News Column

Researchers Submit Patent Application, "Thermoelectric Skutterudite Compositions and Methods for Producing the Same", for Approval

July 24, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Ren, Zhifeng (Houston, TX); Yang, Jian (Brookline, MA); Yan, Xiao (Chicago, IL); He, Qinyu (Guangzhou, CN); Chen, Gang (Carlisle, MA); Hao, Qing (Tucson, AZ), filed on March 5, 2014, was made available online on July 10, 2014.

The patent's assignee is Trustees Of Boston College.

News editors obtained the following quote from the background information supplied by the inventors: "Thermoelectric materials can be utilized in a variety of industrial applications including high quality power generation devices and cooling devices. They can also be used in solar conversion and extraction of automotive or industrial waste heat. The thermoelectric properties of any material can be characterized by a quantity called figure of merit Z (or dimensionless figure of merit ZT), defined as Z=S.sup.2.pi./k, where S is Seebeck coefficient, .sigma. is electrical conductivity, and k is total thermal conductivity. It is desirable to construct materials with high ZT values (e.g., having low thermal conductivity k and/or high power factor S.sup.2.sigma.). Accordingly, researchers continue to seek to produce materials that exhibit superior ZT values.

"Skutterudites are a potentially attractive class of substances that might be used in producing thermoelectric materials. They typically exhibit outstanding electrical properties, including high electrical charge mobilities and substantial Seebeck coefficients--which can result in high power factors. Unfortunately, they also often exhibit high thermal conductivities, which can limit the overall ZT value that can be achieved by a thermoelectric material.

"Accordingly, the need persists to develop thermoelectric materials that exhibit attractive performance properties, including materials that may be related to skutterudites."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Some embodiments of the present invention are directed to methods of fabricating an enhanced thermoelectric material. Such materials can exhibit good ZT values (e.g., greater than about 0.8), which can occur at one or more selected temperatures (e.g., at a temperature below about 800.degree. C.). A plurality of nanoparticles can be generated from one or more starting materials. The starting material(s) can be one or more elements, and/or include one or more skutterudite-based starting materials (e.g., two or more skutterudite-based starting materials). When the latter are used, the densified material can exhibit a higher ZT value at least at one temperature relative to at least one of the skutterudite-based starting materials. The starting material can optionally include one or more types of filler atoms, which can be used in the skutterudite-based structure. Such nanoparticles can be consolidated under pressure and an elevated temperature to form a densified material. The densified material can include a plurality of grains, in which each grain can exhibit a skutterudite-based structure. The skutterudite-based structure, which can be filler-containing, can include a crystal having metal atoms (e.g., having one, two, or more of cobalt, iron, nickel, rhodium, iridium, ruthenium, and osmium) forming a cubic sublattice. The grains can exhibit an average size smaller than about 5 microns, and optionally larger than the average size of the nanoparticles from which the densified material was formed.

"Generation of nanoparticles can be performed using any number of methodologies. In some embodiments, generation of nanoparticles can include grinding (e.g., ball milling) at least one starting material to form the nanoparticles. When multiple starting materials are utilized, the materials can be combined together in any combination and ground, or ground separately to a final disposition for consolidation, or separately ground and then mixed together and ground further to a disposition for consolidation. Materials being grinded can also be cooled, which can promote particle formation in some instances. The average size of the generated nanoparticles can be smaller than about 50 nm.

"Consolidation of nanoparticles can also be performed using any number of techniques. In some embodiments, consolidation is performed using a hot press process (e.g., using at least one of direct current induced hot press, unidirectional hot press, plasma pressure compaction, and isostatic hot press). The consolidation can occur at a pressure in a range from about 10 MPa to about 900 MPa; and/or using a temperature in a range from about 200.degree. C. to about 800.degree. C. The time period to which the nanoparticles are subjected to a pressure and elevated temperature can be between about 1 sec and about 10 hours.

"Other embodiments of the present invention are directed to thermoelectric materials, which can include a plurality of compacted crystalline skutterudite-based grains. Such thermoelectric materials can exhibit a ZT value greater than about 0.5, 0.8, or 1. The crystalline skutterudite-based grains can include crystallites having metal atoms (e.g., having one, two, or more of cobalt, iron, nickel, rhodium, iridium, ruthenium, and osmium) forming a cubic sublattice. Group VA atoms can be included, which can form a plurality of planar rings within the cubic sublattice. Filler atoms can also, optionally, be added, where filler atoms can include at least one a rare earth element and a Group IIA element. The grains can exhibit an average size of less than about 5000 nm or 1000 nm.

