新型层状钙钛矿K2La2/3Ta2O7和Li2La2/3Ta2O7的合成与晶体结构
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"这篇学术论文详细介绍了两种新型层状钙钛矿相——K2La2/3Ta2O7和Li2La2/3Ta2O7的合成及其晶体结构。作者通过固态反应成功制备了这两种材料，它们属于Ruddlesden-Popper系列。在K2La2/3Ta2O7中，镧(La)部分占据12配位的位点，而Li2La2/3Ta2O7的结构则由粉末X射线衍射和单晶X射线衍射数据确定。K2La2/3Ta2O7具有I4/mmm空间群，Z=2，a=3.9679(1) Å，c=22.0807(4) Å；Li2La2/3Ta2O7具有P42/mnm空间群，Z=4，a=5.564(3) Å，c=18.134(5) Å。"
这篇论文揭示了在无机材料科学领域中的新发现，特别是关于层状钙钛矿结构的深入研究。钙钛矿是一类具有广泛应用前景的材料，因其独特的电子性质而在太阳能电池、光电转换、电容器和光催化等领域受到广泛关注。Ruddlesden-Popper系列是钙钛矿的一个亚类，其结构特征为层状排列，这通常涉及到阳离子在不同层间的交替。
论文中提到的K2La2/3Ta2O7和Li2La2/3Ta2O7是这个系列的两个新成员。它们的合成方法是固态反应，这是一种常见的无机化合物制备技术，通常涉及将反应物在高温下混合，以促进化学反应。La的部分占据12配位的位点表明了其在晶体结构中的复杂性，这种现象可能影响材料的电荷传输和光学性质。
K2La2/3Ta2O7的晶体结构由粉末X射线衍射确定，这种方法常用于分析多晶或非单晶材料的结构。其I4/mmm空间群是一种高度对称的四方晶系，Z=2表示每个单元胞中有两个基本单元。另一方面，Li2La2/3Ta2O7的结构通过单晶X射线衍射数据解析，这种方法能提供更精确的原子定位，其P42/mnm空间群属于四方晶系，Z=4表示每个单元胞有四个基本单元。
这些新的层状钙钛矿相的发现为理解和设计新型功能材料提供了宝贵的实验数据。通过改变阳离子种类（如K+和Li+）和配位环境，研究人员可以调控材料的电荷载流子迁移率、能带结构和光学性能，从而有望开发出更高效的光电转换器件或其他高性能电子设备。
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
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