Ruiheng Liu

High-Performance Pseudocubic Thermoelectric Materials from Non-Cubic Chalcopyrite Compounds

J. Zhang, Dr. R. Liu, N. Cheng, Dr. Y. Zhang, Prof. X. Shi, Prof. L. Chen, Prof. W. Zhang State Key Laboratory of High Performance Ceramics and Superfi ne Microstructure Shanghai Institute of Ceramics Chinese Academy of Sciences, 1295 Dingxi Road Shanghai 200050 , China E-mail: xshi@mail.sic.ac.cn; cld@mail.sic.ac.cn; wqzhang@mail.sic.ac.cn J. Zhang, N. Cheng University of Chinese Academy of Sciences Beijing 100049 , China Prof. J. Yang Materials Science and Engineering Department University of Washington Seattle , Washington 98195-2120 , USA Prof. C. Uher Department of Physics, University of Michigan Ann Arbor , Michigan 48109 , USA

Influence of pressures on the crystallization process of an amorphous Fe73.5Cu1Nb3Si13.5B9 alloy

Amorphous Fe73.5Cu1Nb3Si13.5B9 alloys, prepared by a melt-spinning technique, were annealed at a temperature of 823 K under pressures in the range of 1–5 GPa and ambient pressure. The high pressure experiments were carried out in a belt-type pressure apparatus. The microstructure of the annealed alloys has been investigated by x-ray diffraction, electron diffraction, and transmission electron microscopy. Experimental results show that the initial crystalline phase in these annealed alloys is α-Fe solid solution (named as α-Fe phase below), and high pressure has a great influence on the crystallization process of the α-Fe phase. The grain size of the α-Fe phase decreases with the increase of pressure (P). The volume fraction of the α-Fe phase increases with increasing the pressure as the pressure is below 2 GPa, and then decreases (P>2 GPa). The mechanism for the effects of the high pressure on the crystallization process of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy and latent applications of high-pressure anne...

Low thermal conductivity and enhanced thermoelectric performance of Gd-filled skutterudites

With Fe compensation, the heavy rare earth element Gd-filled GdyFexCo4−xSb12 (x<2) skutterudites have been successfully synthesized by melting-annealing approach. Fe substitution on the Co site brings two contrary effects on Gd filling: charge compensation which enhances the filling fraction of Gd, and Lattice expansion which is deleterious for the stability of filled compounds that contain smaller atoms. When Fe content is less than 1.7, pure GdyFexCo4−xSb12 compounds are obtained and the Gd maximum filling fraction (ymax) increases with Fe content. The power factor (S2σ) of the GdyFexCo4−xSb12 increases with Fe content. The lattice thermal conductivity is significantly depressed by Gd filling. The sample Gd0.41Fe1.48Co2.52Sb12 has a lattice thermal conductivity as low as 1.1 W m−1 K−1 at room temperature, and its figure of merit (ZT) reaches a maximum value of 0.83 at 700 K. At high temperature, thermal conductivity shows significant increase due to bipolar diffusion, which obstructs obtaining higher ZT.

Effects of Sn-doping on the electrical and thermal transport properties of p-type Cerium filled skutterudites

Abstract p-type Sn-doped CoSb 3 -based skutterudite compounds have been prepared using melting–quenching–annealing method and spark plasma sintering technique. Sn atoms in our samples are completely soluted on Sb-site with a fixed charge state and non-magnetic feature, providing a better choice to ascertain the effect of element doping at the [Co 4 Sb 12 ] framework on the electrical and thermal transport properties in p-type skutterudites. Doping Sn at the framework introduces additional ionized impurity scattering to affect the electron transport greatly. Similar electrical transport properties between Ce 0.2 Co 4 Sb 11.2 Sn 0.8 and Co 4 Sb 11 Sn 0.6 Te 0.4 suggest that Ce fillers contribute little to the valence band edge. Filling Ce into the voids and doping Sn at the framework introduce additional phonon resonant and point defect scattering mechanisms, thereby reducing lattice thermal conductivity remarkably. Moreover, our data suggest that combining these two effects is more effective to suppress lattice thermal conductivity through scattering broad range of phonons with different frequencies.

Synthesis of carbon nitride crystals at high pressures and temperatures

Carbon nitride crystals have been synthesized from C3N4H4 in the presence of a nickel-based alloy or cobalt as a catalyst at high pressure of 7 GPa and temperature of about 1400 degrees C. Scanning electron microscopy showed rod-like, well-faceted crystals with size of several micrometers, and the N content in these carbon nitride crystals was 47-62%, X-ray diffraction indicated the crystals were composed of alpha-C3N4 and beta-C3N4. The experimental lattice constants of alpha-C3N4 (a = 6.425 Angstrom, c = 4.715 Angstrom) and beta-C3N4 (a = 6.419 Angstrom, c = 2.425 Angstrom) agree with ab initio calculations very well.

