JPMS Conference Issue, Materials 2010 AUTO-COMBUSTION ...mrl.uop.edu.pk/JPMS/issues/materials2010/3.AUTO... · 818 o C 956 o C 952 o C DSC TG Figure 2. TG-DSC thermo-grams of as-synthesized

JPMS Conference Issue, Materials 2010

12

AUTO-COMBUSTION SYNTHESIS AND CHARACTERIZATION OF MULTI-FERROIC (BiFeO3) MATERIALS

Humaira Seema1, S. K. Durrani2*, K. Saeed2, I. Mohammadzai1 and N. Hussain2

1Institute of Chemical Sciences, University of Peshawar. 2Materials Division, Directorate of Technology, PINSTECH, P.O. Nilore, Islamabad.

Email: [email protected] and [email protected]

Abstract

Multiferroic BiFeO3 materials were synthesized by gel-combustion method using citric acid as a fuel. The as-synthesized materials were calcined at 600oC for 4 h to obtain single-phase material. The crystal structure and microstructural study were carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results confirm the formation of single phase BiFeO3 which crystallize into a rhombohedral structure along with a small amount of impurity phases, which are subsequently removed by leaching the samples with dilute nitric acid. The electron micrographs indicated no compositional fluctuations and dense ceramic powder were obtained. TG/ DSC analysis of the samples shows a structural phase change from at 850oC. At higher temperatures appearance of impurity phases due to bismuth loss and liquid phases are seen.

Keywords: Multiferroic , BiFeO3, Ferroelectric, Ferromagnetic and Citrate-nitrate gel combustion, Perovskite oxide,

1. Introduction

With ever-expanding demands for transducers, mechanical actuators, micro-electro-mechanical systems (MEMS), infrared sensors, and data storage applications, materials with superior ferroelectric, piezoelectric, and ferromagnetic responses are of great interest1. Recently, magnetoelectric or multiferroic materials showing the coexistence of magnetic and ferroelectric orders in a certain range of temperature, have attracted increasing attention owing to the rich physical phenomena resulting from multi-order parameter interactions and promising potential applications on the magnetic control of ferroelectric polarization for novel magnetoelectric devices2-5. Multiferroics are a class of materials which exhibit two or more of the ferroic orders, namely ferroelectric,

ferromagnetic and ferroelastic6. Single phase multiferroic materials with strong coupling of ferroelectric and magnetic orderings are still very attractive7. These compounds present opportunities for potential applications in information storage, emerging field of spintronics and sensors. Although, there are a number of materials that possess both ferroelectricity and magnetism, among all the multiferroic materials, perovskite-type bismuth ferrite (BiFeO3) is an interesting multiferroic oxide. It exhibits ferromagnetism (FM) at room temperature with high ferroelectric (FE) Curie temperature (TC ≈ 830

oC) and G-type antiferromagnetic properties (AFM) below Neel point (TN ≈370

oC)8. In addition to the potential magnetoelectric applications, BiFeO3 might find applications as photo- catalytic materials

Humaira Seema, S. K. Durrani, K. Saeed, I. Mohammadzai and N. Hussain: Auto Combustion…...


13

due to its small band-gap. This small band-gap also allows carrier excitation in BiFeO3 with commercially available femto-second laser pulses, hence enable us to develop ferroelectric ultra-fast optoelectronic devices as widely demonstrated in semiconductors. The antiferromagnetic nature of BiFeO3 results in weak magnetism and weak magnetoelectric coupling of BiFeO3

9. In order to understand the properties of nanocrystalline BiFeO3, it is very important to establish a synthesis procedure in a manner such as to avoid the impurity phases. There are several reports on the synthesis of BiFeO3. Recently, BiFeO3 ceramics have been synthesized by several methods like solid state reaction10, simple Co-precipitation11, ferrioxalate precursor12 and microemulsion13, sol-gel14, and hydrothermal process15. Due to difficult to synthesize BiFeO3 materials, nano-metric grains are desirable in a powder preparation route. The auto-combustion synthesis is an effective, low cost method for production of various industrially useful materials. In present work, a detailed gel combustion process to obtain the BiFeO3 ceramic powder was studied.

