Precursor synthesis and magnetic properties of Cd1?xFexO (0 ? x ? 0.07)

Article abstract of DOI:10.1016/j.mencom.2017.09.008

The polycrystalline solid solutions Cd_{1 – x}Fe_xO (0 ? x ? 0.07) possessing ferromagnetic properties at 5 K and room temperature have been synthesized by a precursor method using the formate Cd_{1 – x}Fe_x(HCOO)₂ ·2H₂O.

Full text of DOI:10.1016/j.mencom.2017.09.008

Mendeleev
Communications
Mendeleev Commun., 2017, 27, 456–458
Precursor synthesis and magnetic properties of Cd1−xFe O (0 £ x £ 0.07)
x
a
a
a
a
Vladimir N. Krasil’nikov, Tatyana V. Dyachkova, Alexander P. Tyutyunnik, Olga I. Gyrdasova,*
b
b,c
d
Yuliya A. Perevozchikova, Vyacheslav V. Marchenkov and Harald W. Weber
a
b
Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg,
Russian Federation. E-mail: gyrdasova@ihim.uran.ru
M. N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, 620137 Ekaterinburg,
Russian Federation
Ural Federal University, 620002 Ekaterinburg, Russian Federation
Atominstitut, Vienna University of Technology, 1020 Vienna, Austria
c
d
DOI: 10.1016/j.mencom.2017.09.008
1
.00 x = 0.07
.75
.50
x
Cd1–xFe O
0
The polycrystalline solid solutions Cd1–xFe O (0 £ x £ 0.07)
x = 0.05
x
0
0
possessing ferromagnetic properties at 5 K and room tem­
perature have been synthesized by a precursor method using
the formate Cd1–xFe (HCOO) ∙2H O.
.25 x = 0.025
x = 0.01
0.00
x
2
2
0
100
200
T/K
300
400
CdO
The intensive development of advanced branches of science
and engineering (including spintronics) based on the use of
spin polarization in semiconductors, requires the creation of new
functional materials combining the valuable properties of semi­
conductors and ferromagnetics.1 Cadmium oxide belongs to
such materials owing to a developed defect structure and unique
physical properties, which are responsible for its practical
solutions Cd1–xFe O with a maximum possible degree of iron
x
for cadmium substitution and to examine their structural and
magnetic properties. Cadmium formate Cd(HCOO) ∙2H O in
2
2
2
+
2+
whose structure some Cd positions are replaced by Fe cations
was chosen as a precursor. Cadmium formate belongs to a group
of isostructural M(HCOO) ∙2H O compositions (M = Mg, Mn,
2
2
Fe, Co, Ni, Cu, Zn and Cd) capable of forming numerous solid
2–4
11
applications. The electrical and optical properties of cadmium
oxide depend on the degree of its imperfection, the presence
of heteroatomic impurities and the morphology, surface micro­
structure and particle size, which are determined by the synthesis
conditions. The thermal treatment of CdO powder in a vacuum
or in a hydrogen atmosphere leads to the appearance of room­
solutions with each other. Cadmium and iron formates form
a continuous series of well soluble in hot water solid solutions
12
Cd1–xFe (HCOO) ∙2H O, and their use as a precursor in the
x
2
2
synthesis of Cd1–xFe O gives an unlimited resource of iron.
x
Cd1–xFe (HCOO) ∙2H O (0 £ x £ 0.2) was synthesized by
x
2
2
the dissolution of Cd(HCOO) ∙2H O and Fe(HCOO) ∙2H O
2
2
2
2
4
temperature magnetization. In our opinion, this effect is due to
formate mixtures in hot distilled water and the subsequent evapora­
tion at 60°C in air until the formation of a solid residue. Cadmium
and iron formates were prepared by the following reactions:
an increased structure imperfection of cadmium oxide: annealing
in a vacuum gives rise to oxygen vacancies (V ), and annealing
O
in a hydrogen atmosphere leads to vacancies in the cadmium
CdCO + 2HCOOH + H O = Cd(HCOO) ∙2H O + CO ,
(2)
(3)
sublattice (V ). Vacancies in the cadmium and oxygen sub­
3
2
2
2
2
Cd
lattices induce spin­polarized states of O2p and 4d orbitals of
Cd in the vicinity of the Fermi level, which determines its
ferromagnetic properties. The introduction of transition metal
ions into the crystal structure of cadmium oxide considerably
Fe + 2HCOOH + 2H O = Fe(HCOO) ∙2H O + H .
