1
Electrical Properties Bi24(BiCo)O40
S.S. Aplesnin, M.N. Sitnikov, L.V. Udod, A. I. Galyas

Abstract—The crystal structure of
the bismuth
cobaltite Bi24(CoBi)O40 is determined. The resistivity and
thermoelectromotive force
measurement in the
temperature range of 80-1000 K is performed. The
temperature hysteresis of resistivity
below the
temperature Т = 950 K is revealed. The crossover from
semiconductor
to
metallic
behavior
of
thermoelectromotive force versus temperature is found at
high temperatures .
Index
Terms—
electrical
resistivity,
thermoelectromotive force, activation energy.
I. INTRODUCTION
he compounds with mixed valencies shows a wide variety
Tof electrical properties. For example, the conductivity of
Co3O4 [1] and Mn3O4 [2] which contain bi- and trivalent
cations is low in comparison with Fe3O4 [3]. The high
conductivity is due to the combined effect of mixed valence of
the iron ions on the same octahedral sublattice and the small
distance between neighboring octahedral sites in Fe3O4. The
electron transition may occur either between cations on
tetrahedral and octahedral sites located at a relative large
distance, or between cations on octahedral sites in the
substances Co3O4 and Mn3O4 [1,2]. Charge ordering in these
compounds interrelate with spin and orbital degree of
freedom. The effect of charge ordering on transport properties
without these interactions is investigated on Bi24(CoBi)O40
consisting of the ions with filled 6s2 and empty 6s shells [4].
The aim of this study is to investigate the influence of
charge ordering on the resistivity and thermoelectromotive
force in the temperature range 80 K <T <1000 K.
Manuscript received February 17, 2011.
This work was supported by the Russian Foundation for Basic Research
projects no. 09-02-00554_а, no. 09-02-92001-NNS_a; ADTP "Development
of scientific potential of the higher school" no. 2.1.1/401.
L.V. Udod is with the M. F. Reshetneva Aircosmic Siberian State University,
Krasnoyarsk, 660014, Russia (corresponding author to provide phone/fax: 73912-438923; e-mail: [email protected])
S.S. Aplesnin is with the M. F. Reshetneva Aircosmic Siberian State
University, Krasnoyarsk, 660014, Russia (e-mail: [email protected] )
M.N. Sitnikov is with M. F. Reshetneva Aircosmic Siberian State University,
Krasnoyarsk, 660014, Russia (e-mail: [email protected] )
A. I. Galyas is with State Scientific Production Association ''Material
Science Center of the National Academy of Sciences of Belarus", 220072
Minsk, Belarus
II. EXPERIMANTAL
Polycrystalline samples of Bi24(CoBi)O40 were prepared by
solid state reaction method with multiple calcinations. The
stating materials were Bi2O3 (99,9%) and Co3O4 (99,9%),
mixed together at the stoichiometric ratios. The
homogeneously mixed powder were pressed into circular
pellets of 10 mm in diameter and 4 mm in thickness which
calcined at 800°C for 24 h for several time at atmospheric
pressure.
The XRD analysis of the synthesized samples was carried
out to study the phase compositions and to calculate the
lattice parameter using D8-ADVANCE diffractometer with
Cu-Kα radiation (2θ of 0,016°) at room temperature. For
structure determination and refinement of lattice parameters
we used the Rietveld profile analysis method. The presence of
an impurity phase Co3O4 in number of 23% was detected in
the synthesized samples.
The electrical resistivity of the synthesized Bi24(CoBi)O40
samples was measured by the four-probe in the temperature
range of 80-1000 K.
III. CRYSTAL STRUCTURE
According to the data of X-ray diffraction analysis, the
synthesized substance has the chemical formula Bi24(CoBi)O40
and is characterized by cubic symmetry with the I23 space
group and the lattice parameter is a = 10.1917(1) Å [4].
The crystal structure is shown in Fig 1. The unit cell
contains two formula units Bi12(Co0.5Bi0.5)O20. The structure
consists of five coordinated Bi atoms at the 24f site and a
mixed of Co and Bi atoms at the tetrahedral 2a site. Bismuth
atoms in the tetrahedral sites are apparently displaced toward
vacant oxygen sites leading to a typical lone pair environment
for bismuth. Oxygen atoms are situated in difference
positions, namely, О(1) and О(3) – site 8с, аnd atom О(2) –
site 24 f. Positional and isotropic thermodynamic parameters
(Biso), occupation of positions (p) of Bi24(CoBi)O40 are listed
in TABLE I.
TABLE I. ATOMIC PARAMETERS
Atom
Bi 1
p
1,0
Co
Bi 2
O1
0,5
0,5
1,0
O2
1,0
O3
1,0
x
0,17630
(2)
0
0
0,69700
(1)
0,62700
(1)
0,89500
(2)
y
0,31830
(1)
0
0
0,69700
(1)
0,74300
(2)
0,89500
(2)
z
0,01450
(1)
0
0
0,69700
(1)
0,99600
(3)
0,89500
(2)
Biso.,Å2
1,73
(3)
3,9(2)
3,(2)
2
2
2
2
150 K < T < 250 K . A mixed state consisting of semiconductor and metal is possible exists in the temperature
range 250 T K <T <950 K where α (T) is described by fitting
function α (T) =A/T+B T, where А=162, В=0.0003.
0.7
1
2
, mV/K
0.6
0.5
0.4
Fig.1 Crystal structure Bi24(CoBi)O40 .
200
IV. ELECTRICAL PROPETIES
20
heating
cooling
ln(, ohm cm)
15
10
5
0
2
3
4
5
600
800
1000
T, K
The temperature dependence of resistivity for Bi24(CoBi)O40
is shown in Fiig. 2. The temperature hysteresis of resistivity at
heating and at cooling is observed. The resistance of sample
after cooling increase according to the logarithmic law versus
the measurement time at the fixed temperature. Crystal
structure is retained and X-ray diffraction peaks is shifted
1
400
6
7
3
10 /T
Fig.2 Logarithmic resistivity dependence versus inverse
temperature at heating and at cooling.
towards small angles in results of that the constant lattice is
rised by 0.4%. The decrease of resistance is associated with
increase of a constant lattice that shows on interrelation of
electric and structural properties.
The temperature
dependence of thermoelectromotive force is presented in
Fig.3.
The thermoelectromotive force temperature dependence is
well described by typical semi-conductor dependence α (T) ~
∆E/kT with the activation energy is ∆E=0.23 eV at
Fig3. Thermoelectromotive force dependence on
temperature : 1- experimental data, 2- fitting function α (T)
=A/T+B T, where А=162, В=0.0003.
This work was supported by the Russian Foundation for Basic
Research projects no. 09-02-00554_а, no. 09-02-92001NNS_a; ADTP "Development of scientific potential of the
higher school" no. 2.1.1/401.
So, semiconductor Bi24(CoBi)O40 has charge ordering up to
Т=250 K, above this temperature probably there is coexistence
of regions with uniform distribution of a charge on bismuth
ions, and domains with three- and five valence of bismuth
ions. Heating of sample Bi24(CoBi)O40 causes the uniform
charge distribution and the phase transition to a metal state at
Т=950 K.
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