Geoscience Reference
In-Depth Information
ferromagnetic behavior of such an oxide. Turrillas et al.
[144]
have synthesized
Ca
2
Pt
3
O
8
under hydrothermal conditions (T
5
528
C, P
5
170 MPa). The platinum
ternary oxides have potential uses owing to their good ternary catalytic and electro-
chemical properties, and also semiconductor, insulator, and metallic-conductor
properties. Schwartz and Prewitt
[145]
have studied the structure and properties of
a large number of binary and ternary oxides of platinum. Usually KOH and water
are used as mineralizers. These platinum compounds/oxides are insoluble in water,
nitric acid, hydrochloric acid, or hot aqua regia but soluble in hot hydrobromic
acid. The most prominent feature of Ca
2
Pt
3
O
8
is that it has three polymorphic mod-
ifications (tetragonal, orthorhombic, and hexagonal).
In recent years, there is a growing interest in complex oxides of yttria, ceria,
and zirconia stabilized with a wide range of cations showing excellent catalytic
properties, which also act as structural and electronic promoters of heterogeneous
catalytic reactions and as oxide ion conducting solid electrolytes in electrochemical
cells
[146
148]
. A series of solid solutions based on the perovskite-type structure
showing the above-mentioned physical and chemical properties are being hydro-
thermally prepared. The prominent members among them are as follows:
Figure 9.33 SEM photographs
of BaZr
1
2
x
M
x
O
3
2
x
(M
5
Al, Ga,
In, x
5
0.20): (a) BaZrO
3
,
(b) BaZr
0.9
Al
0.1
O
3
2
α
,
(c) BaZr
0.85
Ga
0.15
O
3
2
α
, and
(d) BaZr
0.80
In
0.20
O
3
2
α
.
[149]
.
