Metal oxide materials

Details Metal oxide materials Metal oxide materials

1989-04-10

2004-02-03

Kopec, Mark (Department: 1751)

Superconductor technology: apparatus, material, process

High temperature , per se

Bismuth containing

Reexamination Certificate

active

06686319

ABSTRACT:

The invention comprises certain novel metal oxide materials which exhibit superconductivity at elevated temperatures and/or which are useful as electrodes or electrolytes in electrochemical cells, sensors, and as catalysts.
It is known that certain classes of metal oxide will exhibit the phenomenon of superconductivity below a particular critical temperature referred to as T
c
. These include as prototypes BaPb
2−x
Bi
x
O
3−d
, Ba
2−x
Sr
x
CuO
4−d
, YBa
2
Cu
3
O
7−d
as described in The Chemistry of High Temperature Superconductors, ed. by Nelson et al, American Chem. Soc. 1987, and Bi
2
Sr
2
CaCu
3
O
5−d
as described by Subramanian et al, Science 239, 1015 (1988). We have identified this last material as the n=2 member in a homologous series of approximate formula Bi
2
(Sr,Ca)
n+1
Cu
n
O
2n+4+d
, n=0, 1, 2, 3, . . . , obtained by inserting an additional layer of Ca and an additional square planar layer of CuO
2
in order to obtain each higher member. These materials often exhibit intergrowth structures deriving from a number of these homologues as well as Bi substitution on the Sr and Ca sites. T
c
is observed to rise as n increases from 1 to 2 to 3. The material YBa
2
Cu
4
O
8+d
has a layered structure similar to the n=2 member of this series Bi
2
Sr
2
CaCu
2
O
8+d
and we expect therefore that YBa
2
Cu
4
O
8−d
belongs to similar series. One such serial could be obtained by insertion of extra Y—CuO
2
layers resulting in the series of materials R
n
Ba
2
Cu
n+3
O
3.5+2.5n−d
, n=1, 2, 3, . . . and another by insertion of extra Ca—CuO
2
layers resulting in the series RBa
2
Ca
n
Cu
n+4
O
8+2n−d
, n=1, 2, . . . By analogy it may be expected that T
c
in these two series should rise with the value of n.
Binary, ternary or higher metal oxide materials containing as cations one or more alkali earth elements, such as these materials and having high oxygen-ion mobility may also be used as electrodes, electrolytes and sensors for electrochemical applications. The oxygen-ions will move through such an electrolyte material under an applied electrical field allowing the construction of oxygen pumps for catalysis and other oxidizing or reduction processes involving the supply or extraction of atomic oxygen. The oxygen-ions will also move through such an electrolyte material under a concentration gradient allowing the construction of batteries, fuel cells and oxygen monitors. For these materials to act effectively as electrolytes in such applications it is necessary that they have high oxygen-ion mobility through the atomic structure of the materials and at the same time have a low electronic conductivity so that the dominant current flow is by oxygen-ions and not electrons. For these materials to act effectively as electrodes in such applications it is necessary that they have a high electronic conductivity as well as a high oxygen-ion mobility so that electrons which are the current carried in the external circuit may couple to oxygen-ions which are the current carrier in the internal circuit. Electrochemical cells including fuel cells, batteries, electrolysis cells, oxygen pumps, oxidation catalysts and sensors are described in “Superionic Solids” by S Chandra (North Holland, Amsterdam 1981).
Solid electrolytes, otherwise known as fast-ion conductors or superionic conductors have self diffusion coefficients for one species of ion contained within their crystalline structure ranging from 10
−7
to 10
−5
cm
2
/sec. A diffusion coefficient of about 10
−5
m
2
