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Aurivillius Phases A Possible New Class of Metal Oxide Superconductors.

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Interpolative decay and empirical absorption correction [13] were applied
(minimum and maximum transmission factors 0.248 and 0.583, respectively). Four-circle diffractometer, Siemens/Stoe AEDZ. Profile-fitted intensi2 0 I 4 0 " . Total number of reflections 12376. 4300 unique
ties [I41 3 I
reflections with Fo 2 6 cr ( F o ) .The structure was solved by Direct Methods
1151 and refined to R = 0.071, R, = 0.0677 [16]. Pt and Ag atoms and
15 CI atoms were anisotropic. The carbon frames of the C,CI, groups were
refined as idealized rigid groups with C-C 1.395 A. The weighting scheme
= u* (6 0.0007 FZ;558 variables. A/esd (max) 0.11. Highest
was M
peaks: 5 peaks between 1.31 and l.0e/A3 close to heavy atoms. Further
details of the crystal structure investigation are available from the Cambridge Crystallographic Data Centre, University Chemical Laboratory,
Lensfield Road, Cambridge CB2 1EW (England), on quoting the fulljournal citation.
[lo] M. Nardelly, Comput. Chem. 7 (1983) 95.
[111 R. Uson, J. Fornies. M. TomBs, J Organomr!. Chern. 358 (1988) 525. and
references cited therein.
[l?] E. Maslowsky, Jr.: Vihrutional Spectra of Orgunomefallic Compounds;Wiley. New York 1977, p. 437, and references cited therein.
[13] N. Walker, D. Stuart, Acfu CrystaNogr. Sect. A39 (1983) 158.
1141 W. Clegg, Aria Crys!uNogr. Seci. A37 (1981) 22.
[15] G. M. Sheldrick, SHELX-86. Universitat Gottingen 1986.
1161 G. M. Sheldrick, SHELX-76 "Program of Crystal Structure Determination". University of Cambridge, Cambridge (England) 1976.
slabs with n as large as 7 have been reported.[41The crystal
structures of Aurivillius phases are strikingly similar to those
of the new high-temperature Bi-Ca-Sr-Cu-0 and TI-CaB a - 0 - 0 s u p e r c ~ n d u c t o r sas
, ~has
~ ~ been pointed out by von
Schnering et a1.[5b1However, the electron count at the metal
is do in known Aurivillius phases, while it is close to d9 in the
copper-oxide superconductors. On the basis of tight-binding
band structure calculations[6-81on 1-3, we shall show that
layered perovskite structures of the Aurivillius type with metal electron counting close to d3 have electronic structures
strikingly similar to those of the Cu-0 superconductors and
thus might form a new class of superconductors.
Aurivillius Phases: A Possible New Class of
Metal Oxide Superconductors**
By Kyeong Ae Yee, Thomas A . Albright, Dongwoon Jung, and
Myung-Hwan Whangbo *
A number of AB,-,Mn03n+l phases contain layered
M n 0 3 n +perovskite structures, where M is typically anearly
transition metal (e.g., Ti, Nb, Ta, Cr, W, Fe), B is an electropositive atom (e.g., Na, K, Ca, Sr, Ba, Gd, La, Y, Pr, Sn,
Pb, Bi), and n is the number of MO, layers within the perovskite
The prototype perovskite slabs for n = 1,
2, and 4 are shown in 1,2, and 3, respectively. Most Aurivillius phases, for which A represents Bi202layers separating
the perovskite slabs and n 5 5, are ferroelectric materials. In
a similar class of AB,_1Mn03n+lcompounds with A = Li,
Na, K, Rb, Cs, TI, Sr, Ba, or NR, (R = alkyl), perovskite
B, 0 oxygen
[*] Prof. T. A. Albright, K. A. Yee
Department of Chemistry, University of Houston
Houston, Texas 77204-5641 (USA)
Prof. M.-H. Whangbo, D. Jung
Department of Chemistry, North Carolina State University
Raleigh, North Carolina 27695-8204 (USA)
[*'I T A . A . thanks the Robert A. Welch Foundation, the Petroleum Research
Fund (administered by the American Chemical Society), and the Texas
Center for Superconductivity at the University of Houston (prime grant
MDA 972-88-G-0002 from the Defense Advanced Research Projects
Agency and the State of Texas) for support and the NSF for a generous
allocation of computer time at the Pittsburgh Supercomputer Center.
M.H . W. thanks DOE, Office of Basic Sciences, Division of Materials
Sciences, for support of this research under grant DE-FG05-86ER45259.
