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Sa H, Lee J, Jo H, Moon D, Kim M, Ok KM, You TS. p-Type Double Doping and the Diamond-like Morphology Shift of the Zintl Phase Thermoelectric Materials: The Ca 11-xA xSb 10-yGe z (A = Na, Li; 0.06(3) ≤ x ≤ 0.17(5), 0.19(1) ≤ y ≤ 0.55(1), 0.13(1) ≤ z ≤ 0.22(1)) System. Inorg Chem 2021; 60:10124-10136. [PMID: 34100596 DOI: 10.1021/acs.inorgchem.0c03705] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Five ternary and quaternary Zintl phases in the solid-solution Ca11-xAxSb10-yGez (A = Na, Li; 0.06(3) ≤ x ≤ 0.17(5), 0.19(1) ≤ y ≤ 0.55(1), 0.13(1) ≤ z ≤ 0.22(1)) system have been successfully synthesized by both of the arc-melting and the molten Pb metal-flux reactions. The crystal structure of these title compounds was characterized by powder and single-crystal X-ray diffractions analyses, and all title compounds crystallized in the Ho11Ge10-type phase in the tetragonal space group I4/mmm (Z = 4, Pearson code tI84). The complex crystal structure can be described as an assembly of 1) three kinds of cationic polyhedra centered by three different Sb and 2) the cage-shaped anionic frameworks built through the connection of two types of Sb. The newly substituted p-type double dopants of the cationic (Na and Li) and anionic (Ge) elements displayed particular site preferences, which were successfully explained by either the size-factor criterion based on the atomic size or the electronic-factor criterion based on the electronegativity of an element. Quite interestingly, as the reaction conditions were changed, the morphology shift of single crystals in Ca10.94(3)Na0.06Sb9.58(1)Ge0.21 occurred from a cubic-shaped to a hummocky-type, to a hopper-type, and eventually to an octahedral-shaped crystal, just like the Yakutian kimberlite diamonds. Moreover, we firmly believe that the inclusion of the p-type Ge dopant for Sb was crucial to trigger this type of morphology shift and complete the octahedral-shaped morphology in the overall crystal-growth mechanism. The theoretical calculations using a DFT method rationalized the observed site preference of Na and the electronic effect of the p-type Ge dopants. The Seebeck coefficient measurements for Ca10.88(4)Li0.12Sb9.45(1)Ge0.21 indicated that some portions of electron charge carriers were effectively eliminated by the p-type double dopants using Li and Ge.
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Affiliation(s)
- Hayeon Sa
- Department of Chemistry and BK21Four Research Team, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea
| | - Junsu Lee
- Department of Chemistry and BK21Four Research Team, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea
| | - Hongil Jo
- Department of Chemistry, Sogang University, Seoul 04107, Republic of Korea
| | - Dohyun Moon
- Beamline Department, Pohang Accelerator Laboratory, Pohang, Gyeongbuk 37673, Republic of Korea
| | - Min Kim
- Department of Chemistry and BK21Four Research Team, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea
| | - Kang Min Ok
- Department of Chemistry, Sogang University, Seoul 04107, Republic of Korea
| | - Tae-Soo You
- Department of Chemistry and BK21Four Research Team, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea
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Lim SJ, Nam G, Shin S, Ahn K, Lee Y, You TS. Anionic Doping and Cationic Site Preference in CaYb 4Al 2Sb 6- xGe x ( x = 0.2, 0.5, 0.7): Origin of the Enhanced Seebeck Coefficient and the Structural Transformation. Inorg Chem 2019; 58:5827-5836. [PMID: 30985118 DOI: 10.1021/acs.inorgchem.9b00181] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Three Zintl phase compounds belonging to the CaYb4Al2Sb6- xGe x ( x = 0.2, 0.5, 0.7; nominal compositions) system with various Ge-doping contents were successfully synthesized by arc-melting and were initially crystallized in the Ba5Al2Bi6-type phase (space group Pbam, Pearson codes oP26). However, after post-heat treatment at an elevated temperature, the originally obtained crystal structure was transformed into the homeotypic Ca5Ga2Sb6-type structure according to powder and single-crystal X-ray diffraction analyses. Two types of crystal structures share some isotypic structural moieties, such as the one-dimensional anionic chains formed by ∞1[Al2Sb8] and the void-filling Ca2+/Yb2+ mixed cations, but the slightly different spatial arrangements in each unit cell make these two structural types distinguishable. This series of title compounds is originally investigated to examine whether anionic p-type doping using Ge can successfully enhance thermoelectric (TE) properties of the Yb-rich CaYb4Al2Sb6- xGe x series even after the phase transition from the Ba5Al2Bi6-type to the Ca5Ga2Sb6-type phase. More interestingly, we also reveal that the given structural transformation is triggered by the particularly different site-preference of Ca2+ and Yb2+ among three available cationic sites in each structure type, which is significantly affected by thermodynamic conditions of this system. Band structure and density of states analyses calculated by density functional theory using the tight-binding linear muffin-tin orbital method also prove that the Ge-doping actually increases band degeneracies and the number of resonant peaks near the Fermi level resulting in the improvement of Seebeck coefficients. Electron localization function analyses for the (0 1 0) sliced-plane and the 3D isosurface nicely illustrates the distortion of the paired-electron densities due to the introduction of Ge. The systematic TE property measurements imply that the attempted anionic p-type doping is indeed effective to improve the TE characteristics of the title CaYb4Al2Sb6- yGe y system.