2
2
2
2
To avoid the possible oxidation of Fe to Fe3+ by atmo­
2
+
1
3
spheric oxygen, the crystallization of iron formate was carried
out by evaporation in a nitrogen atmosphere. An alternative
way of precursor synthesis was to conduct reactions (2) and (3)
simultaneously on heating in air:
5
–10
affects its electrical, magnetic and optical properties.
The
doping of CdO with iron (~1–2 at%) results in an abrupt
5
enhancement of electrical conductivity and in the appearance of
weak ferromagnetic properties6 intensifying upon heating in a
vacuum or in a hydrogen atmosphere. However, upon contact with
hydrogen, some cadmium is reduced to the metal and isolated as
an impurity phase even at relatively low temperatures:
,7
(
1 – x)CdCO3 + xFe + 2HCOOH + (2 – x)H O =
2
= Cd1–xFe (HCOO) ∙2H O + (1 – x)CO + xH2.
(4)
x
2
2
2
To produce Cd1–xFe O, the Cd Fe (HCOO) ∙2H O samples,
x
1–x
x
2
2
0
CdO + H = Cd + H O.
(1)
where x = 0.0, 0.01, 0.025, 0.05, 0.07, 0.075, 0.1, 0.15 or 0.2,
were heated at 250–300°C until complete decomposition to form
a dark brown mass. Then, the products of thermolysis were
thoroughly ground in an agate mortar and annealed at 400°C
for 2 h.
2
2
This fact decreases the value of results6,7 and requires further
investigations to synthesize iron­doped ferromagnetic cadmium
oxide containing no impurities.
The aim of this work was to develop a precursor method for
the synthesis of the phase­homogeneous polycrystalline solid
The Cd(HCOO) ∙2H O and Fe(HCOO) ∙2H O formates
isolated by evaporation are white and light green powders,
2
2
2
2
©
2017 Mendeleev Communications. Published by ELSEVIER B.V.
–
456 –
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.

Mendeleev Commun., 2017, 27, 456–458
respectively. Cadmium formate forms crystals of a flattened
shape with moderate cleavage in the direction parallel to flattening
and bad cleavage in other orientations. The reflective indices of
Cd(HCOO) ∙2H O crystals are N = 1.548, N = 1.509, and
Table 1 Crystallographic characteristics of cadmium oxide and the solid
solutions Cd1–xFe O synthesized by the thermolysis of formates.
x
CSR/nm Microstrain r/g cm–3
Entry Sample
a/Å
2
2
g
m
1
2
3
4
5
CdO
Cd0.99Fe0.01
4.6962(5) 104.9
0.000023
0.000303
0.000425
0.000514
0.000612
8.06(6)
7.96(6)
7.82(3)
7.67(2)
7.66(2)
N = 1.497. Iron formate is characterized by the formation of
p
O
O
O
O
4.6956(5)
4.6946(5)
4.6941(5)
4.6934(5)
87.4
90.4
80.3
80.5
laminar and hexagonal scaly crystals with the reflective indices
Cd0.975Fe0.025
Cd0.95Fe0.05
Cd0.93Fe0.07
N = 1.563, N = 1.536, and N = 1.524. During the evaporation
g
m
p
of solutions of cadmium and iron formate mixtures, almost white
Cd1–xFe (HCOO) ∙2H O powders with a weak yellow­green
x
2
2
tint are formed at x > 0.1. The shape of Cd1–xFe (HCOO) ∙2H O
x
2
2
crystals is also laminar, and the reflective indices differ insigni­
ficantly from those for pure cadmium formate. The reflective
indices of Cd0.95Fe0.05(HCOO) ∙2H O crystals are N = 1.551,
densities, CSR and microstrain values. The formation of metallic
cadmium during the thermal decomposition of precursors can be
induced by the thermally stimulated intramolecular interaction of
the cationic and anionic formate components:
2
2
g
Nm = 1.509, and N = 1.499. The Cd Fe (HCOO) ∙2H O
p
1–x
x
2
2
crystals with iron content of >5 at% feature a wave­like extinction,
which impedes their orientation and measurements of reflective
indices.
