STRUCTURAL PROPERTIES OF MECHANOCHEMICALLY SYNTHESIZED
La2FeCrO6
M.N. MITRIĆ, I.M. BRADARIĆ, Č. JOVALEKIĆ*, K. YOSHII**, B. ANTIĆ, AND V. KUSIGERSKI
The Vinča Institute of Nuclear Sciences, Belgrade, Serbia and Montenegro, [email protected]
*Centre for Multidisciplinary Studies, Belgrade, Serbia and Montenegro, [email protected]
**Synchrotron Radiation Research Center, JAERI, Hyogo, Japan, [email protected]
XRD patterns of the La2O3, Cr2O3 and Fe2O3
– starting powders
ABSTRACT
A mixture of crystalline La2O3, Fe2O3 and Cr2O3 powders in stoichiometric ratio was
mechanochemically treated in a planetary ball mill up to 40 h of milling. The mechanochemical
reaction leading to the formation of the La2FeCrO6 double perovskite phase was followed by X-ray
diffraction and magnetization measurements. The obtained XRD data were refined using Rietveld
method considering two possible space groups: P21/n which corresponds to the rock salt structure
with tilted oxygen octahedra and Pbmn which corresponds to random distribution of Fe and Cr
cations. Analysis of R-factors showed that Pbnm structure provides better correspondence to
experimental data. All structural and microstructural parameters were analyzed. In addition, magnetic
measurements show clear antiferromagnetic ordering bellow 289 K, which supports above
conclusion of random distribution of Fe and Cr cations.
350
La2O3
Cr2O3
Fe2O3
300
Intensity (a.u.)
250
200
150
100
50
0
Perovskite-type complex oxides, RMeO3 (R-rare earth elements, Me - transition metals such as Mn, Fe, Co, Cr), have been studied for utilization as
functional materials such as catalysts, magnetic materials, sensing materials, electrode materials for solid-oxide fuel cell. Properties of these materials, beside
chemical composition, depend on their synthesis procedures, which include dependence on chemical homogeneity, grain size and shape, grain boundary.
Next to a great number of chemical processes for the preparation of ceramic materials, mechanochemical method also
proved
to
be suitable,
due to its
x [Å]
y [Å]
z [Å]
B [Å ]
simplicity and efficiency in obtaining extremely reactive nanocrystalline powders.
The purpose of this work is to exam the possibility of synthesizing La2FeCrO6 phase and to investigate its structural and magnetic properties.
La2O3, Cr2O3 and Fe2O3 crystal powders were mixed in equimolar ratio and mechanochemically treated. A planetary ball mill (Fritsch Pulverisette 5) was
used to grind the starting mixture. The mixture was put in a zirconium oxide pot of 500 ml inner volume with zirconium oxide balls of 8-10 mm diameters. Balls to
powder weight ratio was 1:20. The grinding was operated in air without additional additives. Angular velocities of carrying disc and pots were 32.2 and 40.3 rad s-1,
respectively. Grinding intensity corresponds to an acceleration of 10 g. After precise periods of time (30 min, 1h, 2h, 5h, 10h, 20h, 25h and 40h) the samples of powder
were taken for X-ray diffraction measurements (Philips PW 1050). After X-ray diffraction measurements, the powder was placed back in a pot to obtain the same
grinding conditions (balls to powder weight ratio).
XRD patterns of samples ground for 10 or less hours show certain peak broadening because of both crystallite size decrease and micro-strains. XRD
patterns of samples ground for more than 10 hours show new peaks, which are result of formation of perovskite phase. With further grinding for over 40 hours,
monophased La2FeCrO6 is formed.
20
40
60
2
80
100
(degree)
-2
XRPD patterns of 2La2O3, Cr2O3 and Fe2O3
mixture ground for different milling times
h
40
La2FeCrO6
h
25
Obtained and calculated XRD patterns for sample
obtained by ceramical synthesis
h
THE ESSENTIAL RESULTS OF THE RIETVELD REFINEMENT
SAMPLE OBTAINED BY CERAMIC TECHNOLOGY
SAMPLE OBTAINED BY MECHANOCHEMICAL
TECHNOLOGY
Intensity (a.u.)
20
h
10
h
5
Equipment: Philips PW 1050
Wavelengths [Å]: 1.54051 and 1.54433
2 range: 10.00 - 100.00
Step: 0.02
Exposition per step: 10s
No. of points: 4001
h
2
h
1
RESULTS OF REFINEMENT
30 min
No. of fitted parameters: 21
No. of reflections for pattern: 250/2
20
40
60
2
80
100
(degree)
ATOM PARAMETERS
x [Å]
0.5057(6)
0.50(0)
0.50(0)
0.434(4)
0.215(3)
0.5254(3)
0.00(0)
0.00(0)
0.999(3)
0.241(5)
z [Å]
B [Å-2]
0.25(0)
0.00(0)
0.00(0)
0.250(0)
-0.037(2)
3.08(4)
1.04(6)
5.57(6)
5.5(3)
5.5(3)
x [Å]
y [Å]
0.5066(8)
0.50(0)
0.50(0)
0.456(8)
0.133(6)
0.5421(6)
0.00(0)
0.00(0)
0.952(6)
0.272(9)
z [Å]
0.25(0)
0.00(0)
0.00(0)
0.250(0)
-0.032(4)
CELL PARAMETERS [Å]
5.53761 (42)
5.51922 (36)
7.80588 (60)
5.5556(17)
5.5583(35)
7.8516(18)
B [Å-2]
3.08(4)
1.04(6)
5.57(6)
5.5(3)
5.5(3)
Magnetic susceptibility v.s. temperature
for La2FeCrO6 sample
obtained by classical ceramic method
=90.00
=90.00
=90.00
Overall scale factor
Eta
Preferred orientation
Asym.parameters
Crystal size [Å]
Volumen [Å3]
0.000002387(51)
0.378(11)
0.086(16)
0.0554(73)
1187(12)
238.574(0.030)
0.000001101(67)
0.96(21)
0.056(36)
0.007(98)
1187(12)
238.574(0.030)
3.23
4.67
0.81
0,018
0,017
R FACTORS
Bragg R-factor
RF-factor
Chi-square
0,019
3.23
4.67
0.81
(emu/g)
Obtained and calculated XRD patterns for sample
obtained by mechanochemical synthesis
La
Fe
Cr
O
O
y [Å]
0,016
0,015
0,014
0,013
100
150
200
250
Temperature (K)
300
350
400