Abstract
Ti3Sn has received increasing attention as a high damping metallic material and as an anode material for rechargeable lithium-ion batteries. However, a heated dispute concerning the existence of solid state phase transformation of stoichiometric Ti3Sn impedes its development. Here, thermal-induced reversible phase transformation of Ti3Sn is demonstrated to happen at around 300 K by the means of in-situ variable-temperature X-ray diffraction (XRD) of Ti3Sn powder, which is also visible for bulk Ti3Sn on the thermal expansion curve by a turning at 330 K. The new phase’s crystal structure of Ti3Sn is determined to be orthorhombic with a space group of Cmcm and the lattice parameters of a = 5.87 Å, b = 10.37 Å, c = 4.76 Å respectively, according to selected area electron diffraction patterns in transmission electron microscope (TEM) and XRD profiles. The hexagonal → orthorhombic phase transformation is calculated to be reasonable and consistent with thermodynamics theory. This work contributes to a growing knowledge of intermetallic Ti3Sn, which may provide fundamental insights into its damping mechanism.
Highlights
There are increasing attempts focusing on Sn-based anode materials for rechargeable lithium-ion batteries due to their high storage capacities [1,2,3,4], among which the intermetallic Ti3 Sn seems to be the representative one [5,6]
The results of dynamic mechanical analysis (DMA) of Ti3 Sn with a frequency of 1 Hz measured under heating reveal the interesting points: an obvious damping peak exists at about 310 K which just corresponds to the turning point of storage modulus; when the temperature is lower than 310 K, the damping capacity increases continuously [7]
According to the results of the two kinds of calculations above, both hexagonal phase and orthorhombic phase of Ti3 Sn are stable phases, and ∆H (Ti12 Sn4 ) is more negative than ∆H (Ti6 Sn2 ), which indicates that the orthorhombic phase is more stable than the hexagonal phase, and the phase transformation from hexagonal phase to orthorhombic phase is reasonable according to thermodynamics theory
Summary
There are increasing attempts focusing on Sn-based anode materials for rechargeable lithium-ion batteries due to their high storage capacities [1,2,3,4], among which the intermetallic Ti3 Sn seems to be the representative one [5,6]. Though the basic damping mechanism of Ti3 Sn remains unknown presently, these experimental data suggest the appearance of a phase transformation in Ti3 Sn at near-room temperature (~310 K). The intermetallics has the ordered hexagonal D019 crystal structure with a space group of P63 /mmc (No 194) and the lattice parameters of a = 5.916 ± 0.004 Å and c = 4.764 ± 0.004 Å [10]. Colin McCullough et al in 1993 studied the phase selection in undercooled Ti3 Sn melts, and reported two previously unknown metastable forms of Ti3 Sn: base-centered orthorhombic structure (space group: Cmmm ) with the lattice parameters
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