Stabilized lanthanum sulphur compounds
AssigneeThe United States of America as represented by the United States National Aeronautics and Space Administration
InventorsGeorge H. Reynolds, Norbert B. Elsner, Clyde H. Shearer
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Abstract
Lanthanum sulfide is maintained in the stable cubic phase form over a temperature range of from 500.degree. C. to 1500.degree. C. by adding to it small amounts of calcium, barium, or strontium. This novel compound is an excellent thermoelectric material.
Claims3
The method of forming a thermoelectric material of lanthanum sulfide which exhibits a stable phase form over a temperature range from about 500.degree. C. to 1500.degree. C. wherein thermoelectric properties exist, said method comprising the steps of:
- blending at room temperature lanthanum sulfide and an ingredient selected from calcium, barium or strontium to form a lanthanum sulfide compound having the following formula:
- (La, M)S.sub.1.5-x
- where x is greater than 0 and less than 0.1 and M is selected from the group consisting of calcium, barium or strontium, and M is present in an amount sufficient to stabilize the cubic phase of said material at temperatures as low as about 500.degree. C.;
- selecting M in an amount ranging from 0.1 to 5.0 weight percent;
- slowly heating the blended ingredients in a vacuum to a temperature of about 1100.degree. to 1200.degree. C.;
- allowing a chemical homogenization to occur;
- and
- fabricating said thermoelectric material from the homogenized compound.
The method of forming a thermoelectric material of lanthanum sulfide which exhibits a stable cubic phase form over a temperature range from about 500.degree. C. to 1500.degree. C. wherein thermoelectric properties exist, said method comprising the steps of:
- reacting lanthanum and an ingredient selected from calcium, barium or strontium with a sulfur vapor at a temperature of about 600.degree. C. to 1200.degree. C. in a closed reaction vessel to form a lanthanum sulfide compound having the following formula:
- (La, M)S.sub.1.5-x
- where x is greater than 0 and less than 0.1 and M is selected from the group consisting of calcium, barium or strontium, and M is present in an amount ranging from 0.1 to 5 weight percent sufficient to stabilize the cubic phase of said material at temperatures as low as about 500.degree. C.;
- selecting M in an amount ranging from 0.1 to 5.0 weight percent;
- allowing a chemical homogenization to occur in the reaction vessel;
- and
- fabricating said thermoelectric material from the homogenized compound.
The method of forming a thermoelectric material of lanthanum sulfide which exhibits thermoelectric properties over a temperature range from about 500.degree. C. to 1500.degree. C. by exhibiting a stable cubic phase form over said temperature range, said method comprising the steps of:
- individually heating to about 1200.degree. C. the ingredients of lanthanum, sulphur and one ingredient selected from calcium, barium, or strontium to form a lanthanum sulfide compound having the following formula:
- (La, M)S.sub.1.5-x
- where x is greater than 0 and less than 0.1 and M is selected from the group consisting of calcium, barium, and strontium, and M is present in an amount ranging from 0.1 to 5 weight percent sufficient to stabilize the composition in it's cubic crystalline phase at temperatures as low as about 500.degree. C.;
- cooling the heated compound;
- crushing the compound into powder;
- and
- fabricating said thermoelectric material from said powder.
Dependencies are inferred from the claim text.