Verlagsgesell,schaf!mhH, 0-6940 Weinheim, I989
Fig. 1. a) Dispersion relations of the t,,-block bands calculated for a TiO,
layer in 1, where r = (0,0), X = (a*/2,0), and M = (a*/2, b*/2). Fermi surfaces
of the xy band in (b) and the xz band in (c), calculated for a d" (x = 1-5)
electron count, where the numbers 1- 5 refer to the d-electron count d ' -d5,
Figure 1 a shows the dispersion relations of the t,,-block
bonds calculated for a TiO, layer (1, M = Ti). The dispersion characteristics and density-of-states profile of the xy
band are very similar to the x2 - y2 bands of the CuO, layers
Here, xy is antibonding to
in 0 - 0 superconductor^.^^*
oxygen p orbitals in a R fashion, whereas, in the Cu-0 layers
x 2 - y 2 is antibonding to oxygen in a (T sense. The Fermi
surfaces calculated for d" (x = 1-5) are shown in Figure 1 b
and 1 c for the xy and xz bands, respectively. The yz band has
Fermi surfaces identical with those of the xz band but centered at the M point. Since all the Fermi surfaces are closed,
the three bands are two-dimensional metallic. In particular,
the Fermi surfaces for a d3 count are very close in shape to
those found for the nearly half-filled x2-y2 bands of the
copper-oxide superconductor^.^^* l o ] Thus, layered perovskite structures of the Aurivillius type with electron counting close to d3 might give rise to a new class of superconductors. Valence or charge fluctuations, presumed to be essential
for the 0 - 0 superconductor^,^^^^ ' I 1 would be present in
such perovskite slabs. Hole states (at M or 0),introduced via
chemical doping or having the s bands associated with B (for
n 2 2), cut across the Fermi surface. The linear electron-hole
Angew. Chem. I n f . Ed. Engl. 28 (1989) No. 6
electron-pair model['*] will operate in a way analogous to
that suggested for the Cu-0 superconductors: concerted inplane M-0 breathing motions can be established via local
Jahn-Teller instabilities. Our band calculations on 1 with
two Bi,O, layers sandwiching it show no significant contribution of the Bi,O, layers to the t,,-block bands. Our calculations on 2 and 3 without the embedded atoms, B, show that
the essential features of the t,,-block bands remain unaltered. Small coupling exists between the xz and yz bands via
the out-of-plane oxygen atoms that bridge the MO, layers,
while the xy bands are not coupled via the out-of-plane oxygen atoms. The x2 - yz bands of the Cu-0 superconductors
behave identically.['* I'
So far. all synthetic work on the AB,_lM,O,,+l phases
has been directed towards do systems. The wide tolerance for
atomic substitution of A, B, and M suggests that higher
d-electron variants are possible. The t,,-block bands of 2 and
3 are strongly perturbed by embedded Bi atoms (although
this may well be an artifact of parameterization); thus, more
electropositive atoms are suggested for B. With n = 4 as a
working example, species 4-7 are possible.
(d3 electron count at each W) 4
(Bi,O, )LaPb, W,O,
Another viable series of candidates for superconductivity,
phases with an electron count close to d' at M, should not be
discounted. If the out-of-plane M-0 distances become
shorter than the in-plane ones, as expected for higher electron c o ~ n t s , ~the
' ~ ]xz and yz bands will be raised and the xy
band can become nearly half-filled, even with d' metals. For
the n = 4 model, 8 and 9are possibilities, which lead to d' for
T. R. Askew, R. B. Flippen. U.Chowdhry, A. W. Sleight, ibid. 240 (1988)
631; M. A. Subramanian, J. C. Calabrese, C. C. Torardi. J. Gopdlakrishnan. T. R. Askew. R. B. Flippen, K. J. Morrissey, U . Chowdhry. A. W.
Sleight. Nufure (London) 332 (1988) 420; b) H. G . von Schnering. L.
Walz, M. Schwarz, W. Becker, M. Hartweg, T. Popp, B. Hettich, P. Muller.
G. Kimpf, Angen. Chem. 100 (1988) 604; Angex. Chem. Int. Ed. Engl. 27
(1988) 574; c) Z. Z. Sheng, A. M. Hermann. Nature (London) 332 (1988)
55; d) C. W. Chu, J. Bechtold. L. Gao. P. H. Hor, Z. J. Huang. R. L.
Meng, Y. Y. Sun, Y. Q. Wang, Y Y. Xue, Phys. Rev. Lait. 60 (1988) 941.
[6] The atomic parameters employed in our calculations on 1 (TiO,: NbO,).
its sandwich analogue (Bi,O,),NbO,. 2 (BiNb,O,; Nb,O,). and 3
(Bi,Nb,O,,; Nb,O,,) are as follows: The valence shell ionization potentials and orbital exponents are - 32.3 eV and 2.275 for 0 2s. - 14.8 eV and
2.275 for 0 2p, -21.2 eV and 2.76 for Bi 6s. - 13.0 eV and 2.29 for Bi 6p.
-1O.lOeVand 1.89for Nb5s. -6.86eVand 1.85for Nb5p. -8.97eV
and 1S O for Ti 4s. and - 5.44 eV and 1.50 for Ti 4p. The 3d orbitals ofTi
and the 4d orbitals of Nb are represented by t w o Slater functions with
mixing coefficients in parentheses: - 10.81 eV with 4.55 (0.5206) and 1.40
(0.7839) for Ti 3d. -12.49 eV with 4.08 (0.6401) and 1.64 (0.5516) for
N b 4d.
[7] M:H. Whangbo, R. Hoffmann, J. Am. Chem. Soc. 100 (1978) 6093.