"Other embodiments of the present invention are directed to thermoelectric materials, which can include a skutterudite-based structure. The structure can include grains each exhibiting a unit cell formed from (i) at least one Group VA element, and (ii) at least one of cobalt, iron, nickel, rhodium, iridium, ruthenium, and osmium. The grains can exhibit an average size of less than about 5000 nm or less than about 1000 nm. The structure can also include at least one type of filler atom in each unit cell, such as a rare earth element and/or a Group IIA element. In some instances the at least one filler atom comprises at least one, or at least two, of cerium, neodymium, lanthanum, barium, and ytterbium. In some instances, the structure can be characterized by an enhanced ZT value relative to a bulk material having the skutterudite-based structure. For example, the thermoelectric material can exhibit a ZT value greater than about 0.8 or about 1.0; the ZT value can optionally be exhibited at a temperature below about 600.degree. C.

"Thermoelectric materials, consistent with embodiments of the invention, can include at least one of a n-type material and a p-type material. In some instances, the thermoelectric material is a p-type material. The p-type material can include a composition consistent with the formula

"ReFe.sub.4-yM.sub.ySb.sub..about.12

"where Re is at least one of a rare earth element and a Group IIA element (e.g., barium), M is cobalt or nickel or combinations of them with other elements, and y is zero or a positive number no greater than 4. For instance, the p-type material can include a composition consistent with the formula ReFe.sub.35Co.sub.0.5Sb.sub..about.12, where Re is any one of neodymium, cerium, lanthanum, or ytterbium.

"In other instances, the thermoelectric material is a n-type material. The n-type material can include a composition consistent with the formula

"Re.sub.zM.sub.yCo.sub.4-ySb.sub..about.12

"where Re is at least one of a rare earth element and a Group IIA element, M is a metal, y is zero or a positive number no greater than 4; and z is a positive number no greater than 1. For example, the thermoelectric material can include a composition consistent with a formula: Re.sub.zCo.sub..about.4Sb.sub..about.12, where z is a number between about 0.2 and about 1, and Re is at least one of cerium, neodymium, lanthanum, barium, and ytterbium. In another example, the thermoelectric material comprises a n-type composition consistent with a formula: Re1.sub.Z1Re2.sub.Z2Co.sub..about.4Sb.sub..about.12, where Z1 and Z2 are each independently a number between about 0.2 and about 1 with a sum of Z1 and Z2 not greater than about 1, and Re1 and Re2 are each independently at least one of cerium, neodymium, lanthanum, barium, and ytterbium. In yet another example, the thermoelectric material comprises a composition consistent with a formula: Yb.sub.zM.sub.yCo.sub.4-ySb.sub.12, where z is any number between about 0.2 and about 1, and y is optionally zero.

"Additional embodiments of the invention are drawn toward thermoelectric materials that can include a filler enhanced skutterudite material comprising at least one type of filler, which can be distributed throughout the thermoelectric material. The filler enhanced skutterudite material can exhibit a higher fractional amount of the at least one type of filler relative to a maximum achievable equilibrium fractional amount of the at least one type of filler in a bulk form of the filler enhanced skutterudite-based material. For instance, the materials can include a composition consistent with the formula Yb.sub.zCo.sub.4Sb.sub.12, where z is any number between about 0.2 and about 1, or between about 0.3 and about 0.5 (e.g., 0.3, 0.4, or 0.5).

