.6 × 10 −7 cm 2 s −1 for Na–Ge [ 112 ] ) in DCR‐governed alloying anodes. In this case, the overall diffusion rate is limited by the SEI, rather than by the propagating interface or the trailing bulk region.…”

Large polycrystalline optical germanium Ge:Na plates with improved optical parameters and their application

“…The donor impurity that is most often used and provides the necessary optical properties of Ge crystals is antimony, atoms of which substitute Ge atoms in the crystal lattice. However, we have managed to dope Ge crystals with an interstitial Na and to show that the optical parameters of single-crystalline and coarsegrained Ge:Na are better as compared with those of Ge:Sb grown from the same raw material [5,6].…”

“…As it was shown by us previously [5], among the advantages of Ge:Na crystals over Ge:Sb crystals there is a significantly lower scattering of transmitted radiation. This is due not only to the fact that introduction of smallsize interstitial Na atoms into germanium leads to less distortions of the crystal lattice as compared with substitutional impurity Sb in Ge, but also to lower solubility of Na in Ge (about 10 15 atoms/cm 3 ) [6] as compared with Sb. The maximum solubility of Sb in Ge crystals is 1.2·10 19 atoms/cm 3 [15], Sb has a retrograde solubility in Ge, and, as a result, while cooling the grown Ge:Sb crystals from the growth temperature to the room one, second-phase inclusions of Sb with characteristic sizes about 6…9 µm are formed, and they scatter the infrared radiation [16].…”

“…Similarly to Ge:Na crystals pulled from the melt [5], the resistance of the plates was fairly uniform along their length, decreasing from the beginning of the plate to its end by no more than by 10-12%, most often approximately from 18 to 16 Ohm·cm. The reasons for this higher homogeneity in Ge:Na crystals as compared, for example, with crystals doped with V group elements, have been discussed by us previously [6]. Using specially developed technological tricks, the crystallization front was made maximally close to flat, which, in particular, contributed to a reduction of mechanical stresses in the plates [18].…”