Crystal Chemical and Functional Representation of High-T c Superconductors and Related Phases
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CRYSTAL CHEMICAL AND FUNCTIONAL REPRESENTATION OF HIGH-TC SUPERCONDUCTORS AND RELATED PHASES J. SIGALOVSKY AND B.C. GIESSEN Northeastern University, Chemistry Dept. and Barnett Institute of Chemical Analysis and Materials Science, Boston, MA 02115
ABSTRACT Using crystallographic data on HTSC's and a recently developed description of many HTSC's as intercalation compounds, we review briefly the structural evidence and develop some structural correlations involving the dimensions, coordination and connectivities of functional units.
INTRODUCTION The crystal structures of many high-Tc superconductors (HTSC's) are now well known [1] and structural correlations are possible. We attempt in the following to use crystal chemical concepts and the framework of a recent classification of many HTSC's as intercalation compounds (IC's) to obtain correlations concerning the geometries and dimensions of functional regions in the unit cell of cuprate HTSC's. CLASSIFICATION BASED ON STRUCTURAL AND FUNCTIONAL CRITERIA In a recent classification [2] of HTSC phases (also included in Table I of Ref. 3), the mode of doping [by providing a non-stoichiometric alkaline earth or rare earth (AE or RE) counter-ion or by intercalation of electron withdrawing groups and ions between CuO2 layers] was used as a primary 2* criterion. The first category contains the T phases [T, T' and T (T")] and cubic perovskite with no copper, while the intercalation superconductors include layered compounds with general formulae IC(AE,RE)nI CunO . This flexible and comprehensive concept allows a listing of all currently known HTSC's. To accommodate electron doping in a taxonomy of HTSC's and to emphasize the sign of the doping charge as a prime parameter comparable in importance to the mode of doping, we present here an alternative listing [21 of the HTSC's in terms of charge carrier sign and doping type, with the intercalant group
Table I:
HTSC families arranged according to type and charge carrier sign ELECTRONS
HOLES
Charge Carrier Doping Type
COUNTERION DOPING
Perovskites Ba(Pbi B1)03 -.)0 .Kx)BiO (Ba -x
Single Layer Phase (T) (La Sr.) 2 CUO (LSCO) 4 2 4do.92Ce.08u3.93
3
IC Group
(IC)(AE.RE)n_ 1 CUnO.
Cua 2Om+2+d INTER-
CALATION DOPENG
Single Layer Phase (T') (Nd Ce )C,
Compounds YBa2Cu2+mO0 2 6.5+d
m,-= 1;1.5;2
BiS in GTlBa2 1.5m+2+d
:
TlmEa 2an-iCUnOl.5m+2n+l+d
2 Sr2can-I CUn2n+4+d
(T2,Pb,Bi)Sr2 Pb2CuSr204.5+d,
: :
(TI,Pb,BR)Sr 2 Can-CUnOx Pb2 CuSr 2 (Ca 0. 5 Y0 .5)Cu 2 08
lRC
n
Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
No Known Examples
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and its composition as subsidiary considerations. This approach is implemented in Table I, which contains the classes within each category (for intercalation phases, based on the elements in the intercalant groups), families (based on the intercalant stoichiometry), and specific members within each family (layer number n - 1 to 4) in detail. STRUCTURAL ELEMENTS OF INTERCALATION COMPOUND HTSC's We differentiate three main parts of the cation skeleton: the "perovs
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