Devices and methods for making polycrystalline alloys
A process for preparing alloy products is described using a self-sustaining or self-propagating SHS-type combustion process with point-source ignition, preferably a laser, in a pressurized vessel. Binary, ternary and quaternary alloys can be formed with control over polycrystalline structure and bandgap. Methods to tune the bandgap and the alloys formed are described. The alloy products may be doped. Preferably sulfides, tellurides or selenides are formed. Cooling during reaction takes place.
1. A method of forming a metallic alloy comprising:
blending a mixture of particles of a first metallic substance comprising Cd, having a particle size of less than 100 μm and particles of at least one second substance comprising at least one of Se, Te, S, Hg, or Zn, having a particle size of less than 100 μm, thereby forming a blended mixture, wherein the blended mixture further comprises a quenchant, and wherein the quenchant comprises at least one of CdTe, CdSe, CdS, or ZnTe;
pressurizing the blended mixture to a pressure of about 100 to 20,000 KPa in a pressure reactor;
initiating a self-propagating reaction by directing a point energy source to a localized portion of the blended mixture inside the pressure reactor, and
cooling the pressure reactor during propagation of the exothermic reaction, to remove heat generated from the reaction, thereby forming an alloyed ingot comprising the metallic alloy.
2. The method of claim 1 , wherein the point energy source is a laser.
3. The method of claim 1 , further comprising:
maintaining a pressure during the self-propagating reaction, wherein the pressure is selected from the group consisting of: 2,000-3,000 KPa; 1,000-5,000 KPa; 500-10,000 KPa; and 1,000-10,000 KPa.
4. The method of claim 1 , wherein the blended mixture substantially comprises particles having a size selected from the group consisting of: 1-50 μm; 1-100 μm; and less than 50 μm.
5. The method of claim 1 , further comprising:
loading the alloyed ingot into a furnace; and
annealing the alloyed ingot by maintaining a selected stabilizing temperature for a selected duration,
wherein the stabilizing temperature is selected from: (a) 500 to 800° C.; or (b) 800 to 1100° C.; and
wherein the duration is 2-24 hours.
6. The method of claim 1 , wherein the blended mixture further comprises at least one dopant selected from the group consisting of: Bi; Cl; Cu; Sb; Hg; In; Ga; Ag; Au; Br; I; As; Pb; Na; Li; K; B; Al; Tl; Ge; Sn; P; Si; and F.
7. The method of claim 1 , wherein the alloyed ingot comprising the metallic alloy comprises a CdSe x Te (1-x) composition, wherein x is between 0 and 1, and having a manipulated crystalline structure between cubic and hexagonal structure.
8. The method of claim 7 , wherein x is between 0.20 and 1 and wherein the crystalline structure of the CdSe x Te (1-x) composition is greater than 90% cubic.
9. A method of tuning the bandgap of an alloyed ingot comprising a CdSe x Te (1-x) composition, the method comprising: identifying a desired bandgap value in the range of 1.1 to 1.8 eV;
coarse tuning the bandgap by selecting a value for x, wherein a value for x less than 0.5 corresponds to a bandgap between 1.1 and 1.50, and wherein a value for x greater than 0.5 corresponds to a bandgap between 1.40 and 1.8;
blending Cadmium, Tellurium, and Selenium powders according to the formula CdSe x Te (1-x) with particles size from 1 to 100 μm to form a blended mixture, wherein the blended mixture further comprises a quenchant, and wherein the quenchant comprises at least one of CdTe, CdSe, CdS, or ZnTe;
heating a localized portion of the blended mixture in a pressurized reaction chamber to initiate a self-propagating reaction in the mixture, thereby producing a formed ingot; cooling the pressure reactor during propagation of the exothermic reaction, to remove heat generated from the reaction;
fine tuning the bandgap of the formed ingot, wherein the fine tuning comprises annealing the formed ingot at a selected stabilizing temperature; and
wherein the fine tuning comprises: selecting an annealing temperature to manipulate the crystal structure, whereby the bandgap may be lowered by about 0.02 eV by annealing at a temperature of about 500-750° C., or the bandgap may be increased by about 0.02 eV by annealing at a temperature of about 860-1100° C.;
thereby forming the alloyed ingot with the selected bandgap value.
10. The method of claim 9 , wherein the pressurized reaction chamber is pressurized to a pressure in a range of 100 to 20,000 KPa during the self-propagating reaction.
11. The method claim 1 , wherein the pressure reactor is cooled during the self propagating exothermic reaction by means of coolant fluid circulating about the pressure reactor in a cooling jacket.
12. The method of claim 1 , wherein the metallic alloy is a ternary alloy containing cadmium.
13. The method of claim 1 , wherein the metallic alloy is a binary alloy containing cadmium.
14. The method of claim 1 , wherein the metallic alloy is a quaternary alloy containing cadmium.
15. The method of claim 1 , wherein the metallic alloy is a ternary alloy having an atomic composition of CdSe x Te (1-x) , wherein x is between 0.20 and 0.99.
16. The method of claim 1 , wherein the quenchant comprises CdTe.
17. The method of claim 1 , wherein the quenchant comprises quenchant particles having a size in a range from about 10 μm to about 300 μm, and wherein a composition of the blended mixture comprises from about 5% to about 60% quenchant by weight.
18. The method of claim 1 , wherein the point energy source comprises at least one of a maser or a plasma gun.
19. The method of claim 1 , further comprising:
loading the alloyed ingot into a furnace; and
annealing the alloyed ingot by maintaining a selected temperature for a selected duration,
wherein the selected temperature is in a range of 300° C. to 950° C.; and
wherein the selected duration is in a range of 0.5 hours to 15 hours.
20. The method of claim 1 , wherein the quenchant comprises quenchant particles having a size in a range from about 10 μm to about 300 μm.