Electrical Resistivity Seebeck Coefficient Research Articles

Phase Transformation and Thermoelectric Properties of Fe0.92Mn0.08Si2 Prepared by Mechanical Alloying

In an attempt to enhance phase transformation and homogenization of Mn-doped , mechanical alloying of elemental powders was applied. Cold pressing and sintering in vacuum were carried out to produce a dense microstructure, and then isothermal annealing was employed to induce a phase transformation to the -semiconductor. Phase transitions in this alloy system during the process were investigated by using XRD, EDS and SEM. As-milled powders after 100 h of milling were shown to be metastable state. As-sintered iron silicides consisted of untransformed mixture of -and -FeSi phases. -phase transformation was induced by subsequent isothermal annealing at , and near single phase of -was obtained after 24 h of annealing. Thermoelectric properties in terms of Seebeck coefficient, and electrical conductivity were evaluated and correlated with phase transformation. Seebeck coefficient electrical resistivity and hardness increased with increasing annealing time due to phase transformation.

Irradiation effects on thermoelectric materials

The effects of neutron irradiation on the thermoelectric properties, i.e., electrical resistivity Seebeck coefficient, and relative thermal conductivity, were determined for lead telluride (PbTe), germanium telluride (GeTe), bismuth-germanium telluride (Bi 0.05Ge 0.95Te), and lithium-nickel oxide (Li 0.06Ni 0.94O). Two types of experiments were performed: (1) Using the same apparatus for both pre- and post-irradiation measurements, thermoelectric properties were measured over a range of temperatures, and (2) in situ measurements were made of electrical resistivity and Seebeck coefficient at elevated temperatures. Pre-post- experiments were made on thermoelectric materials irradiated to the total integrated neutron flux ( nvt) levels as noted in the following table: Materials Total integrated neutron flux ( nvt calculated) 1. GeTe 4 · 5 × 10 18 thermal 2. GeTe 1 · 5 × 10 20 fast 3. Bi 0.05Ge 0.95Te 9 · 4 × 10 18 thermal 4. Bi 0.05Ge 0.95Te 2 · 7 × 10 19 thermal 5. Bi 0.05Ge 0.95Te 1 · 5 × 10 20 fast 6. PbTe-n- type 1 · 4 × 10 19 thermal 7. PbTe-n- type 1 · 5 × 10 20 fast 8. PbTe-n- type 1 · 5 × 10 29 fast|none All of the materials irradiated in a thermal flux showed evidence of radiation damage; however, essentially complete recovery of the electrical resistivity, Seebeck coefficient, and thermal conductivity occurred after annealing at average temperatures up to 300°C. Irradiation in a fast flux resulted in damage which was not completely removed by annealing to an average temperature of up to 300°C. In-pile measurements of electrical resitivity and Seebeck coefficient were made on p-type PbTe and Li 0.06Ni 0.94O irradiated to a total integrated thermal neutron flux of 9 × 10 18 at a temperature of approximately 400°C. Measurements made on Li 0.06Ni 0.94O revealed no change in electrical resistivity and Seebeck coefficient as a function of integrated neutron flux. For the PbTe sample, the Seebeck coefficient increased slightly while the electrical resistivity increased by a factor of two. This change is attributed to a loss of sodium volatilization.