Oxidation of half-Heusler NiTiSn materials: Implications for thermoelectric applications

Berche, Alexandre; Jund, Philippe

doi:10.1016/j.intermet.2017.09.014

Cited by 30 publications

(24 citation statements)

References 62 publications

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“…Some oxygen incorporation, most probably from the silica container (a very local reaction could have been initiated at the contact point between the sample and the silica tube during the heat treatment), has even been observed for samples annealed at 1000 • C in which some diffraction lines have been assigned to the ternary oxide Ni 3 Ti 3 O [83,84]. This result is partially consistent with a previous theoretical work predicting the decomposition of NiTiSn in the presence of oxygen to give oxides and nickel stannides [61]. However, titanium oxides like Ti 2 O 3 are expected rather than Ni 3 Ti 3 O (not considered in the study and which may be formed at high temperature).…”

Section: Annealing Temperaturesupporting

confidence: 90%

“…For the Ni-containing phases, the GGA+U method of Dudarev et al has been also used [60]. The need to use a GGA+U description for the Ni-containing phases, described in Reference [61], is motivated by a better description of the experimental ternary phase diagram compared to the standard GGA description. The parameter U eff for the Ni atoms was set to 3.5 eV as detailed in Reference [61].…”

Section: Calculation Methodsmentioning

confidence: 99%

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Synthesis of Pure NiTiSn by Mechanical Alloying: An Investigation of the Optimal Experimental Conditions Supported by First Principles Calculations

Tillard

Berche

Jund

2018

Metals

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Synthesis of NiTiSn by a mechanical alloying process followed by a high temperature thermal annealing was studied. Experiments were conducted varying parameters like the provided energy, the mechanical alloying reaction time, as well as the annealing temperature and duration. Based on the careful investigation of the phases present in the samples by systematic X-ray diffraction (after mechanical alloying and after annealing) and selected microscopy analyses, a reaction mechanism is proposed supported by theoretical calculations at the DFT (Density Functional Theory) level. An energy window to prepare directly NiTiSn has been evidenced. Highly pure NiTiSn has also been obtained by conversion from a multicomponent precursor obtained by low energy mechanical alloying.

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Section: Annealing Temperaturesupporting

confidence: 90%

Section: Calculation Methodsmentioning

confidence: 99%

Synthesis of Pure NiTiSn by Mechanical Alloying: An Investigation of the Optimal Experimental Conditions Supported by First Principles Calculations

Tillard

Berche

Jund

2018

Metals

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“…This method is simple, but it does not take into consideration the phases which are in equilibrium with the compound containing defects [ 4 , 29 ]. To correct this, two methodologies can be used.…”

Section: Determination Of the Energy Of Formation Of Defectsmentioning

confidence: 99%

“…This is why alternative routes for the synthesis, such as ball milling [ 3 ] may be useful to obtain the pure phase. In addition, NiTiSn is also known to be highly sensitive to oxidation [ 4 ] which can also have high effects on its thermoelectric properties. In parallel of experimental investigations, ab initio methods may also provide interesting elements in the choice of the doping elements.…”

Section: Introductionmentioning

confidence: 99%

“…It is then possible to estimate the value of N by calculating the energy of formation of charged defects as previously reported [ 8 ]. In NiTiSn, the most probable defect consists in interstitial Nickel atoms (Ni i ) present on the 4d Wyckoff positions (3/4; 3/4; 3/4) of the half-Heusler phase (space group

, prototype MgAgAs) as predicted by Density Functional Theory (DFT) calculations [ 4 , 9 , 10 ] as well as experimental studies [ 11 , 12 , 13 ]. This paper will focus on the influence of these Ni i defects on the electronic properties (Density of States (DOS) and bandgap) and on the thermoelectric properties.…”

Section: Introductionmentioning

confidence: 99%

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Fully Ab-Initio Determination of the Thermoelectric Properties of Half-Heusler NiTiSn: Crucial Role of Interstitial Ni Defects

Berche

Jund

2018

Materials

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For thermoelectric applications, ab initio methods generally fail to predict the transport properties of the materials because of their inability to predict properly the carrier concentrations that control the electronic properties. In this work, a methodology to fill in this gap is applied on the NiTiSn half Heusler phase. For that, we show that the main defects act as donor of electrons and are responsible of the electronic properties of the material. Indeed, the presence of Nii interstitial defects explains the experimental valence band spectrum and its associated band gap reported in the literature. Moreover, combining the DOS of the solid solutions with the determination of the energy of formation of charged defects, we show that Nii defects are also responsible of the measured carrier concentration in experimentally supposed “pure” NiTiSn compounds. Subsequently the thermoelectric properties of NiTiSn can be calculated using a fully ab initio description and an overall correct agreement with experiments is obtained. This methodology can be extended to predict the result of extrinsic doping and thus to select the most efficient dopant for specific thermoelectric applications.

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Processing and Thermoelectric Properties of TiNiSn Materials: A Review

Young

Reddy

2019

J. of Materi Eng and Perform

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The half-Heusler alloy TiNiSn is a promising material for high-temperature thermoelectric applications due to its good thermal stability and semiconductor-like electrical properties. Numerous synthesis techniques have been utilized to make TiNiSn, but a comparative study on its thermoelectric properties with respect to processing parameters has not been reported. Based on published experimental data, primary melting methods, such as arc melting or induction levitation melting, do not have a noticeable effect on the final thermoelectric properties, although choice of densification technique and annealing parameters correlate with each thermoelectric property. Thermal conductivity (2.47-6.08 W/m K), governed by lattice scattering effects, was maximized with high density from the spark plasma sintering (SPS) technique as well with low inclusions of metallic impurities and interstitial Ni defects from low-temperature, non-densified processes. Electrical resistivity (4.75-30 lX m), inversely related to thermal conductivity, is minimized when density is maximized and chemical defects are favorable from using SPS. All reported TiNiSn alloys contain intermetallic impurities, imparting a global trend of lowered electrical resistivity. Seebeck coefficient (2 273.20 to 2 50.71 lV/K), proportional to electrical resistivity, is maximized when charge carrier concentration is minimized by eliminating phase impurities and Ni defects. Porosity has been observed to scatter low-energy electrons, which can increase Seebeck coefficient and electrical resistivity, although no statistical significance is found. An ideal TiNiSn alloy should have intermediate values of all interconnected thermoelectric properties to maximize ZT. Future research work should strive to include quantitative phase analysis to better characterize the contributions of Ni defects and impurity phases toward thermoelectric properties.

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Oxidation of half-Heusler NiTiSn materials: Implications for thermoelectric applications

Cited by 30 publications

References 62 publications

Synthesis of Pure NiTiSn by Mechanical Alloying: An Investigation of the Optimal Experimental Conditions Supported by First Principles Calculations

Synthesis of Pure NiTiSn by Mechanical Alloying: An Investigation of the Optimal Experimental Conditions Supported by First Principles Calculations

Fully Ab-Initio Determination of the Thermoelectric Properties of Half-Heusler NiTiSn: Crucial Role of Interstitial Ni Defects

Processing and Thermoelectric Properties of TiNiSn Materials: A Review

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