Synthesis and Crystal Structure of Two New Layered
Perovskite Phases K
2
La
2/3
Ta
2
O
7
and Li
2
La
2/3
Ta
2
O
7
M. P. Crosnier-Lopez*, F. Le Berre, and J. L. Fourquet
Le Mans/France, Laboratoire des Fluorures, U.M.R. C.N.R.S. 6010, Faculte
´
des Sciences et des Techniques, Universite
´
du Maine
Received May 15th, 2002.
Abstract. By solid state reaction two new layered perovskites have
been synthesized related to the Ruddlesden-Popper family,
K
2
La
2/3
Ta
2
O
7
and Li
2
La
2/3
Ta
2
O
7,
with La partial occupancy of the
12-coordinated site. The structures of K
2
La
2/3
Ta
2
O
7
and
Li
2
La
2/3
Ta
2
O
7
are respectively determined by powder X-ray diffrac-
tion and by single crystal XRD data : S.G. I4/mmm, Z ⫽ 2, a ⫽
3,9679(1) A
˚
and c ⫽ 22.0807(4) A
˚
for the K derivative and S.G.
P4
2
/mnm, Z ⫽ 4, a ⫽ 5.564(3) A
˚
and c ⫽ 18.134(5) A
˚
for the Li
Synthese und Kristallstrukturen der zwei neuen Schicht-Perowskit-Phasen
K
2
La
2/3
Ta
2
O
7
und Li
2
La
2/3
Ta
2
O
7
Inhaltsübersicht. Durch Festkörperreaktionen wurden zwei neue,
zur Ruddlesden-Popper-Familie gehörenden Schicht-Perowskite,
K
2
La
2/3
Ta
2
O
7
und Li
2
La
2/3
Ta
2
O
7
, dargestellt, in denen die Lanthan-
atome zum Teil die Plätze mit Zwölferkoordination besetzen. Die
Strukturen von K
2
La
2/3
Ta
2
O
7
bzw. Li
2
La
2/3
Ta
2
O
7
wurden durch
Röntgen-Pulverdiffraktogramme bzw. durch Einkristallstruktur-
analyse bestimmt. K
2
La
2/3
Ta
2
O
7
Raumgruppr I4/mmm, Z ⫽ 2, a ⫽
Introduction
Ruddlesden-Popper phases (RP), with the general formula
A’
2
[A
n⫺1
B
n
O
3n⫹1
], are of great interest for many of the
properties they exhibit, such as ion-exchange, intercalation
and ionic conductivity. The structure of these compounds
could be considered as derived from the perovskite struc-
ture with excess A’ atoms and oxygen in-between the BO
6
perovskite layers forming thus planar defects. In the formu-
lation, n defines the number of BO
6
octahedra forming per-
ovskite layers which are separated by A’ cations, A atoms
occupying the 12-coordinated perovskite cages. During our
efforts to synthesize such new phases, we have demonstrated
the formation of a new family of layered perovskites
Li
2
A
0.5n
B
n
O
3n⫹1
, [1] where various members can be formed
with the same set of A and B cations (A ⫽ La, Sr, Ca; B ⫽
Nb, Ta, Ti, Fe), which consequently leads to an increase in
A site deficiency in higher members.
In 1999, we reported the synthesis and the structure of
the new n ⫽ 2 member Li
2
SrTa
2
O
7
[1] and more recently,
* M.P. Crosnier-Lopez
Laboratoire des Fluorures, U.M.R. C.N.R.S. 6010,
Faculte
´
des Sciences et des Techniques, Universite
´
du Maine
72 085 Le Mans Cedex 9 ⫺ France
e-mail : marie-pierre.crosnier-lopez@univ-lemans.fr
Z. Anorg. Allg. Chem. 2002, 628, 2049⫺2056 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0044⫺2313/02/628/2049⫺2056 $ 20.00⫹.50/0 2049
form. The supercell, √2a
p
, √2a
p
, c, observed for the latter phase
results from the kink of the octahedra inside the perovskite layers.