2. Experimental a) Materials and Method

The chemicals Bi(NO3)3.5H2O (99.9% Fluka), Fe(NO3)3.9H2O (99.9% Fluka), citric acid (99.9% Merck), and ammonia (Merck), used were analytical reagent grade and used without further purification.

Bismuth iron based (BiFeO3 1:1 ratios) oxide powders were synthesized using citrate-nitrate sol-combustion process. Known concentration of nitrate solutions were prepared by dissolving different

metal nitrates i.e., bismuth, and ferric nitrates in carbonate free (CO3

-2) double deionized water (DDW). These suctions were then mixed and appropriate amount of citric acid was finally added in the mixed solution. Ammonium hydroxide was added drop wise and pH of the suspension was maintained at 6.2 (acidic nature) with attached pH-meter (J. P. Selecta 2006, Spain) and the mixture was evaporated at 70oC in rotary evaporator (Heidolph Laborota 4001) maintained at 70-80oC for 4h until a viscous sol was obtained. The viscous sol was transferred into a bowel and was heated on a hot plate and temperature of the hot plate was kept 90-180oC. A rapid and vigor auto-ignition was completed within a few minutes. The detailed combustion process is shown in Figure 1. Before grinding some of the powder specimens of BiFeO3 were first heated at 250

oC in static air oven, then calcined at 600oC for 4h. The calcined specimens were furnace-cooled and ground to fine powder.

b) Characterization

The synthesized powders were characterized by using various techniques. The crystallinity and phase analysis were conducted by X-ray diffraction using Rigaku Geiger flux instrument with CuKα radiation (λ = 0.154056 nm).The XRD data were collected in the 2θ range from 15°


14

phase, and thermal decomposition behaviour of dried powder of BiFeO3 was measured by thermogravimetric SDT Q600 analyzer. The TG/DSC patterns were collected as a function of temperature and heat flow under N2 atmosphere at rate of 10oC/min.

3. Results and Discussion

Figure 2 shows the TG-DSC thermograms of as-synthesized BiFeO3 oxide powder derived from precursor solution with pH 6.2 and heated at 180oC. In DSC, heat flow increases with the increase in temperature. The structure is unstable due to oxygen and bismuth loss around 815 to 960oC above which an irreversible chemical decomposition of sample occur. The sharp endothermic peaks were observed at 818oC and 956oC. The peak at 818oC corresponds to a reversible structural phase transition being at low temperature. The peak at 956oC shows bismuth loss phase as Bi2Fe4O9. The observed thermal properties of BiFeO3 powder were found similar to those of earlier observation16. Kaczmarek et al.17 have attributed the peak observed in DSC near 830oC to the ferroelectric phase transition (curie temperature TC) of BiFeO3.

Figure 3(a-b) shows the XRD plots of BiFeO3 powder heated at 180 and 550

oC. The Fig.3a shows XRD pattern of dried gel of citrate-nitrate after heating at 180oC in air. The pattern indicates the sharp peaks of mixed metal nitrates and oxides of cooked gel mixture. The most

prominent Bi2O3 peak was observed and indexed.Fig.4b indicates the phase of BiFeO3 oxide and tiny amount of oxides after calcination at 500oC. It is revealed that the BiFeO3 is a single phase crystalline material. The planes (hkl) in the XRD pattern for BiFeO3 were matched by comparing them with the data of JCPD card of 71-2494. Using 2θ values from XRD plot and hkl values from the standard JCPD card the lattice parameters for hexagonal unit cell were found. Crystallize size of powder calcined at 550oC for 2 h were noted to be 55nm. It is observed that crystallize size increases with the temperature.

