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

Monique Tillard,Alexandre Berche,Philippe Jund

doi:10.3390/met8100835

Abstract

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.

Highlights

As the worldwide energy demand continuously increases, finding new efficient materials to respond to always higher requirements, and to improve properties of already known materials, remains challenging
NiTiSn was primarily prepared by mechanical alloying but for comparison, samples were prepared by classical fusion methods and by solid-liquid reaction from the elements
Analyses of the arc-melted material prepared in this work confirm the presence of NiTiSn and of the secondary phases Ni2 TiSn, Ti6 Sn5, and Sn, visible as grey and white domains in typical scanning electron microscopy (SEM)

Summary

Introduction

As the worldwide energy demand continuously increases, finding new efficient materials to respond to always higher requirements, and to improve properties of already known materials, remains challenging. Thermoelectric (TE) materials, able to reversibly convert thermal energy into electricity, have acquired recently new popularity and renewed and increasing interest. The thermoelectric efficiency of a material depends on its ZT value expressed as α2 T/ρκ where α is the Seebeck coefficient (or thermopower), ρ the electrical resistivity, κ the thermal conductivity, and T the absolute temperature. Among TE materials, the class of Heusler compounds is remarkable for its multifunctional character [1], and therein, NiTiSn is probably the most widely studied half-Heusler compound. Available literature data, considered at the beginning of this study, was mainly dedicated to NiTiSn prepared by arc-melting and submitted to additional treatments

Methods

Results

Conclusion