Subsolidus phase relations in the Al2O3-Li 2O-Ta2O5 (Nb2O5) systems

Article abstract of DOI:10.1134/S0036023607030217

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R ₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂

Full text of DOI:10.1134/S0036023607030217

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 3, pp. 424–426. © Pleiades Publishing, Inc., 2007.
Original Russian Text © M.G. Zuev, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 3, pp. 476–479.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Subsolidus Phase Relations
in the Al2O3–Li2O–Ta2O5 (Nb2O5) Systems
M. G. Zuev
Institute of Solid State Chemistry, Ural Division, Russian Academy of Sciences,
Pervomaiskaya ul. 91, Yekaterinburg, 620219 Russia
Received July 27, 2006
Abstract—The phase composition has been studied and an equilibrium phase diagram has been designed for
the Al2O3–Li2O–R2O5 (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li2O. New
phases with the composition Li1 + xAl1 – xO2 – x, where x = 0–0.67, have been found.
DOI: 10.1134/S0036023607030217
Phase relations in the Li2O–Al2O3–Ta2O5 and Li5GaO4, crystallizes in space group Pbca; for the
Li2O−Al2O3–Nb2O5 systems have not been described. β phase, the space group is Pmmn. The α-Li5AlO4 melt-
The Li2O–R2O5 (R = Ta or Nb) systems are of practical ing temperature is about ~720°C [18].
significance due to the existence of lithium metatanta-
Test samples were prepared in powders in closed
late and lithium metaniobate, which are quantum elec-
containers using multistage air anneals of a blend of the
tronic, ferroelectric, and piezoelectric materials. Com-
starting components at temperatures in the range of
plex oxides of aluminum and niobium have been pro-
(500–1000) 50°ë. The following reagents were used:
posed for use as oxidation-protective coatings on
Li2CO3 (chemically pure), Ta2O5 (TaO-2 grade),
niobium alloy construction materials [1]. Lithium alu-
Nb2O5, and Al(OH)3 (the last two of high purity grade).
minates are used in the production of chemical current
Possible vaporization of the lithium component was
sources and metallic lithium and in other fields [2].
monitored during the annealing. After each annealing
Ceramics based on Al2O3 and Nb2O5 solid solutions are
used as heat insulators [3]. It is pertinent to search for
new compounds with high cation conductivity, which
stage, the temperature was raised by 50°C. The details
of the synthesis are found in work [19]. The total
annealing time was at least 45 h. This period was suffi-
are used, in particular, in lithium chemical cells. In this
cient for ternary systems to acquire equilibrium. It is
context, it is pertinent to study phase relations in the
known that in a system containing an aluminum inter-
Li2O−Al2O3–Ta2O5 and Li2O–Al2O3–Nb2O5 ternary sys-
calation compound and a lithium salt, phases were
tems and to search for new compounds of suggested
obtained at 800°C after a period of up to 10 h [2]. In
composition LixAlyTa(Nb)zOk that can have useful prop-
erties.
work [20], it was studied in detail how the history of
X-ray amorphous Al2O3 samples (prepared by, e.g.,
The phase composition of the boundary binary sys-
Al(OH)3 decomposition) affects the reaction with
tems is described in the literature. In the Li2O–Nb2O5
Li2CO3. It was shown that γ-LiAlO2 was formed in the
system, the following compounds exist in the region in
[Li2CO3] : [Al2O3] = 1 : 1 batch even at 600–700°C in
question at temperatures up to 1000°C: Li2Nb28O71,
anneals lasting from 10 min to 3 h. The Al2O3–Ta2O5
LiNb3O8, LiNbO3, and Li3NbO4 [4–8]. In the
(Nb2O5) systems acquire equilibrium after annealing
Li2O−Ta2O5 system, LiTa3O8, Li3TaO4 (the monoclinic
for about 30–40 h at 1000°C [21]. Phase relations were
system), and LiTaO3 exist [9–13]. In the Al2O3–Nb2O5
determined using powder X-ray diffraction (DRON-2.0
system, monoclinic AlNbO4 and AlNb11O29 exist, while
diffractometer, CuKα radiation). The X-ray diffraction
in the Al2O3–Ta2O5 system, only AlTaO4 exists [14,
experiment was carried out after each 100°C tempera-
15]. In the Li2O–Al2O3 system, the compounds formed
ture rise step and isothermal exposure. After 30 h of
exposure, the X-ray diffraction patterns did not change
any longer, indicating the system’s equilibration.
are LiAl5O8 (spinel), which melts at about ~1290°C
[16], and α-, β-, and γ-LiAlO2 [17] (the transition to the
γ phase occurs at ~850°C). α-LiAlO2 crystallizes in
space group R3 m; for β-LiAlO2, the space group is
Pna21; and for γ-LiAlO2 – P4212, the space group is
In order to determine the positions of quasi-binary
sections in the systems, we studied the phase composi-
tion at 39 points lying along various suggested sections
Li5AlO4 (the tetragonal system). Compound Li5AlO4 is and fields of the system (Table 1). Ternary compounds
have not been found. Compounds Li3RO4 and LiR3O8
also known. The α- and β phases were obtained for this
compound. The α phase, which is isostructural to α- were found to form in the following route:
424

