Intermetallic Clathrates A Challenge for Thermoelectrics Structure - Property Relations Peter Rogl 1 N. Melnychenko-Koblyuk 1 , A. Grytsiv 1 , E. Bauer 2 , H. Kaldarar 2 , H. Michor 2 F. Röhrbacher 2 , Royanian 1,2 , H. Schmidt 1 , G. Giester 3 1 Institute of Physical Chemistry, University of Vienna, Austria 2 Institute of Solid State Physics, Vienna University Technology, Austria 3 Institute Mineralogy, Crystallography, University of Vienna, Austria Research sponsored by Austrian FWF-projects: 16370 & 16778
Contents Crystal Chemistry of Clathrates Formation and Crystal Structure Phase Equilibria Ba,Sr-M-Ge,Si Properties - Clathrates Type I
Definitions Clathrate: An inclusion complex in which particles of one substance are completely enclosed in cavities formed by the crystal lattice or are present in large molecules of another substance, i.e. the crystal takes in foreign molecules during growth, which cannot escape until the crystal is decomposed [1962Wel, 2001Lew]. Zeolite: Consists of (Si,Al) n O 2n framework with a negative charge which is balanced by positive ions in the cavities. A characteristic property of zeolites is the ease with which they take up and lose water, which is loosely held in the structure, and other substances. These foreign molecules can enter or leave the crystal without disturbing the structure [1962Wel]. Clathrasil: Silicate material with clathrate type structure (usually listed in “Zeolite Atlas”). [1962Wel] A.F. Wells, Structural Inorganic Chemistry, 3 rd Ed., Oxford. [2001Lew] R.J. Lewis, Sr., Hawley’s Condensed Chemical Dictionary, Wiley.
Clathrate Research - History 1811 H. Davy First ice-chlorine clathrate “Cl 2 *10H 2 O” 1948 H. Powell Term „Clathrate“ for ß-Quinol Complexes 1950 Stackelberg Ice-gas clathrates of Type I and II 1952 L. Pauling Crystal structure of 6Cl 2 *46H 2 O Solved 1965 J. Kaspar First intermetallic clathrate: Na 8 Si 46 , Na x Si 136 1973 H. Menke First ternary X 8 A 8 Ge 38 (X=Cl,Br,I; A=P,As,Sb) 1986 B. Eisenmann First type VIII clathrate Ba 8 Ga 16 Sn 30 1988 R. Kroener Chiral clathrate Ba 6 In 4 Ge 21 (type IX) 1998 G. Nolas Thermoelectric Properties Sr 8 Ga 16 Ge 30 2000 H. Fukuoka First binary type IX clathrates 2008 Q. Lin First intermetallic type IV clathrate INSPEC <2007: 2420 hits for „Clathrate(s)“
Clathrate Hydrate Intermetallic Clathrate (Cl 2 ) 8-x [H 2 O] 46 Eu 2 Ba 6 [Cu 4 Si 42 ] Framework atoms: Si + Cu Guest atoms : Larger cage Ba Smaller cage Eu Melanophlogite M 8-x [SiO 2 ] 46 Filler atoms form dual structure: Cr 3 Si-type
Framework-Cage Assembly in Type I Clathrates (Ba 2 Ba 6 )[Cu 6 Ge 40 ] Small cages Larger cages Isolated Pentagondodecahedra Channel-like connected Tetrakaidekahedra Space group : Pm-3n; Clathrate type I; a ≈ 1.1 nm Framework []: 46 atoms: 40 Ge in 24k, 16i and 6 Cu in 6d Filleratoms (): Smaller cage: Ba in 2a; Larger cage: Ba in 6c
Structural Units of Intermetallic Clathrates Pentagondodekahedron Tetrakaidekahedron 5 12 5 12 6 2 Clathrate VIII Polyhedron with 3 additional atoms 3 3 4 3 5 9 Pentakaidekahedron Hexakaidekahedron 5 12 6 3 5 12 6 4