Chcm. Phjs. 13 (1963) 1397; H.H. Ammeter, H.-B.
181 R. Hoffmann. .
Burgi, J. C. Thibeault. R. Hoffmann, J. Am. Chem. SOC.100 (1978) 3686.
19) See. e.g., a) M.-H. Whangbo, M. Evain, M. A. Beno, J. M . Williams,
Inorg. Chem. 26 (1987) 1829, 1831, 1832: b) J. K. Burdett. G. V. Kulkarni,
K. Levin, ibid. 26 (1987) 3652; c) L. F. Mattheiss. P h u . R n Lert. 58
(1987) 1028; L. F. Mattheiss. D. R. Hamann, Solid State Conimun. 63
(1987) 395.
1101 F. Herman, R. V. Kasowski, W. Y . Hsu, Phys. Rev. B38 (1988) 204.
[ l l I a) A. Simon, Angew. Cbem. 99(1987) 602; Angex. Cham. Int. Ed. Engl. 26
(1987) 579; b) M. J. S. Dewar, &id. 99 (1987) 1313 and 26 (1987) 1273.
[12] M.-H. Whangbo, E. Canadell, M. Evain. J. M. Williams, Inorg. Chem. 27
(1988) 2394.
[I31 R. A. Wheeler. M.-H. Whangbo. T. Hughbanks. R. Hoffmann, J. K. BurI
A m . Chem. Soc. 108 (1986) 2222.
dett, T. A. Albright, .
1141 T. Ogushi, Y Hakuraku, H. Honjo, G. N. Suresha, S . Higo, Y. Ozono. 1.
Kawano, T. Numota, J. LOB,Temp. P h w 70 (1988) 485.
(x=O) 8
Synthesis, Structure, and Reactivity
of a 1,3-Diphospha-2-silaallylAnion **
(x=O) 9
By Edgar Niecke,* Elke Klein, and Martin Niegev
x = 0. The latter composition is particularly interesting in
view of the recent report of high-temperature superconductivity in Sr-La-NbO films.['41 Substitution of the out-ofplane oxygens with stronger x-donor nitrogen atoms may
also serve to push the xz and yz bands above the xy band.
For n values other than 4,a large number of stoichiometries
can also be proposed. We are well aware of fluorite or pyrochlore structural alternatives and also of the electronic
instabilities such as charge and spin density waves that may
frustrate superconductivity. We have not pinpointed a global
mechanism for superconductivity nor calculated a for any
of these materials. Nevertheless, the persistent electronic
analogy between these layered structures and the Cu-0 superconductors strongly merits experimental investigation.
Received: January 25, 1989 [Z 3140 IE]
German version: Angew. Chem. I01 (1989) 789
[I] B. Aurivillius, A r k . Kemr I (1949) 463, 499; 2 (1950) 519; 5 (1952) 39.
[2] R. E. Newnham, R. W. Wolfe, J. E Dorrian, M a w . Res. Bull. 6 (1971)
[3] L. E. Cross, R. C. Pohanka, M a w . Res. Bull. 6 (1971) 939.
I41 a ) A. J. Jacobson, J. W. Johnson, J. T. Lewandowski, Inorg. Chem. 24
(1985) 3727; b) J. Gopalakrishnan, V. Bhat, B. Raveau, Muter. Res. Bull
22(1987) 41 3; M. A. Subramanian, J. Gopalakrishnan, A. W
. Sleight, ihrd.
23 (1988) 837.
[5] See. e.g.. a) M. A. Subramanian, C. C. Torardi, J. C. Calabrese, J. Gopalakrishnan. K. J. Morrissey, T. R. Askew, R. B. Flippen, U. Chowdhry,
A. W. Sleight, Scienre (Washington D.C.)239 (1988) 1015; C. C . Torardi,
M. A. Subramanian, J. C. Calabrese, J. Gopalakrishnan, K. J. Morrissey.
Angru.. Chenl. lnr. Ed. Engl. 28 (1989) No. 6
The formal replacement of the two terminal positions in
allyl anion A"] by phosphorus centers of coordination number 2 leads to the 1,3-diphosphaallyl system B,121 which is
becoming increasingly important as a complex ligand.[31We
report here the synthesis of the I ,3-diphospha-2-silaallyl anion C, which is analogous to B and is the first example of a
stable, delocalized 3p(x) bonding system.
A S ' h
The surprisingly simple preparation of C was achieved in
a one-pot reaction by treatment of tert-butyltrichlorosilane 1
with four equivalents of lithiophosphane 2 in diethyl ether.L4I
The lithium salt of the allyl anion is obtained as the diether
adduct 4 in the form of deep red, extremely moisture-sensitive, thermally stable crystals (m.p. 150-152 "C). These are
Prof. Dr. E. Niecke, DipLChem. E. Klein. M. Nieger
Institut fur Anorganische Chemie der Universitiit
Gerhard-Domagk-Strasse 1, D-5300 Bonn 1 (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
Q VCH Verlugsgesellschufi mhH, 0-6940 Weinheim, 1989
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class, oxide, aurivillius, metali, possible, superconductors, phase, new
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