Effects of buoyancy convection on phase morphology during solidification of Pd40Ni40P20 alloy

Samples of Pd40Ni40P20 alloy were solidified both on the ground and on board a Chinese Retrievable Satellite in order to study the effects of gravity-induced convection on the phase morphology. In comparison to the secondary dendritic spacing, the effective mass transport coefficient under normal gravity condition was estimated to be 1.95 times as high as that under microgravity conditions at the cooling rate of 0.056 K s(-1). The higher mass transport coefficient value due to the existence of buoyancy convection on the ground led to the formation of coarser dendrites of the primary phase Ni5P2 in the ground-based sample

Optimized thermoelectric properties in pseudocubic diamond-like CuGaTe2 compounds

A pseudocubic structure approach has been proposed recently to screen and design good thermoelectric materials via realizing overlapped band edges for excellent electrical transport properties. A diamond-like compound is a typical example agreeing with the concept of the pseudocubic structure by tuning its lattice distortion parameter to unity. However, besides the band structure, optimized carrier concentration and reduced lattice thermal conductivity are also required for a high thermoelectric figure of merit (zT). In this work, taking CuGaTe2 as an example, we have successfully demonstrated that Cu-deficiency can effectively tune carrier concentrations and In-alloying at Ga sites can effectively lower lattice thermal conductivity. By combining these two strategies, the electrical and thermal transports can be separately optimized in CuGaTe2-based pseudocubic diamond-like compounds, leading to much enhanced zTs, about 24% improvement for Cu0.99In0.6Ga0.4Te2 at 800 K. Furthermore, the average zTs from 300 K to 800 K are improved by 87% compared with that of the CuGaTe2 matrix. This study provides a promising way to optimize the TE performance in pseudocubic diamond-like compounds by simultaneously tuning electrical and thermal transport.

Entropy as a Gene‐Like Performance Indicator Promoting Thermoelectric Materials

High-throughput explorations of novel thermoelectric materials based on the Materials Genome Initiative paradigm only focus on digging into the structure-property space using nonglobal indicators to design materials with tunable electrical and thermal transport properties. As the genomic units, following the biogene tradition, such indicators include localized crystal structural blocks in real space or band degeneracy at certain points in reciprocal space. However, this nonglobal approach does not consider how real materials differentiate from others. Here, this study successfully develops a strategy of using entropy as the global gene-like performance indicator that shows how multicomponent thermoelectric materials with high entropy can be designed via a high-throughput screening method. Optimizing entropy works as an effective guide to greatly improve the thermoelectric performance through either a significantly depressed lattice thermal conductivity down to its theoretical minimum value and/or via enhancing the crystal structure symmetry to yield large Seebeck coefficients. The entropy engineering using multicomponent crystal structures or other possible techniques provides a new avenue for an improvement of the thermoelectric performance beyond the current methods and approaches.

Investigation of interfacial phenomena in Ag-Si multilayers during the annealing process

Interfacial phenomena and microstructure in Ag-Si multilayers with a modulation period of 7.64 nm during annealing from 323 to 573 K were investigated by in situ x-ray diffraction and high-resolution transmission electron microscopy. Uphill and downhill diffusion were observed on annealing. The temperature dependence of the effective diffusion coefficient from 373 K (as to downhill diffusion regime) to 523 K was D(e) = 2.02 x 10(-20) exp(-0.24 eV/k(B)T) m(2)/s. Diffusion of silicon atoms along silver grain boundaries was proposed as the main diffusion mechanism. After annealing, continuous silver sublayers changed to nanometer-sized silver particles (about 4.5 nm) coated completely by amorphous silicon.

Thermoelectric performance of Cu1−x−δAgxInTe2 diamond-like materials with a pseudocubic crystal structure

Multiple degenerate band engineering has been established as an effective approach to maximize electrical transport in thermoelectric materials. A series of polycrystalline samples of chalcopyrite Cu1−x−δAgxInTe2 (x = 0–0.5, δ = 0.02–0.05) was synthesized, to achieve multiple degenerate bands. A pseudocubic structure is realized when x is around 0.2. As a result, the degenerate valence bands influence electrical transport significantly. In addition, the lattice thermal conductivity is significantly depressed in the solid solution due to the strong phonon scattering by strain-field fluctuations, since Ag substitution brings significant anharmonicity to the crystal structure. The highest ZT of 1.24 was obtained at the composition Cu0.75Ag0.2InTe2. This study provides an example how the pseudocubic crystal structure is applied to design and evaluate the TE properties in diamond-like compounds. Introduction to the international collaboration Scientific collaboration between the Shanghai Institute of Ceramics and the Institutes of the Max-Planck Society has a long history. In 2001, the Max-Planck Institute for Chemical Physics of Solids in Dresden and SIC CAS in Shanghai established research cooperation. At the beginning it was focused on the field of solid state chemistry, and later was extended to the studies on thermoelectric materials. Currently this cooperation is intensively realized by the research groups of Prof. Lidong Chen in Shanghai and Prof. Yuri Grin in Dresden. Several publications in journals like Inorganic Chemistry, Dalton Transactions and Chemistry of Materials, as well as numerous presentations in the national and international conferences present the results of the common studies.