Clathrate Types (based on [1984Jef, 1992Mak]) Type Ideal unit cell Polyhedra Space Intermetallic Clathrate formula group K 8 Ge 46-x , Ba 8 Al 16 Ge 30 , a [5 12 6 2 ] 6 [5 12 ] 2 I 6X*2Y*46T Pm-3n Eu 2 Ba 6 Cu 4 Si 42 [5 12 6 4 ] 8 [5 12 ] 16 II 8X*16Y*136T Fd-3m Na x Si 136 , Cs 8 Na 16 Ge 136 [5 12 6 2 ] 16 [5 12 6 3 ] 4 [5 12 ] 10 III 20X*10Y*172T P4 2 /mnm Cs 30 Na (1.33x-10) Sn (172-x), x = 9.6 [5 12 6 2 ] 4 [5 12 6 3 ] 4 [5 12 ] 6 IV 8X*6Y*80T P6/mmm Li 14.7 Mg 36.8 Cu 21.5 Ga 66 P-6m2 [5 12 6 4 ] 4 [5 12 ] 8 V 4X*8Y*68T P6 3 /mmc - [4 3 5 9 6 2 7 3 ] 16 [4 4 5 4 ] 12 VI 16X*156T I-43d - [4 6 6 8 ] 2 VII 2X*12T Im-3m - [3 3 4 3 5 9 ] 8 d VIII 8Y*46T Im-3m Ba 8 Ga 16 Sn 30 , Eu 8 Ga 16 Ge 30 [5 12 ] 8 + [4 10 ] 4 +... e IX 16Y*8X*100T P4 1 32 Ba 6 Ge 21 In 4 , Ba 6 Ge 25 a X – big cage, Y – small cage, T – four-coordinated framework atom d cage not exactly defined e structure consists of both clathrate and typical intermetallic units [1984Jef] G.A. Jeffrey „Inclusion Compounds” , Academic Press [1992Mak] T.C.W. Mak, G.-D. Zhou, “ Crystallography in Modern Chemistry” , J. Wiley & Sons
Elements Forming Intermetallic Clathrates I H He Li Be B C N O F Ne Na’ Mg Al Si P S Cl Ar K Ni Cu Z n Ga° Ge° Ca Sc Ti V Cr Mn Fe Co As Se Br Kr Rb’ Sr Y Zr Nb Mo Tc Ru Rh Pd Ag C d In Sn°’ Sb Te I Xe Cs’ Ba° La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Ku Ns La Ce* Pr Nd Pm Sm Eu° Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr “Guest atoms” – occupy large cages. M Elements forming clathrate II compounds Most important framework elements Elements forming clathrate IX compounds Elements randomly substitute Si,Ge,Sn ‘ Elements forming clathrate III compounds Elements form clathrates with halogens only. ° Elements forming clathrate VIII compounds Sb can also partially substitute Ge. * Elements forming “Cordier” phases only Ce-compound not confirmed
Clathrate-like Structures Na 204 Ba 16 Sn 310 a=2.52 F-43m Na 10 Cs 3 Sn 23 a=1.24 c=5.15 R-3m S. Bobev, S. Sevov, JACS 124 (2002) 3359 S. Bobev, S. Sevov, InorgChem 39 (2000) 5930
Dual Structures s Definition: A dual structure is a packing of polyhedra (with three faces meeting at each vertex), whose vertices are at the tetrahedral holes of the parent structure. Examples: The regular pentagonal dodecahedron (with 12 pentagon faces [5 12 ]) is dual to the icosahedron. [5 12 6 2 ], [5 12 6 3 ], [5 12 6 4 ] are dual to the Frank-Kasper polyhedra of 14,15,16 vertices •Type I hydrate dual to Cr 3 Si type •Type II hydrate dual to MgCu 2 type •Type IV clathrate dual to Zr 4 Al 3 type The water molecules are centered in each of the tetrahedra of the triangulated metal coordination polyhedra. Intergrowth structures combining types I, II, IV ⇒
Dual Structure, Na x Si 136 , Fd-3m Definition: A dual structure is a packing of polyhedra (with three faces meeting at each vertex), whose vertices are at the tetrahedral holes of the parent structure.
