Geoscience Reference
In-Depth Information
Table 7.18 New Series of Alkali-Free Rare Earth Germanates
[44]
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er
Tm Yb Lu Y
Ln
4
GeO
6
(OH, F)
4
11
Ln
7
Ge
2
O
12
(F,OH)
5
11
LN
4
Ge
3
O
9
(OH)
6
11 11 11 11 11 11 11 11 11 11
Ln
3
GeO
5
(OH)
3
11 11 11 11 11 11 11
Ln
4
[Ge
2
O
7
]
[GeO
4
](OH)
2
11
Ln
4
GeO
8
11
11 11 11
Ln
13
Ge
6
O
31
F
11
11
Ln
2
Ge
2
O
7
(cubic)
11 11 11
N
= 2:1-1:2
Na
2
R[GeO
4
](OH)
La
Pr
NaR[GeO
4
]
(TETRA.)
Nd
Sm
NaR
3
[GeO
4
]
2
(OH)
2
Eu
Gd
Tb
Dy
NaR[GeO
4
]
(RHOMB.II)
Ho
Er
Tu
Yb
Lu
Y
NaOH
5% 20%
60%
90%
100%
Figure 7.44 NC diagram for sodium rare earth germinate system: T
5
450
C
[44]
.
earth elements lie as discrete polyhedra. For example, among germanates, the struc-
ture type Na
3
RSi
2
O
7
does not exist. The second important structure elucidation
among germanates is connected with more of olivine-type structures. Therefore,
rare earth germanates are the closer analogs of silicates.
A detailed work on the system Na
2
O
a
R
2
O
3
a
GeO
2
a
H
2
O indicates that with
surplus R
2
O
3
in the nutrient (GeO
2
/R
2
O
3
5
Gd, three
types of germanates form: NaR
3
Ge
2
O
8
(OH)
2
, NaRGeO
4
, and Na
2
RGeO
4
(OH).
Their synthesis takes place with a temperature gradient. NaR
3
Ge
2
O
8
(OH)
2
crystal-
lizes within a narrow interval of GeO
2
/R
2
O
3
ratio
1:1
1:4) for groups La
a
2.5:1
1.75:1 with NaOH
5