Figure 4(a-b) shows the SEM and EPMA image of BiFeO3 powder calcined at 550oC. It is shown that fine grains were grown in flaky particle shape and agglomerated in narrow size distribution. The Fig.6a revealed that the powder specimen calcined sintered at 550oC for 2h has an average grain size of~200nm (Fig.4a). The black spots in SEM micrographs are pores. Figure 4b shows the compositional analysis of BiFeO3 estimated by EPMA. The unit cell formula was estimated using oxide formula method and the exact formula was found to be Bi0.95 Fe0.96O3.05.The particle size could be estimated from SEM image. The particle size is slightly greater than the crystallize size obtained by the Scherrer’s equation because of the agglomeration of particles.



15

`

Figure 1: Self-combustion process, a) metal nitrate and citric acid sol at pH 6.24 and 80oC, b) sol heated at 180oC, c) initiation of combustion of sol, d) complete combustion, e) end of combustion reaction and f) BiFeO3

e f

d c

b a



16

0 200 400 600 800 1000

96

98

100

102

104

106

Temperature / oC

We

igh

t L

oss

%

-8

-6

-4

-2

0

Heat

Flo

w (

W/g

)

Exo

up

818 o

C

956

oC

95

2 o

C

DSC

TG

Figure 2. TG-DSC thermo-grams of as-synthesized BiFeO3 oxide powder derived from precursor solution with pH 6.2 and heated at 180oC.

10 20 30 40 50 60 70 80

0

500

1000

1500

2000

2500

3000

3500•••• BiFeO

3

• •

•

• •

• •

• •

•

*

*

* Bi2O

3

Inte

nsit

y (

a.u

)

2 Theta(degree)

550 oC

180 oC

Figure 3. XRD patterns of BiFeO3 powder prepared by combustion process, a) sample heated at 180oC and b) sample heated at 550oC.

Figure 4(a-b) shows the SEM and EPMA images of BiFeO3 powder calcined at 550oC. It is shown that fine grains were grown in flaky particle shape and agglomerated in narrow size distribution. The Figure.6a revealed that the powder specimen calcined sintered at 550oC for

2h has an average grain size of ~ 200nm (Figure.4a). The black spots in SEM micrographs are pores. Figure 4b shows the compositional analysis of BiFeO3 estimated by EPMA. The unit cell formula was estimated using oxide formula method and the exact formula was found

% W

eig

ht

Lo

ss


to be Bi0.95 Fe0.96O3.05.The particle size could be estimated from SEM image. The particle size is slightly greater than the

Figure 4(a-b). SEM and EPMA images of BiFeOprocess and calcined 550

Conclusion

• The fine and homogeneous crystals of BiFeO3 perovskite oxide powder were grown by citratecombustion process.

• The XRD and SEM studies confirmed that the citratecombustion process produces single phase perovskite BiFeO

• The synthesized product had composition uniformity, lower residual oxides and carbonates, nearly single perovskite phase with a ratio of bismuth and iron close to 1:1:3 or Bi0.95 Fe0.96 O3.05particle size (200nm).

Acknowledgement

One of authors (Humaira Seema, Ph.D. Scholar) would like to thank to Mr. M. A. Haq SE, (PD) and Sumaira JS, for SEM and TG/DSC analysis central diagnostic laboratory (CDL) PINSTECH respectively.

Humaira Seema, S. K. Durrani, K. Saeed, I. Mohammadzai and N. Hussain


17

The particle size could be estimated from SEM image. The particle size is slightly greater than the

crystallize size obtained by the Scherrer’s equation because of the agglomeration of particles.

SEM and EPMA images of BiFeO3 powder prepared by combustion process and calcined 550oC, a) SEM image and b) EPMA pattern.

The fine and homogeneous crystals perovskite oxide powder

were grown by citrate- nitrate gel-

The XRD and SEM studies confirmed that the citrate-nitrate gel-combustion process produces single phase perovskite BiFeO3 oxide.

The synthesized product had mity, lower

residual oxides and carbonates, nearly single perovskite phase with a ratio of bismuth and iron close to

3.05 and smaller

One of authors (Humaira Seema, Ph.D. to thank to Mr. M. A.

