Geoscience Reference
In-Depth Information
Figure 7.49 The characteristic photographs of rare earth germanates
[44]
.
Source: Courtesy of L.N. Demianets.
the K
2
O
f
shows the characteristic
photographs of rare earth germanates
[44]
.
Tables 7.19 and 7.20
give the structure
types of alkali-free rare earth germanates, structure types of alkali and alkaline
earth rare earth germanates, respectively.
a
Sc
2
O
3
a
GeO
2
a
H
2
O system.
Figure 7.49a
7.11.2 Zirconium Germanates
The study of zirconium germanate crystallization continues to be popular under
hydrothermal conditions. Recently, the number of sodium
zirconium germanates
synthesized under hydrothermal conditions has increased enormously.
In the
Na
2
O
H
2
O system, the following germanates can be synthesized
(
Figure 7.50
): ZrGeO
4
,Na
2
ZrGeO
5
(Ge/Zr
a
ZrO
2
a
GeO
2
a
1,Q
1
), Na
2
ZrGe
2
O
7
(Q
2
), Na
4
Zr
2
Ge
3
O
12
(Q
1.5
), Na
3
HZrGe
2
O
8
(Q
2
Na), and Na
4
Zr
2
Ge
5
O
16
5
H
2
O(Q
2.5
).
The subscript of letter Q indicates the value of the Ge/Zr ratio in the solid phase.
The crystallization regions of these phases are shown in
Figures 7.50 and 7.51
,
respectively. Five sodium
zirconium germanates were synthesized in the system
Na
2
O
H
2
O. New compounds are marked with asterisks. All the
compounds are characterized by the same Zr and Ge coordination and in all the
compounds zirconium atoms occupy octahedra, while germanium atoms occupy
tetrahedra.
The positions of phase boundaries (crystallization of individual compounds)
are determined by the NaOH concentration and the initial ratio of zirconium and
a
ZrO
2
a
GeO
2
a