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Affiliation(s)
- Sung-Ji Lim
- Department of Chemistry and BK21Plus Research Team , Chungbuk National University , Cheongju , Chungbuk 28644 , Republic of Korea
| | - Gnu Nam
- Department of Chemistry and BK21Plus Research Team , Chungbuk National University , Cheongju , Chungbuk 28644 , Republic of Korea
| | - Seungeun Shin
- Department of Chemistry and BK21Plus Research Team , Chungbuk National University , Cheongju , Chungbuk 28644 , Republic of Korea
| | - Kyunghan Ahn
- Department of Applied Physics , Kyung Hee University , Yong-in 17104 , Republic of Korea
| | - Yunho Lee
- Department of Chemistry , Korea Advanced Institute of Science and Technology , Daejeon 34141 , Republic of Korea
| | - Tae-Soo You
- Department of Chemistry and BK21Plus Research Team , Chungbuk National University , Cheongju , Chungbuk 28644 , Republic of Korea
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Choi W, Lee J, Lee Y, Ahn K, You TS. Single and double-doping effects on the thermoelectric properties of two Zintl compounds: Eu 11Bi 8.07(2)Sn 1.93 and Eu 10.74(2)K 0.26Bi 9.14(2)Sn 0.86. Dalton Trans 2017; 46:11840-11850. [PMID: 28848966 DOI: 10.1039/c7dt02410j] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two Zintl phase thermoelectric compounds of Eu11-xKxBi10-ySny (x = 0, 0.26(1); y = 0.86(2), 1.93(2)) have been synthesized by a high-temperature solid-state reaction and arc-melting methods. The two isotypic crystal structures are characterized by both single-crystal and powder X-ray diffractions, and adopt a tetragonal Ho11Ge10-type structure (space group I4/mmm, Z = 2, Pearson code tI84) containing nine crystallographically independent asymmetric atomic sites in a unit cell. The chemical compositions are confirmed by EDS analysis. The complex crystal structure of the two title compounds can be described as an assembly of three different types of co-facial polyhedra formed by cations and 3-dimensional anionic frameworks surrounding these polyhedra. A quaternary title compound, Eu10.74(2)K0.26Bi9.14(2)Sn10.86, which simultaneously contains both cationic and anionic p-dopants in a single compound, was successfully crystallized for the first time in the A11M10 (A = alkaline-earth metals, rare-earth metals; M = triels, tetrels, pnictogens) series. In particular, two different types of p-dopants K and Sn show particular site-preferences, respectively, where K and Sn prefer to occupy the cationic Wyckoff 4e site and the anionic Wyckoff 8h site. These noticeable site preferences can be elucidated by either a size-factor criterion for the K-doping case or by an electronic-factor criterion for the Sn-doping case. The tight-binding linear muffin-tin orbital calculations show that as the double p-doping is applied to the Eu11-xKxBi10-ySny system, some extra holes are generated on the electronic structures according to the density of states curves. However, a series of thermoelectric property measurements prove that this extra hole-carrier doping is hardly effective enough to completely suppress a bipolar conduction of holes and electrons due to the rigid metallic band structure of the title system.
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Affiliation(s)
- Woongjin Choi
- Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea.