Cd2+ + 2HCOO– = Cd + H O + CO + CO
0
(5)
2
2
or
†
According to the X­ray phase analysis data, the products of
Cd2+ + 2HCOO = Cd + H + 2CO .
–
0
(6)
2
2
thermal decomposition of Cd1–xFe (HCOO) ∙2H O (0 < x £
x
2
2
£
(
4
0.075) at 250–300°C mainly consist of CdO and small amounts
~0.5 wt%) of a cadmium metal impurity. Upon annealing at
00°C in a muffle furnace, they represent monophase samples of
Indeed, on heating in air at 300–350°C, Cd(HCOO) ∙2H O
2 2
decomposes to afford CdO containing ~1% Cd. When heating
occurs in a helium atmosphere, thermal decomposition gives rise
to metallic cadmium in the form of a grey powder.
the solid solutions Cd1–xFe O with assigned iron concentrations.
x
The existence of these solid solutions is confirmed by a regular
decrease in the lattice parameter and density when the iron con­
centration increases up to 7 at% (Table 1). A further increase in
the iron concentration leads to the formation of an impurity
phase of CdFe O ferrite. Figure 1 presents X­ray diffraction
The magnetization m(H) curves at 5 and 300 K (Figures 2
and 3) show that the Cd1–xFe O samples are ferromagnetic. This
x
conclusion is confirmed by the presence of a hysteresis and
residual magnetization (insets in Figures 2 and 3). The Curie
temperature of Cd0.95Fe0.05O is 560 K. The magnetization of
2
4
and microstrain patterns of Cd1–xFe O samples, where x = 0.0,
Cd1–xFe O increases with the iron concentration in the whole
x
x
0
.01, 0.025, 0.05 and 0.07. Table 1 gives the lattice parameters,
examined interval reaching maximal values for the sample with
–1
–1
x = 0.07: m = 2.450 emu g at T = 5 K and m = 0.900 emu g
S
S
(
a)
at T = 300 K (Figures 2 and 3, Table 2). Pure CdO behaves as
a diamagnetic with a ferromagnetic component at both tempe­
5
4
3
ratures (insets in Figures 2 and 3), in agreement with the results
4
reported earlier. The magnetic characteristics of Cd Fe O
1–x
x
samples were compared with the available literature data using
Cd0.99Fe0.01O as an example, since powders of the same com­
2
1
6
,7
position were studied at room temperature. The saturation
magnetization of the synthesized Cd0.99Fe0.01O sample is
3
0
40
50
60
–
1
2
q/deg
0.018 emu g at T = 300 K, which is much higher than m =
S
–
1
(
b) 0.3
= 0.00293 and m = 0.0055 emu g (see refs. 6 and 7, respec­
S
5
tively). As noted above, the annealing of the Cd0.99Fe0.01O powder
in helium results in a stepwise growth of the saturation mag­
netization of Cd Fe O powders to m = 0.00837 and m =
4
0
0
0
.3
.3
.0
1
–x
x
S
S
–1
3
2
= 0.00594 emu g (see ref. 6 and 7, respectively). This effect is
connected with the partial reduction of cadmium and its isolation
1
1
–1
(a)
3
2
0.01
0.00
5
4
0
80
120
2
q/deg
4
3
1
–2
Figure 1 (a) X­ray diffraction patterns and (b) peak widths (FWHM) of
Cd1–xFe O [x = (1) 0.0, (2) 0.01, (3) 0.025, (4) 0.05, and (5) 0.07] solid
solutions synthesized by the heat treatment of Cd1–xFe (HCOO) ∙2H O
in air at the maximal annealing temperature of 400°C.
