Increasing figure-of-merit of ZrNiSn half-Heusler alloy by minimal substitution and thermal conductivity reduction

摘要

Thermal conductivity of ZrNiSn limits figure-of-merit and hence combination of isoelectronic and non-isoelectronic substitutions, (Zr1-xTix)Ni(Sn(1-y)A(y)) with A=Ge, Si, Sb have been made to reduce thermal conductivity. All alloys are essentially single phase with large grains and uniform chemical composition. Electrical resistivity of all the substituted alloys is in the range 0.4-5mcm, lower than the pristine alloy resistivity of 9mcm. The carrier concentration of the alloys is similar to 10(20)cm(-3) with the mobility varying between 2.7 and 27.1cm(2)V(-1)s(-1) indicating band structure changes with substitutions. All the alloys are n-type with a reduced Seebeck in the range 50-100 mu VK-1 compared to the pristine alloy. The ZrNiSn0.95Ge0.05 alloy with a carrier mass of 2.49m(e) has the highest Seebeck compared to the double substituted alloy Zr0.75Ti0.25NiSn0.97Si0.03 which has a carrier mass of 0.85 me. The thermal conductivity of this alloy however is found to be lowest similar to 3.2Wm(-1)K(-1) due to alloy scattering. The ZrNiSn0.95Ge0.05 alloy however has the highest power factor of 2.9mWm(-1)K(-2) with a 35% reduced thermal conductivity resulting in highest figure-of-merit compared to all the other alloys including the pristine alloy. The leg efficiency of this alloy is found to be 6% with a power output of 2.3Wcm(-2) at 1000K.