BRIEF DESCRIPTION OF THE FIGURES

"FIG. 1 presents a perspective schematic diagram of a CoSb.sub.3 skutterudite crystal structure, consistent with some embodiments of the present invention;

"FIG. 2a presents a transmission electron micrograph image of a ball milled sample particles before hot pressing, consistent with some embodiments of the invention;

"FIG. 2b presents a transmission electron micrograph at higher magnification that the image of FIG. 2a within the circular region shown in FIG. 2a;

"FIG. 3 presents a scanning electron microscopy image of a DC hot pressed sample of Yb.sub.0.35Co.sub.4Sb.sub.12, in accord with some embodiments;

"FIG. 4 presents superimposed graphs of intensity versus angle 20 taken from x-ray diffraction scans of five hot-pressed samples each having a stoichiometry corresponding with the formula Yb.sub.xCo.sub.4Sb.sub.12, where for individual samples x is equal to one of 0.3, 0.35, 0.4, 0.5 and 1.0, consistent with some embodiments;

"FIG. 5a presents a transmission electron microscopy image of a hot pressed sample having a composition following the formula Yb.sub.0.35Co.sub.4Sb.sub.12, consistent with some embodiments;

"FIG. 5b presents a transmission electron microscopy image of the hot pressed sample shown in FIG. 5a at higher magnification;

"FIG. 6 presents graphs of carrier concentration and Hall mobility at room temperature for various hot pressed samples having a stoichiometry consistent with the formula Yb.sub.xCo.sub.4Sb.sub.12, where x ranges from 0.3 to 0.5, consistent with some embodiments;

"FIG. 7a presents graphs of the measured electrical conductivity as a function of temperature for hot pressed samples consistent with the formula Yb.sub.xCo.sub.4Sb.sub.12, where x is 0.3, 0.35, 0.4, 0.5, and 1, consistent with some embodiments;

"FIG. 7b presents graphs of the measured Seebeck coefficient as a function of temperature for the hot pressed samples in FIG. 7a;

"FIG. 7c presents graphs of the measured thermal conductivity as a function of temperature for the hot pressed samples in FIG. 7a;

"FIG. 7d presents graphs of ZT values as a function of temperature for the hot pressed samples in FIG. 7a;

"FIG. 8a presents graphs of the measured resistivity as a function of temperature for hot pressed samples having the following stoichiometries: La.sub.0.3Co.sub.4Sb.sub.12, Nd.sub.0.3Co.sub.4Sb.sub.12, and Yb.sub.0.3Co.sub.4Sb.sub.12, consistent with some embodiments;

"FIG. 8b presents graphs of the measured Seebeck coefficient as a function of temperature for the hot pressed samples in FIG. 8a;

"FIG. 8c presents graphs of the calculated power factor as a function of temperature for the hot pressed samples in FIG. 8a;

"FIG. 8d presents graphs of the measured thermal conductivity as a function of temperature for the hot pressed samples in FIG. 8a;

"FIG. 8e presents graphs of the lattice thermal conductivity as a function of temperature for the hot pressed samples in FIG. 8a;

"FIG. 8f presents graphs of ZT values as a function of temperature for the hot pressed samples in FIG. 8a;

"FIG. 9a presents graphs of the measured resistivity as a function of temperature for hot pressed samples having the following stoichiometries: La.sub.0.1Yb.sub.0.3Co.sub.4Sb.sub.12, Ce.sub.0.03Yb.sub.0.3Co.sub.4Sb.sub.12, Ba.sub.0.1Yb.sub.0.3Co.sub.4Sb.sub.12, and Yb.sub.0.3Co.sub.4Sb.sub.12, consistent with some embodiments;

"FIG. 9b presents graphs of the measured Seebeck coefficient as a function of temperature for the hot pressed samples in FIG. 9a;

"FIG. 9c presents graphs of the calculated power factor as a function of temperature for the hot pressed samples in FIG. 9a;

"FIG. 9d presents graphs of the measured thermal conductivity as a function of temperature for the hot pressed samples in FIG. 9a;

"FIG. 9e presents graphs of the lattice thermal conductivity as a function of temperature for the hot pressed samples in FIG. 8a;

"FIG. 9f presents graphs of ZT values as a function of temperature for the hot pressed samples in FIG. 8a;

"FIG. 10a presents a transmission electron microscopy image of particles having a composition consistent with the formula CeFe.sub.3.5Co.sub.0.5Sb.sub.12 after 20 hours of ball milling, consistent with some embodiments;

"FIG. 10b presents a transmission electron microscopy image of the particles of FIG. 10a at a higher magnification;

"FIG. 11a presents a scanning electron microscopy image of a DC hot pressed sample of particles made from materials having the stoichiometry CeFe.sub.3.5Co.sub.0.5Sb.sub.12 after 20 hours of ball milling, consistent with some embodiments;

"FIG. 11b presents a transmission electron microscopy image of the sample in FIG. 11a;

