Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7963
A very standard one is preparation by solid-state reactions:
the starting materials, generally oxides, or carbonates
(ii) this fluorination can be carried out with relatively simple
equipment under mild conditions; (iii) fluorination processes
can be easily controlled by the applied potential, current, and
electricity; (iv) it is an economic method, where a fluoride salt
can be used as the fluoride ion source and supporting
electrolyte.
(
BaCO , SrCO , CaCO , CuO, Y O , Bi O , etc.) are replaced
3 3 3 2 3 2 3
by the corresponding fluorides or oxyfluorides (BaF , SrF ,
2
2
2
,15
16
16a
17
18
CaF2, CuF , YF , BiOF, YOF, etc.). Additionally,
by laser-
ablation techniques on La CuO . Some experiments were also
2
3
1
3
9,20
La CuO F thin films were generated on SrTiO
2
4
x
Electrochemical fluorination has scarcely been appro-
ached in inorganic chemistry and was used essentially in
organic chemistry using either the Simons or the Philips
2
4
performed with inorganic fluorinating agents such as NH F
4
21
or transition metal difluorides.
30,31
process.
Another process is fluorination by solid-gas reactions,
which are generally performed at temperatures around
As an example, the fluorination of yttrium
barium copper oxide (YBa Cu O ) was reported using a
2
3
7-x
6
,22
8,16,23
32
3
00 °C using a fluorinated gas such as NF3
or F2.
solid-state electrochemical method at 400 °C. The prepara-
tion of low-temperature fluorinated oxides by anodic oxida-
tion in dilute hydrofluosilicic acid (H SiF ) solution was also
Such a fluorination has attracted considerable attention as a
technique to introduce carriers for inducing superconductiv-
ity, resulting in drastic changes in structures and super-
However, great care is required
in handling the toxic F2 gas. To solve this problem,
fluorination by ionic bombardment with a fluoride beam
2
6
33
performed to yield SiO2.
As a matter of fact, we have also been developing for nearly
8,11
conducting properties.
24
34,35
two decades now
an electrochemical insertion of anions
such as oxygen ones, a process which can be carried out in the
air, at room temperature, in alkaline media and which
allowed the preparation of noteworthy materials, some hav-
ing never been obtained with classical synthesis routes used in
solid-state chemistry. Even if most of these oxides with high
oxidation states for metalcations showa rather high chemical
stability with respect to the electrolytic solution, these experi-
ments often require long polarization times (a few hours to
several days), and mechanical or chemical degradation of the
materials may occur due to the combined action of water
(hydrolysis) and carbonate anions (carbonatation) present in
strong alkaline solutions. Thus, some materials, for example,
could never been prepared this way (YBa Cu O , BaFeO ).
16,25
has been developed.
Another efficient way to overcome this disadvantage was
sought in chemical fluorination based on the use of fluorinat-
18,26-28
ing reagents such as NH F,
but here the temperature
4
is still higher than 200 °C and generates the release of fluorine
by thermal decomposition. In this method, starting materials
are simply heatedtogetherwith the reagent. HF was also used
29
in organic media. However, all of these methodswere not so
easy to handle, with consequences on the results such as
various divergences in the literature, as pointed out by
14
Fadeeva et al. in their review paper. Besides these techni-
ques, electrochemical fluorination was investigated since it is
a method which exhibits, among others, the following
advantages: (i) hazardous or toxic reagents can be avoided;
2
3
7
3
In order to kill this degradation, we developed this electro-
chemical insertion in nonaqueous electrolytes, using organic
36,37
media.
38
We have shown, in a previous paper, that organic media
without any external source of oxygen (KO or H O) could
(
(
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of oxygen in the well-known La CuO material. Various
2
4
electrochemical processes occur, implying not only the
decomposition of the “oxygen-bearing” solvents but also
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(
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-
•
species as O or O , able to oxidize the material. Dimethyl-
(
sulfoxide (DMSO) associated with nBu NClO appeared to
4
4
(
be the most relevant electrolyte for oxidizing La CuO into
2
4
La CuO4.10. The use of fluorine-containing salts during
2
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(
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(
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2