R. Martin-Lopez

Preparation and transport properties of polycrystalline Bi and Bi–SiO2 nanocomposites

Bismuth–silica nanocomposites and polycrystalline bismuth were prepared via powder metallurgy in order to study the influence of silica inclusions on the thermoelectric properties of bismuth. Bi–SiO2 powders containing from 0.5 to 15 vol. % of silica and pure Bi powders were produced by an arc-plasma processing. Transmission electron microscopy investigations revealed the presence of a nanometric silica shell around the Bi grains. The powders were cold pressed and sintered close to the melting temperature of bismuth. The bulk microstructures are very different for the bismuth and the Bi–SiO2 nanocomposites because silica, which is primarily dispersed at grain boundaries, inhibits the grain growth during sintering. The electrical resistivity was measured from 5 to 300 K, while the thermoelectric power and the thermal conductivity were measured from 65 to 300 K on both polycrystalline bismuth and Bi–SiO2 samples containing 0.5, 4, and 15 vol. % of silica, respectively. The transport properties are mainly di...

Mechanical alloying of BiSb semiconducting alloys

Abstract Polycrystalline Bi 100− x Sb x ( x =7, 10, 12, 15, 22) semiconducting alloys were synthesized by mechanical alloying in order to achieve performant homogeneous thermoelectric materials. The influence of the milling parameters on the final homogeneity and morphology of the powders, such as ball-to-powder weight ratios (BPR=10:1, 40:1, 92:1) and balls sizes (diameters of 30 and 20 mm), was investigated. Powder samples were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and electron microprobe analysis. The results show that the samples obtained with the 10:1 BPR and four balls of 30 mm in diameter present the best homogeneity whatever the alloy composition.

Production of ultrafine powders of BiSb solid solution

Investigations of the synthesis and consolidation of bismuth-antimony alloys submicrometric powders were performed. Powders containing from 6 to 20 atomic percent of antimony were prepared by evaporation of Bi-Sb pre-alloyed targets using arc energy under argon-hydrogen atmosphere. Chemical analyses, EDS analyses, morphological and microstructural studies were performed on the product powders. The influence of the evaporation parameters on the powder generation yield and the local chemical composition of the powders was studied. We show that the control of the powder permits adjustment in the powder particle size from 25 nm to 0.8 μm. Finally, we present the influence of the ultrafine powder morphology on the microstructure of bulk alloys prepared by cold pressing powders.

Unusual growth of pulsed laser deposited bismuth films on Si(100)

Abstract Pulsed laser deposition of bismuth films was performed from a Nd:YAG laser ( λ =532 nm) in a high vacuum chamber onto glass or Si(100) substrates. The influences of deposition temperature and deposition duration on the film growth were checked on both substrates. The films were characterised by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and X-ray diffraction. Unusual growth was observed at the beginning of the process with films deposited on Si(100) at low and high temperature as compared to glass and also to more conventional deposition techniques. The strong texture observed for room temperature deposited films and the increase of rate growth as compared with glass are discussed in terms of epitaxial growth.

Thermoelectric materials of p and n type from the (Bi,Sb,Te) phase diagram

It seems that the lower figure of merit for sintered n type telluride compounds is due to the selenium segregation at the grain boundaries. We present the transport properties of the Bi/sub 2/Te/sub 3/ and Sb/sub 2/Te/sub 3/ binary compounds in terms of stoichiometric deviation. We discuss these properties along the pseudo-binary phase diagram to determine the domain of existence of Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ solid solutions. The study of the (Bi,Sb,Te) phase diagram allowed us to identify a zone where n-type materials can be obtained.

On the use of bismuth in quantum wells

A rapid survey of some theoretical considerations concerning the use of multiple quantum well structures (MQWS) in thermoelectricity is given as well as why bismuth can be a prospective material for the development of a new class of thermoelectric systems. Problems arising from Bi film synthesis are discussed, in relation with the preparation of Bi-based MQWS. Some experimental results are reported on pulsed laser deposited Bi films prepared in our laboratory.

Observation of the grain size influence on the thermoelectric properties of polycrystalline bismuth-antimony alloys

This paper is devoted to the study of the transport properties of polycrystalline Bi/sub 86.5/Sb/sub 13.5/ alloys. Pellets of polycrystalline alloys were prepared by cold pressing and sintering of ultrafine powders. The average grain size of the bulk materials was adjusted from 0.1 /spl mu/m to 200 /spl mu/m. The influence of the microstructure and the grain size on both electrical and thermal conductivity, thermoelectric power and thermoelectric figure of merit is presented.

Influence of the consolidation technique on the thermoelectric properties of mechanically alloyed Bi-Sb

The aim of this work is multiple: first the synthesis by mechanical alloying of homogeneous Bi/sub 85/Sb/sub 15/ polycrystalline powder alloys, that have been achieved with an adequate ball to powder weight ratio (10:1), second the consolidation of the powders either by sintering or by hot extrusion in order to try to introduce a texture in the material and finally to measure the thermoelectric properties of the consolidated samples in the 77-300 K temperature range.