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Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Ba
3
CuOs
2
O
9
and Ba
3
ZnOs
2
O
9
, a comparative study
Hai L. Feng, (冯海)
⁎
, Martin Jansen
⁎
Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, Dresden 01187, Germany
ARTICLE INFO
Keywords:
Osmium
Hexagonal triple perovskite
Os
2
O
9
dimer
Antiferromagnetic order
ABSTRACT
Polycrystalline samples of Ba
3
CuOs
2
O
9
and Ba
3
ZnOs
2
O
9
were synthesized by solid-state reactions. Ba
3
CuOs
2
O
9
crystallizes in Cmcm, while Ba
3
ZnOs
2
O
9
adopts the hexagonal space group P6
3
/mmc. Both the crystal
structures consist of face-sharing Os-centered octahedra forming dimer-like Os
2
O
9
units, which are inter-
connected by corner-sharing CuO
6
, or ZnO
6
octahedra, respectively. In Ba
3
CuOs
2
O
9
, the CuO
6
octahedra show a
characteristic Jahn-Teller distortion. Both, Ba
3
CuOs
2
O
9
and Ba
3
ZnOs
2
O
9
, are electrically insulating. Magnetic
and specific heat measurements confirm that Ba
3
CuOs
2
O
9
is antiferromagnetically ordered below 47 K. Analysis
of the magnetic data indicated that its magnetic properties are dominated by Cu
2+
ions. The magnetic
susceptibility of Ba
3
ZnOs
2
O
9
is weakly temperature-dependent with a broad maximum ≈ 280 K, indicating the
presence of strong exchange interactions within the Os
2
O
9
dimer. The residual magnetic susceptibility at low
temperatures also suggests the presence of appreciable exchange coupling between the dimers.
1. Introduction
3d-5d(4d) oxides continue to attract great attention, due e.g. to the
half-metallic nature found for the double perovskite Sr
2
FeMoO
6
,
showing a magnetic transition temperature higher than 400 K [1]. It
thus appears prospective for spintronic applications. This discovery has
triggered considerable efforts in the synthesis and characterization of
3d-5d(4d) double perovskite oxides. Among them, Sr
2
CrReO
6
shows a
high-temperature ferrimagnetic transition at 635 K and a nearly half-
metallic nature [2], while insulating Sr
2
CrOsO
6
and Ca
2
FeOsO
6
feature
high-temperature ferrimagnetic transitions above room temperature
[3–5]. A ferromagnetic insulator, Ba
2
NiOsO
6
, with T
C
≈ 100 K was
reported [6], and Mn
2
BReO
6
(B = Fe, Mn) show attractive magnetic
and magnetoresistive properties [7–9]. The hexagonal perovskite
Ba
2
Fe
1.12
Os
0.88
O
6
exhibits a high-temperature ferrimagnetic transition
(≈ 370 K) with large coercivity and exchange bias [10].
Hexagonal triple perovskites with formula Ba
3
MM′
2
O
9
have been
well studied as ruthenates and iridates, Ba
3
MM′
2
O
9
(M = Li, Na, Mg,
Ca, Sr, Zn, Cu, Ni, Co, Fe, Ti, Zr, Bi, or a lanthanide; M′ = Ru or Ir)
[11–29]. They adopt 6H-BaTiO
3
related structures: M ions occupy the
corner-sharing octahedral sites (MO
6
), while the Ru or Ir ions take the
face-sharing octahedral sites forming Ru
2
O
9
or Ir
2
O
9
dimers. Based on
such structural features complex and diverse magnetic exchange
patterns develop，and it appears appealing to investigate other 5d
species, e.g. osmates, more extensively. So far, only Ba
3
MOs
2
O
9
(M =
Li, Na) have been reported [30], to the best of our knowledge. In this
work, new triple perovskite osmate Ba
3
CuOs
2
O
9
was synthesized, and
in order to understand the contributions of Cu and of the Os
2
O
9
dimer
to the magnetic exchange interactions, Ba
3
ZnOs
2
O
9
was also synthe-
sized and studied in comparison.
2. Experimental
Polycrystalline samples of Ba
3
CuOs
2
O
9
and Ba
3
ZnOs
2
O
9
were
synthesized by solid-state reactions from BaO (decomposition of
BaCO
3
, Alfa 99.8%), CuO (Alfa 99.9995%), ZnO (Alfa 99.9%), and Os
(Alfa 99.95%) in two steps. First, BaO and Os in a 3/2.4 mol ratio were
well ground together and pressed into pellets. Each pellet was then
loaded into a corundum crucible, which was placed into a silica tube
along with a second corundum crucible containing MnO
2
(Alfa 99.9%).
The silica tube was then sealed under the dynamic vacuum using a H
2
/
O
2
torch, and heated at 750 °C for 48 h in a tube furnace. MnO
2
decomposes into ½ Mn
2
O
3
+¼O
2
at 550 °C and acts as an oxygen
source for the reaction. The molar ratio of Os and MnO
2
applied was 1/
5. This synthesis process is similar to that of Ba
3
Os
2
O
9
[31]. Secondly,
the products obtained were mixed with CuO or ZnO with weight ratios
of 1/0.0849 or 1/0.0869, corresponding to 1/1 molar ratios of
Ba
3
Os
2
O
9
/CuO or Ba
3
Os
2
O
9
/ZnO, to synthesize Ba
3
CuOs
2
O
9
and
Ba
3
ZnOs
2
O
9
, respectively. The mixed powders were pressed to pellets
and loaded into corundum crucibles which were placed in silica tubes.
The silica tubes were sealed under dynamic vacuum and then heated at
950 °C for 48 h in a tube furnace. Hazard: in order to avoid any contact
with highly toxic OsO
4
after heating, the ampoules must be carefully
opened under a fume hood.
https://doi.org/10.1016/j.jssc.2017.12.013
Received 3 November 2017; Received in revised form 8 December 2017; Accepted 10 December 2017
⁎
Corresponding authors.
E-mail addresses: Hai.Feng@cpfs.mpg.de (H.L. Feng), M.Jansen@fkf.mpg.de (M. Jansen).
Journal of Solid State Chemistry 258 (2018) 776–780
Available online 13 December 2017
0022-4596/ © 2017 Elsevier Inc. All rights reserved.
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