Haq SE, (PD) and Sumaira JS, for SEM and TG/DSC analysis central diagnostic laboratory (CDL) PINSTECH respectively.

References

1. Ramesh, R.; Spaldin, N. A. Mater. 2007, 6,

2. Fiebig, M. J. Phys. D: Appl.Phys. 2005, 38, R 123

3. Eerenstein, W.; Mathur, N. D.; Scott, J. F. Nature765.

4. Lottermoser, T.; Lonkai, T.; Amann, U.; Hohlwein, D.; Ihringer, J.; Fiebig, M. 541 - 544.

5. Fiebig, M. J. Phys. D: Appl.Phys. 2005, 38, R 123

6. Mathur, N. Nature.592.

7. Zhao, T.; Scholl, A.; Zavaliche, F.; Lee, K.; Barry, M.; Doran, A.; Cruz, M. P.; Chu, Y. H.; Ederer, C.; Spaldin, N. A.; Das, R. R.; Kim, D. M.; Baek, S.H.; Eom, C. B.; Ramesh, R. Nature Mater823 - 829.

b

a



crystallize size obtained by the Scherrer’s equation because of the agglomeration of

powder prepared by combustion b) EPMA pattern.

, R.; Spaldin, N. A. Nature 6, 21 - 29.

J. Phys. D: Appl.Phys. , R 123 – R 152.

Eerenstein, W.; Mathur, N. D.; Nature. 2006, 442, 759-

Lottermoser, T.; Lonkai, T.; Amann, U.; Hohlwein, D.; Ihringer,

Fiebig, M. Nature. 2004, 430,

J. Phys. D: Appl.Phys. , R 123 – R 152.

Nature. 2008, 454, 591-

Zhao, T.; Scholl, A.; Zavaliche, F.; Lee, K.; Barry, M.; Doran, A.; Cruz, M. P.; Chu, Y. H.; Ederer, C.;

A.; Das, R. R.; Kim, D. M.; Baek, S.H.; Eom, C. B.;

Nature Mater. 2006, 5,

Auto Combustion…...


18

8. Kubel, F.; Schmid, H. Acta Crystallogr. 1990, 46, 698 - 702.

9. Ederer, C.; Spaldin, N. A. Phys. Rev. B. 2005, 71, R 060401.

10. Venevstev, Y. N.; Zhdanov, G. S.; Soloviev, S. N.; Bezus, E. V.; Ivanova, V. V.; Fedulov, S. A.; Kapishev, A. G. Acta crystallogr. 1960, 13, 1073- 1073.

11. Shetty, S.; Palkar, V. R.; Pinto, R. Pramana J. Phys. 2002, 58, 1027 – 1030.

12. Ghosh, S.; Dasgupta, S.; Sen, A.; Maiti, H. S. Mater. Res. Bull. 2005, 40, 2073 –2079.

13. Das, N.; Majumdar, R.; Sen, A.; Maiti, H. S. Mater. Lett. 2007, 61, 2100 – 2104.

14. Xu, J.; Ke, H.; Jia, D.; Wang, W.; Zhou, Y. J. Alloys and Compounds. 2009, 472 – 477.

15. Farhadi, S.; Zaidi, M. J. Mol. Catal. A: Chem. 2009, 299, 18 – 25.

16. Chen, C.; Cheng, J. R.; Yu, S. W.; Che, L. J.; Meng, Z. Y. J. Cryst. Growth. 2006, 291,135 –139.

17. Kaczmarek, W.; Pajak, Z,.; Polomska, M. Solid State Commun. 1975, 17, 807- 810.


Documents

JPMS Conference Issue, Materials 2010 AUTO-COMBUSTION ...mrl.uop.edu.pk/JPMS/issues/materials2010/3.AUTO... · 818 o C 956 o C 952 o C DSC TG Figure 2. TG-DSC thermo-grams of as-synthesized