Intergrowth structures among clathrate I, II, IV based on [1998OKe] Ideal unit cell Space Lattice Type Polyhedra Intermetallic Clathrate formula group param. [5 12 ] 98 [5 12 6 2 ] 18 [5 12 6 4 ] 46 a ~ 2.74 98X*18Y*46P* I + II dual type: Pm-3n ? 920T nm deriv.- Mg 32 (Al,Zn) 49 [5 12 ] 98 [5 12 6 2 ] 12 [5 12 6 3 ] 12 [5 12 6 4 ] 40 a ~ 2.78 98X*12Y*12Z* II + IV Im-3 ? 40P*920T nm dual type Mg 32 (Al,Zn) 49 [5 12 ] 21 [5 12 6 2 ] 6 [5 12 6 3 ] 6 a ~ 1.0 [5 12 6 4 ] 6 21X*6Y*6Z*6P* II + IV R-3m c ~ 5.6 ? 222T dual type nm μ -phase W 6 Fe 7 [5 12 ] 10 [5 12 6 2 ] 16 [5 12 6 3 ] 4 a ~ 2.3 10X*16Y*4Z* Cs 30 Na (1.33x-10) Sn (172-x) III=I+IV dual type P4 2 /mnm c ~ 1.2 172T x = 9.6 σ phase Cr 6 Fe 7 nm M. O’Keeffe, G.B. Adams, O.F. Sankey, Phil. Mag. 78 (1998) 21
Clathrasils- Topologically distinct frameworks Space Cell Formula # Clathrasil Unit Cell Cage Types Group Family in nm cages/unit cell 46Si0 2 * 2M 12 * 6M 14 2[5 12 ]*6[5 12 6 2 ] Melanophlogites Pm-3n a =1.344 (Mel) clathrate I 136SiO 2 *16M 12 * 8M’ 16 16[5 12 ]*8[5 12 6 4 ] Dodecasils 3C Fd-3m a =1.940 clathrate II (D3C) 34SiO 2 *3M 12 *2M’ 12 *M 20 3[5 12 ]*[4 3 5 6 6 3 ]* Dodecasils 1H P6/mmm a =1.378 [5 12 6 8 ] (D1H) c =1.119 120SiO 2 *6M 10 * 9M 12 *6M’ 19 6[4 3 5 6 6 1 ] 9[5 12 ] Deca-dodecasils R-3m a =1.386 3R(DD3R) 6[4 3 5 12 6 1 8 3 ] c =4.089 a =2.223 88SiO 2 *8M 8 *8M’ 9 *4M’’ 20 8[5 4 6 4 ]*8[4 1 5 8 ]* Nonasils Fmmm b =1.506 4[5 8 6 12 ] (Non) c =1.363 120SiO 2 *6M 10 *9M 12 6[4 3 5 6 6 1 ]*9[5 12 ]* Deca-dodecasils R3 to a =1.389 3H (DD3H) [4 6 5 6 8 3 ]*4[4 3 5 12 6 1 M 15 *4M 19 *1M 23 R-3m c= 4.099 8 3 ]* [5 18 6 2 8 3 ] 12SiO 2 *2M 14 2[4 6 6 8 ] Silica-sodalites Im-3m a =0.884 (Sod) clathrate VII # M f guest molecule located in a cage with f faces. H. Gies, in Inclusion Compounds, Vol. 5, Oxford Univ. Press, NY, 1991
Clathrasils – Cages and Cage Volumes Number Free Cage of Volume 1000nm 3 Faces [5 4 6 4 ] 8 25 [4 1 5 8 ] 9 30 [4 3 5 6 6 1 ] 10 35 [5 12 ] 12 80 [4 3 5 6 6 3 ] 12 100 [4 6 6 8 ] 14 130 [5 12 6 2 ] 14 160 [4 6 5 6 8 3 ] 15 200 [5 12 6 4 ] 16 250 [4 3 5 12 6 1 8 3 ] 19 350 [5 8 6 12 ] 20 290 [5 12 6 8 ] 20 430 [5 18 6 2 8 3 ] 23 540 [1992Mak] T.C.W. Mak, G.-D. Zhou, “ Crystallography in Modern Chemistry” , Wiley&Sons
Are Clathrates „Zintl Compounds“ ? Rule of thumb for quick selection of TE compositions � In a Zintl compound, each constituent attains a closed valence shell via a formal charge transfer for the formation of covalent bonds. � The electropositive ‚guest‘ atoms donate electrons to the more electronegative host atoms (cage). � The host atoms complete their valence requirement (octet rule) and establish a covalently bonded cage structure. � Engaging all valence electrons in covalent bonds would render clathrates to be semiconductors. Ba 8 Ge 43 3 ≡ [Ba 2+ ] 8 [Ge 0 ] 43 [ -4 ] 3 ≡ 4 electrons Sr 8 Ga 16 Ge 30 0 ≡ [Sr 2+ ] 8 [Ga 1- ] 16 [Ge 0 ] 30 ≡ semicond Ba 8 (Zn,Cd) 8 Ge 38 0 ≡ [Ba 2+ ] 8 [Zn 2- ] 8 [Ge 0 ] 38 ≡ semic. E. Zintl, Angewandte Chemie, 52 (1939) 1
Recommend
More recommend