SUBSOLIDUS PHASE RELATIONS IN THE Al2O3–Li2O–Ta2O5 (Nb2O5) SYSTEMS
425
Table 1. Phase composition at points along suggested sections of the Al2O3–Li2O–Ta2O5 (Nb2O5) systems
Compound
Al2O3
Li2O
mol %
Ta2O5
Nb2O5
Phase composition
Ta2O5–Li2O
76.07
50
24.79
17.10
50
23.93
50
Li3TaO4;
LiTaO3;
LiTa3O8
LiTa5O8;
LiAlO2;
Li1 + xAl1 – xO2 – x
Li1 + xAl1 – xO2 – x
AlTaO4
75.21
82.90
50
Al2O3–Li2O
35
65
83.76
;
16.24
50
17
Al2O3–Ta2O5
LiAlO2–Li3TaO4
50
16
67
LiAlO2, LiTaO3,
Li1 + xAl1 – xO2 – x
LiAlO2–LiTaO3
37
50
13
LiAlO2,
LiTaO3
25
50
25
13
50
37
Ta2O5–LiAlO2
33.35
33.35
33.35
LaAl5O8,
LiTaO3, AlTaO4;
LiTaO3, AlTaO4;
LiTa3O8, AlTaO4
LiAl5O8,
25
16
50
25
16
25
50
68
25
Al2O3–LiTaO3
Nb2O5–Li2O
LiTaO3, AlTaO4;
LiAl5O8,
AlTaO4
Li2Nb28O71,
Nb2O5;
76
12.5
5.13
11.5
94.87
7.24
15.38
92.76
84.62
Li2Nb28O71;
Li2Nb28O71,
LiNb3O8;
24.79
35
75.21
65
LiNb3O8;
LiNb3O8,
LiNbO3;
50
76.07
50
LiNbO3;
23.93
50
Li3NbO4
Al2O3–Nb2O5
Nb2O5–LiAlO2
50
9.09
6
AlNbO4;
90.91
87
AlNb11O29
AlNb11O29,
LiNb3O8;
7
16
20
16
20
68
60
AlNbO4,
LiNb3O8;
AlNbO4,
LiNb3O8, LiNbO3
LiNbO3, AlNbO4
AlNbO4,
25
30
25
28
50
42
LiNbO3, LiAl5O8
AlNbO4,
33.33
33.33
33.33
LiNbO3,
LiAl5O8;
Al2O3–LiNbO3
76
50
12.5
25
11.5
25
AlNbO4,
LiAl5O8;
AlNbO4,
LiNbO3,
LiAl5O8
LiAlO2–LiNbO3
AlNbO4–Li2O
37
25
13
17
50
50
50
67
13
25
37
16
LiAlO2, LiNbO3
solid solution on the ba-
sis of LiAlO2,
LiNbO3;
Li3NbO4,
Li1 + xAl1 – xO2 – x
10
80
10
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 3 2007

426
ZUEV
for M = Co or Ni and Li1 – xNaxAlO2 was reported and
Li2O
lithium diffusion in γ-LiAlO2 was modeled in works
[26–28]. Thus, apparently, the use of an Al(OH)3 inter-
calation compound in the synthesis facilitates the for-
mation of Li1 + xAl1 – xO2 – x solid solution.
Li3RO4
Li1 + xAl1 – xO2 – x
LiRO3
LiAlO2
ACKNOWLEDGMENTS
The author acknowledges the help of A.I. Kadin in
the experiments.
LiR3O8
Li2Nb28O71
AlNb11O29 R2O5
LiAl5O8
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x
a, Å
c, Å
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5.171
5.159
5.136
6.284
6.251
6.248
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