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Nam G, Choi W, Lee J, Lim SJ, Jo H, Ok KM, Ahn K, You TS. Effect of MultiSubstitution on the Thermoelectric Performance of the Ca 11-xYb xSb 10-yGe z (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) System: Experimental and Theoretical Studies. Inorg Chem 2017; 56:7099-7110. [PMID: 28558202 DOI: 10.1021/acs.inorgchem.7b00617] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Zintl phase solid-solution Ca11-xYbxSb10-yGez (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) system with the cationic/anionic multisubstitution has been synthesized by molten Sn metal flux and arc-melting methods. The crystal structure of the nine title compounds were characterized by both powder and single-crystal X-ray diffractions and adopted the Ho11Ge10-type structure with the tetragonal space group I4/mmm (Z = 4, Pearson Code tI84). The overall isotypic structure of the nine title compounds can be illustrated as an assembly of three different types of cationic polyhedra sharing faces with their neighboring polyhedra and the three-dimensional cage-shaped anionic frameworks consisting of the dumbbell-shaped Sb2 units and the square-shaped Sb4 or (Sb/Ge)4 units. During the multisubstitution trials, interestingly, we observed a metal-to-semiconductor transition as the Ca and Ge contents increased in the title system from Yb11Sb10 to Ca9Yb2Sb7Ge3 (nominal compositions) on the basis of a series of thermoelectric property measurements. This phenomenon can be elucidated by the suppression of a bipolar conduction of holes and electrons via an extra hole-carrier doping. The tight-binding linear muffin-tin orbital calculations using four hypothetical structural models nicely proved that the size of a pseudogap and the magnitude of the density of states at the Fermi level are significantly influenced by substituting elements as well as their atomic sites in a unit cell. The observed particular cationic/anionic site preferences, the historically known abnormalities of atomic displacement parameters, and the occupation deficiencies of particular atomic sites are further rationalized by the QVAL value criterion on the basis of the theoretical calculations. The results of SEM, EDS, and TGA analyses are also provided.
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Affiliation(s)
- Gnu Nam
- Department of Chemistry, Chungbuk National University , Cheongju, Chungbuk 28644, Republic of Korea
| | - Woongjin Choi
- Department of Chemistry, Chungbuk National University , Cheongju, Chungbuk 28644, Republic of Korea
| | - Junsu Lee
- Department of Chemistry, Chungbuk National University , Cheongju, Chungbuk 28644, Republic of Korea
| | - Seong-Ji Lim
- Department of Chemistry, Chungbuk National University , Cheongju, Chungbuk 28644, Republic of Korea
| | - Hongil Jo
- Department of Chemistry, Chung-Ang University , Seoul 06974, Republic of Korea
| | - Kang Min Ok
- Department of Chemistry, Chung-Ang University , Seoul 06974, Republic of Korea
| | - Kyunghan Ahn
- School of Chemical and Biological Engineering and Institute of Chemical Processes, Seoul National University , Seoul 08826, Republic of Korea
| | - Tae-Soo You
- Department of Chemistry, Chungbuk National University , Cheongju, Chungbuk 28644, Republic of Korea
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Nam G, Jang E, Jo H, Han MK, Kim SJ, Ok KM, You TS. Cationic Site-Preference in the Yb 14-xCa xAlSb 11 (4.81 ≤ x ≤ 10.57) Series: Theoretical and Experimental Studies. MATERIALS 2016; 9:ma9070553. [PMID: 28773676 PMCID: PMC5456874 DOI: 10.3390/ma9070553] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Revised: 06/21/2016] [Accepted: 07/01/2016] [Indexed: 11/16/2022]
Abstract
Four quaternary Zintl phases with mixed-cations in the Yb14-xCaxAlSb11 (4.81 ≤ x ≤ 10.57) series have been synthesized by using the arc-melting and the Sn metal-flux reaction methods, and the isotypic crystal structures of the title compounds have been characterized by both powder and single-crystal X-ray diffraction (PXRD and SXRD) analyses. The overall crystal structure adopting the Ca14AlSb11-type can be described as a pack of four different types of the spiral-shaped one-dimensional octahedra chains with various turning radii, each of which is formed by the distorted ((Yb/Ca)Sb₆) octahedra. Four symmetrically-independent cationic sites contain mixed occupations of Yb2+ and Ca2+ with different mixing ratios and display a particular site preference by two cationic elements. Two hypothetical structural models of Yb₄Ca10AlSb11 with different cationic arrangements were designed and exploited to study the details of site and bond energies. QVAL values provided the rationale for the observed site preference based on the electronegativity of each atom. Density of states (DOS) curves indicated a semiconducting property of the title compounds, and crystal orbital Hamilton population (COHP) plots explained individual chemical bonding between components. Thermal conductivity measurement was performed for Yb8.42(4)Ca5.58AlSb11, and the result was compared to compounds without mixed cations.
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Affiliation(s)
- Gnu Nam
- Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644, Korea.
| | - Eunyoung Jang
- Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644, Korea.
| | - Hongil Jo
- Department of Chemistry, Chung-Ang University, Seoul 06974, Korea.
| | - Mi-Kyung Han
- Department of Chemistry and Nano Science, Ewha Woman University, Seoul 03760, Korea.
| | - Sung-Jin Kim
- Department of Chemistry and Nano Science, Ewha Woman University, Seoul 03760, Korea.
| | - Kang Min Ok
- Department of Chemistry, Chung-Ang University, Seoul 06974, Korea.
| | - Tae-Soo You
- Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644, Korea.
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