XAFS Study on Nitrogenation of CoTiSn

Abstract

Gas-phase nitrogenation of CoTiSn compound with the MgAgAs-type structure has been examined by means of x-ray diffraction (XRD) and x-ray absorption fine structure (XAFS). The XRD suggests that the nitrogenation product is composed of the corresponding Cu2MnAl-type compound with expanded unit-cell volume comparable to that of Co2TiSn and subtle trace of Ti6Sn5 and Sn. Whereas the x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectra for the Ti, Co and Sn K-edges clearly indicate the coexistence of TiN and Co1+yTiSn phases in the product. It is also revealed that more Co atoms than expected from the chemical formulas are introduced into the vacancy site of the MgAgAs structure in Co1+yTiSn with 0≤y≤0.4.

Transmission electron microscopy observation of the half-Heusler compound Ti0.5(Zr0.5Hf0.5)0.5NiSn0.998Sb0.002

“…And the partial vacancy-occupation of the Co, Sn and Ni atoms was reported in Ti-Co-Sn [5][6][7] and the Ti-Ni-Sn [8] systems. In the present work, the high performance thermoelectric compound half-Heusler peak is asymmetry and accompanies a bump at the high-angle side.…”

TEM observation of coexistent Heusler and half-Heusler phases in TiNi1.5Sn

“…The slight increase of the Ni composition for halfHeusler B-C domain is noticed. The wrong-site occupation of slight atoms or the existence of vacancies is expected for these compositions, as reported in previous papers [5][6][7].…”

“…For example of the atomic substitution, high ZT performances were previously realized by the substitutional effect for Zr 0.5 Hf 0.5 NiSn 0.99 Sb 0.01 [1], Zr 0.5 Hf 0.5 Ni 0.8 Pd 0.2 Sn 0.99 Sb 0.01 [2,3] and Ti 0.5 (Zr 0.5 Hf 0.5 ) 0.5 NiSn 0.998 Sb 0.002 [4]. For the other example, the occupations of excessive Co or Sn atoms on vacancy sites were reported in Ti-Co-Sn system with the halfHeusler structure [5][6][7]. In the present work, the existent phases and the microstructure in a Ni-excessive TiNi 1.5 Sn are observed and analyzed by an X-ray diffraction (XRD) and a transmission electron microscopy (TEM).…”

Microstructures of Annealed TiNiSn-Based Alloy Ribbons

“…It was reported that atomic disordering and partial occupation of the vacancy site can occur easily in the half-Heusler lattice. [8][9][10][11][12] Those imperfect atomic configurations in the half-Heusler lattice may occur and lead the halfHeusler composition to the nonstoichiometric one under the present preparation conditions.…”