Neutron diffraction study on the Heusler compound Co1.50TiSn and its nitrogenation products

Nobata, Tatsuhito; Nakamoto, G.; Kurisu, Makio; Makihara, Y.; Ohoyama, Kenji; Ohashi, Masayoshi

doi:10.1016/s0925-8388(02)00402-4

Cited by 16 publications

(9 citation statements)

References 13 publications

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“…An apparently different situation is found in Co 2 TiSn, for which we found the CoTiSn ground state to be the C1 b structure but lying outside the Co 2 TiSn stability range. Investigations performed by Nobata et al 56 found, on the other hand, that certain growth conditions favor the formation of the the Co 1.50 TiSn with a half-filled vacancy sublattice instead of the stoichiometric compound CoTiSn. This way, the obtained negative formation energy of Co 2 TiSn:Vc Co is consistent with the experimental findings.…”

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Native defects in the Co2TiZ (Z=Si,Ge,Sn) full Heusler alloys: Formation an

et al. 2017

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We have performed first-principles investigations on the native defects in the half-metallic, ferromagnetic full Heusler alloys Co2TiZ (Z one of the group IV elements Si, Ge, Sn), determining their formation energies and how they influence the transport properties. We find that the Co vacancies (Vc), the TiSn as well as the CoZ or CoTi anti-sites exhibit the smallest formation energies. The most abundant native defects were modeled as dilute alloys, treated with the coherent potential approximation in combination with the multiple-scattering theory Green function approach. The self-consistent potentials determined this way were used to calculate the residual resistivity via the Kubo-Greenwood formula and, based on its energy dependence, the Seebeck coefficient of the systems. The latter is shown to depend significantly on the type of defect, leading to variations that are related to subtle, spin-orbit coupling induced, changes in the electronic structure above the half-metallic gap. Two of the systems, VcCo and CoZ , are found to exhibit a negative Seebeck coefficient. This observation, together with their low formation energy, offers an explanation for the experimentally observed negative Seebeck coefficient of the Co2TiZ compounds as being due to unintentionally created native defects.

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Native defects in the Co2TiZ (Z=Si,Ge,Sn) full Heusler alloys: Formation an

et al. 2017

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“…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.…”

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

2008

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High-performance thermoelectric compound Ti 0.5 (Zr 0.5 Hf 0.5 ) 0.5 NiSn 0.998 Sb 0.002 with half-Heusler lattice was measured and observed by an XRD and a TEM. Each half-Heusler peak in the XRD pattern accompanied a bump at the high-angle side. Granular domains, a few nanometer in dimension, were observed in a bright-field TEM image. A Fourier-transformation and an inverse Fourier-transformation for the HRTEM image revealed that the granular structure consists of the half-Heusler domains with ordering and with disordering between second nearest neighbor atoms.

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“…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.…”

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Microstructures of Annealed TiNiSn-Based Alloy Ribbons

Morimura

Hasaka

Shimoda

et al. 2009

Journal of Elec Materi

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The thermoelectric half-Heusler compounds Ti x NiSn 0.998 Sb 0.002 (x = 1.0 to 1.2) and Ti y Zr 0.25 Hf 0.25 NiSn 0.998 Sb 0.002 (y = 0.5 to 0.65) with nonstoichiometric nominal compositions were prepared by spin-casting and subsequent annealing at 1073 K for 24 h. The dimensionless figure of merit ZT at room temperature was maximized at x = 1.1 and y = 0.6 in Ti-rich compounds through an increase in absolute Seebeck coefficients despite a decrease in electrical conductivities. ZT reached 0.07 at x = 1.1 and 0.14 at y = 0.6. In powder x-ray diffraction analysis, minor phases of b-Sn, TiNi, Ti 2 Sn, and Ti 5 Sn 3 were observed in addition to a major phase of half-Heusler. The quantity of the minor phases was minimized at x = 1.1 and y = 0.55, where the absolute Seebeck coefficients are maximized. In transmission electron microscopic (TEM) analysis of Ti 0.55 Zr 0.25 Hf 0.25 NiSn 0.998 Sb 0.002 , crystal grains of the half-Heusler phase, from several hundred nanometers to several micrometers in size, were observed. TEM energy-dispersive spectroscopy measurements indicated that fluctuations of Ti, Zr, and Hf compositions within the Ti-site in the half-Heusler phase may occur. Thermoelectric properties were improved at x = 1.1 and y = 0.6 rather than at the stoichiometric compositions of x = 1.0 and y = 0.5 due to minimization of the precipitate quantities.

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Neutron diffraction study on the Heusler compound Co1.50TiSn and its nitrogenation products

Cited by 16 publications

References 13 publications

Native defects in the Co2TiZ (Z=Si,Ge,Sn) full Heusler alloys: Formation an

Native defects in the Co2TiZ (Z=Si,Ge,Sn) full Heusler alloys: Formation an

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

Microstructures of Annealed TiNiSn-Based Alloy Ribbons

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