I claim:
1. A process for producing bismuth telluride comprising the steps of:
dissolving tellurium to form a tellurium first solution;
heating said first solution to approximately 70.degree. C.;
stirring said first solution;
adding an amount of bismuth trioxide to said first solution to produce a second solution wherein the ratio of Bi: Te equals 2:3;
cooling said second solution to approximately 25.degree. C.;
preparing a solution of concentrated aqueous ammonia and distilled water;
adding said solution of concentrated aqueous ammonia and distilled water dropwise to said second solution at approximately 25.degree. C. to form a third solution;
stirring said third solution to produce a precipitate therefrom;
separating said precipitate from said third solution by centrifuging to produce a separated precipitate;
washing said separated precipitate to produce a washed precipitate;
drying said washed precipitate in air to produce a dried precursor powder; and
heating said dried precursor powder to 250.degree. C.-275.degree. C.; while
exposing said dried precursor powder to flowing hydrogen at 1 atmosphere pressure for a period of 3 to 12 hours to produce a final black powder of bismuth telluride.
2. The process as claimed in claim 1 wherein:
said precursor powder comprises Bi.sub.2 Te.sub.3 O.sub.9.xH.sub.2 O, where x=1.
3. The process as claimed in claim 2 wherein:
said precursor powder is formed in accordance with the chemical reaction (1): @@STR2@@ and said bismuth telluride is formed in accordance with the chemical reaction (2): @@STR3@@
4. The process as claimed in claim 2 wherein:
said dissolving step to form said tellurium first solution comprises dissolving 0.44 moles of tellurium in 300 ml of 6M nitric acid;
said solution of concentrated aqueous ammonia and distilled water comprises 370 ml concentrated aqueous ammonia and 370 ml distilled water; and
said washing comprises washing three times with distilled water.
5. The process as claimed in claim 2 and further comprising:
compacting said bismuth telluride powder to form compacted powder; and
sintering said compacted powder in hydrogen at 400.degree. C.
6. The process as claimed in claim 3 and further comprising:
compacting said bismuth telluride powder to form compacted powder; and
sintering said compacted powder in hydrogen at 400.degree. C.
7. The process as claimed in claim 4 and further comprising:
compacting said bismuth telluride powder to form compacted powder; and
sintering said compacted powder in hydrogen at 400.degree. C.
8. The process as claimed in claim 1 wherein:
said dissolving step to form said tellurium first solution comprises dissolving said tellurium in nitric acid.