Physica C 470 (2010) S764–S765
Physica C
Low-temperature synthesis of the infinite-layer compound LaNiO using CaH
2
2
as reductant
*
Tomohisa Takamatsu , Masatsune Kato, Takashi Noji, Yoji Koike
Department of Applied Physics, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Accepted 28 October 2009
Available online 31 October 2009
2
We have successfully synthesized bulk samples of the infinite-layer compound LaNiO by reduction of the
perovskite LaNiO
nite-layer compound LaNiO
excess of CaH in an evacuated Pyrex tube at 300 °C for 24 h.
3
using CaH
2
. First, LaNiO
has been synthesized by heating LaNiO
3
has been prepared using molten KOH at 450 °C. Next, the infi-
2
3
mixed with a double stoichiometric
2
Keywords:
Ó 2009 Elsevier B.V. All rights reserved.
LaNiO
Infinite-layer
CaH
Low-temperature synthesis
2
2
1
. Introduction
In this paper, we report the synthesis of bulk samples of the infi-
nite-layer compound LaNiO by low-temperature reduction of La-
NiO using CaH . Here, we have prepared the parent compound
LaNiO by the method using molten KOH, which is useful for the
preparation of compounds containing transition metals in the ele-
vated oxidation state, and is much easier than the sol–gel and
coprecipitation methods used by Crespin et al. [1] and Hayward
et al. [2], respectively.
2
The compound LaNiO
2
with formally monovalent Ni-ions syn-
3
2
thesized first by Crespin et al. [1] has attracted great interest, be-
cause it is isostructural to the so-called infinite-layer compound
SrCuO
3
2
c
which is a parent material of high-T superconducting cup-
9
rates, as shown in Fig. 1. Moreover, the 3d electronic configuration
+
2+
of Ni is the same as that of Cu in the high-T
ingly, LaNiO is a promising candidate for a parent material of
new high-T superconductors. The synthesis of LaNiO by Crespin
et al. [1] was done by topotactic reduction of the perovskite LaNiO
using H at 250–450 °C, but, it was hard to synthesize it reproduc-
ibly. Later, the reproducible synthesis of LaNiO was achieved by
Hayward et al. [2] through oxygen deintercalation from LaNiO
using NaH as reductant in a narrow temperature range of 190–
10 °C, which was limited by the low decomposition-temperature
c
cuprates. Accord-
2
c
2
3
2
. Experimental
2
2
Polycrystalline bulk samples of LaNiO
follows. First, powdered samples of LaNiO
2
were synthesized as
3
with the perovskite
3
structure were prepared using molten KOH. KOH of 50 g was
placed in an alumina crucible and melted at 450 °C in air. After
2
of NaH (210 °C).
6
.5 h, a mixture of La
2 3
O of 0.3428 g and NiO of 0.1572 g
Recently, an infinite-layer compound SrFeO
2
has been synthe-
using
has a high
decomposition-temperature (885 °C) and is relatively stable, it is
easier to handle CaH than NaH. In addition, very recently, both
Kawai et al. and Kaneko et al. have successfully synthesized a thin
film of LaNiO by low-temperature reduction using CaH and H
respectively [4,5].
(
La:Ni = 1:1 in molar ratio) was added. The crucible was kept
sized by low-temperature reduction of the perovskite SrFeO
CaH at 280 °C by Tsujimoto et al. [3]. Since CaH
3
at 450 °C for 6 h and then cooled to room temperature. Black
polycrystalline powder was isolated by dissolving the hydroxides
with distilled water and dried at 130 °C in air [6]. Next, the
2
2
2
reduction of LaNiO
The obtained powder of LaNiO
chiometric excess of CaH , ground finely and then pressed into
3
was performed using CaH
2
as reductant.
3
was mixed with a double stoi-
2
2
2
,
2
pellets in an Ar-filled glove box. Then, the pellets were sealed
in an evacuated Pyrex tube and then heated at 150–400 °C for
2
4 h. The products were washed with NH
nol to remove the residual CaH and the reaction byproduct CaO.
All products were characterized by powder X-ray diffraction
using Cu K radiation at room temperature.
4
Cl in anhydrous etha-
2
*
a
Takamatsu, Tomohisa