1
–0.01
x
2
1
–
60 –40 –20
0
20 40 60
x
2
2
0
(
b)
0
.2
5
1
†
–1
–2
–3
The phase analysis of the precursors and their thermolysis products
was carried out on a polarization transmission microscope (the refractive
indices were determined by the immersion method at room temperature)
and a STADI­P X­ray powder automatic diffractometer (STOE) in CuKa1
radiation using the library of X­ray diffraction data PDF­2 (ICDD
Release 2009). The coherent scattering regions (CSRs) and microstrain
of particles were determined by X­ray diffraction using the Williamson–
4
2
0.0
0
–0.2
3
–1
–
2
–1
0
1
2
–
60
–40
–20
0
20
40
60
Hall method.14 The density of the Cd1–xFe O powders was determined
Magnetic field/kOe
x
with the use of an AccuPyc II 1340 automatic helium pycnometer with
a 1 cm working chamber. The magnetic properties were measured on
an MPMS XL7 SQUID magnetometer (Quantum Design) in magnetic
fields to 60 kOe.
Figure 2 Magnetization curves of the Cd1–xFe O [x = (1) 0.0, (2) 0.01,
x
3
(
3) 0.025, (4) 0.05, and (5) 0.07] samples at 5 K. Insets: (a) magnetiza­
tion curves for pure CdO (1–1) before and (1–2) after subtraction of the
diamagnetic contribution; (b) hysteresis loops for the Cd1–xFe O samples.
x
–
457 –

Mendeleev Commun., 2017, 27, 456–458
Table 2 Coercive force HC and saturation magnetization m for CdO and
of iron. The advantage of the developed synthesis method is that
S
Cd1–xFe O samples at T = 5 and 300 K.
x
it allows one to accurately assign the elemental composition of
both a precursor and its thermolysis product. Moreover, for the
preparation of samples with high magnetization values, there is
no need to use annealing in a hydrogen atmosphere. The thermal
decomposition of the Cd1–xFe (HCOO) ∙2H O precursor in air
–
1
Entry Sample
H /Oe
m /emu g
T/K
C
S
1
2
3
4
5
CdO
230
0.0075
0.0012
0.480
0.018
0.810
0.140
1.520
0.500
5
300
5
300
5
300
5
300
5
0
x
2
2
Cd0.99Fe0.01
O
800
provides conditions sufficient for the production of impurity­free
1
0
oxide Cd1–xFe O with a rock salt structure and for the formation
Cd0.975Fe0.025
O
580
x
1
0
of its magnetic properties. The saturation magnetization of the
Cd0.95Fe0.05
O
O
460
solid solutions Cd1–xFe O (Table 2) are comparable with those
x
1
2
of Zn1–xFe O synthesized earlier by the precursor method using
x
Cd0.93Fe0.07
450
2.450
0.900
5
300
15
the Zn1–xFe (HCOO) ∙2H O formate.
x
2
2
2
2
This work was suported in part by the Russian Foundation for
Basic Research (project no. 15­03­02908­a) and the Presidium
of the Ural Branch of the Russian Academy of Sciences (project
no. 15­9­3­31).
1
–1
(a)
5
1
0
0
.0
.5
.0
0
0
.01
.00
4
3
1
–2
References
–
0.01
1
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–
–
–
–
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0.3 –0.2 –0.1
0
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0
20
40
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7
2
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Figure 3 Magnetization curves of the Cd1–xFe O [x = (1) 0.0, (2) 0.01,
x
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9
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magnetic contribution; (b) hysteresis loops for the Cd1–xFe O samples.
x
2
1
2
from the oxide structure in the form of metal. Consequently, the
growth of magnetization of Cd Fe O upon exposure in a
1
1
1
1 D. Stoilova, J. Mol. Struct., 2006, 798, 141.
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3 R. D. Pierce and S. A. Friedberg, Phys. Rev. B, 1971, 3, 934.
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1
–x
x
reducing hydrogen atmosphere6 can be explained not only by
an increased concentration of VCd vacancies caused by the removal
of metal from the oxide but also by the enhancement of the iron
content related to this process, which agrees with the results of
our studies (Figures 2 and 3).
,7
V. V. Marchenkov and H. W. Weber, Mater. Chem. Phys., 2015, 162, 1.
Thus, the use of the Cd1–xFe (HCOO) ∙2H O formate as a
x
2
2
precursor makes it possible to obtain ferromagnetic solid solu­
tions Cd1–xFe O stable in time, whose saturation magnetization
x
at low and room temperatures increases with the concentration
Received: 18th January 2017; Com. 17/5152
–
458 –