DocumentCode :
2214702
Title :
Physical properties of rare-earth-based Heusler phases REPdZ and REPd2Z (Z = Sb,Bi)
Author :
Gofryk, K. ; Kaczorowski, D. ; Jasper, A.L. ; Grin, Yu.
Author_Institution :
Inst. of Low Temp. & Structure Res., Polish Acad. of Sci., Wroclaw, Poland
fYear :
2005
fDate :
19-23 June 2005
Firstpage :
380
Lastpage :
383
Abstract :
Four series of ternary compounds REPdSb (RE = Y, Ho, Er), REPdBi (RE = Nd, Y, Dy, Ho, Er), REPd2Sb (RE = Y, Gd-Er) and REPd2Bi (RE = Y, Dy-Er) were studied by means of magnetization, magnetic susceptibility, electrical resistivity, and thermoelectric power measurements performed in the temperature range 1.7-300 K and in magnetic fields up to 5 T. Magnetic susceptibility measurements of the Heusler phases REPdZ and REPd2Z (RE = Y, Gd-Er; Z = Sb, Bi) have revealed that at low temperatures the compounds studied are either paramagnetic or antiferromagnetic with the Neel points of several Kelvin. For all these compounds but Y-based alloys experimental values of the effective magnetic moment are close to the theoretical ones for respective RE3+ ions. Electrical resistivity measurements of the half-Heusler phases REPdX (X = Sb, Bi) have indicated their half-metallic or semimetallic character. At low temperatures the resistivity exhibits a metallic-like behaviour, which is probably due to an impurity band possibly overlapping with the conduction band. At high temperatures the electrical conductivities follow the activation law that accounts for gradual thermal depopulation of impurity levels. The positive sign of the Seebeck coefficient could indicate that holes arising from some acceptor centres are dominant carriers. The energy gaps near the Fermi level are of the order of tens millielectron volts and thus are much smaller than values estimated from the electronic structure calculations made for similar compounds. The Seebeck coefficient is quite large, of the order expected for low carrier density semimetals. The thermoelectric figure of merit evaluated for ErPdSb is ZT ≈ 0.15 at room temperature. While half-Heusler alloys have been characterised as narrow-gap semiconductors all the REPd2Sb and REPd2Bi ternaries have been found to exhibit metallic-like conductivity. For the REPd2Bi series a structural transformation from cubic to lower symmetry structures occurs that manifests itself as distinct anomalies in the transport characteristics. The thermoelectric power for these materials is much lower than that of the REPdX alloys.
Keywords :
Neel temperature; Seebeck effect; antiferromagnetic materials; dysprosium alloys; electrical resistivity; energy gap; erbium alloys; gadolinium alloys; holmium alloys; impurity states; magnetic moments; magnetic susceptibility; magnetisation; narrow band gap semiconductors; neodymium alloys; paramagnetic materials; solid-state phase transformations; terbium alloys; thermoelectric power; yttrium alloys; 1.7 to 300 K; DyPdBi; ErPdBi; ErPdSb; Fermi level; GdPd2Sb; HoPdBi; HoPdSb; NdPdBi; Seebeck coefficient; TbPd2Sb; YPdBi; YPdSb; antiferromagnetism; cubic-lower-symmetry structural transformation; electrical resistivity; energy gaps; impurity levels; magnetic moment; magnetic susceptibility; magnetization; narrow-gap semiconductors; paramagnetism; physical properties; rare-earth-based Heusler phases; thermal depopulation; thermoelectric figure of merit; thermoelectric power; Bismuth; Electric resistance; Electric variables measurement; Erbium; Magnetic field measurement; Magnetic susceptibility; Phase measurement; Power measurement; Temperature distribution; Thermoelectricity;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Thermoelectrics, 2005. ICT 2005. 24th International Conference on
ISSN :
1094-2734
Print_ISBN :
0-7803-9552-2
Type :
conf
DOI :
10.1109/ICT.2005.1519966
Filename :
1519966
Link To Document :
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