/sec is comparable to that of the ions in a molten salt and thus represents the upper limit for ion mobility in a solid and is tantamount to the sublattice of that particular ion being molten within the rigid sublattice of the other ions present. Such high diffusion mobilities translate to electrical conductivities ranging from 10
−2
to 1 S/cm, the latter limit corresponding to that commonly found in molten salts. The n=0 member of the series Bi
2+e−x
Pb
x
(Sr,Ca)
n+1−s
Cu
n
O
2n+4+d
and various substituted derivatives are identified as solid electrolytes with high oxygen-ion mobility. The n=1, 2 and 3 members of the series may have high oxygen-ion mobility as well as high electron conductivity and thus are potentially applicable as electrode materials.
The invention provides certain novel metal oxide materials which exhibit superconductivity at low temperatures and/or which are useful in such electrode, electrolyte, cell and sensor applications, or as electrochemical catalysts.
In broad terms the invention comprises metal oxide materials within the formula
R
n+1−u−s
A
u
M
m+e
Cu
n
O
w
  (1)
where n≧0 and n is an integer or a non-integer, 1≦m≦2, 0≦s≦0.4, 0≦e≦4, and 2n+(1/2)≦w≦(5/2)n+4, with the provisos that u is 2 for n≧1, u is n+1 for 0≦n<1
and where
R and A are each any of or any combination of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Ba, Li, Na, K, Rb or Cs,
M is any of or any combination of Cu, Bi, Sb, Pb, Tl or any other transition metal,
Cu is Cu or Cu partially substituted by any of or any combination of Bi, Sb, Pb, Ti or any other transition metal,
O is O or O partially substituted by any of N, P, S, Se, or F.
and wherein the structure of the materials is characterised by distorted or undistorted substantially square planar sheets of CuO
2
when n>0 and distorted or undistorted substantially square sheets of R for n>1.
excluding where M is Bi, R is Ca and Sr, A is Sr and Ca, and s and e are 0 and where n=1, the material Bi
2
(Sr
1−x
Ca
x
)
2
CuO
8−d
with 0≦x≦0.3, and where n=2 the material Bi
2
(Sr
1−x
Ca
x
)
3
Cu
2
O
10−d
with 0.6≦x≦0.33
and excluding RBa
2
Cu
3
O
7−d
and excluding, where R is as above excluding Ca, Sr, Ba, Li, Na, K, Rb or Cs, the material having formula
RBa
2
Cu
4
O
8−d
.
The n=1, 2, 3, 4, 5, . . . materials have pseudo-tetragonal structures with lattice parameters a, b and c given by 5.3 Å≦a,b≦5.5 Å and c=18.3±v+(6.3±v′)n Å where 0≦v, v′≦0.3. The n=0 material extends over the solubility range 0≦e≦4 and has orthorhombic or rhombohedral symmetry with lattice parameter c=19.1±v Å.
Preferred materials of the invention are those of formula (1) wherein m is 2 and R is Ca and R is predominantly Bi and having the formula
 Bi
2+e−x
L
x
Ca
n+1−u−s
A
u
Cu
n
O
w
  (2)
where L is any of or any combination of Pb, Sb, or Ti, and 0≦x≦0.4.
More preferred materials of the invention are those of formula (2) where n≧1 and 0≦e≦0.4 and having the formula
Bi
2+e−x
L
x
Ca
n+y−1−s
Sr
2−y
A
z
Cu
n
O
2n+4+d
  (3)
and where 0≦z≦0.4, −2≦y≦2, and −1≦d≦1.
Materials or formula (3) of the invention wherein n is 3 have the formula
Bi
2+e−x
L
x
Ca
2+y−s
Sr
2−y
A
z
Cu
3
O
10+d
.  (4)
Preferably in the n=3 materials of formula (4) L is Pb and 0≦x≦0.4 and −1≦y, d≦1. A may preferably be Y or Na and 0≦z≦0.4 and preferably 0, with preferably 0.5≦y≦0.5 and −1≦d≦1. Preferably d is fixed in a range determined by annealing in air at between 300° C. and 550° C., or by annealing in an atmosphere at an oxygen pressure or partial pressure and temperature equivalent to.annealing in air at between 300° C. and 550° C. Most preferably 0.2≦e, s≦0.3, 0.3≦x≦0.4 and −0.1≦y≦0.1.
Especially preferred n=3 materials of the invention are Bi
1.9
Pb
0.35
Ca
2
Sr
2
Cu
3
O
10+d
, Bi
2.1
Ca
2
Sr
2
Cu
3
O
10+d
, preferably wherein d is fixed in a range determined by annealing in air at between 300° C. and 550° C., o

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