Effects of Microstructural Evolution on the Thermoelectric Properties of Spark-Plasma-Sintered Ti0.3Zr0.35Hf0.35NiSn Half-Heusler Compound

The MNiSn (M = Ti, Zr, Hf) half-Heusler semiconducting compounds are widely investigated due to their good potential for thermoelectric (TE) power generation applications. In the current work, the evolution of the transport and structural properties of the Ti0.3Zr0.35Hf0.35NiSn compound upon various thermal treatments was studied. The nominal composition was arc melted, ball milled, and spark plasma sintered (SPS). Following SPS, large Hf-rich domains were found by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Subsequently, the samples were subjected to homogenization treatments at 1163 K for 480 h and 610 h under argon atmosphere. Following these thermal treatments, the relative amount of the Hf-rich domains was reduced and they became smaller in size, with increasing thermal treatment duration. Nevertheless, no uniphased structure was reached. The dissolution of the Hf-rich domains in the half-Heusler matrix resulted in increase of both the Seebeck coefficient and electrical resistivity values and a decrease of the carrier concentration, attributed to elimination of these metallic domains. Resulting from the high atomic disorder caused by substitution at the M site, low thermal conductivity values of ~3.8 W m−1 K−1 were obtained leading to high ZT values of up to 0.82 following SPS.

[1]  J. C. Phillips.  Icosahedral ordering in quasicrystals and metallic glasses , 1986 .

[2]  Joseph Callaway,et al.  Effect of Point Imperfections on Lattice Thermal Conductivity , 1960 .

[3]  Claudia Felser,et al.  Simple rules for the understanding of Heusler compounds , 2011 .

[4]  B. Iversen,et al.  Interrelation between atomic switching disorder and thermoelectric properties of ZrNiSn half-Heusler compounds , 2012 .

[5]  C. Goldmann,et al.  Efficient dopants for ZrNiSn-based thermoelectric materials , 1999 .

[6]  Ye-Min Lu,et al.  High figure of merit in (Ti,Zr,Hf)NiSn half-Heusler alloys , 2012 .

[7]  Terry M. Tritt,et al.  Effect of substitutions on the thermoelectric figure of merit of half-Heusler phases at 800 °C , 2006 .

[8]  Peter L. Balise,et al.  Applications of Thermoelectricity , 1960 .

[9]  Xinbing Zhao,et al.  High-performance half-Heusler thermoelectric materials Hf1−x ZrxNiSn1−ySby prepared by levitation melting and spark plasma sintering , 2009 .

[10]  S. Yamanaka,et al.  Effect of spark plasma sintering temperature on thermoelectric properties of (Ti,Zr,Hf)NiSn half-Heusler compounds , 2005 .

[11]  Donald T. Morelli,et al.  Transport properties of pure and doped M NiSn ( M =Zr, Hf) , 1999 .

[12]  C. Felser,et al.  Half-Heusler compounds: novel materials for energy and spintronic applications , 2012 .

[13]  S. Yamanaka,et al.  Thermoelectric properties of titanium-based half-Heusler compounds , 2004 .

[14]  F. Aliev,et al.  Gap at the Fermi level in the intermetallic vacancy system RBiSn(R=Ti,Zr,Hf) , 1989 .

[15]  Jun Zhao,et al.  Low temperature transport and thermal properties of half-Heusler alloy Zr0.25Hf0.25Ti0.5NiSn , 2009 .

[16]  Naoki Shutoh,et al.  Thermoelectric properties of the Tix(Zr0.5Hf0.5)1-xNiSn half-Heusler compounds , 2005 .