While Li
2
La
2/3
Ta
2
O
7
shows no water intercalation, a spontaneous
rapid hydration is observed for K
2
La
2/3
Ta
2
O
7
, leading to the
hydrate K
2
La
2/3
Ta
2
O
7
.2H
2
O.
Keywords: Lanthanum; Tantalum; Perovskites (layered); Structure
elucidation
3,9679(1) und c ⫽ 22,0807(4) A
˚
;Li
2
La
2/3
Ta
2
O
7
: Raumgruppe
P4
2
/mmm, Z ⫽ 4, a ⫽ 5,564(3) und c ⫽ 18,134(5) A
˚
. Die Über-
strukturzelle, √2a
p
, √2a
p
, c, die für die letztgenannte Phase beob-
achtet wurde, resultiert aus dem Abknicken der Oktaeder in den
Perowskitschichten. Während für Li
2
La
2/3
Ta
2
O
7
keine Intercalation
von Wasser beobachtet wird, zeigt K
2
La
2/3
Ta
2
O
7
schnelle Hydra-
tation, was zu K
2
La
2/3
Ta
2
O
7
·2H
2
O führt.
we have prepared and studied the layered RP phases,
K
2
SrTa
2
O
7
[2]; in both compounds, the A sites were fully
occupied by Sr
2⫹
cations. In order to test the stability of
these layered perovskite structures versus the vacancies
number in A sites, we substituted completely the Sr
2⫹
cat-
ions by La
3⫹
cations leading to a nominal vacancy rate of
1/3. In this paper, we present the synthesis and the struc-
tural determination of K
2
La
2/3
Ta
2
O
7
and Li
2
La
2/3
Ta
2
O
7
.
The first one, as already observed for many potassium lay-
ered perovskites, intercalates water leading to the hydrated
form K
2
La
2/3
Ta
2
O
7
.2H
2
O.
Experimental
Sample preparation
The synthesis of these two compounds requires very critical con-
ditions such as starting composition, temperature and cooling rate,
due both to the volatility of the lithium and potassium oxides at
higher temperatures and the formation of impurities (K
2
LaTa
5
O
15
[3] for K
2
La
2/3
Ta
2
O
7
and a mixture of LaTaO
4
[4], LiTaO
3
[5] and
Li
3
TaO
4
[6] for Li
2
La
2/3
Ta
2
O
7
). The two phases were prepared by
solid state reaction in air (total weight 1g) from stoichiometric
amounts of dry La
2
O
3
(Johnson Mattey, purity > 99.99%) (pre-
heated to 1000°C for 12h), Ta
2
O
5
(Johnson Mattey, purity >
99.85%), Li
2
CO
3
and K
2
CO
3
(Aldrich, purity > 99.99%). As often
mentioned for the synthesis of similar phases [1, 2, 7⫺10], an excess
下载后可阅读完整内容，剩余7页未读，立即下载
weixin_38682086
- 粉丝: 6
- 资源: 984
我的内容管理
展开
最新资源
- 最优条件下三次B样条小波边缘检测算子研究
- 深入解析：wav文件格式结构
- JIRA系统配置指南：代理与SSL设置
- 入门必备：电阻电容识别全解析
- U盘制作启动盘：详细教程解决无光驱装系统难题
- Eclipse快捷键大全：提升开发效率的必备秘籍
- C++ Primer Plus中文版：深入学习C++编程必备
- Eclipse常用快捷键汇总与操作指南
- JavaScript作用域解析与面向对象基础
- 软通动力Java笔试题解析
- 自定义标签配置与使用指南
- Android Intent深度解析：组件通信与广播机制
- 增强MyEclipse代码提示功能设置教程
- x86下VMware环境中Openwrt编译与LuCI集成指南
- S3C2440A嵌入式终端电源管理系统设计探讨
- Intel DTCP-IP技术在数字家庭中的内容保护
资源上传下载、课程学习等过程中有任何疑问或建议，欢迎提出宝贵意见哦~我们会及时处理！
点击此处反馈