"FIG. 12a presents graphed data of the measured electrical conductivity as a function of temperature for hot pressed samples of particles having the stoichiometry NdFe.sub.3.5Co.sub.0.5Sb.sub.12, where individual samples used particles ball milled for 15, 20, or 25 hours, consistent with some embodiments;

"FIG. 12b presents graphed data of measured Seebeck coefficient as a function of temperature for the samples in FIG. 12a;

"FIG. 12c presents graphed data of calculated values of the product of the power factor with temperature as a function of temperature for the samples in FIG. 12a;

"FIG. 12d presents graphed data of measured thermal conductivity as a function of temperature for the samples in FIG. 12a;

"FIG. 12e presents graphed data of ZT values as a function of temperature for the samples in FIG. 12a;

"FIG. 13a presents graphed data of the measured electrical conductivity as a function of temperature for hot pressed samples of particles having the stoichiometries NdFe.sub.3.5Co.sub.0.5Sb.sub.12, LaFe.sub.3.5Co.sub.0.5Sb.sub.12, YbFe.sub.3.5Co.sub.0.5Sb.sub.12, and CeFe.sub.3.5Co.sub.0.5Sb.sub.12, where samples used particles ball milled for 20 hours, consistent with some embodiments;

"FIG. 13b presents graphed data of measured Seebeck coefficient as a function of temperature for the samples in FIG. 13a;

"FIG. 13c presents graphed data of calculated values of the product of the power factor with temperature as a function of temperature for the samples in FIG. 13a;

"FIG. 13d presents graphed data of measured thermal conductivity as a function of temperature for the samples in FIG. 13a;

"FIG. 13e presents graphed data of ZT values as a function of temperature for the samples in FIG. 13a;

"FIG. 14a presents graphed data of the measured electrical conductivity as a function of temperature for hot pressed samples of particles having the stoichiometries NdFe.sub.3.5Co.sub.0.5Sb.sub.12 and Nd.sub.0.9Fe.sub.3.5Co.sub.0.5Sb.sub.12, where samples used particles ball milled for 15s hours, consistent with some embodiments;

"FIG. 14b presents graphed data of measured Seebeck coefficient as a function of temperature for the samples in FIG. 14a;

"FIG. 14c presents graphed data of calculated values of the product of the power factor with temperature as a function of temperature for the samples in FIG. 14a;

"FIG. 14d presents graphed data of measured thermal conductivity as a function of temperature for the samples in FIG. 14a;

"FIG. 14e presents graphed data of ZT values as a function of temperature for the samples in FIG. 14a;

"FIG. 15a presents graphed data of the measured electrical conductivity as a function of temperature for hot pressed samples of particles having the stoichiometries LaFe.sub.3.5Co.sub.0.5Sb.sub.12 and La.sub.0.9Yb.sub.0.1Fe.sub.3.5Co.sub.0.5Sb.sub.12, where samples used particles ball milled for 15s hours, consistent with some embodiments;

"FIG. 15b presents graphed data of measured Seebeck coefficient as a function of temperature for the samples in FIG. 15a;

"FIG. 15c presents graphed data of calculated values of the product of the power factor with temperature as a function of temperature for the samples in FIG. 15a;

"FIG. 15d presents graphed data of measured thermal conductivity as a function of temperature for the samples in FIG. 15a; and

"FIG. 15e presents graphed data of ZT values as a function of temperature for the samples in FIG. 15a."

For additional information on this patent application, see: Ren, Zhifeng; Yang, Jian; Yan, Xiao; He, Qinyu; Chen, Gang; Hao, Qing. Thermoelectric Skutterudite Compositions and Methods for Producing the Same. Filed March 5, 2014 and posted July 10, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3713&p=75&f=G&l=50&d=PG01&S1=20140703.PD.&OS=PD/20140703&RS=PD/20140703

Keywords for this news article include: Barium, Cerium, Nickel, Neodymium, Ytterbium, Heavy Metals, Nanoparticle, Nanotechnology, Transition Elements, Alkaline Earth Metals, Emerging Technologies, Lanthanoid Series Elements, Trustees Of Boston College.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Politics & Government Week


Story Tools






HispanicBusiness.com Facebook Linkedin Twitter RSS Feed Email Alerts & Newsletters